Fully kinetic Biermann battery and associated generation of pressure anisotropy

NASA Astrophysics Data System (ADS)

Schoeffler, K. M.; Loureiro, N. F.; Silva, L. O.

2018-03-01

The dynamical evolution of a fully kinetic, collisionless system with imposed background density and temperature gradients is investigated analytically. The temperature gradient leads to the generation of temperature anisotropy, with the temperature along the gradient becoming larger than that in the direction perpendicular to it. This causes the system to become unstable to pressure anisotropy driven instabilities, dominantly to the electron Weibel instability. When both density and temperature gradients are present and nonparallel to each other, we obtain a Biermann-like linear-in-time magnetic field growth. Accompanying particle-in-cell numerical simulations are shown to confirm our analytical results.

Influences of a temperature gradient and fluid inertia on acoustic streaming in a standing wave.

PubMed

Thompson, Michael W; Atchley, Anthony A; Maccarone, Michael J

2005-04-01

Following the experimental method of Thompson and Atchley [J. Acoust. Soc. Am. 117, 1828-1838 (2005)] laser Doppler anemometry (LDA) is used to investigate the influences of a thermoacoustically induced axial temperature gradient and of fluid inertia on the acoustic streaming generated in a cylindrical standing-wave resonator filled with air driven sinusoidally at a frequency of 308 Hz. The axial component of Lagrangian streaming velocity is measured along the resonator axis and across the diameter at acoustic-velocity amplitudes of 2.7, 4.3, 6.1, and 8.6 m/s at the velocity antinodes. The magnitude of the axial temperature gradient along the resonator wall is varied between approximately 0 and 8 K/m by repeating measurements with the resonator either surrounded by a water jacket, suspended within an air-filled tank, or wrapped in foam insulation. A significant correlation is observed between the temperature gradient and the behavior of the streaming: as the magnitude of the temperature gradient increases, the magnitude of the streaming decreases and the shape of the streaming cell becomes increasingly distorted. The observed steady-state streaming velocities are not in agreement with any available theory.

Two-fluid flowing equilibria of spherical torus sustained by coaxial helicity injection

NASA Astrophysics Data System (ADS)

Kanki, Takashi; Steinhauer, Loren; Nagata, Masayoshi

2007-11-01

Two-dimensional equilibria in helicity-driven systems using two-fluid model were previously computed, showing the existence of an ultra-low-q spherical torus (ST) configuration with diamagnetism and higher beta. However, this computation assumed purely toroidal ion flow and uniform density. The purpose of the present study is to apply the two-fluid model to the two-dimensional equilibria of helicity-driven ST with non-uniform density and both toroidal and poloidal flows for each species by means of the nearby-fluids procedure, and to explore their properties. We focus our attention on the equilibria relevant to the HIST device, which are characterized by either driven or decaying λ profiles. The equilibrium for the driven λ profile has a diamagnetic toroidal field, high-β (βt = 32%), and centrally broad density. By contrast, the decaying equilibrium has a paramagnetic toroidal field, low-β (βt = 10%), and centrally peaked density with a steep gradient in the outer edge region. In the driven case, the toroidal ion and electron flows are in the same direction, and two-fluid effects are less important since the ExB drift is dominant. In the decaying case, the toroidal ion and electron flows are opposite in the outer edge region, and two-fluid effects are significant locally in the edge due to the ion diamagnetic drift.

Rheological Properties of Quasi-2D Fluids in Microgravity

NASA Technical Reports Server (NTRS)

Trittel, Torsten; Stannarius, Ralf; Eremin, Alexey; Harth, Kirsten; Clark, Noel A.; Maclennan, Joseph; Glaser, Matthew; Park, Cheol; Hall, Nancy; Tin, Padetha

2016-01-01

Freely suspended smectic films of sub-micrometer thickness and lateral extensions of several millimeters are used to study thermally driven convection and diffusion in the film plane. The experiments were performed during a six minute microgravity phase of a TEXUS suborbital rocket flight (Texus 52, launched April 27, 2015). The project served as a preliminary test for a planned ISS Experiment with liquid crystal films (OASIS), and in addition it provided new experimental data on smectic films exposed to in-plane thermal gradients.We find an attraction of the smectic material towards the cold edge of the film in a temperature gradient, similar to a Soret effect. This process is reversed when this edge is heated up again. Thermal convection driven by two thermocontacts in the film is practically absent, even at temperature gradients up to 10 Kmm, thermally driven convection sets in when the hot post reaches the transition temperature to the nematic phase.An additional experiment was performed under microgravity conditions to test the stability of liquid crystal bridges in different smectic phases.

Roles of Magnetic Reconnection and Developments of Modern Theory^*

NASA Astrophysics Data System (ADS)

Coppi, B.

2007-11-01

The role of reconnection was recognized in Solar and Space Physics and auroral substorms were suggested to originate in the night-side of the Earth's magnetosphere as a result collisionless reconnectionootnotetextB. Coppi, Nature 205, 998 (1965). well before the kind of modern theory employed for this became applied to laboratory plasmas. Experiments have reached low collisionality regimes where, like in space plasmas, the features of the electron distribution and in particular of the electron temperature gradient become important and the factors contributing to the electron thermal energy balance equation (transverse thermal and longitudinal diffusivities, or electron Landau dampingootnotetextB. Coppi, J.W.-K. Mark, L. Sugiyama, G. Bertin, Phys. Rev. Letters 42, 1058 (1978) and J. Drake, et al., Phys. Fluids 26, 2509 (1983). play a key role. For this an asymptotic theory of modes producing macroscopic islands has been developed involving 3 regions, the innermost one related to finite resistivity and the intermediate one to the finite ratio of the to thermal conductivitiesootnotetextB. Coppi, C. Crabtree, and V. Roytershteyn contribution to Paper TH/R2-19, I.A.E.A. Conference 2006.,^4. A background of excited micro-reconnecting modes, driven by the electron temperature gradient, is considered to make this ratio significantootnotetextB. Coppi, in``Collective Phenomena in Macroscopic Systems'' Eds. G. Bertin et al. (World Scientific, 2007) MIT-LNS Report 06/11(2006). ^*Supported in part by the US D.O.E.

Advances in Electrically Driven Thermal Management

NASA Technical Reports Server (NTRS)

Didion, Jeffrey R.

2017-01-01

Electrically Driven Thermal Management is a vibrant technology development initiative incorporating ISS based technology demonstrations, development of innovative fluid management techniques and fundamental research efforts. The program emphasizes high temperature high heat flux thermal management required for future generations of RF electronics and power electronic devices. This presentation reviews i.) preliminary results from the Electrohydrodynamic (EHD) Long Term Flight Demonstration launched on STP-H5 payload in February 2017 ii.) advances in liquid phase flow distribution control iii.) development of the Electrically Driven Liquid Film Boiling Experiment under the NASA Microgravity Fluid Physics Program.

Time-resolved lateral spin-caloric transport of optically generated spin packets in n-GaAs

NASA Astrophysics Data System (ADS)

Göbbels, Stefan; Güntherodt, Gernot; Beschoten, Bernd

2018-05-01

We report on lateral spin-caloric transport (LSCT) of electron spin packets which are optically generated by ps laser pulses in the non-magnetic semiconductor n-GaAs at K. LSCT is driven by a local temperature gradient induced by an additional cw heating laser. The spatio-temporal evolution of the spin packets is probed using time-resolved Faraday rotation. We demonstrate that the local temperature-gradient induced spin diffusion is solely driven by a non-equilibrium hot spin distribution, i.e. without involvement of phonon drag effects. Additional electric field-driven spin drift experiments are used to verify directly the validity of the non-classical Einstein relation for moderately doped semiconductors at low temperatures for near band-gap excitation.

Scaling laws and bulk-boundary decoupling in heat flow.

PubMed

del Pozo, Jesús J; Garrido, Pedro L; Hurtado, Pablo I

2015-03-01

When driven out of equilibrium by a temperature gradient, fluids respond by developing a nontrivial, inhomogeneous structure according to the governing macroscopic laws. Here we show that such structure obeys strikingly simple scaling laws arbitrarily far from equilibrium, provided that both macroscopic local equilibrium and Fourier's law hold. Extensive simulations of hard disk fluids confirm the scaling laws even under strong temperature gradients, implying that Fourier's law remains valid in this highly nonlinear regime, with putative corrections absorbed into a nonlinear conductivity functional. In addition, our results show that the scaling laws are robust in the presence of strong finite-size effects, hinting at a subtle bulk-boundary decoupling mechanism which enforces the macroscopic laws on the bulk of the finite-sized fluid. This allows one to measure the marginal anomaly of the heat conductivity predicted for hard disks.

Electron temperature gradient mode instability and stationary vortices with elliptic and circular boundary conditions in non-Maxwellian plasmas

NASA Astrophysics Data System (ADS)

Haque, Q.; Zakir, U.; Qamar, A.

2015-12-01

Linear and nonlinear dynamics of electron temperature gradient mode along with parallel electron dynamics is investigated by considering hydrodynamic electrons and non-Maxwellian ions. It is noticed that the growth rate of ηe-mode driven linear instability decreases by increasing the value of spectral index and increases by reducing the ion/electron temperature ratio along the magnetic field lines. The eigen mode dispersion relation is also found in the ballooning mode limit. Stationary solutions in the form of dipolar vortices are obtained for both circular and elliptic boundary conditions. It is shown that the dynamics of both circular and elliptic vortices changes with the inclusion of inhomogeneity and non-Maxwellian effects.

Experimental observation and numerical simulation of permeability changes in dolomite at CO2 sequestration conditions

NASA Astrophysics Data System (ADS)

Tutolo, B. M.; Luhmann, A. J.; Kong, X.; Saar, M. O.; Seyfried, W. E.

2013-12-01

Injecting surface temperature CO2 into geothermally warm reservoirs for geologic storage or energy production may result in depressed temperature near the injection well and thermal gradients and mass transfer along flow paths leading away from the well. Thermal gradients are particularly important to consider in reservoirs containing carbonate minerals, which are more soluble at lower temperatures, as well as in CO2-based geothermal energy reservoirs where lowering heat exchanger rejection temperatures increases efficiency. Additionally, equilibrating a fluid with cation-donating silicates near a low-temperature injection well and transporting the fluid to higher temperature may enhance the kinetics of mineral precipitation in such a way as to overcome the activation energy required for mineral trapping of CO2. We have investigated this process by subjecting a dolomite core to a 650-hour temperature series experiment in which the fluid was saturated with CO2 at high pressure (110-126 bars) and 21°C. This fluid was recirculated through the dolomite core, increasing permeability from 10-16 to 10-15.2 m2. Subsequently, the core temperature was raised to 50° C, and permeability decreased to 10-16.2 m2 after 289 hours, due to thermally-driven CO2 exsolution. Increasing core temperature to 100°C for the final 145 hours of the experiment caused dolomite to precipitate, which, together with further CO2 exsolution, decreased permeability to 10-16.4 m2. Post-experiment x-ray computed tomography and scanning electron microscope imagery of the dolomite core reveals abundant matrix dissolution and enlargement of flow paths at low temperatures, and subsequent filling-in of the passages at elevated temperature by dolomite. To place this experiment within the broader context of geologic CO2 sequestration, we designed and utilized a reactive transport simulator that enables dynamic calculation of CO2 equilibrium constants and fugacity and activity coefficients by incorporating mineral, fluid, and aqueous species equations of state into its structure. Phase equilibria calculations indicate that fluids traveling away from the depressed temperature zone near the injection well may exsolve and precipitate up to 200 cc CO2, 1.45 cc dolomite, and 2.3 cc calcite, per kg, but we use the reactive transport simulator to place more realistic limits on these calculations. The simulations show that thermally-induced CO2 exsolution creates velocity gradients within the modeled domain, leading to increased velocities at lower pressure due to the increasingly gas-like density of CO2. Because dolomite precipitation kinetics strongly depend on temperature, modeled dolomite precipitation effectively concentrates within high temperature regions, while calcite precipitation is predicted to occur over a broader range. Additionally, because the molar volume of dolomite is almost double that of calcite, transporting a low temperature, dolomite-saturated fluid across a thermal gradient can lead to more substantial pore space clogging. We conclude that injecting cool CO2 into geothermally warm reservoirs may substantially alter formation porosity, permeability, and injectivity, and can result in favorable conditions for permanent storage of CO2 as a solid carbonate phase.

Extreme hydrothermal conditions at an active plate-bounding fault.

PubMed

Sutherland, Rupert; Townend, John; Toy, Virginia; Upton, Phaedra; Coussens, Jamie; Allen, Michael; Baratin, Laura-May; Barth, Nicolas; Becroft, Leeza; Boese, Carolin; Boles, Austin; Boulton, Carolyn; Broderick, Neil G R; Janku-Capova, Lucie; Carpenter, Brett M; Célérier, Bernard; Chamberlain, Calum; Cooper, Alan; Coutts, Ashley; Cox, Simon; Craw, Lisa; Doan, Mai-Linh; Eccles, Jennifer; Faulkner, Dan; Grieve, Jason; Grochowski, Julia; Gulley, Anton; Hartog, Arthur; Howarth, Jamie; Jacobs, Katrina; Jeppson, Tamara; Kato, Naoki; Keys, Steven; Kirilova, Martina; Kometani, Yusuke; Langridge, Rob; Lin, Weiren; Little, Timothy; Lukacs, Adrienn; Mallyon, Deirdre; Mariani, Elisabetta; Massiot, Cécile; Mathewson, Loren; Melosh, Ben; Menzies, Catriona; Moore, Jo; Morales, Luiz; Morgan, Chance; Mori, Hiroshi; Niemeijer, Andre; Nishikawa, Osamu; Prior, David; Sauer, Katrina; Savage, Martha; Schleicher, Anja; Schmitt, Douglas R; Shigematsu, Norio; Taylor-Offord, Sam; Teagle, Damon; Tobin, Harold; Valdez, Robert; Weaver, Konrad; Wiersberg, Thomas; Williams, Jack; Woodman, Nick; Zimmer, Martin

2017-06-01

Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre. At temperatures above 300-450 degrees Celsius, usually found at depths greater than 10-15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional-mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.

Extreme hydrothermal conditions at an active plate-bounding fault

NASA Astrophysics Data System (ADS)

Sutherland, Rupert; Townend, John; Toy, Virginia; Upton, Phaedra; Coussens, Jamie; Allen, Michael; Baratin, Laura-May; Barth, Nicolas; Becroft, Leeza; Boese, Carolin; Boles, Austin; Boulton, Carolyn; Broderick, Neil G. R.; Janku-Capova, Lucie; Carpenter, Brett M.; Célérier, Bernard; Chamberlain, Calum; Cooper, Alan; Coutts, Ashley; Cox, Simon; Craw, Lisa; Doan, Mai-Linh; Eccles, Jennifer; Faulkner, Dan; Grieve, Jason; Grochowski, Julia; Gulley, Anton; Hartog, Arthur; Howarth, Jamie; Jacobs, Katrina; Jeppson, Tamara; Kato, Naoki; Keys, Steven; Kirilova, Martina; Kometani, Yusuke; Langridge, Rob; Lin, Weiren; Little, Timothy; Lukacs, Adrienn; Mallyon, Deirdre; Mariani, Elisabetta; Massiot, Cécile; Mathewson, Loren; Melosh, Ben; Menzies, Catriona; Moore, Jo; Morales, Luiz; Morgan, Chance; Mori, Hiroshi; Niemeijer, Andre; Nishikawa, Osamu; Prior, David; Sauer, Katrina; Savage, Martha; Schleicher, Anja; Schmitt, Douglas R.; Shigematsu, Norio; Taylor-Offord, Sam; Teagle, Damon; Tobin, Harold; Valdez, Robert; Weaver, Konrad; Wiersberg, Thomas; Williams, Jack; Woodman, Nick; Zimmer, Martin

2017-06-01

Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre. At temperatures above 300-450 degrees Celsius, usually found at depths greater than 10-15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional-mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.

Suppressing Electron Turbulence and Triggering Internal Transport Barriers with Reversed Magnetic Shear in the National Spherical Torus Experiment

NASA Astrophysics Data System (ADS)

Peterson, Jayson Luc

2011-10-01

Observations in the National Spherical Torus Experiment (NSTX) have found electron temperature gradients that greatly exceed the linear threshold for the onset for electron temperature gradient-driven (ETG) turbulence. These discharges, deemed electron internal transport barriers (e-ITBs), coincide with a reversal in the shear of the magnetic field and with a reduction in electron-scale density fluctuations, qualitatively consistent with earlier gyrokinetic predictions. To investigate this phenomenon further, we numerically model electron turbulence in NSTX reversed-shear plasmas using the gyrokinetic turbulence code GYRO. These first-of-a-kind nonlinear gyrokinetic simulations of NSTX e-ITBs confirm that reversing the magnetic shear can allow the plasma to reach electron temperature gradients well beyond the critical gradient for the linear onset of instability. This effect is very strong, with the nonlinear threshold for significant transport approaching three times the linear critical gradient in some cases, in contrast with moderate shear cases, which can drive significant ETG turbulence at much lower gradients. In addition to the experimental implications of this upshifted nonlinear critical gradient, we explore the behavior of ETG turbulence during reversed shear discharges. This work is supported by the SciDAC Center for the Study of Plasma Microturbulence, DOE Contract DE-AC02-09CH11466, and used the resources of NCCS at ORNL and NERSC at LBNL. M. Ono et al., Nucl. Fusion 40, 557 (2000).

Properties of ion temperature gradient and trapped electron modes in tokamak plasmas with inverted density profiles

NASA Astrophysics Data System (ADS)

Du, Huarong; Jhang, Hogun; Hahm, T. S.; Dong, J. Q.; Wang, Z. X.

2017-12-01

We perform a numerical study of linear stability of the ion temperature gradient (ITG) mode and the trapped electron mode (TEM) in tokamak plasmas with inverted density profiles. A local gyrokinetic integral equation is applied for this study. From comprehensive parametric scans, we obtain stability diagrams for ITG modes and TEMs in terms of density and temperature gradient scale lengths. The results show that, for the inverted density profile, there exists a normalized threshold temperature gradient above which the ITG mode and the TEM are either separately or simultaneously unstable. The instability threshold of the TEM for the inverted density profile is substantially different from that for normal and flat density profiles. In addition, deviations are found on the ITG threshold from an early analytic theory in sheared slab geometry with the adiabatic electron response [T. S. Hahm and W. M. Tang, Phys. Fluids B 1, 1185 (1989)]. A possible implication of this work on particle transport in pellet fueled tokamak plasmas is discussed.

Observations of Time-Dependent Behavior in the Two-Layer Rayleigh-Benard System

NASA Technical Reports Server (NTRS)

Andereck, C. David; Colovas, Peter W.; Degen, Michael M.

1996-01-01

In this paper we present results from experiments with a system consisting of two immiscible fluid layers in rectangular and annular geometries, driven by a vertical temperature gradient. Time-dependent variations in the type of coupling observed between the two layers are described and characterized.

Thermal rectification in thin films driven by gradient grain microstructure

NASA Astrophysics Data System (ADS)

Cheng, Zhe; Foley, Brian M.; Bougher, Thomas; Yates, Luke; Cola, Baratunde A.; Graham, Samuel

2018-03-01

As one of the basic components of phononics, thermal rectifiers transmit heat current asymmetrically similar to electronic rectifiers in microelectronics. Heat can be conducted through them easily in one direction while being blocked in the other direction. In this work, we report a thermal rectifier that is driven by the gradient grain structure and the inherent gradient in thermal properties as found in these materials. To demonstrate their thermal rectification properties, we build a spectral thermal conductivity model with complete phonon dispersion relationships using the thermophysical properties of chemical vapor deposited (CVD) diamond films which possess gradient grain microstructures. To explain the observed significant thermal rectification, the temperature and thermal conductivity distribution are studied. Additionally, the effects of temperature bias and film thickness are discussed, which shed light on tuning the thermal rectification based on the gradient microstructures. Our results show that the columnar grain microstructure makes CVD materials unique candidates for mesoscale thermal rectifiers without a sharp temperature change.

A Geophysical Flow Experiment in a Compressible Critical Fluid

NASA Technical Reports Server (NTRS)

Hegseth, John; Garcia, Laudelino

1996-01-01

The first objective of this experiment is to build an experimental system in which, in analogy to a geophysical system, a compressible fluid in a spherical annulus becomes radially stratified in density through an A.C. electric field. When this density gradient is demonstrated, the system will be augmented so that the fluid can be driven by heating and rotation and tested in preparation for a microgravity experiment. This apparatus consists of a spherical capacitor filled with critical fluid in a temperature controlled environment. To make the fluid critical, the apparatus will be operated near the critical pressure, critical density, and critical temperature of the fluid. This will result in a highly compressible fluid because of the properties of the fluid near its critical point. A high voltage A.C. source applied across the capacitor will create a spherically symmetric central force because of the dielectric properties of the fluid in an electric field gradient. This central force will induce a spherically symmetric density gradient that is analogous to a geophysical fluid system. To generate such a density gradient the system must be small (approx. 1 inch diameter). This small cell will also be capable of driving the critical fluid by heating and rotation. Since a spherically symmetric density gradient can only be made in microgravity, another small cell, of the same geometry, will be built that uses incompressible fluid. The driving of the fluid by rotation and heating in these small cells will be developed. The resulting instabilities from the driving in these two systems will then be studied. The second objective is to study the pattern forming instabilities (bifurcations) resulting from the well controlled experimental conditions in the critical fluid cell. This experiment will come close to producing conditions that are geophysically similar and will be studied as the driving parameters are changed.

Transitions in Convection of a Low Prandtl Number Fluid Driven by a Horizontal Temperature Gradient

NASA Astrophysics Data System (ADS)

Hung, Ming-Cheng

The transitions in convection of a low Prandtl number fluid (mercury) contained in enclosed rectangular cavities driven by horizontal temperature gradients were investigated. These cavities have insulating top, bottom and side boundaries. The other two end walls are highly conducting. The temperatures on the conducting walls were varied to control the temperature gradient inside. Both the temperature and the velocity of the fluid inside the cavity were measured. A traversing system allowed the probe position to be changed with the cavity always sealed. The temperature gradient, controlled by a computer, was ramped very slowly. At every 0.2 or 0.12 degree the ramping was held and a data file of several hours was taken. The Prandtl number of the fluid was varied from 0.025 to 0.035 by changing the average temperature. The cavity size effect on the transitions was investigated. The primary (large) cavity had aspect ratio (length:height:width) of 17.8:1:17.8 (height = 0.9 cm). The other cavities for size effect investigation were shorter and narrower. Fourier transform was used to analyze the time series. Phase portraits were constructed in 3d using time delay method and correlation dimensions were computed for some trajectories. For the large cavity, the observed onset of the longitudinal oscillatory state at Grashof number Gr = 18490 was far above the predicted value of 10610 for an infinite long cavity (height/length = 0). At low Grashof numbers, the flow was time independent. As Gr was increased, it changed to a noisy state with a periodic component and then became purely chaotic. Finally the longitudinal oscillatory state appeared with two frequencies and noise. The longitudinal oscillatory state was observed to be a standing wave with a wavelength of about 3 cm. The critical Gr was affected by the cavity width and length. The narrower the cavity, the more stable the flow. The critical Gr for oscillation decreased as the length was increased. An unusual subharmonic transition sequence was observed for the cavity with aspect ratio 4:1:2. With frequency components f and f/2 appear at the onset of oscillation, they were followed by f/3, f/6, f/9 and f/18. After the appearance of f/18, the subharmonics started to disappear and noise background kept increasing. Finally, it became pure chaotic.

Shadowgraph Study of Gradient Driven Fluctuations

NASA Technical Reports Server (NTRS)

Cannell, David; Nikolaenko, Gennady; Giglio, Marzio; Vailati, Alberto; Croccolo, Fabrizio; Meyer, William

2002-01-01

A fluid or fluid mixture, subjected to a vertical temperature and/or concentration gradient in a gravitational field, exhibits greatly enhanced light scattering at small angles. This effect is caused by coupling between the vertical velocity fluctuations due to thermal energy and the vertically varying refractive index. Physically, small upward or downward moving regions will be displaced into fluid having a refractive index different from that of the moving region, thus giving rise to the enhanced scattering. The scattered intensity is predicted to vary with scattering wave vector q, as q(sup -4), for sufficiently large q, but the divergence is quenched by gravity at small q. In the absence of gravity, the long wavelength fluctuations responsible for the enhanced scattering are predicted to grow until limited by the sample dimensions. It is thus of interest to measure the mean-squared amplitude of such fluctuations in the microgravity environment for comparison with existing theory and ground based measurements. The relevant wave vectors are extremely small, making traditional low-angle light scattering difficult or impossible because of stray elastically scattered light generated by optical surfaces. An alternative technique is offered by the shadowgraph method, which is normally used to visualize fluid flows, but which can also serve as a quantitative tool to measure fluctuations. A somewhat novel shadowgraph apparatus and the necessary data analysis methods will be described. The apparatus uses a spatially coherent, but temporally incoherent, light source consisting of a super-luminescent diode coupled to a single-mode optical fiber in order to achieve extremely high spatial resolution, while avoiding effects caused by interference of light reflected from the various optical surfaces that are present when using laser sources. Results obtained for a critical mixture of aniline and cyclohexane subjected to a vertical temperature gradient will be presented. The sample was confined between two horizontal parallel sapphire plates with a vertical spacing of 1 mm. The temperatures of the sapphire plates were controlled by independent circulating water loops that used Peltier devices to add or remove heat from the room air as required. For a mixture with a temperature gradient, two effects are involved in generating the vertical refractive index gradient, namely thermal expansion and the Soret effect, which generates a concentration gradient in response to the applied temperature gradient. For the aniline/cyclohexane system, the denser component (aniline) migrates toward the colder surface. Consequently, when heating from above, both effects result in the sample density decreasing with altitude and are stabilizing in the sense that no convective motion occurs regardless of the magnitude of the applied temperature gradient. The Soret effect is strong near a binary liquid critical point, and thus the dominant effect is due to the induced concentration gradient. The results clearly show the divergence at low q and the predicted gravitational quenching. Results obtained for different applied temperature gradients at varying temperature differences from the critical temperature, clearly demonstrate the predicted divergence of the thermal diffusion ratio. Thus, the more closely the critical point is approached, the smaller becomes the temperature gradient required to generate the same signal. Two different methods have been used to generate pure concentration gradients. In the first, a sample cell was filled with a single fluid, ethylene glycol, and a denser miscible fluid, water, was added from below thus establishing a sharp interface to begin the experiment. As time went on the two fluids diffused into each other, and large amplitude fluctuations were clearly observed at low q. The effects of gravitational quenching were also evident. In the second method, the aniline/cyclohexane sample was used, and after applying a vertical temperature gradient for several hours, the top and bottom temperatures were set equal and the thermal gradient died on a time scale of seconds, leaving the Soret induced concentration gradient in place. Again, large-scale fluctuations were observed and died away slowly in amplitude as diffusion destroyed the initial concentration gradient.

Buoyancy-Marangoni convection in confined volatile binary fluids subject to a horizontal temperature gradient

NASA Astrophysics Data System (ADS)

Qin, Tongran; Grigoriev, Roman

2017-11-01

We consider convection in a layer of binary fluid with free surface subject to a horizontal temperature gradient in the presence of noncondensable gases, which is driven by a combination of three different forces: buoyancy, thermocapillarity, and solutocapillarity. Unlike buoyancy, both thermo- and solutocapillary stresses depend sensitively on the local phase equilibrium at the liquid-gas interface. In particular, thermocapillarity associated with the interfacial temperature gradient is controlled by the vapors' concentration along the interface, and solutocapillarity associated with the interfacial concentration gradient is controlled by differential phase change of two components of the liquid, which is strongly influenced by the presence of noncondensables. Therefore, flows in both phases, phase change, and effect of noncondensables all have to be considered. Numerical simulations based on a comprehensive model taking these effects into account show qualitative agreement with recent experiments which identified a number of flow regimes at various compositions of both phases. In particular,we find that the composition of both the gas and liquid phase have a significant effect on the observed convection patterns; this dependence can be understood using a simple analytical model. This material is based upon work supported by the National Science Foundation under Grant No. 1511470.

From convection rolls to finger convection in double-diffusive turbulence

PubMed Central

Verzicco, Roberto; Lohse, Detlef

2016-01-01

Double-diffusive convection (DDC), which is the buoyancy-driven flow with fluid density depending on two scalar components, is ubiquitous in many natural and engineering environments. Of great interests are scalars' transfer rate and flow structures. Here we systematically investigate DDC flow between two horizontal plates, driven by an unstable salinity gradient and stabilized by a temperature gradient. Counterintuitively, when increasing the stabilizing temperature gradient, the salinity flux first increases, even though the velocity monotonically decreases, before it finally breaks down to the purely diffusive value. The enhanced salinity transport is traced back to a transition in the overall flow pattern, namely from large-scale convection rolls to well-organized vertically oriented salt fingers. We also show and explain that the unifying theory of thermal convection originally developed by Grossmann and Lohse for Rayleigh–Bénard convection can be directly applied to DDC flow for a wide range of control parameters (Lewis number and density ratio), including those which cover the common values relevant for ocean flows. PMID:26699474

Transient Interfacial Phenomena in Miscible Polymer Systems (TIPMPS)

NASA Technical Reports Server (NTRS)

Pojman, John A.; Bessonov, Nicholas; Volpert, Vitaly; Wilke, Hermann

2003-01-01

Almost one hundred years ago Korteweg published a theory of how stresses could be induced in miscible fluids by concentration gradients, causing phenomena that would appear to be the same as with immiscible fluids. Miscible fluids could manifest a transient or effective interfacial tension (EIT). To this day, there has been no definitive experiment to confirm Korteweg's model but numerous fascinating and suggestive experiments have been reported. The goal of TIPMPS is to answer the question: Can concentration and temperature gradients in miscible materials induce stresses that cause convection? Many polymer processes involving miscible monomer and polymer systems could be affected by fluid flow and so this work could help understand miscible polymer processing, not only in microgravity, but also on earth. Demonstrating the existence of this phenomenon in miscible fluids will open up a new area of study for materials science. The science objectives of TIPMPS are: (1) Determine if convection can be induced by variation of the width of a miscible interface; (2) Determine if convection can be induced by variation of temperature along a miscible interface; (3) Determine if convection can be induced by variation of conversion along a miscible interface An interface between two miscible fluids can best be created via a spatially-selective photopolymerization of dodecyl acrylate with a photoinitiator, which allows the creation of precise and accurate concentration gradients between polymer and monomer. Optical techniques will be used to measure the refractive index variation caused by the resultant temperature and concentration fields. The viscosity of the polymer will be measured from the increase in the fluorescence of pyrene. Because the large concentration and temperature gradients cause buoyancy-driven convection that prevents the observation of the predicted flows, the experiment must be done in microgravity. In this report, we will consider our efforts to estimate the square gradient parameter, k, and our use of the estimates in modeling of the planned TIPMPS experiments. We developed a model consisting of the heat and diffusion equations with convective terms and of the Navier-Stokes equations with an additional volume force written in the form of the Korteweg stresses arising from nonlocal interaction in the fluid. The fluid's viscosity dependence on polymer conversion and temperature was taken from measurements of poly(dodecyl acrylate). Numerical modeling demonstrated that significant flows would arise for conditions corresponding to the planned experiments.

Geometric effects on bilayer convection in cylindrical containers

NASA Astrophysics Data System (ADS)

Johnson, Duane Thomas

The study of convection in two immiscible fluid layers is of interest for reasons both theoretical as well as applied. Recently, bilayer convection has been used as a model of convection in the earth's mantle. It is also an interesting system to use in the study of pattern formation. Bilayer convection also occurs in a process known as liquid encapsulated crystal growth, which is used to grow compound semiconductors. It is the last application which motivates this study. To analyze bilayer convection, theoretical models, numerical calculations and experiments were used. One theoretical model involves the derivation of the Navier- Stokes and energy equation for two immiscible fluid layers, using the Boussinesq approximation. A weakly nonlinear analysis was also performed to study the behavior of the system slightly beyond the onset of convection. Numerical calculations were necessary to solve both models. The experiments involved a single liquid layer of silicone oil, superposed by a layer of air. The radius and height of each fluid layer were changed to observe different flow patterns at the onset of convection. From the experiments and theory, two major discoveries were made as well as several interesting observations. The first discovery is the existence of codimension-two points-particular aspect ratios where two flow patterns coexist-in cylindrical containers. At these points, dynamic switching between different flow patterns was observed. The second discovery was the effect of air convection on the flow pattern in silicone oil. Historically, air has been considered a passive medium that has no effect on the lower fluid. However, experiments were done to show that for large air heights, convection in the air can cause radial temperature gradients at the liquid interface. These temperature gradients then cause surface tension gradient-driven flows. It was also shown that changing the radius of the container can change the driving force of convection from a surface tension gradient-driven to buoyancy-driven and back again. Finally, the weakly nonlinear analysis was able to give a qualitative description of codimension-two points as well as the change in flow patterns due to the convecting air layer.

Natural convection in binary gases driven by combined horizontal thermal and vertical solutal gradients

NASA Technical Reports Server (NTRS)

Weaver, J. A.; Viskanta, Raymond

1992-01-01

An investigation of natural convection is presented to examine the influence of a horizontal temperature gradient and a concentration gradient occurring from the bottom to the cold wall in a cavity. As the solutal buoyancy force changes from augmenting to opposing the thermal buoyancy force, the fluid motion switches from unicellular to multicellular flow (fluid motion is up the cold wall and down the hot wall for the bottom counterrotating flow cell). Qualitatively, the agreement between predicted streamlines and smoke flow patterns is generally good. In contrast, agreement between measured and predicted temperature and concentration distributions ranges from fair to poor. Part of the discrepancy can be attributed to experimental error. However, there remains considerable discrepancy between data and predictions due to the idealizations of the mathematical model, which examines only first-order physical effects. An unsteady flow, variable thermophysical properties, conjugate effects, species interdiffusion, and radiation were not accounted for in the model.

Thin film instabilities: Rayleigh-Taylor with thermocapillarity and Kolmogorov flow in a soap film

NASA Astrophysics Data System (ADS)

Burgess, John Matthew

The Rayleigh-Taylor instability occurs when a more dense fluid layer is suspended above a less dense fluid layer in a gravitational field. The horizontal interface between the two fluids is unstable to infinitesimal deformations and the dense fluid falls. To counteract the destabilizing effects of gravity on the interface between two thin fluid layers, we apply a vertical temperature gradient, heating from below. The dependence of surface tension on temperature (``thermocapillarity'') can cause spatially-varying interfacial forces between two immiscible fluid layers if a variation in temperature along the interface is introduced. With an applied vertical temperature gradient, the deforming interface spontaneously develops temperature variations which locally adjust the surface tension to restore a flat interface. We find that these surface tension gradients can stabilize a more dense thin fluid layer (silicone oil, 0.015 cm thick) above a less dense thin fluid layer (air, 0.025 cm thick) in a gravitational field, in qualitative agreement with linear stability analysis. This is the first experimental observation of the stabilization of Rayleigh-Taylor instability by thermocapillary forces. We also examine the instability of a soap film flow driven by a time-independent force that is spatially periodic in the direction perpendicular to the forcing (Kolmogorov flow). The film is in the x- y plane, where the forcing approximates a shape sin (y)x̂. Linear stability analysis of an idealized model of this flow predicts a critical Reynolds number Rc~2 . In our soap film experiment, we find a critical value Rc~70 . This discrepancy can be ascribed to frictional effects from viscous coupling of gas to the film, which is neglected in the idealized model. The kinematic viscosity of the surrounding gas and the thickness of gas layers on each side of the soap film are varied in the experiments to better understand these frictional effects. We conclude that flows in soap films cannot be decoupled from flows in the surrounding gas.

Streamer formation and transport for parameters characteristic of H-mode pedestals

NASA Astrophysics Data System (ADS)

Blackmon, Austin; Hatch, D. R.; Kotschenreuther, M.; Mahajan, S.; Hazeltine, R. D.

2017-10-01

We investigate, through gyrokinetic simulations, the formation of streamers as a consequence of electron temperature gradient driven, electron scale instabilities. We also study the interaction of velocity shear with streamers for parameters typical of H-mode pedestals, exploring both the higher as well as lower temperature gradient regions. Without ExB shear, the streamers form at the pedestal top causing large heat fluxes; the modes, however, did not saturate. When ExB shear was turned on, the streamers dissipated, and heat flux was lowered, though still of significant magnitude. In the middle of the pedestal, with high temperature gradient, heat flux was insignificant. There was no evidence of streamers in this region, leading to a conclusion that streamers have a strong influence on heat flux. Work supported by US DOE under DE-FG02-04ER54742.

A Multi Water Bag model of drift kinetic electron plasmaa

NASA Astrophysics Data System (ADS)

Morel, Pierre; Ghiro, Florent Dreydemy; Berionni, Vincent; Coulette, David; Besse, Nicolas; Gürcan, Özgür D.

2014-08-01

A Multi Water Bag model is proposed for describing drift kinetic plasmas in a magnetized cylindrical geometry, relevant for various experimental devices, solar wind modeling... The Multi Water Bag (MWB) model is adapted to the description of a plasma with kinetic electrons as well as an arbitrary number of kinetic ions. This allows to describe the kinetic dynamics of the electrons, making possible the study of electron temperature gradient (ETG) modes, in addition to the effects of non adiabatic electrons on the ion temperature gradient (ITG) modes, that are of prime importance in the magnetized plasmas micro-turbulence [X. Garbet, Y. Idomura, L. Villard, T.H. Watanabe, Nucl. Fusion 50, 043002 (2010); J.A. Krommes, Ann. Rev. Fluid Mech. 44, 175 (2012)]. The MWB model is shown to link kinetic and fluid descriptions, depending on the number of bags considered. Linear stability of the ETG modes is presented and compared to the existing results regarding cylindrical ITG modes [P. Morel, E. Gravier, N. Besse, R. Klein, A. Ghizzo, P. Bertrand, W. Garbet, Ph. Ghendrih, V. Grandgirard, Y. Sarazin, Phys. Plasmas 14, 112109 (2007)].

Thermoelectricity in Heterogeneous Nanofluidic Channels.

PubMed

Li, Long; Wang, Qinggong

2018-05-01

Ionic fluids are essential to energy conversion, water desalination, drug delivery, and lab-on-a-chip devices. Ionic transport in nanoscale confinements and complex physical fields still remain elusive. Here, a nanofluidic system is developed using nanochannels of heterogeneous surface properties to investigate transport properties of ions under different temperatures. Steady ionic currents are observed under symmetric temperature gradients, which is equivalent to generating electricity using waste heat (e.g., electronic chips and solar panels). The currents increase linearly with temperature gradient and nonlinearly with channel size. Contributions to ion motion from temperatures and channel properties are evaluated for this phenomenon. The findings provide insights into the study of confined ionic fluids in multiphysical fields, and suggest applications in thermal energy conversion, temperature sensors, and chip-level thermal management. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Terahertz-driven linear electron acceleration

PubMed Central

Nanni, Emilio A.; Huang, Wenqian R.; Hong, Kyung-Han; Ravi, Koustuban; Fallahi, Arya; Moriena, Gustavo; Dwayne Miller, R. J.; Kärtner, Franz X.

2015-01-01

The cost, size and availability of electron accelerators are dominated by the achievable accelerating gradient. Conventional high-brightness radio-frequency accelerating structures operate with 30–50 MeV m−1 gradients. Electron accelerators driven with optical or infrared sources have demonstrated accelerating gradients orders of magnitude above that achievable with conventional radio-frequency structures. However, laser-driven wakefield accelerators require intense femtosecond sources and direct laser-driven accelerators suffer from low bunch charge, sub-micron tolerances and sub-femtosecond timing requirements due to the short wavelength of operation. Here we demonstrate linear acceleration of electrons with keV energy gain using optically generated terahertz pulses. Terahertz-driven accelerating structures enable high-gradient electron/proton accelerators with simple accelerating structures, high repetition rates and significant charge per bunch. These ultra-compact terahertz accelerators with extremely short electron bunches hold great potential to have a transformative impact for free electron lasers, linear colliders, ultrafast electron diffraction, X-ray science and medical therapy with X-rays and electron beams. PMID:26439410

Terahertz-driven linear electron acceleration

DOE PAGES

Nanni, Emilio A.; Huang, Wenqian R.; Hong, Kyung-Han; ...

2015-10-06

The cost, size and availability of electron accelerators are dominated by the achievable accelerating gradient. Conventional high-brightness radio-frequency accelerating structures operate with 30–50 MeVm -1 gradients. Electron accelerators driven with optical or infrared sources have demonstrated accelerating gradients orders of magnitude above that achievable with conventional radio-frequency structures. However, laser-driven wakefield accelerators require intense femtosecond sources and direct laser-driven accelerators suffer from low bunch charge, sub-micron tolerances and sub-femtosecond timing requirements due to the short wavelength of operation. Here we demonstrate linear acceleration of electrons with keV energy gain using optically generated terahertz pulses. Terahertz-driven accelerating structures enable high-gradient electron/protonmore » accelerators with simple accelerating structures, high repetition rates and significant charge per bunch. As a result, these ultra-compact terahertz accelerators with extremely short electron bunches hold great potential to have a transformative impact for free electron lasers, linear colliders, ultrafast electron diffraction, X-ray science and medical therapy with X-rays and electron beams.« less

Global simulation of edge pedestal micro-instabilities

NASA Astrophysics Data System (ADS)

Wan, Weigang; Parker, Scott; Chen, Yang

2011-10-01

We study micro turbulence of the tokamak edge pedestal with global gyrokinetic particle simulations. The simulation code GEM is an electromagnetic δf code. Two sets of DIII-D experimental profiles, shot #131997 and shot #136051 are used. The dominant instabilities appear to be two kinds of modes both propagating in the electron diamagnetic direction, with comparable linear growth rates. The low n mode is at the Alfven frequency range and driven by density and ion temperature gradients. The high n mode is driven by electron temperature gradient and has a low real frequency. A β scan shows that the low n mode is electromagnetic. Frequency analysis shows that the high n mode is sometimes mixed with an ion instability. Experimental radial electric field is applied and its effects studied. We will also show some preliminary nonlinear results. We thank R. Groebner, P. Snyder and Y. Zheng for providing experimental profiles and helpful discussions.

Vibration isolation technology: Sensitivity of selected classes of experiments to residual accelerations

NASA Technical Reports Server (NTRS)

Alexander, J. Iwan D.

1990-01-01

The solution was sought of a 2-D axisymmetric moving boundary problem for the sensitivity of isothermal and nonisothermal liquid columns and the sensitivity of thermo-capillary flows to buoyancy driven convection caused by residual accelerations. The sensitivity of a variety of space experiments to residual accelerations are examined. In all the cases discussed, the sensitivity is related to the dynamic response of a fluid. In some cases the sensitivity can be defined by the magnitude of the response of the velocity field. This response may involve motion of the fluid associated with internal density gradients, or the motion of a free liquid surface. For fluids with internal density gradients, the type of acceleration to which the experiment is sensitive will depend on whether buoyancy driven convection must be small in comparison to other types of fluid motion (such as thermocapillary flow), or fluid motion must be suppressed or eliminated (such as in diffusion studies, or directional solidification experiments). The effect of the velocity on the composition and temperature field must be considered, particularly in the vicinity of the melt crystal interface. As far as the response to transient disturbances is concerned the sensitivity is determined by both the magnitude and frequency the acceleration and the characteristic momentum and solute diffusion times.

Neutral recycling effects on ITG turbulence

DOE PAGES

Stotler, D. P.; Lang, J.; Chang, C. S.; ...

2017-07-04

Here, the effects of recycled neutral atoms on tokamak ion temperature gradient (ITG) driven turbulence have been investigated in a steep edge pedestal, magnetic separatrix configuration, with the full-f edge gryokinetic code XGC1. An adiabatic electron model has been used; hence, the impacts of neutral particles and turbulence on the density gradient are not considered, nor are electromagnetic turbulence effects. The neutral atoms enhance the ITG turbulence, first, by increasing the ion temperature gradient in the pedestal via the cooling effects of charge exchange and, second, by a relative reduction in themore » $$E\\times B$$ shearing rate.« less

Neutral recycling effects on ITG turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stotler, D. P.; Lang, J.; Chang, C. S.

Here, the effects of recycled neutral atoms on tokamak ion temperature gradient (ITG) driven turbulence have been investigated in a steep edge pedestal, magnetic separatrix configuration, with the full-f edge gryokinetic code XGC1. An adiabatic electron model has been used; hence, the impacts of neutral particles and turbulence on the density gradient are not considered, nor are electromagnetic turbulence effects. The neutral atoms enhance the ITG turbulence, first, by increasing the ion temperature gradient in the pedestal via the cooling effects of charge exchange and, second, by a relative reduction in themore » $$E\\times B$$ shearing rate.« less

Sloshing dynamics modulated fluid angular momentum and moment fluctuations driven by orbital gravity gradient and jitter accelerations in microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Pan, H. L.

1995-01-01

The dynamical behavior of spacecraft propellant affected by the asymmetric combined gravity gradient and jitter accelerations, in particular the effect of surface tension on partially-filled rotating fluids applicable to a full-scale Gravity Probe-B Spacecraft dewar tank has been investigated. Three different cases of orbital accelerations: (1) gravity gradient-dominated, (2) equally weighted between gravity gradient and jitter, and (3) gravity jitter-dominated accelerations are studied. The results of slosh wave excitation along the liquid-vapor interface induced by gravity gradient-dominated accelerations provide a torsional moment with tidal motion of bubble oscillations in the rotating dewar. The results are clearly seen from the twisting shape of the bubble oscillations driven by gravity gradient-dominated acceleration. The results of slosh wave excitation along the liquid-vapor interface induced by gravity jitter-dominated acceleration indicate the results of bubble motion in a manner of down-and-up and leftward-and-rightward movement of oscillation when the bubble is rotating with respect to rotating dewar axis. Fluctuations of angular momentum, fluid moment and bubble mass center caused by slosh wave excitations driven by gravity gradient acceleration or gravity jitter acceleration are also investigated.

Suppressing electron turbulence and triggering internal transport barriers with reversed magnetic shear in the National Spherical Torus Experimenta)

NASA Astrophysics Data System (ADS)

Peterson, J. L.; Bell, R.; Candy, J.; Guttenfelder, W.; Hammett, G. W.; Kaye, S. M.; LeBlanc, B.; Mikkelsen, D. R.; Smith, D. R.; Yuh, H. Y.

2012-05-01

The National Spherical Torus Experiment (NSTX) [M. Ono et al., Nucl. Fusion 40, 557 (2000)] can achieve high electron plasma confinement regimes that are super-critically unstable to the electron temperature gradient driven (ETG) instability. These plasmas, dubbed electron internal transport barriers (e-ITBs), occur when the magnetic shear becomes strongly negative. Using the gyrokinetic code GYRO [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)], the first nonlinear ETG simulations of NSTX e-ITB plasmas reinforce this observation. Local simulations identify a strongly upshifted nonlinear critical gradient for thermal transport that depends on magnetic shear. Global simulations show e-ITB formation can occur when the magnetic shear becomes strongly negative. While the ETG-driven thermal flux at the outer edge of the barrier is large enough to be experimentally relevant, the turbulence cannot propagate past the barrier into the plasma interior.

Free swimming organisms: Microgravity as an investigative tool

NASA Technical Reports Server (NTRS)

Kessler, John O.

1989-01-01

On earth, micro-organisms are in the grip of gravitational and viscous forces. These forces, in combination with sensory stimuli, determine the average orientation of the organisms' swimming trajectories relative to the fluid environment. Microgravity provides the opportunity to study the rules which govern the summation or orienting influences and to develop quantitative physical measurements of sensory responses, e.g. the measurement of phototactic orientation tendency in torque units. Also, by reducing or eliminating density anisotropy-driven buoyant convection, it will be possible to study illumination, temperature gradient and concentration gradient-mediated collective dynamics.

Observation of 690 MV m -1 Electron Accelerating Gradient with a Laser-Driven Dielectric Microstructure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wootton, K. P.; Wu, Z.; Cowan, B. M.

Acceleration of electrons using laser-driven dielectric microstructures is a promising technology for the miniaturization of particle accelerators. In this work, experimental results are presented of relativistic electron acceleration with 690±100 MVm -1 gradient. This is a record-high accelerating gradient for a dielectric microstructure accelerator, nearly doubling the previous record gradient. To reach higher acceleration gradients the present experiment employs 90 fs duration laser pulses.

Effects of finite electron temperature on gradient drift instabilities in partially magnetized plasmas

NASA Astrophysics Data System (ADS)

Lakhin, V. P.; Ilgisonis, V. I.; Smolyakov, A. I.; Sorokina, E. A.; Marusov, N. A.

2018-01-01

The gradient-drift instabilities of partially magnetized plasmas in plasma devices with crossed electric and magnetic fields are investigated in the framework of the two-fluid model with finite electron temperature in an inhomogeneous magnetic field. The finite electron Larmor radius (FLR) effects are also included via the gyroviscosity tensor taking into account the magnetic field gradient. This model correctly describes the electron dynamics for k⊥ρe>1 in the sense of Padé approximants (here, k⊥ and ρe are the wavenumber perpendicular to the magnetic field and the electron Larmor radius, respectively). The local dispersion relation for electrostatic plasma perturbations with the frequency in the range between the ion and electron cyclotron frequencies and propagating strictly perpendicular to the magnetic field is derived. The dispersion relation includes the effects of the equilibrium E ×B electron current, finite ion velocity, electron inertia, electron FLR, magnetic field gradients, and Debye length effects. The necessary and sufficient condition of stability is derived, and the stability boundary is found. It is shown that, in general, the electron inertia and FLR effects stabilize the short-wavelength perturbations. In some cases, such effects completely suppress the high-frequency short-wavelength modes so that only the long-wavelength low-frequency (with respect to the lower-hybrid frequency) modes remain unstable.

Parallel closure theory for toroidally confined plasmas

NASA Astrophysics Data System (ADS)

Ji, Jeong-Young; Held, Eric D.

2017-10-01

We solve a system of general moment equations to obtain parallel closures for electrons and ions in an axisymmetric toroidal magnetic field. Magnetic field gradient terms are kept and treated using the Fourier series method. Assuming lowest order density (pressure) and temperature to be flux labels, the parallel heat flow, friction, and viscosity are expressed in terms of radial gradients of the lowest-order temperature and pressure, parallel gradients of temperature and parallel flow, and the relative electron-ion parallel flow velocity. Convergence of closure quantities is demonstrated as the number of moments and Fourier modes are increased. Properties of the moment equations in the collisionless limit are also discussed. Combining closures with fluid equations parallel mass flow and electric current are also obtained. Work in collaboration with the PSI Center and supported by the U.S. DOE under Grant Nos. DE-SC0014033, DE-SC0016256, and DE-FG02-04ER54746.

Magic angle spinning NMR below 6 K with a computational fluid dynamics analysis of fluid flow and temperature gradients

NASA Astrophysics Data System (ADS)

Sesti, Erika L.; Alaniva, Nicholas; Rand, Peter W.; Choi, Eric J.; Albert, Brice J.; Saliba, Edward P.; Scott, Faith J.; Barnes, Alexander B.

2018-01-01

We report magic angle spinning (MAS) up to 8.5 kHz with a sample temperature below 6 K using liquid helium as a variable temperature fluid. Cross polarization 13C NMR spectra exhibit exquisite sensitivity with a single transient. Remarkably, 1H saturation recovery experiments show a 1H T1 of 21 s with MAS below 6 K in the presence of trityl radicals in a glassy matrix. Leveraging the thermal spin polarization available at 4.2 K versus 298 K should result in 71 times higher signal intensity. Taking the 1H longitudinal relaxation into account, signal averaging times are therefore predicted to be expedited by a factor of >500. Computer assisted design (CAD) and finite element analysis were employed in both the design and diagnostic stages of this cryogenic MAS technology development. Computational fluid dynamics (CFD) models describing temperature gradients and fluid flow are presented. The CFD models bearing and drive gas maintained at 100 K, while a colder helium variable temperature fluid stream cools the center of a zirconia rotor. Results from the CFD were used to optimize the helium exhaust path and determine the sample temperature. This novel cryogenic experimental platform will be integrated with pulsed dynamic nuclear polarization and electron decoupling to interrogate biomolecular structure within intact human cells.

Hybrid simulations of radial transport driven by the Rayleigh-Taylor instability

NASA Astrophysics Data System (ADS)

Delamere, P. A.; Stauffer, B. H.; Ma, X.

2017-12-01

Plasma transport in the rapidly rotating giant magnetospheres is thought to involve a centrifugally-driven flux tube interchange instability, similar to the Rayleigh-Taylor (RT) instability. In three dimensions, the convective flow patterns associated with the RT instability can produce strong guide field reconnection, allowing plasma mass to move radially outward while conserving magnetic flux (Ma et al., 2016). We present a set of hybrid (kinetic ion / fluid electron) plasma simulations of the RT instability using high plasma beta conditions appropriate for Jupiter's inner and middle magnetosphere. A density gradient, combined with a centrifugal force, provide appropriate RT onset conditions. Pressure balance is achieved by initializing two ion populations: one with fixed temperature, but varying density, and the other with fixed density, but a temperature gradient that offsets the density gradient from the first population and the centrifugal force (effective gravity). We first analyze two-dimensional results for the plane perpendicular to the magnetic field by comparing growth rates as a function of wave vector following Huba et al. (1998). Prescribed perpendicular wave modes are seeded with an initial velocity perturbation. We then extend the model to three dimensions, introducing a stabilizing parallel wave vector. Boundary conditions in the parallel direction prohibit motion of the magnetic field line footprints to model the eigenmodes of the magnetodisc's resonant cavity. We again compare growth rates based on perpendicular wave number, but also on the parallel extent of the resonant cavity, which fixes the size of the largest parallel wavelength. Finally, we search for evidence of strong guide field magnetic reconnection within the domain by identifying areas with large parallel electric fields or changes in magnetic field topology.

Calculations of Alfven Wave Driving Forces, Plasma Flow and Current Drive in Tokamak Plasmas

NASA Astrophysics Data System (ADS)

Elfimov, Artur; Galvao, Ricardo; Amarante-Segundo, Gesil; Nascimento, Ivan

2000-10-01

A general form of time-averaged poloidal ponderomotive forces induced by fast and kinetic Alfvin waves by direct numerical calculations and in geometric optics approximation are analyzed on the basis of the collisionless two fluid (ions and electrons) magneto-hydrodynamics equation. Analytical approximations are used to clarify the effect of Larmour radius on radio-frequency (RF) ponderomotive forces and on poloidal flows induced by them in tokamak plasmas.The RF ponderomotive force is expressed as a sum of a gradient part and of a wave momentum transfer force, which is proportional to wave dissipation. The gradient electromagnetic stress force is combined with fluid dynamic (Reynolds) stress force. It is shown that accounting only Reynolds stress term can overestimate the plasma flow and it is found that the finite ion Larmor radius effect play fundamental role in ponderomotive forces that can drive a poloidal flow, which is larger than a flow driven by a wave momentum transfer force. Finally, balancing the RF forces by the electron-ion friction and viscous force the current and plasma flows driven by ponderomotive forces are calculated for tokamak plasmas, using a kinetic code [Phys. Plasmas, v.6 (1999) p.2437]. Strongly sheared current and plasma flow waves is found.

Temperature gradients due to adiabatic plasma expansion in a magnetic nozzle

NASA Astrophysics Data System (ADS)

Sheehan, J. P.; Longmier, B. W.; Bering, E. A.; Olsen, C. S.; Squire, J. P.; Ballenger, M. G.; Carter, M. D.; Cassady, L. D.; Díaz, F. R. Chang; Glover, T. W.; Ilin, A. V.

2014-08-01

A mechanism for ambipolar ion acceleration in a magnetic nozzle is proposed. The plasma is adiabatic (i.e., does not exchange energy with its surroundings) in the diverging section of a magnetic nozzle so any energy lost by the electrons must be transferred to the ions via the electric field. Fluid theory indicates that the change in plasma potential is proportional to the change in average electron energy. These predictions were compared to measurements in the VX-200 experiment which has conditions conducive to ambipolar ion acceleration. A planar Langmuir probe was used to measure the plasma potential, electron density, and electron temperature for a range of mass flow rates and power levels. Axial profiles of those parameters were also measured, showing consistency with the adiabatic ambipolar fluid theory.

Kinetic theory of two-temperature polyatomic plasmas

NASA Astrophysics Data System (ADS)

Orlac'h, Jean-Maxime; Giovangigli, Vincent; Novikova, Tatiana; Roca i Cabarrocas, Pere

2018-03-01

We investigate the kinetic theory of two-temperature plasmas for reactive polyatomic gas mixtures. The Knudsen number is taken proportional to the square root of the mass ratio between electrons and heavy-species, and thermal non-equilibrium between electrons and heavy species is allowed. The kinetic non-equilibrium framework also requires a weak coupling between electrons and internal energy modes of heavy species. The zeroth-order and first-order fluid equations are derived by using a generalized Chapman-Enskog method. Expressions for transport fluxes are obtained in terms of macroscopic variable gradients and the corresponding transport coefficients are expressed as bracket products of species perturbed distribution functions. The theory derived in this paper provides a consistent fluid model for non-thermal multicomponent plasmas.

Nonlinear verification of a linear critical gradient model for energetic particle transport by Alfven eigenmodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bass, Eric M.; Waltz, R. E.

Here, a “stiff transport” critical gradient model of energetic particle (EP) transport by EPdriven Alfven eigenmodes (AEs) is verified against local nonlinear gyrokinetic simulations of a well-studied beam-heated DIII-D discharge 146102. A greatly simplifying linear “recipe” for the limiting EP-density gradient (critical gradient) is considered here. In this recipe, the critical gradient occurs when the AE linear growth rate, driven mainly by the EP gradient, exceeds the ion temperature gradient (ITG) or trapped electron mode (TEM) growth rate, driven by the thermal plasma gradient, at the same toroidal mode number (n) as the AE peak growth, well below the ITG/TEMmore » peak n. This linear recipe for the critical gradient is validated against the critical gradient determined from far more expensive local nonlinear simulations in the gyrokinetic code GYRO, as identified by the point of transport runaway when all driving gradients are held fixed. The reduced linear model is extended to include the stabilization from equilibrium E×B velocity shear. The nonlinear verification unambiguously endorses one of two alternative recipes proposed in Ref. 1: the EP-driven AE growth rate should be determined with rather than without added thermal plasma drive.« less

Nonlinear verification of a linear critical gradient model for energetic particle transport by Alfven eigenmodes

DOE PAGES

Bass, Eric M.; Waltz, R. E.

2017-12-08

Here, a “stiff transport” critical gradient model of energetic particle (EP) transport by EPdriven Alfven eigenmodes (AEs) is verified against local nonlinear gyrokinetic simulations of a well-studied beam-heated DIII-D discharge 146102. A greatly simplifying linear “recipe” for the limiting EP-density gradient (critical gradient) is considered here. In this recipe, the critical gradient occurs when the AE linear growth rate, driven mainly by the EP gradient, exceeds the ion temperature gradient (ITG) or trapped electron mode (TEM) growth rate, driven by the thermal plasma gradient, at the same toroidal mode number (n) as the AE peak growth, well below the ITG/TEMmore » peak n. This linear recipe for the critical gradient is validated against the critical gradient determined from far more expensive local nonlinear simulations in the gyrokinetic code GYRO, as identified by the point of transport runaway when all driving gradients are held fixed. The reduced linear model is extended to include the stabilization from equilibrium E×B velocity shear. The nonlinear verification unambiguously endorses one of two alternative recipes proposed in Ref. 1: the EP-driven AE growth rate should be determined with rather than without added thermal plasma drive.« less

Evidence of a New Instability in Gyrokinetic Simulations of LAPD Plasmas

NASA Astrophysics Data System (ADS)

Terry, P. W.; Pueschel, M. J.; Rossi, G.; Jenko, F.; Told, D.; Carter, T. A.

2015-11-01

Recent experiments at the LArge Plasma Device (LAPD) have focused on structure formation driven by density and temperature gradients. A central difference relative to typical, tokamak-like plasmas stems from the linear geometry and absence of background magnetic shear. At sufficiently high β, strong excitation of parallel (compressional) magnetic fluctuations was observed. Here, linear and nonlinear simulations with the Gene code are used to demonstrate that these findings can be explained through the linear excitation of a Gradient-driven Drift Coupling mode (GDC). This recently-discovered instability, unlike other drift waves, relies on the grad-B drift due to parallel magnetic fluctuations in lieu of a parallel electron response, and can be driven by density or temperature gradients. The linear properties of the GDC for LAPD parameters are studied in detail, and the corresponding turbulence is investigated. It is found that, despite the very large collisionality in the experiment, many properties are recovered fairly well in the simulations. In addition to confirming the existence of the GDC, this opens up interesting questions regarding GDC activity in astrophysical and space plasmas. Supported by USDOE.

Derivation of the threshold condition for the ion temperature gradient mode with an inverted density profile from a simple physics picture

NASA Astrophysics Data System (ADS)

Jhang, Hogun

2018-05-01

We show that the threshold condition for the toroidal ion temperature gradient (ITG) mode with an inverted density profile can be derived from a simple physics argument. The key in this picture is that the density inversion reduces the ion compression due to the ITG mode and the electron drift motion mitigates the poloidal potential build-up. This condition reproduces the same result that has been reported from a linear gyrokinetic calculation [T. S. Hahm and W. M. Tang, Phys. Fluids B 1, 1185 (1989)]. The destabilizing role of trapped electrons in toroidal geometry is easily captured in this picture.

Stability of Gas Hydrates on Continental Margins: Implications of Subsurface Fluid Flow

NASA Astrophysics Data System (ADS)

Nunn, J. A.

2008-12-01

Gas hydrates are found at or just below the sediment-ocean interface in continental margins settings throughout the world. They are also found on land in high latitude regions such as the north slope of Alaska. While gas hydrate occurrence is common, gas hydrates are stable under a fairly restricted range of temperatures and pressures. In a purely conductive thermal regime, near surface temperatures depend on basal heat flow, thermal conductivity of sediments, and temperature at the sediment-water or sediment-air interface. Thermal conductivity depends on porosity and sediment composition. Gas hydrates are most stable in areas of low heat flow and high thermal conductivity which produce low temperature gradients. Older margins with thin continental crust and coarse grained sediments would tend to be colder. Another potentially important control on subsurface temperatures is advective heat transport by recharge/discharge of groundwater. Upward fluid flow depresses temperature gradients over a purely conductive regime with the same heat flow which would make gas hydrates more stable. Downward fluid flow would have the opposite effect. However, regional scale fluid flow may substantially increase heat flow in discharge areas which would destabilize gas hydrates. For example, discharge of topographically driven groundwater along the coast in the Central North Slope of Alaska has increased surface heat flow in some areas by more than 50% over a purely conductive thermal regime. Fluid flow also alters the pressure regime which can affect gas hydrate stability. Modeling results suggest a positive feedback between gas hydrate formation/disassociation and fluid flow. Disassociation of gas hydrates or permafrost due to global warming could increase permeability. This could enhance fluid flow and associated heat transport causing a more rapid and/or more spatially extensive gas hydrate disassociation than predicted solely from conductive propagation of temporal changes in surface or water bottom temperature. Model results from both the North Slope of Alaska and the Gulf of Mexico are compared.

Importance of Ambipolar Electric Field in the Ion Loss from Mars- Results from a Multi-fluid MHD Model with the Electron Pressure Equation Included

NASA Astrophysics Data System (ADS)

Ma, Y.; Dong, C.; van der Holst, B.; Nagy, A. F.; Bougher, S. W.; Toth, G.; Cravens, T.; Yelle, R. V.; Jakosky, B. M.

2017-12-01

The multi-fluid (MF) magnetohydrodynamic (MHD) model of Mars is further improved by solving an additional electron pressure equation. Through the electron pressure equation, the electron temperature is calculated based on the effects from various electrons related heating and cooling processes (e.g. photo-electron heating, electron-neutral collision and electron-ion collision), and thus the improved model is able to calculate the electron temperature and the electron pressure force self-consistently. Electron thermal conductivity is also considered in the calculation. Model results of a normal case with electron pressure equation included (MFPe) are compared in detail to an identical case using the regular MF model to identify the effect of the improved physics. We found that when the electron pressure equation is included, the general interaction patterns are similar to that of the case with no electron pressure equation. The model with electron pressure equation predicts that electron temperature is much larger than the ion temperature in the ionosphere, consistent with both Viking and MAVEN observations. The inclusion of electron pressure equation significantly increases the total escape fluxes predicted by the model, indicating the importance of the ambipolar electric field(electron pressure gradient) in driving the ion loss from Mars.

Role of density gradient driven trapped electron mode turbulence in the H-mode inner core with electron heating

DOE PAGES

Ernst, D. R.; Burrell, K. H.; Guttenfelder, W.; ...

2016-05-10

In a series of DIII-D [J. L. Luxon, Nucl. Fusion 42 614 (2002)] low torque quiescent H-mode experiments show that density gradient driven TEM (DGTEM) turbulence dominates the inner core of H-Mode plasmas during strong electron cyclotron heating (ECH). By adding 3.4 MW ECH doubles T e/T i from 0.5 to 1.0, which halves the linear DGTEM critical density gradient, locally reducing density peaking, while transport in all channels displays extreme stiffness in the density gradient. This then suggests fusion -heating may degrade inner core confinement in H-Mode plasmas with moderate density peaking and low collisionality, with equal electron andmore » ion temperatures, key conditions expected in burning plasmas. Gyrokinetic simulations using GYRO [J. Candy and R. E. Waltz, J. Comp. Phys. 186 545 (2003)] (and GENE [F. Jenko et al., Phys. Plasmas 7, 1904 (2000)]) closely match not only particle, energy, and momentum fluxes, but also density fluctuation spectra from Doppler Backscattering (DBS), with and without ECH. Inner core DBS density fluctuations display discrete frequencies with adjacent toroidal mode numbers, which we identify as DGTEMs. GS2 [W. Dorland et al., Phys. Rev. Lett. 85 5579 (2000)] predictions show the DGTEM can be suppressed, to avoid degradation with electron heating, by broadening the current density profile to attain q 0 > q min > 1.« less

A comparative study of the influence of buoyancy driven fluid flow on GaAs crystal growth

NASA Technical Reports Server (NTRS)

Kafalas, J. A.; Bellows, A. H.

1988-01-01

A systematic investigation of the effect of gravity driven fluid flow on GaAs crystal growth was performed. It includes GaAs crystal growth in the microgravity environment aboard the Space Shuttle. The program involves a controlled comparative study of crystal growth under a variety of earth based conditions with variable orientation and applied magnetic field in addition to the microgravity growth. Earth based growth will be performed under stabilizing as well as destabilizing temperature gradients. The boules grown in space and on earth will be fully characterized to correlate the degree of convection with the distribution of impurities. Both macro- and micro-segregation will be determined. The space growth experiment will be flown in a self-contained payload container through NASA's Get Away Special program.

Mechanism of nonlinear flow pattern selection in moderately non-Boussinesq mixed convection.

PubMed

Suslov, Sergey A

2010-02-01

Nonlinear (non-Boussinesq) variations in fluid's density, viscosity, and thermal conductivity caused by a large temperature gradient in a flow domain lead to a wide variety of instability phenomena in mixed convection channel flow of a simple gas such as air. It is known that in strongly nonisothermal flows, the instabilities and the resulting flow patterns are caused by competing buoyancy and shear effects [see S. A. Suslov and S. Paolucci, J. Fluid Mech. 302, 91 (1995)]. However, as is the case in the Boussinesq limit of small temperature gradients, in moderately non-Boussinesq regimes, only a shear instability mechanism is active. Yet in contrast to Boussinesq flows, multiple instability modes are still detected. By reducing the system of full governing Navier-Stokes equations to a dynamical system of coupled Landau-type disturbance amplitude equations we compute a comprehensive parametric map of various shear-driven instabilities observed in a representative moderately non-Boussinesq regime. Subsequently, we analyze nonlinear interaction of unstable modes and reveal physical reasons for their appearance.

Transport of heat and mass in near-critical fluids

NASA Astrophysics Data System (ADS)

Garrabos, Yves; Leneindre, B.; Guenoun, P.; Perrot, F.; Beysens, Daniel

1992-08-01

In order to investigate some aspects of heat and mass transport in fluids in the absence of gravity, thermal cycles were performed near the liquid-phase critical point of CO2 and SF6 in the TEXUS 25 rocket and during the International Microgravity Laboratory (IML-1) Spacelab mission. In the absence of gravity driven convection, the heat transport is expected to be diffusive and very slow. Experimentally, although the local density and temperature gradients indeed relax by a diffusive process, clear evidence is found of fast and uniform thermal equilibration. This new mechanism is a 'piston effect'.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Parker, Scott; Chen, Yang

This is the Final Technical Report for University of Colorado's portion of the SciDAC project 'Center for Gyrokinetic Particle Simulation of Turbulent Transport.' This is funded as a multi-institutional SciDAC Center and W.W. Lee at the Princeton Plasma Physics Laboratory is the lead Principal Investigator. Scott Parker is the local Principal Investigator for University of Colorado and Yang Chen is a Co-Principal Investigator. This is Cooperative Agreement DE-FC02-05ER54816. Research personnel include Yang Chen (Senior Research Associate), Jianying Lang (Graduate Research Associate, Ph.D. Physics Student) and Scott Parker (Associate Professor). Research includes core microturbulence studies of NSTX, simulation of trapped electronmore » modes, development of efficient particle-continuum hybrid methods and particle convergence studies of electron temperature gradient driven turbulence simulations. Recently, the particle-continuum method has been extended to five-dimensions in GEM. We find that actually a simple method works quite well for the Cyclone base case with either fully kinetic or adiabatic electrons. Particles are deposited on a 5D phase-space grid using nearest-grid-point interpolation. Then, the value of delta-f is reset, but not the particle's trajectory. This has the effect of occasionally averaging delta-f of nearby (in the phase space) particles. We are currently trying to estimate the dissipation (or effective collision operator). We have been using GEM to study turbulence and transport in NSTX with realistic equilibrium density and temperature profiles, including impurities, magnetic geometry and ExB shear flow. Greg Rewoldt, PPPL, has developed a TRANSP interface for GEM that specifies the equilibrium profiles and parameters needed to run realistic NSTX cases. Results were reported at the American Physical Society - Division of Plasma Physics, and we are currently running convergence studies to ensure physical results. We are also studying the effect of parallel shear flows, which can be quite strong in NSTX. Recent long-time simulations of electron temperature gradient driven turbulence, show that zonal flows slowly grow algebraically via the Rosenbluth-Hinton random walk mechanism. Eventually, the zonal flow gets to a level where it shear suppresses the turbulence. We have demonstrated this behavior with Cyclone base-case parameters, except with a 30% lower temperature gradient. We can demonstrate the same phenomena at higher gradients, but so far, have been unable to get a converged result at the higher temperature gradient. We find that electron ion collisions cause the zonal flows to grow at a slower rate and results in a higher heat flux. So, far all ETG simulations that come to a quasi-steady state show continued build up of zonal flow, see it appears to be a universal phenomena (for ETG). Linear and nonlinear simulations of Collisional and Collisionless trapped electron modes are underway. We find that zonal flow is typically important. We can, however, reproduce the Tannert and Jenko result (that zonal flow is unimportant) using their parameters with the electron temperature three times the ion temperature. For a typical weak gradient core value of density gradient and no temperature gradient, the CTEM is dominant. However, for a steeper density gradient (and still no temperature gradient), representative of the edge, higher k drift-waves are dominant. For the weaker density gradient core case, nonlinear simulations using GEM are routine. For the steeper gradient edge case, the nonlinear fluctuations are very high and a stationary state has not been obtained. This provides motivation for the particle-continuum algorithm. We also note that more physics, e.g. profile variation and equilibrium ExB shear flow should be significantly stabilizing, making such simulations feasible using standard delta-f techniques. This research is ongoing.« less

Microbial community structure across fluid gradients in the Juan de Fuca Ridge hydrothermal system.

PubMed

Anderson, Rika E; Beltrán, Mónica Torres; Hallam, Steven J; Baross, John A

2013-02-01

Physical and chemical gradients are dominant factors in shaping hydrothermal vent microbial ecology, where archaeal and bacterial habitats encompass a range between hot, reduced hydrothermal fluid and cold, oxidized seawater. To determine the impact of these fluid gradients on microbial communities inhabiting these systems, we surveyed bacterial and archaeal community structure among and between hydrothermal plumes, diffuse flow fluids, and background seawater in several hydrothermal vent sites on the Juan de Fuca Ridge using 16S rRNA gene diversity screening (clone libraries and terminal restriction length polymorphisms) and quantitative polymerase chain reaction methods. Community structure was similar between hydrothermal plumes and background seawater, where a number of taxa usually associated with low-oxygen zones were observed, whereas high-temperature diffuse fluids exhibited a distinct phylogenetic profile. SUP05 and Arctic96BD-19 sulfur-oxidizing bacteria were prevalent in all three mixing regimes where they exhibited overlapping but not identical abundance patterns. Taken together, these results indicate conserved patterns of redox-driven niche partitioning between hydrothermal mixing regimes and microbial communities associated with sinking particles and oxygen-deficient waters. Moreover, the prevalence of SUP05 and Arctic96BD-19 in plume and diffuse flow fluids indicates a more cosmopolitan role for these groups in the ecology and biogeochemistry of the dark ocean. © 2012 Federation of European Microbiological Societies. Published by Blackwell Publishing Ltd. All rights reserved.

Magnetism of toroidal field in two-fluid equilibrium of CHI driven spherical torus

NASA Astrophysics Data System (ADS)

Kanki, T.; Nagata, M.

2016-10-01

Double-pulsing CHI (D-CHI) experiment has been conducted in the HIST device to achieve a quasi-steady sustainment and good confinement of spherical torus (ST) plasmas. The feature of CHI driven ST such as diamagnetic toroidal field in the central open flux column (OFC) region and strong poloidal flow shear around the separatrix in the high field side suggests the two-fluid effect. The relationship between the magnetism of the toroidal field and the poloidal flow velocity is investigated by modelling the D-CHI (mainly driving the poloidal electron flow along the open flux) in the two-fluid equilibrium calculations. The poloidal component of Ampere's law leads that the toroidal field is related to the difference between the stream functions of ion ψi and electron ψe for the poloidal flow, indicating that the toroidal field with ψe >ψi results in a diamagnetic profile, while that with ψe <ψi results in a paramagnetic one. The gradient of the stream function determines the polarity and the strength of the poloidal flow velocity. It is found that the two-fluid equilibrium of CHI driven ST satisfies ψe > 0 and ψi < 0 in the OFC region, and ψe < 0 and ψi < 0 in the closed flux region. The toroidal field is a diamagnetic profile in the OFC region due to ψe >ψi and |uez | > |uiz | , where uez and uiz denote the poloidal electron and ion flow velocities, respectively. It becomes from a diamagnetic to a paramagnetic profile in the closed flux region, because ψe (uez) approaches ψi (uiz) around the magnetic axis. The poloidal ion flow shear is enhanced in the OFC region due to the ion inertial effect through the toroidal ion flow velocity.

Multiscale modeling and simulation for polymer melt flows between parallel plates

NASA Astrophysics Data System (ADS)

Yasuda, Shugo; Yamamoto, Ryoichi

2010-03-01

The flow behaviors of polymer melt composed of short chains with ten beads between parallel plates are simulated by using a hybrid method of molecular dynamics and computational fluid dynamics. Three problems are solved: creep motion under a constant shear stress and its recovery motion after removing the stress, pressure-driven flows, and the flows in rapidly oscillating plates. In the creep/recovery problem, the delayed elastic deformation in the creep motion and evident elastic behavior in the recovery motion are demonstrated. The velocity profiles of the melt in pressure-driven flows are quite different from those of Newtonian fluid due to shear thinning. Velocity gradients of the melt become steeper near the plates and flatter at the middle between the plates as the pressure gradient increases and the temperature decreases. In the rapidly oscillating plates, the viscous boundary layer of the melt is much thinner than that of Newtonian fluid due to the shear thinning of the melt. Three different rheological regimes, i.e., the viscous fluid, viscoelastic liquid, and viscoelastic solid regimes, form over the oscillating plate according to the local Deborah numbers. The melt behaves as a viscous fluid in a region for ωτR≲1 , and the crossover between the liquidlike and solidlike regime takes place around ωτα≃1 (where ω is the angular frequency of the plate and τR and τα are Rouse and α relaxation time, respectively).

Multiscale modeling and simulation for polymer melt flows between parallel plates.

PubMed

Yasuda, Shugo; Yamamoto, Ryoichi

2010-03-01

The flow behaviors of polymer melt composed of short chains with ten beads between parallel plates are simulated by using a hybrid method of molecular dynamics and computational fluid dynamics. Three problems are solved: creep motion under a constant shear stress and its recovery motion after removing the stress, pressure-driven flows, and the flows in rapidly oscillating plates. In the creep/recovery problem, the delayed elastic deformation in the creep motion and evident elastic behavior in the recovery motion are demonstrated. The velocity profiles of the melt in pressure-driven flows are quite different from those of Newtonian fluid due to shear thinning. Velocity gradients of the melt become steeper near the plates and flatter at the middle between the plates as the pressure gradient increases and the temperature decreases. In the rapidly oscillating plates, the viscous boundary layer of the melt is much thinner than that of Newtonian fluid due to the shear thinning of the melt. Three different rheological regimes, i.e., the viscous fluid, viscoelastic liquid, and viscoelastic solid regimes, form over the oscillating plate according to the local Deborah numbers. The melt behaves as a viscous fluid in a region for omegatauR < approximately 1 , and the crossover between the liquidlike and solidlike regime takes place around omegataualpha approximately equal 1 (where omega is the angular frequency of the plate and tauR and taualpha are Rouse and alpha relaxation time, respectively).

Thermal gradients for the stabilization of a single domain wall in magnetic nanowires.

PubMed

Mejía-López, J; Velásquez, E A; Mazo-Zuluaga, J; Altbir, D

2018-08-24

By means of Monte Carlo simulations we studied field driven nucleation and propagation of transverse domain walls (DWs) in magnetic nanowires subjected to temperature gradients. Simulations identified the existence of critical thermal gradients that allow the existence of reversal processes driven by a single DW. Critical thermal gradients depend on external parameters such as temperature, magnetic field and wire length, and can be experimentally obtained through the measurement of the mean velocity of the magnetization reversal as a function of the temperature gradient. Our results show that temperature gradients provide a high degree of control over DW propagation, which is of great importance for technological applications.

Expansion of Non-Quasi-Neutral Limited Plasmas Driven by Two-Temperature Electron Clouds

NASA Astrophysics Data System (ADS)

Murakami, Masakatsu; Honrubia, Javier

2017-10-01

Fast heating of an isolated solid mass, under irradiation of ultra-intense ultra-short laser pulse, to averaged temperatures of order of keV is theoretically studied. Achievable maximum ion temperatures are determined as a consequence of the interplay of the electron-to-ion energy deposition and nonrelativistic plasma expansion, where fast ion emission plays an important role in the energy balance. To describe the plasma expansion, we develop a self-similar solution, in which the plasma is composed of three fluids, i.e., ions and two-temperature electrons. Under the condition of isothermal electron expansion in cylindrical geometry, such a fluid system, self-consistently incorporated with the Poisson equation, is fully solved. The charge separation and resultant accelerated ion population due to the induced electrostatic field are quantitatively presented. The analytical model is compared with two-dimensional hydrodynamic simulations to provide practical working windows for the target and laser parameters for the fast heating.

Endogenous Magnetic Reconnection in Solar Coronal Loops

NASA Astrophysics Data System (ADS)

Asgari-Targhi, M.; Coppi, B.; Basu, B.; Fletcher, A.; Golub, L.

2017-12-01

We propose that a magneto-thermal reconnection process occurring in coronal loops be the source of the heating of the Solar Corona [1]. In the adopted model, magnetic reconnection is associated with electron temperature gradients, anisotropic electron temperature fluctuations and plasma current density gradients [2]. The input parameters for our theoretical model are derived from the most recent observations of the Solar Corona. In addition, the relevant (endogenous) collective modes can produce high energy particle populations. An endogenous reconnection process is defined as being driven by factors internal to the region where reconnection takes place. *Sponsored in part by the U.S. D.O.E. and the Kavli Foundation* [1] Beafume, P., Coppi, B. and Golub, L., (1992) Ap. J. 393, 396. [2] Coppi, B. and Basu, B. (2017) MIT-LNS Report HEP 17/01.

Hall effects on unsteady MHD oscillatory free convective flow of second grade fluid through porous medium between two vertical plates

NASA Astrophysics Data System (ADS)

VeeraKrishna, M.; Subba Reddy, G.; Chamkha, A. J.

2018-02-01

The effects of radiation and Hall current on an unsteady magnetohydrodynamic free convective flow in a vertical channel filled with a porous medium have been studied. We consider an incompressible viscous and electrically conducting incompressible viscous second grade fluid bounded by a loosely packed porous medium. The fluid is driven by an oscillating pressure gradient parallel to the channel plates, and the entire flow field is subjected to a uniform inclined magnetic field of strength Ho inclined at an angle of inclination α with the normal to the boundaries in the transverse xy-plane. The temperature of one of the plates varies periodically, and the temperature difference of the plates is high enough to induce the radiative heat transfer. The effects of various parameters on the velocity profiles, the skin friction, temperature field, rate of heat transfer in terms of their amplitude, and phase angles are shown graphically.

Influence of Hall Current and Viscous Dissipation on Pressure Driven Flow of Pseudoplastic Fluid with Heat Generation: A Mathematical Study.

PubMed

Noreen, Saima; Qasim, Muhammad

2015-01-01

In this paper, we study the influence of heat sink (or source) on the peristaltic motion of pseudoplastic fluid in the presence of Hall current, where channel walls are non-conducting in nature. Flow analysis has been carried out under the approximations of a low Reynolds number and long wavelength. Coupled equations are solved using shooting method for numerical solution for the axial velocity function, temperature and pressure gradient distributions. We analyze the influence of various interesting parameters on flow quantities. The present study can be considered as a mathematical presentation of the dynamics of physiological organs with stones.

Magnetic field gradient driven self-assembly of superparamagnetic nanoparticles using programmable magnetically-recorded templates

NASA Astrophysics Data System (ADS)

Ye, L.; Qi, B.; Lawton, T. G.; Mefford, O. T.; Rinaldi, C.; Garzon, S.; Crawford, T. M.

2013-03-01

Using the enormous magnetic field gradients (100 MT/m @ z =20 nm) present near the surface of magnetic recording media, we demonstrate the fabrication of diffraction gratings with lines consisting entirely of magnetic nanoparticles assembled from a colloidal fluid onto a disk drive medium, followed by transfer to a flexible and transparent polymer thin film. These nanomanufactured gratings have line spacings programmed with commercial magnetic recording and are inherently concave with radii of curvature controlled by varying the polymer film thickness. The diffracted intensity increases non-monotonically with the length of time the colloidal fluid remains on the disk surface. In addition to comparing longitudinal and perpendicular magnetic recording, a combination of spectral diffraction efficiency measurements, magnetometry, scanning electron microscopy and inductively coupled plasma atomic emmission spectroscopy of these gratings are employed to understand colloidal nanoparticle dynamics in this extreme gradient limit. Such experiments are necessary to optimize nanoparticle assembly and obtain uniform patterned features. This low-cost and sustainable approach to nanomanufacturing could enable low-cost, high-quality diffraction gratings as well as more complex polymer nanocomposite materials assembled with single-nanometer precision.

Surface Tension Induced Instabilities in Reduced Gravity: the Benard Problem

NASA Technical Reports Server (NTRS)

Koschmieder, E.; Chai, A. T.

1985-01-01

A Benard convection experiment has been set up, and the onset of convection in shallow layers of silicone oil two millimeters or less deep has been studied. The onset has been observed visually or has been determined by the break in the heat transfer curve which accompanies the onset of convection. The outcome of these experiments has been very surprising, from the point of view of theoretical expectations. The onset of convection at temperature differences far below the critical value for fluid depths smaller than 2mm was observed. The discrepancy between experiments and theory increases with decreasing fluid depth. According to theoretical considerations, the effects of surface tension become more important as the fluid depth is decreased. Actually, one observes that the onset of convection tales place in two stages. There is first an apparently surface tension driven instability, occuring at subcritical temperature differences according to conventional theory. If then the temperature difference is increased, a second instability occurs which transform the first pattern into conventional strong hexagonal Benard cells. The second instability is in agreement with the critical temperature gradients predicted by Nield.

Magnetothermal Convection in Nonconducting Diamagnetic and Paramagnetic Fluids

NASA Technical Reports Server (NTRS)

Edwards, Boyd F.; Gray, Donald D.; Huang, Jie

1996-01-01

Nonuniform magnetic fields exert a magnetic body force on electrically nonconducting classical fluids. These include paramagnetic fluids such as gaseous and liquid oxygen and diamagnetic fluids such as helium. Recent experiments show that this force can overwhelm the force of gravity even at the surface of the earth; it can levitate liquids and gases, quench candle flames, block gas flows, and suppress heat transport. Thermal gradients render the magnetic force nonuniform through the temperature-dependent magnetic susceptibility. These thermal gradients can therefore drive magnetic convection analogous to buoyancy-driven convection. This magnetothermal convection can overwhelm convection driven by gravitational buoyancy in terrestrial experiments. The objectives of the proposed ground-based theoretical study are (a) to supply the magnetothermohydrodynamic theory necessary to understand these recent experiments and (b) to explore the consequences of nonuniform magnetic fields in microgravity. Even the linear theory for the onset of magnetothermal convection is lacking in the literature. We intend to supply the linear and nonlinear theory based on the thermohydrodynamic equations supplemented by the magnetic body force. We intend to investigate the effect of magnetic fields on gas blockage and heat transport in microgravity. Since magnetic fields provide a means of creating arbitrary, controllable body force distributions, we intend to investigate the possibility of using magnetic fields to position and control fluids in microgravity. We also intend to investigate the possibility of creating stationary terrestrial microgravity environments by using the magnetic force to effectively cancel gravity. These investigations may aid in the design of space-based heat-transfer, combustion, and human-life-support equipment.

A New Global Multi-fluid MHD Model of the Solar Corona

NASA Astrophysics Data System (ADS)

van der Holst, B.; Chandran, B. D. G.; Alterman, B. L.; Kasper, J. C.; Toth, G.

2017-12-01

We present a multi-fluid generalization of the AWSoM model, a global magnetohydrodynamic (MHD) solar corona model with low-frequency Alfven wave turbulence (van der Holst et al., 2014). This new extended model includes electron and multi-ion temperatures and velocities (protons and alpha particles). The coronal heating and acceleration is addressed via outward propagating low-frequency Alfven waves that are partially reflected by Alfven speed gradients. The nonlinear interaction of these counter-propagating waves results in turbulent energy cascade. To apportion the wave dissipation to the electron and ion temperatures, we employ the results of the theories of linear wave damping and nonlinear stochastic heating as described by Chandran et al. (2011, 2013). This heat partitioning results in a more than mass proportional heating among ions.

Fluid helium at conditions of giant planetary interiors

PubMed Central

Stixrude, Lars; Jeanloz, Raymond

2008-01-01

As the second most-abundant chemical element in the universe, helium makes up a large fraction of giant gaseous planets, including Jupiter, Saturn, and most extrasolar planets discovered to date. Using first-principles molecular dynamics simulations, we find that fluid helium undergoes temperature-induced metallization at high pressures. The electronic energy gap (band gap) closes at 20,000 K at a density half that of zero-temperature metallization, resulting in electrical conductivities greater than the minimum metallic value. Gap closure is achieved by a broadening of the valence band via increased s–p hydridization with increasing temperature, and this influences the equation of state: The Grüneisen parameter, which determines the adiabatic temperature–depth gradient inside a planet, changes only modestly, decreasing with compression up to the high-temperature metallization and then increasing upon further compression. The change in electronic structure of He at elevated pressures and temperatures has important implications for the miscibility of helium in hydrogen and for understanding the thermal histories of giant planets.

Increased electron temperature turbulence during suppression of edge localized mode by resonant magnetic perturbations in the DIII-D tokamak [Increased electron temperature turbulence during edge localized mode (ELM) suppression by resonant magnetic perturbations (RMPs) in the DIII-D tokamak

DOE PAGES

Sung, Choongki; Wang, G.; Rhodes, Terry L.; ...

2017-11-16

We report the first observation of increased edge electron temperature turbulence correlated with changes in gradients and the ELM suppression time which occurs after the application of resonant magnetic perturbations (RMP) on DIII-D H-mode plasmas. This increase (T ~ e/T e approximately doubles) occurs in the region extending from the top of the pedestal outward to the upper part of the edge steep gradient region. This is significant as it is consistent with increased turbulence driven transport potentially replacing some part of the edge localized mode (ELM) driven transport. However, temperature turbulence does not change with the initial RMP applicationmore » while ELMs are still present, indicating the turbulence changes are not causative in the development of ELM suppression or initial profile evolution with RMP – but rather a response to these effects. This temperature turbulence is broadband and long wavelength, k θρ s < 0.5, where k θ = poloidal wavenumber, ρ s = ion sound gyroradius. As has been reported previously, long wavelength density turbulence (k θρ s < 1.0) in the same location also increases after ELMs were suppressed by the RMP. Since the decrease of the density starts nearly immediately with RMP application, these results suggest that the so-called RMP “density pump-out” is not linked to these long wavelength turbulent transport changes. Comparison with linear stability analysis finds both consistencies and inconsistencies in this important region.« less

Increased electron temperature turbulence during suppression of edge localized mode by resonant magnetic perturbations in the DIII-D tokamak [Increased electron temperature turbulence during edge localized mode (ELM) suppression by resonant magnetic perturbations (RMPs) in the DIII-D tokamak

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sung, Choongki; Wang, G.; Rhodes, Terry L.

We report the first observation of increased edge electron temperature turbulence correlated with changes in gradients and the ELM suppression time which occurs after the application of resonant magnetic perturbations (RMP) on DIII-D H-mode plasmas. This increase (T ~ e/T e approximately doubles) occurs in the region extending from the top of the pedestal outward to the upper part of the edge steep gradient region. This is significant as it is consistent with increased turbulence driven transport potentially replacing some part of the edge localized mode (ELM) driven transport. However, temperature turbulence does not change with the initial RMP applicationmore » while ELMs are still present, indicating the turbulence changes are not causative in the development of ELM suppression or initial profile evolution with RMP – but rather a response to these effects. This temperature turbulence is broadband and long wavelength, k θρ s < 0.5, where k θ = poloidal wavenumber, ρ s = ion sound gyroradius. As has been reported previously, long wavelength density turbulence (k θρ s < 1.0) in the same location also increases after ELMs were suppressed by the RMP. Since the decrease of the density starts nearly immediately with RMP application, these results suggest that the so-called RMP “density pump-out” is not linked to these long wavelength turbulent transport changes. Comparison with linear stability analysis finds both consistencies and inconsistencies in this important region.« less

Viscous relaxation of impact crater relief on Venus - Constraints on crustal thickness and thermal gradient

NASA Technical Reports Server (NTRS)

Grimm, Robert E.; Solomon, Sean C.

1988-01-01

Models for the viscous relaxation of impact crater topography are used to constrain the crustal thickness (H) and the mean lithospheric thermal gradient beneath the craters on Venus. A general formulation for gravity-driven flow in a linearly viscous fluid has been obtained which incorporates the densities and temperature-dependent effective viscosities of distinct crust and mantle layers. An upper limit to the crustal volume of Venus of 10 to the 10th cu km is obtained which implies either that the average rate of crustal generation has been much smaller on Venus than on earth or that some form of crustal recycling has occurred on Venus.

The LTX- β Research Program

NASA Astrophysics Data System (ADS)

Majeski, R.; Bell, R. E.; Boyle, D. P.; Hughes, P. E.; Kaita, R.; Kozub, T.; Merino, E.; Zhang, X.; Biewer, T. M.; Canik, J. M.; Elliott, D. B.; Reinke, M. L.; Bialek, J.; Hansen, C.; Jarboe, T.; Kubota, S.; Rhodes, T.; Dorf, M. A.; Rognlien, T.; Scotti, F.; Soukhanovskii, V. A.; Koel, B. E.; Donovan, D.; Maan, A.

2017-10-01

LTX- β, the upgrade to the Lithium Tokamak Experiment, approximately doubles the toroidal field (to 3.4 kG) and plasma current (to 150 - 175 kA) of LTX. Neutral beam injection at 20 kV, 30 A will be added in February 2018, with systems provided by Tri-Alpha Energy. A 9.3 GHz, 100 kW, short-pulse (5-10 msec) source will be available in summer 2018 for electron Bernstein wave heating. New lithium evaporation sources will allow between-shots recoating of the walls. Upgrades to the diagnostic set are intended to strengthen the research program in the critical areas of equilibrium, core transport, scrape-off layer physics, and plasma-material interactions. The LTX- β research program will combine the capability for gradient-free temperature profiles, to stabilize ion and electron temperature gradient-driven modes, with approaches to stabilization of ∇n-driven modes, such as the trapped electron mode (TEM). Candidate stabilization mechanisms for the TEM include sheared flow stabilization, which can be tested on LTX- β. The goal will be to minimize anomalous transport in a low aspect ratio tokamak, which would lead to a very compact, tokamak-based fusion core. This work supported by US DOE contracts DE-AC02-09CH11466 and DE-AC05-00OR22725.

Self-consistent fluid modeling and simulation on a pulsed microwave atmospheric-pressure argon plasma jet

NASA Astrophysics Data System (ADS)

Chen, Zhaoquan; Yin, Zhixiang; Chen, Minggong; Hong, Lingli; Xia, Guangqing; Hu, Yelin; Huang, Yourui; Liu, Minghai; Kudryavtsev, A. A.

2014-10-01

In present study, a pulsed lower-power microwave-driven atmospheric-pressure argon plasma jet has been introduced with the type of coaxial transmission line resonator. The plasma jet plume is with room air temperature, even can be directly touched by human body without any hot harm. In order to study ionization process of the proposed plasma jet, a self-consistent hybrid fluid model is constructed in which Maxwell's equations are solved numerically by finite-difference time-domain method and a fluid model is used to study the characteristics of argon plasma evolution. With a Guass type input power function, the spatio-temporal distributions of the electron density, the electron temperature, the electric field, and the absorbed power density have been simulated, respectively. The simulation results suggest that the peak values of the electron temperature and the electric field are synchronous with the input pulsed microwave power but the maximum quantities of the electron density and the absorbed power density are lagged to the microwave power excitation. In addition, the pulsed plasma jet excited by the local enhanced electric field of surface plasmon polaritons should be the discharge mechanism of the proposed plasma jet.

Transport Barriers in Bootstrap Driven Tokamaks

NASA Astrophysics Data System (ADS)

Staebler, Gary

2017-10-01

Maximizing the bootstrap current in a tokamak, so that it drives a high fraction of the total current, reduces the external power required to drive current by other means. Improved energy confinement, relative to empirical scaling laws, enables a reactor to more fully take advantage of the bootstrap driven tokamak. Experiments have demonstrated improved energy confinement due to the spontaneous formation of an internal transport barrier in high bootstrap fraction discharges. Gyrokinetic analysis, and quasilinear predictive modeling, demonstrates that the observed transport barrier is due to the suppression of turbulence primarily due to the large Shafranov shift. ExB velocity shear does not play a significant role in the transport barrier due to the high safety factor. It will be shown, that the Shafranov shift can produce a bifurcation to improved confinement in regions of positive magnetic shear or a continuous reduction in transport for weak or negative magnetic shear. Operation at high safety factor lowers the pressure gradient threshold for the Shafranov shift driven barrier formation. The ion energy transport is reduced to neoclassical and electron energy and particle transport is reduced, but still turbulent, within the barrier. Deeper into the plasma, very large levels of electron transport are observed. The observed electron temperature profile is shown to be close to the threshold for the electron temperature gradient (ETG) mode. A large ETG driven energy transport is qualitatively consistent with recent multi-scale gyrokinetic simulations showing that reducing the ion scale turbulence can lead to large increase in the electron scale transport. A new saturation model for the quasilinear TGLF transport code, that fits these multi-scale gyrokinetic simulations, can match the data if the impact of zonal flow mixing on the ETG modes is reduced at high safety factor. This work was supported by the U.S. Department of Energy under DE-FG02-95ER54309 and DE-FC02-04ER54698.

Theoretical and computational studies of the sheath of a planar wall

NASA Astrophysics Data System (ADS)

Giraudo, Martina; Camporeale, Enrico; Delzanno, Gian Luca; Lapenta, Giovanni

2012-03-01

We present an investigation of the stability and nonlinear evolution of the sheath of a planar wall. We focus on the electrostatic limit. The stability analysis is conducted with a fluid model where continuity and momentum equations for the electrons and ions are coupled through Poisson's equation. The effect of electron emission from the wall is studied parametrically. Our results show that a sheath instability associated with the emitted electrons can exist. Following Ref. [1], it is interpreted as a Rayleigh-Taylor instability driven by the favorable combination of the sheath electron density gradient and electric field. Fully kinetic Particle-In-Cell (PIC) simulations will also be presented to investigate whether this instability indeed exists and to study the nonlinear effect of electron emission on the sheath profiles. The simulations will be conducted with CPIC, a new electrostatic PIC code that couples the standard PIC algorithm with strategies for generation and adaptation of the computational grid. [4pt] [1] G.L. Delzanno, ``A paradigm for the stability of the plasma sheath against fluid perturbations,'' Phys. Plasmas 18, 103508 (2011).

EMPFASIS: A Publication of the National Electronics Manufacturing Center of Excellence

DTIC Science & Technology

2010-01-01

for moisture, salt spray, and wind driven rain protection. • Conversion to ruggedized electrical and fluid connectors. • Additional circuitry, if...computer control technology, designed for safe lead free and eutectic rework applications. Available in two models, the RD-500 series features a three-stage...shock, Temperature Humidity Bias (THB) Testing, Highly Accelerated Stress Testing (HAST), salt fog, high temperature storage, or other environmental

Electron temperature critical gradient and transport stiffness in DIII-D

DOE PAGES

Smith, Sterling P.; Petty, Clinton C.; White, Anne E.; ...

2015-07-06

The electron energy flux has been probed as a function of electron temperature gradient on the DIII-D tokamak, in a continuing effort to validate turbulent transport models. In the scan of gradient, a critical electron temperature gradient has been found in the electron heat fluxes and stiffness at various radii in L-mode plasmas. The TGLF reduced turbulent transport model [G.M. Staebler et al, Phys. Plasmas 14, 055909 (2007)] and full gyrokinetic GYRO model [J. Candy and R.E. Waltz, J. Comput. Phys. 186, 545 (2003)] recover the general trend of increasing electron energy flux with increasing electron temperature gradient scale length,more » but they do not predict the absolute level of transport at all radii and gradients. Comparing the experimental observations of incremental (heat pulse) diffusivity and stiffness to the models’ reveals that TGLF reproduces the trends in increasing diffusivity and stiffness with increasing electron temperature gradient scale length with a critical gradient behavior. Furthermore, the critical gradient of TGLF is found to have a dependence on q 95, contrary to the independence of the experimental critical gradient from q 95.« less

On the tertiary instability formalism of zonal flows in magnetized plasmas

NASA Astrophysics Data System (ADS)

Rath, F.; Peeters, A. G.; Buchholz, R.; Grosshauser, S. R.; Seiferling, F.; Weikl, A.

2018-05-01

This paper investigates the so-called tertiary instabilities driven by the zonal flow in gyro-kinetic tokamak core turbulence. The Kelvin Helmholtz instability is first considered within a 2D fluid model and a threshold in the zonal flow wave vector kZF>kZF,c for instability is found. This critical scale is related to the breaking of the rotational symmetry by flux-surfaces, which is incorporated into the modified adiabatic electron response. The stability of undamped Rosenbluth-Hinton zonal flows is then investigated in gyro-kinetic simulations. Absolute instability, in the sense that the threshold zonal flow amplitude tends towards zero, is found above a zonal flow wave vector kZF,cρi≈1.3 ( ρi is the ion thermal Larmor radius), which is comparable to the 2D fluid results. Large scale zonal flows with kZF

Return current instability driven by a temperature gradient in ICF plasmas

DOE PAGES

Rozmus, W.; Brantov, A. V.; Sherlock, M.; ...

2017-10-12

Here, hot plasmas with strong temperature gradients in inertial confinement fusion (ICF) experiments are examined for ion acoustic instabilities produced by electron heat flow. The return current instability (RCI) due to a neutralizing current of cold electrons arising in response to a large electron heat flux has been considered. First, the linear threshold and growth rates are derived in the nonlocal regime of thermal transport. They are compared with the results of Vlasov-Fokker-Planck (VFP) simulations in one spatial dimension. Very good agreement has been found between kinetic VFP simulations and the linear theory of the RCI. A quasi-stationary state ofmore » ion acoustic turbulence produced by the RCI is achieved in the VFP simulations. Saturation of the RCI involves heating of ions in the tail of the ion distribution function and convection of the enhanced ion acoustic fluctuations from the unstable region of the plasma. Further evolution of the ion acoustic turbulence and its effects on absorption and transport are also discussed.« less

Return current instability driven by a temperature gradient in ICF plasmas

NASA Astrophysics Data System (ADS)

Rozmus, W.; Brantov, A. V.; Sherlock, M.; Bychenkov, V. Yu

2018-01-01

Hot plasmas with strong temperature gradients in inertial confinement fusion experiments are examined for ion acoustic instabilities produced by electron heat flow. The return current instability (RCI) due to a neutralizing current of cold electrons arising in response to a large electron heat flux has been considered. First, the linear threshold and growth rates are derived in the non-local regime of thermal transport. They are compared with the results of Vlasov-Fokker-Planck (VFP) simulations in one spatial dimension. Very good agreement has been found between kinetic VFP simulations and the linear theory of the RCI. A quasi-stationary state of ion acoustic turbulence (IAT) produced by the RCI is achieved in the VFP simulations. Saturation of the RCI involves heating of ions in the tail of the ion distribution function and convection of the enhanced ion acoustic fluctuations from the unstable region of the plasma. Further evolution of the IAT and its effects on absorption and transport are also discussed.

Surface effects on friction-induced fluid heating in nanochannel flows.

PubMed

Li, Zhigang

2009-02-01

We investigate the mechanism of friction-induced fluid heating under the influence of surfaces. The temperature distributions of liquid argon and helium in nanoscale Poiseuille flows are studied through molecular dynamics simulations. It is found that the fluid heating is mainly caused by the viscous friction in the fluid when the external force is small and there is no slip at the fluid-solid interface. When the external force is larger than the fluid-surface binding force, the friction at the fluid-solid interface dominates over the internal friction of the fluid and is the major contribution to fluid heating. An asymmetric temperature gradient in the fluid is developed in the case of nonidentical walls and the general temperature gradient may change sign as the dominant heating factor changes from internal to interfacial friction with increasing external force. The effect of temperature on the fluid heating is also discussed.

Weld pool development during GTA and laser beam welding of Type 304 stainless steel; Part II-experimental correlation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zacharia, T.; David, S.A.; Vitek, J.M.

1989-12-01

In part I of the paper, the results of the heat flow and the fluid flow analysis were presented. Here, in Part II of the paper, predictions of the computational model are verified by comparing the numerically predicted and experimentally observed fusion zone size and shape. Stationary gas tungsten arc and laser beam welds were made on Type 304 stainless steel for different times to provide a variety of solidification conditions such as cooling rate and temperature gradient. Calculated temperatures and cooling rates are correlated with the experimentally observed fusion zone structure. In addition, the effect of sulfur on GTAmore » weld penetration was quantitatively evaluated by considering two heats of 304 stainless steel containing 90 and 240 ppm sulfur. Sulfur, as expected, increased the depth/width ratio by altering the surface tension gradient driven flow in the weld pool.« less

Control system for fluid heated steam generator

DOEpatents

Boland, J.F.; Koenig, J.F.

1984-05-29

A control system for controlling the location of the nucleate-boiling region in a fluid heated steam generator comprises means for measuring the temperature gradient (change in temperature per unit length) of the heating fluid along the steam generator; means for determining a control variable in accordance with a predetermined function of temperature gradients and for generating a control signal in response thereto; and means for adjusting the feedwater flow rate in accordance with the control signal.

Control system for fluid heated steam generator

DOEpatents

Boland, James F.; Koenig, John F.

1985-01-01

A control system for controlling the location of the nucleate-boiling region in a fluid heated steam generator comprises means for measuring the temperature gradient (change in temperature per unit length) of the heating fluid along the steam generator; means for determining a control variable in accordance with a predetermined function of temperature gradients and for generating a control signal in response thereto; and means for adjusting the feedwater flow rate in accordance with the control signal.

Heat currents in electronic junctions driven by telegraph noise

NASA Astrophysics Data System (ADS)

Entin-Wohlman, O.; Chowdhury, D.; Aharony, A.; Dattagupta, S.

2017-11-01

The energy and charge fluxes carried by electrons in a two-terminal junction subjected to a random telegraph noise, produced by a single electronic defect, are analyzed. The telegraph processes are imitated by the action of a stochastic electric field that acts on the electrons in the junction. Upon averaging over all random events of the telegraph process, it is found that this electric field supplies, on the average, energy to the electronic reservoirs, which is distributed unequally between them: the stronger is the coupling of the reservoir with the junction, the more energy it gains. Thus the noisy environment can lead to a temperature gradient across an unbiased junction.

Gyrofluid theory and simulation of electromagnetic turbulence and transport in tokamak plasmas

NASA Astrophysics Data System (ADS)

Snyder, Philip Benjamin

1999-11-01

Turbulence and transport in toroidal plasmas is studied via the development of an electromagnetic gyrofluid model, and its implementation in realistic nonlinear simulations. This work extends earlier electrostatic gyrofluid models to include magnetic fluctuations and non-adiabatic passing electron dynamics. A new set of electron fluid equations is derived from the drift kinetic equation, via an expansion in the electron-ion mass ratio. These electron equations include descriptions of linear and nonlinear drift motion, Landau damping, and electron-ion collisions. Ion moment equations are derived from the electromagnetic gyrokinetic equation, and the gyrokinetic Poisson's Equation and Ampere's Law close the system. The model is benchmarked with linear gyrokinetic calculations, and good agreement is found for both the finite-β ion temperature gradient (ITG) and kinetic Alfvén ballooning (KBM) instabilities. Nonlinear simulations of ITG and KBM-driven turbulence are performed in toroidal flux tube geometry at a range of values of plasma β, and electromagnetic effects are found to significantly impact turbulent heat and particle transport. At low values of β, transport is reduced, as expected due to the finite-β stabilization of the ITG mode. However, as β approaches the Ideal-MHD stability threshold, transport can increase. In the presence of dissipation provided by a model of electron Landau damping and electron-ion collisions, this transport increase can be quite dramatic. Finally, the results of the simulations are compared to tokamak experiments, and encouraging agreement is found with measured density and temperature fluctuation spectra. Direct comparisons of transport fluxes reveal that electromagnetic effects are important at characteristic edge parameters, bringing predicted fluxes more closely in line with observations.

Lagrangian transport in a class of three-dimensional buoyancy-driven flows

NASA Astrophysics Data System (ADS)

Contreras, Sebastian; Speetjens, Michel; Clercx, Herman

2017-11-01

The study concerns the Lagrangian dynamics of three-dimensional (3D) buoyancy-driven cavity flows under steady and laminar conditions due to a global temperature gradient imposed via an opposite hot and cold sidewall. This serves as archetypal configuration for natural-convection flows in which gravity is perpendicular to the global temperature gradient. Limited insight into the Lagrangian properties of this class of flows motivates this study. The 3D Lagrangian dynamics are investigated in terms of the generic structure of the Lagrangian flow topology that is described in terms of the Grashof number (Gr) and the Prandtl number (Pr). Gr is the principal control parameter for the flow topology: vanishing Gr yields a state of closed streamlines (integrable state); increasing Gr causes the formation of toroidal coherent structures embedded in chaotic streamlines governed by Hamiltonian mechanisms. Fluid inertia prevails for ``smaller'' Gr. A buoyancy-induced bifurcation of the flow topology occurs for ``larger'' Gr and underlies the emergence of ``secondary rolls'' and secondary tori for ``larger'' Pr. Stagnation points and corresponding manifold interactions are key to the dynamics. S.C. acknowledges financial support from Consejo Nacional de Ciencia y Tecnología (CONACYT).

Laser induced fluorescence measurements of ion velocity and temperature of drift turbulence driven sheared plasma flow in a linear helicon plasma device

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chakraborty Thakur, S.; Fedorczak, N.; Manz, P.

2012-08-15

Using laser induced fluorescence (LIF), radial profiles of azimuthal ion fluid velocity and ion temperature are measured in the controlled shear de-correlation experiment (CSDX) linear helicon plasma device. Ion velocities and temperatures are derived from the measured Doppler broadened velocity distribution functions of argon ions. The LIF system employs a portable, high power (>300 mW), narrowband ({approx}1 MHz) tunable diode laser-based system operating at 668.614 nm. Previous studies in CSDX have shown the existence of a radially sheared azimuthal flow as measured with time delay estimation methods and Mach probes. Here, we report the first LIF measurements of sheared plasmamore » fluid flow in CSDX. Above a critical magnetic field, the ion fluid flow profile evolves from radially uniform to peaked on axis with a distinct reversed flow region at the boundary, indicating the development of a sheared azimuthal flow. Simultaneously, the ion temperature also evolves from a radially uniform profile to a profile with a gradient. Measurements in turbulent and coherent drift wave mode dominated plasmas are compared.« less

Characteristics of temperature rise in variable inductor employing magnetorheological fluid driven by a high-frequency pulsed voltage source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Ho-Young; Kang, In Man, E-mail: imkang@ee.knu.ac.kr; Shon, Chae-Hwa

2015-05-07

A variable inductor with magnetorheological (MR) fluid has been successfully applied to power electronics applications; however, its thermal characteristics have not been investigated. To evaluate the performance of the variable inductor with respect to temperature, we measured the characteristics of temperature rise and developed a numerical analysis technique. The characteristics of temperature rise were determined experimentally and verified numerically by adopting a multiphysics analysis technique. In order to accurately estimate the temperature distribution in a variable inductor with an MR fluid-gap, the thermal solver should import the heat source from the electromagnetic solver to solve the eddy current problem. Tomore » improve accuracy, the B–H curves of the MR fluid under operating temperature were obtained using the magnetic property measurement system. In addition, the Steinmetz equation was applied to evaluate the core loss in a ferrite core. The predicted temperature rise for a variable inductor showed good agreement with the experimental data and the developed numerical technique can be employed to design a variable inductor with a high-frequency pulsed voltage source.« less

The electric field in capacitively coupled RF discharges: a smooth step model that includes thermal and dynamic effects

NASA Astrophysics Data System (ADS)

Brinkmann, Ralf Peter

2015-12-01

The electric field in radio-frequency driven capacitively coupled plasmas (RF-CCP) is studied, taking thermal (finite electron temperature) and dynamic (finite electron mass) effects into account. Two dimensionless numbers are introduced, the ratios ε ={λ\\text{D}}/l of the electron Debye length {λ\\text{D}} to the minimum plasma gradient length l (typically the sheath thickness) and η ={ω\\text{RF}}/{ω\\text{pe}} of the RF frequency {ω\\text{RF}} to the electron plasma frequency {ω\\text{pe}} . Assuming both numbers small but finite, an asymptotic expansion of an electron fluid model is carried out up to quadratic order inclusively. An expression for the electric field is obtained which yields (i) the space charge field in the sheath, (ii) the generalized Ohmic and ambipolar field in the plasma, and (iii) a smooth interpolation for the transition in between. The new expression is a direct generalization of the Advanced Algebraic Approximation (AAA) proposed by the same author (2009 J. Phys. D: Appl. Phys. 42 194009), which can be recovered for η \\to 0 , and of the established Step Model (SM) by Godyak (1976 Sov. J. Plasma Phys. 2 78), which corresponds to the simultaneous limits η \\to 0 , ε \\to 0 . A comparison of the hereby proposed Smooth Step Model (SSM) with a numerical solution of the full dynamic problem proves very satisfactory.

THE COUPLED EVOLUTION OF ELECTRONS AND IONS IN CORONAL MASS EJECTION-DRIVEN SHOCKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manchester IV, W. B.; Van der Holst, B.; Toth, G.

2012-09-01

We present simulations of coronal mass ejections (CMEs) performed with a new two-temperature coronal model developed at the University of Michigan, which is able to address the coupled thermodynamics of the electron and proton populations in the context of a single fluid. This model employs heat conduction for electrons, constant adiabatic index ({gamma} = 5/3), and includes Alfven wave pressure to accelerate the solar wind. The Wang-Sheeley-Arge empirical model is used to determine the Alfven wave pressure necessary to produce the observed bimodal solar wind speed. The Alfven waves are dissipated as they propagate from the Sun and heat protonsmore » on open magnetic field lines to temperatures above 2 MK. The model is driven by empirical boundary conditions that includes GONG magnetogram data to calculate the coronal field, and STEREO/EUVI observations to specify the density and temperature at the coronal boundary by the Differential Emission Measure Tomography method. With this model, we simulate the propagation of fast CMEs and study the thermodynamics of CME-driven shocks. Since the thermal speed of the electrons greatly exceeds the speed of the CME, only protons are directly heated by the shock. Coulomb collisions low in the corona couple the protons and electrons allowing heat exchange between the two species. However, the coupling is so brief that the electrons never achieve more than 10% of the maximum temperature of the protons. We find that heat is able to conduct on open magnetic field lines and rapidly propagates ahead of the CME to form a shock precursor of hot electrons.« less

A motor-driven syringe-type gradient maker for forming immobilized pH gradient gels.

PubMed

Fawcett, J S; Sullivan, J V; Chidakel, B E; Chrambach, A

1988-05-01

A motor driven gradient maker based on the commercial model (Jule Inc., Trumbull, CT) was designed for immobilized pH gradient gels to provide small volumes, rapid stirring and delivery, strict volume and temperature control and air exclusion. The device was constructed and by a convenient procedure yields highly reproducible gradients either in solution or on polyacrylamide gels.

Pathways of fluid transport and reabsorption across the peritoneal membrane.

PubMed

Asghar, R B; Davies, S J

2008-05-01

The three-pore model of peritoneal fluid transport predicts that once the osmotic gradient has dissipated, fluid reabsorption will be due to a combination of small-pore reabsorption driven by the intravascular oncotic pressure, and an underlying disappearance of fluid from the cavity by lymphatic drainage. Our study measured fluid transport by these pathways in the presence and absence of an osmotic gradient. Paired hypertonic and standard glucose-dwell studies were performed using radio-iodinated serum albumin as an intraperitoneal volume marker and changes in intraperitoneal sodium mass to determine small-pore versus transcellular fluid transport. Disappearance of iodinated albumin was considered to indicate lymphatic drainage. Variability in transcellular ultrafiltration was largely explained by the rate of small-solute transport across the membrane. In the absence of an osmotic gradient, fluid reabsorption occurred via the small-pore pathway, the rate being proportional to the small-solute transport characteristics of the membrane. In most cases, fluid removal from the peritoneal cavity by this pathway was faster than by lymphatic drainage. Our study shows that the three-pore model describes the pathways of peritoneal fluid transport well. In the presence of high solute transport, poor transcellular ultrafiltration was due to loss of the osmotic gradient and an enhanced small-pore reabsorption rate after this gradient dissipated.

The AGCE related studies of baroclinic flows in spherical geometry

NASA Technical Reports Server (NTRS)

Hyun, J. M.

1983-01-01

Steady state, axisymmetric motions of a Boussineaq fluid continued in rotating spherical anmulus are considered. The motions are driven by latitudinally varying temperature gradient at the shells. Linearized formulations for a narrow gap are derived and the flow field is divided into the Ekman layers and the geostrophic interior. The Ekman layer flows are consistent with the known results for cylindrical geometries. Within the framework of rather restrictive assumptions, the interior flows are solved by a series of associated Legendre polynomials. The solutions show qualitative features valid at midlatitudes.

Increased electron temperature turbulence during suppression of edge localized mode by resonant magnetic perturbations in the DIII-D tokamak

NASA Astrophysics Data System (ADS)

Sung, C.; Wang, G.; Rhodes, T. L.; Smith, S. P.; Osborne, T. H.; Ono, M.; McKee, G. R.; Yan, Z.; Groebner, R. J.; Davis, E. M.; Zeng, L.; Peebles, W. A.; Evans, T. E.

2017-11-01

The first observation of increased electron temperature turbulence during edge localized mode (ELM) suppression by resonant magnetic perturbations (RMPs) is presented. These are long wavelength fluctuations (kθρs ≤ 0.2, where kθ = poloidal wavenumber and ρs = ion sound gyroradius) observed during H-mode plasmas on the DIII-D. This increase occurs only after ELMs are suppressed and are not observed during the initial RMP application. The T˜ e/Te increases ( >60%) are coincident with changes in normalized density and electron temperature gradients in the region from the top of the pedestal outward to the upper portion of the steep edge gradient. Density turbulence (kθρs ≤ 0.4) in this location was also observed to increase only after ELM suppression. These results are significant since they indicate that increased gradient-driven turbulent transport is one possible mechanism to regulate and maintain ELM-free H-mode operation. Investigation of linear stability of drift wave instabilities using the CGYRO code [Candy et al., J. Comput. Phys. 324, 73 (2016)] shows that the dominant mode moves closer to the electron mode branch from the ion mode branch only after ELMs are suppressed, correlated with the increased turbulence. The increased turbulence during ELM suppression, rather than with the initial RMP application, indicates that the often observed RMP induced "density pump-out" cannot be attributed to long wavelength edge turbulence level changes.

Microfluid oscillator based on thermocapillarity

NASA Astrophysics Data System (ADS)

Huang, Teng-chao; Shen, Yi-bing; Liu, Xu; Bai, Jian; Hou, Xiyun; Ye, Hui; Lou, Di

2004-12-01

A novel micro fluid oscillator with a boron diffused resistor is proposed in this paper. The actuation principle is based on the combination of Marangoni effect. The contemporary microfabrication technique enables us to fabricate microheater tiny enough to control temperature so quickly and precisely in micro length scale. The devices exhibiting the Marangoni effect in square channels were designed and fabricated from one silicon substrate and two quartz substrates. And the three substrates were aligned, bonded and packaged for testing. In this actuator there is a pair of micro-heaters to produce a thermal gradient along the slit. The driving wattage is about 0.1W and the resistors can make a temperature difference about 100 degrees during 0.1s with a pulsewidth of 20us for 0.1A current pulses. Then the movement is driven towards the lower temperature direction by the interfacial tension of the air-liquid interface. This micro fluid actuator can play important role in many liquid micro-systems such as in micromotor and micro valve.

Nanostructures study of CNT nanofluids transport with temperature-dependent variable viscosity in a muscular tube

NASA Astrophysics Data System (ADS)

Akbar, Noreen Sher; Abid, Syed Ali; Tripathi, Dharmendra; Mir, Nazir Ahmed

2017-03-01

The transport of single-wall carbon nanotube (CNT) nanofluids with temperature-dependent variable viscosity is analyzed by peristaltically driven flow. The main flow problem has been modeled using cylindrical coordinates and flow equations are simplified to ordinary differential equations using long wavelength and low Reynolds' number approximation. Analytical solutions have been obtained for axial velocity, pressure gradient and temperature. Results acquired are discussed graphically for better understanding. It is observed that with an increment in the Grashof number the velocity of the governing fluids starts to decrease significantly and the pressure gradient is higher for pure water as compared to single-walled carbon nanotubes due to low density. As the specific heat is very high for pure water as compared to the multi-wall carbon nanotubes, it raises temperature of the muscles, in the case of pure water, as compared to the multi-walled carbon nanotubes. Furthermore, it is noticed that the trapped bolus starts decreasing in size as the buoyancy forces are dominant as compared to viscous forces. This model may be applicable in biomedical engineering and nanotechnology to design the biomedical devices.

Confinement effects in premelting dynamics

NASA Astrophysics Data System (ADS)

Pramanik, Satyajit; Wettlaufer, John

2017-11-01

We examine the effects of confinement on the dynamics of premelted films driven by thermomolecular pressure gradients. Our approach is to modify a well-studied setting in which the thermomolecular pressure gradient is driven by a temperature gradient parallel to an interfacially premelted elastic wall. The modification treats the increase in viscosity associated with the thinning of films studied in a wide variety of materials using a power law and we examine the consequent evolution of the elastic wall. We treat (i) a range of interactions that are known to underlie interfacial premelting and (ii) a constant temperature gradient wherein the thermomolecular pressure gradient is a constant. The difference between the cases with and without the proximity effect arises in the volume flux of premelted liquid. The proximity effect increases the viscosity as the film thickness decreases thereby requiring the thermomolecular pressure driven flux to be accommodated at larger temperatures where the premelted film thickness is the largest. Implications for experiment and observations of frost heave are discussed.

Confinement effects in premelting dynamics

NASA Astrophysics Data System (ADS)

Pramanik, Satyajit; Wettlaufer, John S.

2017-11-01

We examine the effects of confinement on the dynamics of premelted films driven by thermomolecular pressure gradients. Our approach is to modify a well-studied setting in which the thermomolecular pressure gradient is driven by a temperature gradient parallel to an interfacially premelted elastic wall. The modification treats the increase in viscosity associated with the thinning of films, studied in a wide variety of materials, using a power law and we examine the consequent evolution of the confining elastic wall. We treat (1) a range of interactions that are known to underlie interfacial premelting and (2) a constant temperature gradient wherein the thermomolecular pressure gradient is a constant. The difference between the cases with and without the proximity effect arises in the volume flux of premelted liquid. The proximity effect increases the viscosity as the film thickness decreases thereby requiring the thermomolecular pressure driven flux to be accommodated at higher temperatures where the premelted film thickness is the largest. Implications for experiment and observations of frost heave are discussed.

SciDAC Center for Gyrokinetic Particle Simulation of Turbulent Transport in Burning Plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Zhihong

2013-12-18

During the first year of the SciDAC gyrokinetic particle simulation (GPS) project, the GPS team (Zhihong Lin, Liu Chen, Yasutaro Nishimura, and Igor Holod) at the University of California, Irvine (UCI) studied the tokamak electron transport driven by electron temperature gradient (ETG) turbulence, and by trapped electron mode (TEM) turbulence and ion temperature gradient (ITG) turbulence with kinetic electron effects, extended our studies of ITG turbulence spreading to core-edge coupling. We have developed and optimized an elliptic solver using finite element method (FEM), which enables the implementation of advanced kinetic electron models (split-weight scheme and hybrid model) in the SciDACmore » GPS production code GTC. The GTC code has been ported and optimized on both scalar and vector parallel computer architectures, and is being transformed into objected-oriented style to facilitate collaborative code development. During this period, the UCI team members presented 11 invited talks at major national and international conferences, published 22 papers in peer-reviewed journals and 10 papers in conference proceedings. The UCI hosted the annual SciDAC Workshop on Plasma Turbulence sponsored by the GPS Center, 2005-2007. The workshop was attended by about fifties US and foreign researchers and financially sponsored several gradual students from MIT, Princeton University, Germany, Switzerland, and Finland. A new SciDAC postdoc, Igor Holod, has arrived at UCI to initiate global particle simulation of magnetohydrodynamics turbulence driven by energetic particle modes. The PI, Z. Lin, has been promoted to the Associate Professor with tenure at UCI.« less

Density gradient free electron collisionally excited x-ray laser

DOEpatents

Campbell, E.M.; Rosen, M.D.

1984-11-29

An operational x-ray laser is provided that amplifies 3p-3s transition x-ray radiation along an approximately linear path. The x-ray laser is driven by a high power optical laser. The driving line focused optical laser beam illuminates a free-standing thin foil that may be associated with a substrate for improved structural integrity. This illumination produces a generally cylindrically shaped plasma having an essentially uniform electron density and temperature, that exists over a long period of time, and provides the x-ray laser gain medium. The x-ray laser may be driven by more than one optical laser beam. The x-ray laser has been successfully demonstrated to function in a series of experimental tests.

Alternative modeling methods for plasma-based Rf ion sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Veitzer, Seth A., E-mail: veitzer@txcorp.com; Kundrapu, Madhusudhan, E-mail: madhusnk@txcorp.com; Stoltz, Peter H., E-mail: phstoltz@txcorp.com

Rf-driven ion sources for accelerators and many industrial applications benefit from detailed numerical modeling and simulation of plasma characteristics. For instance, modeling of the Spallation Neutron Source (SNS) internal antenna H{sup −} source has indicated that a large plasma velocity is induced near bends in the antenna where structural failures are often observed. This could lead to improved designs and ion source performance based on simulation and modeling. However, there are significant separations of time and spatial scales inherent to Rf-driven plasma ion sources, which makes it difficult to model ion sources with explicit, kinetic Particle-In-Cell (PIC) simulation codes. Inmore » particular, if both electron and ion motions are to be explicitly modeled, then the simulation time step must be very small, and total simulation times must be large enough to capture the evolution of the plasma ions, as well as extending over many Rf periods. Additional physics processes such as plasma chemistry and surface effects such as secondary electron emission increase the computational requirements in such a way that even fully parallel explicit PIC models cannot be used. One alternative method is to develop fluid-based codes coupled with electromagnetics in order to model ion sources. Time-domain fluid models can simulate plasma evolution, plasma chemistry, and surface physics models with reasonable computational resources by not explicitly resolving electron motions, which thereby leads to an increase in the time step. This is achieved by solving fluid motions coupled with electromagnetics using reduced-physics models, such as single-temperature magnetohydrodynamics (MHD), extended, gas dynamic, and Hall MHD, and two-fluid MHD models. We show recent results on modeling the internal antenna H{sup −} ion source for the SNS at Oak Ridge National Laboratory using the fluid plasma modeling code USim. We compare demonstrate plasma temperature equilibration in two-temperature MHD models for the SNS source and present simulation results demonstrating plasma evolution over many Rf periods for different plasma temperatures. We perform the calculations in parallel, on unstructured meshes, using finite-volume solvers in order to obtain results in reasonable time.« less

Alternative modeling methods for plasma-based Rf ion sources.

PubMed

Veitzer, Seth A; Kundrapu, Madhusudhan; Stoltz, Peter H; Beckwith, Kristian R C

2016-02-01

Rf-driven ion sources for accelerators and many industrial applications benefit from detailed numerical modeling and simulation of plasma characteristics. For instance, modeling of the Spallation Neutron Source (SNS) internal antenna H(-) source has indicated that a large plasma velocity is induced near bends in the antenna where structural failures are often observed. This could lead to improved designs and ion source performance based on simulation and modeling. However, there are significant separations of time and spatial scales inherent to Rf-driven plasma ion sources, which makes it difficult to model ion sources with explicit, kinetic Particle-In-Cell (PIC) simulation codes. In particular, if both electron and ion motions are to be explicitly modeled, then the simulation time step must be very small, and total simulation times must be large enough to capture the evolution of the plasma ions, as well as extending over many Rf periods. Additional physics processes such as plasma chemistry and surface effects such as secondary electron emission increase the computational requirements in such a way that even fully parallel explicit PIC models cannot be used. One alternative method is to develop fluid-based codes coupled with electromagnetics in order to model ion sources. Time-domain fluid models can simulate plasma evolution, plasma chemistry, and surface physics models with reasonable computational resources by not explicitly resolving electron motions, which thereby leads to an increase in the time step. This is achieved by solving fluid motions coupled with electromagnetics using reduced-physics models, such as single-temperature magnetohydrodynamics (MHD), extended, gas dynamic, and Hall MHD, and two-fluid MHD models. We show recent results on modeling the internal antenna H(-) ion source for the SNS at Oak Ridge National Laboratory using the fluid plasma modeling code USim. We compare demonstrate plasma temperature equilibration in two-temperature MHD models for the SNS source and present simulation results demonstrating plasma evolution over many Rf periods for different plasma temperatures. We perform the calculations in parallel, on unstructured meshes, using finite-volume solvers in order to obtain results in reasonable time.

Passive injection control for microfluidic systems

DOEpatents

Paul, Phillip H.; Arnold, Don W.; Neyer, David W.

2004-12-21

Apparatus for eliminating siphoning, "dead" regions, and fluid concentration gradients in microscale analytical devices. In its most basic embodiment, the present invention affords passive injection control for both electric field-driven and pressure-driven systems by providing additional fluid flow channels or auxiliary channels disposed on either side of a sample separation column. The auxiliary channels are sized such that volumetric fluid flow rate through these channels, while sufficient to move the sample away from the sample injection region in a timely fashion, is less than that through the sample separation channel or chromatograph.

Isochoric heating and strong blast wave formation driven by fast electrons in solid-density targets

NASA Astrophysics Data System (ADS)

Santos, J. J.; Vauzour, B.; Touati, M.; Gremillet, L.; Feugeas, J.-L.; Ceccotti, T.; Bouillaud, R.; Deneuville, F.; Floquet, V.; Fourment, C.; Hadj-Bachir, M.; Hulin, S.; Morace, A.; Nicolaï, Ph; d'Oliveira, P.; Reau, F.; Samaké, A.; Tcherbakoff, O.; Tikhonchuk, V. T.; Veltcheva, M.; Batani, D.

2017-10-01

We experimentally investigate the fast (< 1 {ps}) isochoric heating of multi-layer metallic foils and subsequent high-pressure hydrodynamics induced by energetic electrons driven by high-intensity, high-contrast laser pulses. The early-time temperature profile inside the target is measured from the streaked optical pyrometry of the target rear side. This is further characterized from benchmarked simulations of the laser-target interaction and the fast electron transport. Despite a modest laser energy (< 1 {{J}}), the early-time high pressures and associated gradients launch inwards a strong compression wave developing over ≳ 10 ps into a ≈ 140 {Mbar} blast wave, according to hydrodynamic simulations, consistent with our measurements. These experimental and numerical findings pave the way to a short-pulse-laser-based platform dedicated to high-energy-density physics studies.

Surface-tension-driven flow in a glass melt

NASA Technical Reports Server (NTRS)

Mcneil, Thomas J.; Cole, Robert; Shankar Subramanian, R.

1985-01-01

Motion driven by surface tension gradients was observed in a vertical capillary liquid bridge geometry in a sodium borate melt. The surface tension gradients were introduced by maintaining a temperature gradient on the free melt surface. The flow velocities at the free surface of the melt, which were measured using a tracer technique, were found to be proportional to the applied temperature difference and inversely proportional to the melt viscosity. The experimentally observed velocities were in reasonable accord with predictions from a theoretical model of the system.

Effects of eletron heating on the current driven electrostatic ion cyclotron instability and plasma transport processes along auroral field lines

NASA Technical Reports Server (NTRS)

Ganguli, Supriya B.; Mitchell, Horace G.; Palmadesso, Peter J.

1988-01-01

Fluid simulations of the plasma along auroral field lines in the return current region have been performed. It is shown that the onset of electrostatic ion cyclotron (EIC) related anomalous resistivity and the consequent heating of electrons leads to a transverse ion temperature that is much higher than that produced by the current driven EIC instability (CDICI) alone. Two processes are presented for the enhancement of ion heating by anomalous resistivity. The anomalous resistivity associated with the turbulence is limited by electron heating, so that CDICI saturates at transverse temperature that is substantially higher than in the absence of resistivity. It is suggested that this process demonstrates a positive feedback loop in the interaction between CDICI, anomalous resistivity, and parallel large-scale dynamics in the topside ionosphere.

Simulation of sloshing dynamics induced forces and torques actuated on dewar container driven by gravity gradient and jitter accelerations in microgravity

NASA Technical Reports Server (NTRS)

Hung, R. J.; Pan, H. L.

1993-01-01

Some experimental spacecraft use superconducting sensors for gyro read-out and so must be maintained at a very low temperature. The boil-off from the cryogenic liquid used to cool the sensors can also be used, as the Gravity Probe B (GP-B) spacecraft does, as propellant to maintain attitude control and drag-free operation of the spacecraft. The cryogenic liquid for such spacecraft is, however, susceptible to both slosh-like motion and non-axisymmetric configurations under the influence of various kinds of gravity jitter and gravity gradient accelerations. Hence, it is important to quantify the magnitude of the liquid-induced perturbations on the spacecraft. We use the example of the GP-B to investigate such perturbations by numerical simulations. For this spacecraft disturbances can be imposed on the liquid by atmospheric drag, spacecraft attitude control maneuvers, and the earth's gravity gradient. More generally, onboard machinery vibrations and crew motion can also create disturbances. Recent studies suggest that high frequency disturbances are relatively unimportant in causing liquid motions in comparison to low frequency ones. The results presented here confirm this conclusion. After an initial calibration period, the GP-B spacecraft rotates in orbit at 0.1 rpm about the tank symmetry axis. For this rotation rate, the equilibrium liquid free surface shape is a 'doughnut' configuration for all residual gravity levels of 10(exp -6) g(sub 0) or less, as shown by experiments and by numerical simulations; furthermore, the superfluid behavior of the 1.8 K liquid helium used in GP-B eliminates temperature gradients and therefore such effects as Marangoni convection do not have to be considered. Classical fluid dynamics theory is used as the basis of the numerical simulations here, since Mason's experiments show that the theory is applicable for cryogenic liquid helium in large containers. To study liquid responses to various disturbances, we investigate and simulate three levels of gravity jitter (10(exp -6), 10(exp -7), and 10(exp -8) g(sub 0)) each at three predominant frequencies (0.1, 1.0, and 10 Hz), combined with a gravity gradient appropriate for the GP-B orbit. Dynamical evolution of sloshing dynamics excited fluid forces and torque fluctuations exerted on the dewar container driven by the combined gravity gradient and jitter accelerations are also investigated and simulated.

Laboratory Layered Latte

NASA Astrophysics Data System (ADS)

Xue, Nan; Khodaparast, Sepideh; Zhu, Lailai; Nunes, Janine; Kim, Hyoungsoo; Stone, Howard

2017-11-01

Layered composite fluids are sometimes observed in confined systems of rather chaotic initial states, for example, layered lattes formed by pouring espresso into a glass of warm milk. In such configurations, pouring forces a lower density liquid (espresso) into a higher density ambient, which is similar to the fountain effects that characterize a wide range of flows driven by injecting a fluid into a second miscible phase. Although the initial state of the mixture is complex and chaotic, there are conditions where the mixture cools at room temperature and exhibits an organized layered pattern. Here we report controlled experiments injecting a fluid into a miscible phase and show that, above a critical injection velocity, layering naturally emerges over the time scale of minutes. We perform experimental and numerical analyses of the time-dependent flows to observe and understand the convective circulation in the layers. We identify critical conditions to produce the layering and relate the results quantitatively to the critical Rayleigh number in double-diffusive convection, which indicates the competition between the horizontal thermal gradient and the vertical density gradient generated by the fluid injection. Based on this understanding, we show how to employ this single-step process to produce layered structures in soft materials, where the local elastic properties as well as the local material concentration vary step-wise along the length of the material.

Sloshing of Cryogenic Helium Driven by Lateral Impulse/Gravity Gradient-Dominated/or g-Jitter-Dominated Accelerations and Orbital Dynamics

NASA Technical Reports Server (NTRS)

Hung, R. J.; Long, Y. T.; Zu, G. J.

1996-01-01

The coupling of slosh dynamics within a partially filled rotating dewar of superfluid helium 11 with spacecraft orbital dynamics is investigated in response to the environmental disturbances of (a) lateral impulses, (b) gravity gradients and (c) g-jitter forces. The purpose of this study is to investigate how the coupling of helium 11 fluid slosh dynamics driven by three cases of environmental force with spacecraft dynamics can affect the bubble deformations and their associated fluid and spacecraft mass centre fluctuations. The numerical computation of slosh dynamics is based on a rotational frame, while the spacecraft dynamics is associated with a non-rotational frame. Results show that the major contribution of orbital dynamics is driven by coupling with slosh dynamics. Neglecting the effect of slosh dynamics acting on the spacecraft may lead to the wrong results for the development of orbital and attitude control techniques.

Salt-Finger Convection in a Stratified Fluid Layer Induced by Thermal and Solutal Capillary Motion

NASA Technical Reports Server (NTRS)

Chen, Chuan F.; Chan, Cho Lik

1996-01-01

Salt-finger convection in a double-diffusive system is a motion driven by the release of gravitational potential due to different diffusion rates. Normally, when the gravitational field is reduced, salt-finger convection together with other convective motions driven by buoyancy forces will be rapidly suppressed. However, because the destabilizing effect of the concentration gradient is amplified by the Lewis number, with values varying from 10(exp 2) for aqueous salt solutions to 10 (exp 4) for liquid metals, salt-finger convection may be generated at much reduced gravity levels. In the microgravity environment, the surface tension gradient assumes a dominant role in causing fluid motion. In this paper, we report on some experimental results showing the generation of salt-finger convection due to capillary motio on the surface of a stratified fluid layer. A numerical simulation is presented to show the cause of salt-finger convection.

Demonstration of acceleration of relativistic electrons at a dielectric microstructure using femtosecond laser pulses

DOE PAGES

Wootton, Kent P.; Wu, Ziran; Cowan, Benjamin M.; ...

2016-06-02

Acceleration of electrons using laser-driven dielectric microstructures is a promising technology for the miniaturization of particle accelerators. Achieving the desired GV m –1 accelerating gradients is possible only with laser pulse durations shorter than ~1 ps. In this Letter, we present, to the best of our knowledge, the first demonstration of acceleration of relativistic electrons at a dielectric microstructure driven by femtosecond duration laser pulses. Furthermore, using this technique, an electron accelerating gradient of 690±100 MV m –1 was measured—a record for dielectric laser accelerators.

Role of turbulence regime on determining the local density gradient

DOE PAGES

Wang, X.; Mordijck, Saskia; Doyle, E. J.; ...

2017-11-16

In this study we show that the local density gradient in the plasma core depends on the calculated mode-frequency of the most unstable linear mode and reaches a maximum when this frequency is close to zero. Previous theoretical and experimental work on AUG has shown that the ratio of electron to ion temperature, and as such the frequency of the dominant linear gyrokinetic mode, affects the local density gradient close to ρ = 0.3 [1, 2]. On DIII-D we find that by adding Electron Cyclotron Heating (ECH), we modify the dominant unstable linear gyro kinetic mode from an Ion Temperaturemore » Gradient (ITG) mode to a Trapped Electron Mode (TEM), which means that the frequency of the dominant mode changes sign (from the ion to the electron direction). Local density peaking around mid-radius increases by 50% right around the cross-over between the ITG and TEM regimes. By comparing how the particle flux changes, through the derivative of the electron density, n e, with respect to time, ∂n e/∂t, we find that the particle flux also exhibits the same trend versus mode frequency. As a result, we find that the changes in local particle transport are inversely proportional to the changes in electron density, indicating that the changes are driven by a change in thermo-diffusive pinch.« less

Suppression of Electron Thermal Conduction in the Intracluster Medium

NASA Astrophysics Data System (ADS)

Roberg-Clark, Gareth; Drake, James; Swisdak, M.; Reynolds, Christopher S.

2017-08-01

The Intracluster Medium (ICM) contains high-temperature dilute plasma in which the quantity beta, defined as the ratio of the thermal pressure of the gas to the local magnetic field pressure, is much larger than unity. In addition, the collisional mean free path of particles in the ICM is typically large compared to the magnetic gyro-radius of individual particles. These conditions allow for the growth of robust microinstabilities that can significantly alter the transport of particles and heat along the local magnetic field line. Here we explore such an instability using driven two-dimensional Particle-In-Cell simulations of a magnetized plasma with a temperature gradient imposed at the boundaries. The system is highly unstable and develops large-amplitude magnetic fluctuations that effectively scatter the orbits of electrons crossing the simulation domain, resulting in a collisionless suppression of thermal conduction across the temperature gradient and magnetic field. The results suggest that the spontaneous development of small-scale plasma turbulence in the ICM may play a pivotal role in determining the thermal conductivity of ICM-like plasmas.

Bernoulli's Principle Applied to Brain Fluids: Intracranial Pressure Does Not Drive Cerebral Perfusion or CSF Flow.

PubMed

Schmidt, Eric; Ros, Maxime; Moyse, Emmanuel; Lorthois, Sylvie; Swider, Pascal

2016-01-01

In line with the first law of thermodynamics, Bernoulli's principle states that the total energy in a fluid is the same at all points. We applied Bernoulli's principle to understand the relationship between intracranial pressure (ICP) and intracranial fluids. We analyzed simple fluid physics along a tube to describe the interplay between pressure and velocity. Bernoulli's equation demonstrates that a fluid does not flow along a gradient of pressure or velocity; a fluid flows along a gradient of energy from a high-energy region to a low-energy region. A fluid can even flow against a pressure gradient or a velocity gradient. Pressure and velocity represent part of the total energy. Cerebral blood perfusion is not driven by pressure but by energy: the blood flows from high-energy to lower-energy regions. Hydrocephalus is related to increased cerebrospinal fluid (CSF) resistance (i.e., energy transfer) at various points. Identification of the energy transfer within the CSF circuit is important in understanding and treating CSF-related disorders. Bernoulli's principle is not an abstract concept far from clinical practice. We should be aware that pressure is easy to measure, but it does not induce resumption of fluid flow. Even at the bedside, energy is the key to understanding ICP and fluid dynamics.

Process modelling for Space Station experiments

NASA Technical Reports Server (NTRS)

Alexander, J. Iwan D.; Rosenberger, Franz; Nadarajah, Arunan; Ouazzani, Jalil; Amiroudine, Sakir

1990-01-01

Examined here is the sensitivity of a variety of space experiments to residual accelerations. In all the cases discussed the sensitivity is related to the dynamic response of a fluid. In some cases the sensitivity can be defined by the magnitude of the response of the velocity field. This response may involve motion of the fluid associated with internal density gradients, or the motion of a free liquid surface. For fluids with internal density gradients, the type of acceleration to which the experiment is sensitive will depend on whether buoyancy driven convection must be small in comparison to other types of fluid motion, or fluid motion must be suppressed or eliminated. In the latter case, the experiments are sensitive to steady and low frequency accelerations. For experiments such as the directional solidification of melts with two or more components, determination of the velocity response alone is insufficient to assess the sensitivity. The effect of the velocity on the composition and temperature field must be considered, particularly in the vicinity of the melt-crystal interface. As far as the response to transient disturbances is concerned, the sensitivity is determined by both the magnitude and frequency of the acceleration and the characteristic momentum and solute diffusion times. The microgravity environment, a numerical analysis of low gravity tolerance of the Bridgman-Stockbarger technique, and modeling crystal growth by physical vapor transport in closed ampoules are discussed.

Simulation of Mach Probes in Non-Uniform Magnetized Plasmas: the Influence of a Background Density Gradient

NASA Astrophysics Data System (ADS)

Haakonsen, Christian Bernt; Hutchinson, Ian H.

2013-10-01

Mach probes can be used to measure transverse flow in magnetized plasmas, but what they actually measure in strongly non-uniform plasmas has not been definitively established. A fluid treatment in previous work has suggested that the diamagnetic drifts associated with background density and temperature gradients affect transverse flow measurements, but detailed computational study is required to validate and elaborate on those results; it is really a kinetic problem, since the probe deforms and introduces voids in the ion and electron distribution functions. A new code, the Plasma-Object Simulator with Iterated Trajectories (POSIT) has been developed to self-consistently compute the steady-state six-dimensional ion and electron distribution functions in the perturbed plasma. Particle trajectories are integrated backwards in time to the domain boundary, where arbitrary background distribution functions can be specified. This allows POSIT to compute the ion and electron density at each node of its unstructured mesh, update the potential based on those densities, and then iterate until convergence. POSIT is used to study the impact of a background density gradient on transverse Mach probe measurements, and the results compared to the previous fluid theory. C.B. Haakonsen was supported in part by NSF/DOE Grant No. DE-FG02-06ER54512, and in part by an SCGF award administered by ORISE under DOE Contract No. DE-AC05-06OR23100.

The potential for free and mixed convection in sedimentary basins

USGS Publications Warehouse

Raffensperger, Jeff P.; Vlassopoulos, D.

1999-01-01

Free thermal convection and mixed convection are considered as potential mechanisms for mass and heat transport in sedimentary basins. Mixed convection occurs when horizontal flows (forced convection) are superimposed on thermally driven flows. In cross section, mixed convection is characterized by convection cells that migrate laterally in the direction of forced convective flow. Two-dimensional finite-element simulations of variable-density groundwater flow and heat transport in a horizontal porous layer were performed to determine critical mean Rayleigh numbers for the onset of free convection, using both isothermal and semi-conductive boundaries. Additional simulations imposed a varying lateral fluid flux on the free-convection pattern. Results from these experiments indicate that forced convection becomes dominant, completely eliminating buoyancy-driven circulation, when the total forced-convection fluid flux exceeds the total flux possible due to free convection. Calculations of the thermal rock alteration index (RAI=q????T) delineate the patterns of potential diagenesis produced by fluid movement through temperature gradients. Free convection produces a distinct pattern of alternating positive and negative RAIs, whereas mixed convection produces a simpler layering of positive and negative values and in general less diagenetic alteration. ?? Springer-Verlag.

Density gradient free electron collisionally excited X-ray laser

DOEpatents

Campbell, Edward M.; Rosen, Mordecai D.

1989-01-01

An operational X-ray laser (30) is provided that amplifies 3p-3s transition X-ray radiation along an approximately linear path. The X-ray laser (30) is driven by a high power optical laser. The driving line focused optical laser beam (32) illuminates a free-standing thin foil (34) that may be associated with a substrate (36) for improved structural integrity. This illumination produces a generally cylindrically shaped plasma having an essentially uniform electron density and temperature, that exists over a long period of time, and provides the X-ray laser gain medium. The X-ray laser (30) may be driven by more than one optical laser beam (32, 44). The X-ray laser (30) has been successfully demonstrated to function in a series of experimental tests.

Marshburn works with Marangoni Experiment Hardware in Kibo

NASA Image and Video Library

2013-03-19

ISS035e006147 (19 March 2013) --- NASA astronaut Tom Marshburn, Expedition 35 flight engineer, works on the Marangoni Inside core cleaning in the Kibo Japanese Experiment Module onboard the Earth-orbiting International Space Station. Marangoni convection is the flow driven by the presence of a surface tension gradient which can be produced by temperature difference at a liquid/gas interface. The convection in liquid bridge of silicone oil is generated by heating the one disc higher than the other. Scientists are observing flow patterns of how fluids move to learn more about how heat is transferred in microgravity.

BSRs Elevated by Fluid Upwelling on the Upper Amazon Fan : Bottom-up Controls on Gas Hydrate Stability

NASA Astrophysics Data System (ADS)

Praeg, D.; Silva, C. G.; dos Reis, A. T.; Ketzer, J. M.; Unnithan, V.; Perovano Da Silva, R. J.; Cruz, A. M.; Gorini, C.

2017-12-01

The stability of natural gas hydrate accumulations on continental margins has mainly been considered in terms of changes in seawater pressures and temperatures driven from above by climate. We present evidence from the Amazon deep-sea fan for stability zone changes driven from below by fluid upwelling. A grid of 2D and 3D multichannel seismic data show the upper Amazon fan in water depths of 1200-2000 m to contain a discontinuous bottom-simulating seismic reflection (BSR) that forms `patches' 10-50 km wide and up to 140 km long, over a total area of at least 5000 km2. The elongate BSR patches coincide with anticlinal thrust-folds that record on-going gravitational collapse of the fan above décollements at depths of up to 10 km. The BSR lies within 100-300 m of seafloor, in places rising beneath features that seafloor imagery show to be pockmarks and mud volcanoes, some venting gas to the water column. The BSR patches are up to 500 m shallower than predicted for methane hydrate based on geothermal gradients as low as 17˚C/km measured within the upper fan, and inversion of the BSR to obtain temperatures at the phase boundary indicates gradients 2-5 times background levels. We interpret the strongly elevated BSR patches to record upwelling of warm gas-rich fluids through thrust-fault zones 101 km wide. We infer this process to favour gas hydrate occurrences that are concentrated in proportion to flux and locally pierced by vents, and that will be sensitive to temporal variations in the upward flux of heat and gas. Thus episodes of increased flux, e.g. during thrusting, could dissociate gas hydrates to trigger slope failures and/or enhanced gas venting to the ocean. Structurally-driven fluid flow episodes could account for evidence of recurrent large-scale failures from the compressive belt on the upper fan during its Neogene collapse, and provide a long-term alternative to sea level triggering. The proposed mechanism of upward flux links the distribution and stability of gas hydrate occurrences (and gas vents) to the internal dynamics of deep-sea depocentres, in all water depths that structural pathways for fluid migration may form. Gravitational collapse is increasingly recognized to affect passive continental margins, and our findings challenge global models of hydrate inventory over time based solely on in situ methanogenesis.

Centrifuge in space fluid flow visualization experiment

NASA Technical Reports Server (NTRS)

Arnold, William A.; Wilcox, William R.; Regel, Liya L.; Dunbar, Bonnie J.

1993-01-01

A prototype flow visualization system is constructed to examine buoyancy driven flows during centrifugation in space. An axial density gradient is formed by imposing a thermal gradient between the two ends of the test cell. Numerical computations for this geometry showed that the Prandtl number plays a limited part in determining the flow.

Nonthermal plasmas around black holes, relevant collective modes, new configurations, and magnetic field amplification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Coppi, B., E-mail: coppi@mit.edu

The radiation emission from Shining Black Holes is most frequently observed to have nonthermal features. It is therefore appropriate to consider relevant collective processes in plasmas surrounding black holes that contain high energy particles with nonthermal distributions in momentum space. A fluid description with significant temperature anisotropies is the simplest relevant approach. These anisotropies are shown to have a critical influence on: (a) the existence and characteristics of stationary plasma and field ring configurations, (b) the excitation of “thermo-gravitational modes” driven by temperature anisotropies and gradients that involve gravity and rotation, (c) the generation of magnetic fields over macroscopic scalemore » distances, and (d) the transport of angular momentum.« less

Directional Solidification of Mercury Cadmium Telluride During the Second United States Microgravity Payload Mission (USMP-2)

NASA Technical Reports Server (NTRS)

Gillies, D. C.; Lehoczky, S. L.; Szofran, F. R.; Watring, D. A.; Alexander, H. A.; Jerman, G. A.

1996-01-01

As a solid solution semiconductor having, a large separation between liquidus and solidus, mercury cadmium telluride (MCT) presents a formidable challenge to crystal growers desiring an alloy of high compositional uniformity. To avoid constitutional supercooling during Bridgman crystal growth it is necessary to solidify slowly in a high temperature gradient region. The necessary translation rate of less than 1 mm/hr results in a situation where fluid flow induced by gravity on earth is a significant factor in material transport. The Advanced Automated Directional Solidification Furnace (AADSF) is equipped to provide the stable thermal environment with a high gradient, and the required slow translation rate needed. Ground based experiments in AADSF show clearly the dominance of flow driven transport. The first flight of AADSF in low gravity on USMP-2 provided an opportunity to test theories of fluid flow in MCT and showed several solidification regimes which are very different from those observed on earth. Residual acceleration vectors in the orbiter during the mission were measured by the Orbital Acceleration Research Experiment (OARE), and correlated well with observed compositional differences in the samples.

Flux tube gyrokinetic simulations of the edge pedestal

NASA Astrophysics Data System (ADS)

Parker, Scott; Wan, Weigang; Chen, Yang

2011-10-01

The linear instabilities of DIII-D H-mode pedestal are studied with gyrokinetic micro-turbulence simulations. The simulation code GEM is an electromagnetic δf code with global tokamak geometry in the form of Miller equilibrium. Local flux tube simulations are carried out for multiple positions of two DIII-D profiles: shot #98889 and shot #131997. Near the top of the pedestal, the instability is clearly ITG. The dominant instability of the pedestal appears at the steep gradient region, and it is identified as a low frequency mode mostly driven by electron temperature gradient. The mode propagates along the electron diamagnetic direction for low n and may propagate along the ion direction for high n. At some positions near the steep gradient region, an ion instability is found which shows some characteristics of kinetic ballooning mode (KBM). These results will be compared to the results of E. Wang et al. and D. Fulton et al. in the same session. We thank R. Groebner and P. Snyder for providing experimental profiles and helpful discussions.

Thermodynamic understanding of Sn whisker growth on the Cu surface in Cu(top)-Sn(bottom) bilayer system upon room temperature aging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Lin; Jian, Wei; Lin, Bing

2015-06-07

Sn whiskers are observed by scanning electron microscope on the Cu surface in Cu(top)-Sn(bottom) bilayer system upon room temperature aging. Only Cu{sub 6}Sn{sub 5} phase appears in the X-ray diffraction patterns and no Sn element is detected in the Cu sublayer by scanning transmission electron microscopy. Based on the interfacial thermodynamics, the intermetallic Cu{sub 6}Sn{sub 5} compound phase may form directly at the Sn grain boundary. Driven by the stress gradient during the formation of Cu{sub 6}Sn{sub 5} compound at Sn grain boundaries, Sn atoms segregate onto the Cu surface and accumulate to form Sn whisker.

MHD pulsatile flow of engine oil based carbon nanotubes between two concentric cylinders

NASA Astrophysics Data System (ADS)

Haq, Rizwan Ul; Shahzad, Faisal; Al-Mdallal, Qasem M.

In this article, thermal performance of engine oil in the presence of both single and multiple wall carbon nanotubes (SWCNTs and MWCNTs) between two concentric cylinders is presented. Flow is driven with oscillatory pressure gradient and magneto-hydrodynamics (MHDs) effects are also introduced to control the random motion of the nanoparticles. Arrived broad, it is perceived that the inclusion of nanoparticles increases the thermal conductivity of working fluid significantly for both turbulent and laminar regimes. Fundamental momentum and energy equations are based upon partial differential equations (PDEs) that contain thermos-physical properties of both SWCNTs and MWCNTs. The solution has been evaluated for each mixture, namely: SWCNT-engine oil and MWCNT-engine oil. Results are determined for each velocity, temperature, pressure and stress gradient. Graphical results for the numerical values of the emerging parameters, namely: Hartmann number (M), the solid volume fraction of the nanoparticles (ϕ), Reynolds number (Reω), and the pulsation parameter based on the periodic pressure gradient are analyzed for pressure difference, frictional forces, velocity profile, temperature profile, crux, streamlines and vorticity phenomena. In addition, the assets of various parameters on the flow quantities of observation are investigated.

Gradient Drift Turbulence from Electron Bite-Outs: Dependence on Atmospheric Parameters.

NASA Astrophysics Data System (ADS)

Young, M.; Oppenheim, M. M.; Dimant, Y. S.

2017-12-01

Electron bite-outs are regions of decreased electron density without a corresponding decrease in ion density, often caused by electron attachment to dust grains. They typically occur in the upper D-/lower E-region ionosphere and the accompanying electron gradient provides free energy to drive the gradient drift instability (GDI). The major difference between classical GDI and electron bite-out driven GDI is that the instability occurs on the top side of the bite-out region in the latter, as opposed to the bottom side in the former, in the presence of a vertical background electric field. Moreover, the mobile plasma population contains a gradient in only one species while the entire system remains quasineutral. This modified geometry presents new pathways for instabilities as the ions build up near the bite-out layer, leaving behind depletions that ascend away from the layer. Previous simulation runs showed that the presence of an electron gradient drives GDI-like turbulence even when ions and electrons start in momentum balance. Furthermore, a simulation run that replaced the electron bite-out with a layer of enhanced ion density, as though ions and electrons had filled in the bite-out region, did not lead to instability. This work examines the role of atmospheric parameters at altitudes between 80-100 km in instability formation and turbulence development, including the role of collisions in impeding instability growth as altitude decreases. Key parameters include the ambient electric field, which plays a critical role in triggering the gradient-drift instability; collision frequencies and temperature, which vary with altitude and effect the turbulent growth rate; and relative charge density of the bite-out, which increases the electron gradient strength. This work provides insight into how electron bite-out layers can produce turbulence that ground-based high frequency (HF) radars may be able to observe. The upper D-/lower E-region ionosphere is generally difficult to study in situ, making simulations of ground-based observables much more important. Assuming that electron bite-out layers result from dust charging in particular will allow the community to use the predictions of this work to study the ionospheric dust population.

Identifying Time Periods of Minimal Thermal Gradient for Temperature-Driven Structural Health Monitoring.

PubMed

Reilly, John; Glisic, Branko

2018-03-01

Temperature changes play a large role in the day to day structural behavior of structures, but a smaller direct role in most contemporary Structural Health Monitoring (SHM) analyses. Temperature-Driven SHM will consider temperature as the principal driving force in SHM, relating a measurable input temperature to measurable output generalized strain (strain, curvature, etc.) and generalized displacement (deflection, rotation, etc.) to create three-dimensional signatures descriptive of the structural behavior. Identifying time periods of minimal thermal gradient provides the foundation for the formulation of the temperature-deformation-displacement model. Thermal gradients in a structure can cause curvature in multiple directions, as well as non-linear strain and stress distributions within the cross-sections, which significantly complicates data analysis and interpretation, distorts the signatures, and may lead to unreliable conclusions regarding structural behavior and condition. These adverse effects can be minimized if the signatures are evaluated at times when thermal gradients in the structure are minimal. This paper proposes two classes of methods based on the following two metrics: (i) the range of raw temperatures on the structure, and (ii) the distribution of the local thermal gradients, for identifying time periods of minimal thermal gradient on a structure with the ability to vary the tolerance of acceptable thermal gradients. The methods are tested and validated with data collected from the Streicker Bridge on campus at Princeton University.

Convectively driven PCR thermal-cycling

DOEpatents

Benett, William J.; Richards, James B.; Milanovich, Fred P.

2003-07-01

A polymerase chain reaction system provides an upper temperature zone and a lower temperature zone in a fluid sample. Channels set up convection cells in the fluid sample and move the fluid sample repeatedly through the upper and lower temperature zone creating thermal cycling.

Suppression of electron temperature gradient turbulence via negative magnetic shear in NSTX.

PubMed

Yuh, H Y; Kaye, S M; Levinton, F M; Mazzucato, E; Mikkelsen, D R; Smith, D R; Bell, R E; Hosea, J C; LeBlanc, B P; Peterson, J L; Park, H K; Lee, W

2011-02-04

Negative magnetic shear is found to suppress electron turbulence and improve electron thermal transport for plasmas in the National Spherical Torus Experiment (NSTX). Sufficiently negative magnetic shear results in a transition out of a stiff profile regime. Density fluctuation measurements from high-k microwave scattering are verified to be the electron temperature gradient (ETG) mode by matching measured rest frequency and linear growth rate to gyrokinetic calculations. Fluctuation suppression under negligible E×B shear conditions confirm that negative magnetic shear alone is sufficient for ETG suppression. Measured electron temperature gradients can significantly exceed ETG critical gradients with ETG mode activity reduced to intermittent bursts, while electron thermal diffusivity improves to below 0.1 electron gyro-Bohms.

Two-Dimensional Heat Transfer Modeling of the Formosa Ridge Offshore SW Taiwan: Implication for Fluid Migrating Paths of a Cold Seep Site

NASA Astrophysics Data System (ADS)

Tsai, Y.; Chi, W.; Liu, C.; Shyu, C.

2011-12-01

The Formosa Ridge, a small ridge located on the passive China continental slope offshore southwestern Taiwan, is an active cold seep site. Large and dense chemosynthetic communities were found there by the ROV Hyper-Dolphin during the 2007 NT0705 cruise. A vertical blank zone is clearly observed on all the seismic profiles across the cold seep site. This narrow zone is interpreted to be the fluid conduit of the seep site. Previous studies suggest that cold sea water carrying large amount of sulfate could flow into the fluid system from flanks of the ridge, and forms a very effective fluid circulation system that emits both methane and hydrogen sulfide to feed the unusual chemosynthetic communities observed at the Formosa Ridge cold seep site. Here we use thermal signals to study possible fluid flow migration paths. In 2008 and 2010, we have collected vdense thermal probe data at this site. We also study the temperatures at Bottom-Simulating Reflectors (BSRs) based on methane hydrate phase diagram. We perform 2D finite element thermal conductive simulations to study the effects of bathymetry on the temperature field in the ridge, and compare the simulation result with thermal probe and BSR-derived datasets. The boundary conditions include insulated boundaries on both sides, and we assign a fix temperature at the bottom of the model using an average regional geothermal gradient. Sensitivity tests and thermal probe data from a nearby region give a regional background geothermal gradient of 0.04 to 0.05 °C/m. The outputs of the simulation runs include geothermal gradient and temperature at different parts of the model. The model can fit the geothermal gradient at a distance away from the ridge where there is less geophysics evidence of fluid flow. However our model over-predicts the geothermal gradient by 50% at the ridge top. We also compare simulated temperature field and found that under the flanks of the ridge the temperature is cooled by 2 °C compared with the BSR-derived temperatures. These results are consistent with the interpretation of cold seawater being pumped into the ridge from both flanks, cooling the temperature field. In summary, the thermal data are consistence with previously proposed fluid circulation model.

Geochemistry driven trends in microbial diversity and function across a temperature transect of a shallow water hydrothermal system off Milos (Greece)

NASA Astrophysics Data System (ADS)

Bühring, Solveig I.; Amend, Jan P.; Gómez Sáez, Gonzalo V.; Häusler, Stefan; Hinrichs, Kai-Uwe; Pichler, Thomas; Pop Ristova, Petra; Price, Roy E.; Santi, Ioulia; Sollich, Miriam

2014-05-01

The shallow water hydrothermal vents off Milos Island, Greece, discharge hot, slightly acidic, reduced fluids into colder, slightly alkaline, oxygenated seawater. Gradients in temperature, pH, and geochemistry are established as the two fluids mix, leading to the formation of various microbial microniches. In contrast to deep-sea hydrothermal systems, the availability of sun light allows for a combination of photo- and chemotrophic carbon fixation. Despite the comparably easy accessibility of shallow water hydrothermal systems, little is known about their microbial diversity and functioning. We present data from a shallow hydrothermal system off Milos Island, one of the most hydrothermally active regions in the Mediterranean Sea. The physico-chemical changes from ambient seafloor to hydrothermal area were investigated and documented by in situ microsensor profiling of temperature, pH, total reduced sulfur and dissolved oxygen alongside porewater geochemistry. The spatial microbial diversity was determined using a combination of gene- and lipid-based approaches, whereas microbial functioning was assessed by stable isotope probing experiments targeting lipid biomarkers. In situ microprofiles indicated an extreme environment with steep gradients, offering a variety of microniches for metabolically diverse microbial communities. We sampled a transect along a hydrothermal patch, following an increase in sediment surface temperature from background to 90°C, including five sampling points up to 20 cm sediment depth. Investigation of the bacterial diversity using ARISA revealed differences in the community structure along the geochemical gradients, with the least similarity between the ambient and highly hydrothermally impacted sites. Furthermore, using multivariate statistical analyses it was shown that variations in the community structure could be attributed to differences in the sediment geochemistry and especially the sulfide content, and only indirectly to shifts in temperature. Results from intact polar lipid analyses were consistent with the ARISA data and clearly differentiated those samples located close to the vent from those found in less affected areas. Changes from phospho- and betaine lipids within the top layer of the unaffected area to glyco- and ornithine lipids in the hydrothermally influenced sediment layers reflected a change from photoautotrophic algae to a bacteria-dominated community as predominant lipid sources. A clear dominance of archaeal lipids indicated archaea as key players in the deeper, hotter layers of the hydrothermal sediment. We performed stable isotope probing experiments with 13C-bicarbonate in the dark to investigate if chemolithotrophy, as opposed to phototrophy, plays any significant role for carbon fixation in shallow vent systems. Different amendments revealed that not only chemolithotrophy represents an important pathway for carbon fixation in these ecosystems, but that diverse ways of dark CO2 fixation exist, with hydrogen being the most effective electron donor under high temperature conditions.

A quasi-linear analysis of the impurity effect on turbulent momentum transport and residual stress

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ko, S. H., E-mail: shko@nfri.re.kr; Jhang, Hogun; Singh, R.

2015-08-15

We study the impact of impurities on turbulence driven intrinsic rotation (via residual stress) in the context of the quasi-linear theory. A two-fluid formulation for main and impurity ions is employed to study ion temperature gradient modes in sheared slab geometry modified by the presence of impurities. An effective form of the parallel Reynolds stress is derived in the center of mass frame of a coupled main ion-impurity system. Analyses show that the contents and the radial profile of impurities have a strong influence on the residual stress. In particular, an impurity profile aligned with that of main ions ismore » shown to cause a considerable reduction of the residual stress, which may lead to the reduction of turbulence driven intrinsic rotation.« less

Utilizing Ocean Thermal Energy in a Submarine Robot

NASA Technical Reports Server (NTRS)

Jones, Jack; Chao, Yi

2009-01-01

A proposed system would exploit the ocean thermal gradient for recharging the batteries in a battery-powered unmanned underwater vehicle [UUV (essentially, a small exploratory submarine robot)] of a type that has been deployed in large numbers in research pertaining to global warming. A UUV of this type travels between the ocean surface and depths, measuring temperature and salinity. The proposed system is related to, but not the same as, previously reported ocean thermal energy conversion (OTEC) systems that exploit the ocean thermal gradient but consist of stationary apparatuses that span large depth ranges. The system would include a turbine driven by working fluid subjected to a thermodynamic cycle. CO2 has been provisionally chosen as the working fluid because it has the requisite physical properties for use in the range of temperatures expected to be encountered in operation, is not flammable, and is much less toxic than are many other commercially available refrigerant fluids. The system would be housed in a pressurized central compartment in a UUV equipped with a double hull (see figure). The thermodynamic cycle would begin when the UUV was at maximum depth, where some of the CO2 would condense and be stored, at relatively low temperature and pressure, in the annular volume between the inner and outer hulls. The cycle would resume once the UUV had ascended to near the surface, where the ocean temperature is typically greater than or equals 20 C. At this temperature, the CO2 previously stored at depth in the annular volume between the inner and outer hulls would be pressurized to approx. equals 57 bar (5.7 MPa). The pressurized gaseous CO2 would flow through a check valve into a bladder inside the pressurized compartment, thereby storing energy of the relatively warm, pressurized CO2 for subsequent use after the next descent to maximum depth.

Anomalous magnon Nernst effect of topological magnonic materials

NASA Astrophysics Data System (ADS)

Wang, X. S.; Wang, X. R.

2018-05-01

The magnon transport driven by a thermal gradient in a perpendicularly magnetized honeycomb lattice is studied. The system with the nearest-neighbor pseudodipolar interaction and the next-nearest-neighbor Dzyaloshinskii–Moriya interaction has various topologically nontrivial phases. When an in-plane thermal gradient is applied, a transverse in-plane magnon current is generated. This phenomenon is termed as the anomalous magnon Nernst effect that closely resembles the anomalous Nernst effect for an electronic system. The anomalous magnon Nernst coefficient and its sign are determined by the magnon Berry curvature distributions in the momentum space and magnon populations in the magnon bands. We predict a temperature-induced sign reversal in anomalous magnon Nernst effect under certain conditions.

Insulator-to-conducting transition in dense fluid helium.

PubMed

Celliers, P M; Loubeyre, P; Eggert, J H; Brygoo, S; McWilliams, R S; Hicks, D G; Boehly, T R; Jeanloz, R; Collins, G W

2010-05-07

By combining diamond-anvil-cell and laser-driven shock wave techniques, we produced dense He samples up to 1.5 g/cm(3) at temperatures reaching 60 kK. Optical measurements of reflectivity and temperature show that electronic conduction in He at these conditions is temperature-activated (semiconducting). A fit to the data suggests that the mobility gap closes with increasing density, and that hot dense He becomes metallic above approximately 1.9 g/cm(3). These data provide a benchmark to test models that describe He ionization at conditions found in astrophysical objects, such as cold white dwarf atmospheres.

Transport simulation of EAST long-pulse H-mode discharge with integrated modeling

NASA Astrophysics Data System (ADS)

Wu, M. Q.; Li, G. Q.; Chen, J. L.; Du, H. F.; Gao, X.; Ren, Q. L.; Li, K.; Chan, Vincent; Pan, C. K.; Ding, S. Y.; Jian, X.; Zhu, X.; Lian, H.; Qian, J. P.; Gong, X. Z.; Zang, Q.; Duan, Y. M.; Liu, H. Q.; Lyu, B.

2018-04-01

In the 2017 EAST experimental campaign, a steady-state long-pulse H-mode discharge lasting longer than 100 s has been obtained using only radio frequency heating and current drive, and the confinement quality is slightly better than standard H-mode, H98y2 ~ 1.1, with stationary peaked electron temperature profiles. Integrated modeling of one long-pulse H-mode discharge in the 2016 EAST experimental campaign has been performed with equilibrium code EFIT, and transport codes TGYRO and ONETWO under integrated modeling framework OMFIT. The plasma current is fully-noninductively driven with a combination of ~2.2 MW LHW, ~0.3 MW ECH and ~1.1 MW ICRF. Time evolution of the predicted electron and ion temperature profiles through integrated modeling agree closely with that from measurements. The plasma current (I p ~ 0.45 MA) and electron density are kept constantly. A steady-state is achieved using integrated modeling, and the bootstrap current fraction is ~28%, the RF drive current fraction is ~72%. The predicted current density profile matches the experimental one well. Analysis shows that electron cyclotron heating (ECH) makes large contribution to the plasma confinement when heating in the core region while heating in large radius does smaller improvement, also a more peaked LHW driven current profile is got when heating in the core. Linear analysis shows that the high-k modes instability (electron temperature gradient driven modes) is suppressed in the core region where exists weak electron internal transport barriers. The trapped electron modes dominates in the low-k region, which is mainly responsible for driving the electron energy flux. It is found that the ECH heating effect is very local and not the main cause to sustained the good confinement, the peaked current density profile has the most important effect on plasma confinement improvement. Transport analysis of the long-pulse H-mode experiments on EAST will be helpful to build future experiments.

Harnessing Active Fins to Segregate Nanoparticles from Binary Mixtures

NASA Astrophysics Data System (ADS)

Liu, Ya; Kuksenok, Olga; Bhattacharya, Amitabh; Ma, Yongting; He, Ximin; Aizenberg, Joanna; Balazs, Anna

2014-03-01

One of the challenges in creating high-performance polymeric nanocomposites for optoelectronic applications, such as bilayer solar cells, is establishing effective and facile routes for controlling the properties of interface and segregation of binary particles with hole conductor particles and electron conductor particles. We model nanocomposites that encompass binary particles and binary blends in a microchannel. An array of oscillating microfins is immersed in the fluid and tethered to the floor of the microchannel; the fluid containing mixture of nanoparticles is driven along the channel by an imposed pressure gradient. During the oscillations, the fins with the specific chemical wetting reach the upper fluid when they are upright and are entirely within the lower stream when they are tilted. We introduce specific interaction between the fins and particulates in the solution. Fins can selectively ``catch'' target nanoparticles within the upper fluid stream and then release them into the lower stream. We focus on different modes of fins motion to optimize selective segregation of particles within binary mixture. Our approach provides an effective means of tailoring the properties and ultimate performance of the composites.

The interaction of evaporative and convective instabilities

NASA Astrophysics Data System (ADS)

Ozen, O.

Evaporative convection arises in a variety of natural and industrial processes, such as drying of lakebeds, heat pipe technology and dry-eye syndrome. The phenomenon of evaporative convection leads to an interfacial instability where an erstwhile flat surface becomes undulated as a control variable, such as temperature drop, exceeds a critical value. This instability has been investigated by others assuming that the vapor phase is infinitely deep and passive, i.e. vapor fluid dynamics has been ignored. However, when we look at some engineering processes, such as distillation columns, heat pipes and drying technologies where phase change takes place we might imagine that the assumption of an infinitely deep vapor layer or at least that of a passive vapor is inappropriate. Previous work on convection in bilayer systems with no phase-change suggests that active vapor layers play a major role in determining the stability of an interface. Hence, for the case of convection with phase-change, we will address this issue and try to answer the question whether the infinitely deep and passive vapor layer is a valid assumption. We have also investigated, theoretically, the gravity and surface tension gradient-driven instabilities occurring during the evaporation of a liquid into its own vapor taking into account the fluid dynamics of both phases and the finiteness of the domains of each phase, i.e. the liquid and its vapor are assumed to be confined between two horizontal plates, and different heating arrangements are applied. The effects of fluid layer depths, the evaporation rate and the temperature gradient applied across the fluids on the stability of the interface are studied. The modes of the flow pattern are determined for each scenario. The physics of the instability are explained and a comparison is made with the results of similar, yet physically different problems.

Identifying Time Periods of Minimal Thermal Gradient for Temperature-Driven Structural Health Monitoring

PubMed Central

Reilly, John; Glisic, Branko

2018-01-01

Temperature changes play a large role in the day to day structural behavior of structures, but a smaller direct role in most contemporary Structural Health Monitoring (SHM) analyses. Temperature-Driven SHM will consider temperature as the principal driving force in SHM, relating a measurable input temperature to measurable output generalized strain (strain, curvature, etc.) and generalized displacement (deflection, rotation, etc.) to create three-dimensional signatures descriptive of the structural behavior. Identifying time periods of minimal thermal gradient provides the foundation for the formulation of the temperature–deformation–displacement model. Thermal gradients in a structure can cause curvature in multiple directions, as well as non-linear strain and stress distributions within the cross-sections, which significantly complicates data analysis and interpretation, distorts the signatures, and may lead to unreliable conclusions regarding structural behavior and condition. These adverse effects can be minimized if the signatures are evaluated at times when thermal gradients in the structure are minimal. This paper proposes two classes of methods based on the following two metrics: (i) the range of raw temperatures on the structure, and (ii) the distribution of the local thermal gradients, for identifying time periods of minimal thermal gradient on a structure with the ability to vary the tolerance of acceptable thermal gradients. The methods are tested and validated with data collected from the Streicker Bridge on campus at Princeton University. PMID:29494496

Ancient Living Organisms Escaping from, or Imprisoned in, the Vents?

PubMed Central

Jackson, J. Baz

2017-01-01

We have recently criticised the natural pH gradient hypothesis which purports to explain how the difference in pH between fluid issuing from ancient alkali vents and the more acidic Hadean ocean could have driven molecular machines that catalyse reactions that are useful in prebiotic and autotrophic chemistry. In this article, we temporarily suspend our earlier criticism while we consider difficulties for primitive organisms to have managed their energy supply and to have left the vents and become free-living. We point out that it may have been impossible for organisms to have acquired membrane-located proton (or sodium ion) pumps to replace the natural pH gradient, and independently to have driven essential molecular machines such as the ATP synthase. The volumes of the ocean and of the vent fluids were too large for a membrane-located pump to have generated a significant ion concentration gradient. Our arguments apply to three of the four concurrent models employed by the proponents of the natural pH gradient hypothesis. A fourth model is exempt from these arguments but has other intrinsic difficulties that we briefly consider. We conclude that ancient organisms utilising a natural pH gradient would have been imprisoned in the vents, unable to escape and become free-living. PMID:28914790

Convective flows in enclosures with vertical temperature or concentration gradients

NASA Technical Reports Server (NTRS)

Wang, L. W.; Chai, A. T.; Sun, D. J.

1988-01-01

The transport process in the fluid phase during the growth of a crystal has a profound influence on the structure and quality of the solid phase. In vertical growth techniques the fluid phase is often subjected to vertical temperature and concentration gradients. The main objective is to obtain more experimental data on convective flows in enclosures with vertical temperature or concentration gradients. Among actual crystal systems the parameters vary widely. The parametric ranges studied for mass transfer are mainly dictated by the electrochemical system employed to impose concentration gradients. Temperature or concentration difference are maintained between two horizontal end walls. The other walls are kept insulated. Experimental measurements and observations were made of the heat transfer or mass transfer, flow patterns, and the mean and fluctuating temperature distribution. The method used to visualize the flow pattern in the thermal cases is an electrochemical pH-indicator method. Laser shadowgraphs are employed to visualize flow patterns in the solutal cases.

Convective flows in enclosures with vertical temperature or concentration gradients

NASA Technical Reports Server (NTRS)

Wang, L. W.; Chai, A. T.; Sun, D. J.

1989-01-01

The transport process in the fluid phase during the growth of a crystal has a profound influence on the structure and quality of the solid phase. In vertical growth techniques the fluid phase is often subjected to vertical temperature and concentration gradients. The main objective is to obtain more experimental data on convective flows in enclosures with vertical temperature or concentration gradients. Among actual crystal systems the parameters vary widely. The parametric ranges studied for mass transfer are mainly dictated by the electrochemical system employed to impose concentration gradients. Temperature or concentration difference are maintained between two horizontal end walls. The other walls are kept insulated. Experimental measurements and observations were made of the heat transfer or mass transfer, flow patterns, and the mean and fluctuating temperature distribution. The method used to visualize the flow pattern in the thermal cases is an electrochemical pH-indicator method. Laser shadowgraphs are employed to visualize flow patterns in the solutal cases.

Extending the validation of multi-mode model for anomalous transport to high beta poloidal tokamak scenario in DIII-D

NASA Astrophysics Data System (ADS)

Pankin, A. Y.; Kritz, A. H.; Rafiq, T.; Garofalo, A. M.; Holod, I.; Weiland, J.

2018-05-01

The Multi-Mode Model (MMM7.1) for anomalous transport is tested in predictive modeling of temperature profiles of a high beta poloidal DIII-D discharge. This new H-mode plasma regime, with high beta poloidal and high bootstrap currents, has been studied in DIII-D tokamak discharges [A. Garofalo et al., Nucl. Fusion 55, 123025 (2015)]. The role of instabilities that can drive the anomalous transport described by MMM7.1 is investigated. The temperature profiles for a high beta poloidal DIII-D discharge are computed using the NCLASS model for the neoclassical transport and the Weiland and Electron Temperature Gradient (ETG) components of the MMM7.1 model for the anomalous transport. The neoclassical transport is found to be the main contributor to the ion thermal transport in the plasma core. The contributions from the ion temperature gradient driven modes are found to be important only outside of the internal transport barrier. The magnitudes of the predicted temperature profiles are found to be in a reasonable agreement with experimental profiles. The simulation results approximately reproduce the internal transport barrier in the ion temperature profile but not in the electron temperature profile due to a weak dependence of the ETG driven transport on the Shafranov shift in the ETG component of MMM7.1. Possible effects that can contribute to stabilization of these modes, for example, effects associated with the large beta poloidal such as the Shafranov shift stabilization in the MMM7.1 model, are discussed. It is demonstrated that the E × B flow shear has a relatively small effect in the formation of the internal transport barrier in the high beta poloidal DIII-D discharge 154406. The Shafranov shift (alpha stabilization) and small or reversed magnetic shear profiles are found to be the primary reasons for quenched anomalous transport in this discharge.

Overview of recent HL-2A experiments

NASA Astrophysics Data System (ADS)

Duan, X. R.; Liu, Yi; Xu, M.; Yan, L. W.; Xu, Y.; Song, X. M.; Dong, J. Q.; Ding, X. T.; Chen, L. Y.; Lu, B.; Liu, D. Q.; Rao, J.; Xuan, W. M.; Yang, Q. W.; Zheng, G. Y.; Zou, X. L.; Liu, Y. Q.; Zhong, W. L.; Zhao, K. J.; Ji, X. Q.; Mao, W. C.; Wang, Q. M.; Li, Q.; Cao, J. Y.; Cao, Z.; Lei, G. J.; Zhang, J. H.; Li, X. D.; Bai, X. Y.; Cheng, J.; Chen, W.; Cui, Z. Y.; Delpech, L.; Diamond, P. H.; Dong, Y. B.; Ekedahl, A.; Hoang, T.; Huang, Y.; Ida, K.; Itoh, K.; Itoh, S.-I.; Isobe, M.; Inagaki, S.; Mazon, D.; Morita, S.; Peysson, Y.; Shi, Z. B.; Wang, X. G.; Xiao, G. L.; Yu, D. L.; Yu, L. M.; Zhang, Y. P.; Zhou, Y.; Cui, C. H.; Feng, B. B.; Huang, M.; Li, Y. G.; Li, B.; Li, G. S.; Li, H. J.; Li, Qing; Peng, J. F.; Wang, Y. Q.; Yuan, B. S.; Liu, Yong; HL-2A Team

2017-10-01

Since the last Fusion Energy Conference, significant progress has been made in the following areas. The first high coupling efficiency low-hybrid current drive (LHCD) with a passive-active multi-junction (PAM) antenna was successfully demonstrated in the H-mode on the HL-2A tokamak. Double critical impurity gradients of electromagnetic turbulence were observed in H-mode plasmas. Various ELM mitigation techniques have been investigated, including supersonic molecular beam injection (SMBI), impurity seeding, resonant magnetic perturbation (RMP) and low-hybrid wave (LHW). The ion internal transport barrier was observed in neutral beam injection (NBI) heated plasmas. Neoclassical tearing modes (NTMs) driven by the transient perturbation of local electron temperature during non-local thermal transport events have been observed, and a new type of non-local transport triggered by the ion fishbone was found. A long-lasting runaway electron plateau was achieved after argon injection and the runaway current was successfully suppressed by SMBI. It was found that low-n Alfvénic ion temperature gradient (AITG) modes can be destabilized in ohmic plasmas, even with weak magnetic shear and low-pressure gradients. For the first time, the synchronization of geodesic acoustic mode (GAM) and magnetic fluctuations was observed in edge plasmas, revealing frequency entrainment and phase lock. The spatiotemporal features of zonal flows were also studied using multi-channel correlation Doppler reflectometers.

Non local-thermodynamical-equilibrium effects in the simulation of laser-produced plasmas

NASA Astrophysics Data System (ADS)

Klapisch, M.; Bar-Shalom, A.; Oreg, J.; Colombant, D.

1998-05-01

Local thermodynamic equilibrium (LTE) breaks down in directly or indirectly driven laser plasmas because of sharp gradients, energy deposition, etc. For modeling non-LTE effects in hydrodynamical simulations, Busquet's model [Phys. Fluids B 5, 4191 (1993)] is very convenient and efficient. It uses off-line generated LTE opacities and equation of states via an effective, radiation-dependent ionization temperature Tz. An overview of the model is given. The results are compared with an elaborate collisional radiative model based on superconfigurations. The agreements for average charge Z* and opacities are surprisingly good, even more so when the plasma is immersed in a radiation field. Some remaining discrepancy at low density is attributed to dielectronic recombination. Improvement appears possible, especially for emissivities, because the concept of ionization temperature seems to be validated.

A mixed pseudospectral/finite difference method for a thermally driven fluid in a nonuniform gravitational field

NASA Technical Reports Server (NTRS)

Macaraeg, M. G.

1985-01-01

A numerical study of the steady, axisymmetric flow in a heated, rotating spherical shell is conducted to model the Atmospheric General Circulation Experiment (AGCE) proposed to run aboard a later Shuttle mission. The AGCE will consist of concentric rotating spheres confining a dielectric fluid. By imposing a dielectric field across the fluid a radial body force will be created. The numerical solution technique is based on the incompressible Navier-Stokes equations. In the method a pseudospectral technique is used in the latitudinal direction, and a second-order accurate finite difference scheme discretizes time and radial derivatives. This paper discusses the development and performance of this numerical scheme for the AGCE which has been modeled in the past only by pure FD formulations. In addition, previous models have not investigated the effect of using a dielectric force to simulate terrestrial gravity. The effect of this dielectric force on the flow field is investigated as well as a parameter study of varying rotation rates and boundary temperatures. Among the effects noted are the production of larger velocities and enhanced reversals of radial temperature gradients for a body force generated by the electric field.

Relativistic klystron driven compact high gradient accelerator as an injector to an X-ray synchrotron radiation ring

DOEpatents

Yu, David U. L.

1990-01-01

A compact high gradient accelerator driven by a relativistic klystron is utilized to inject high energy electrons into an X-ray synchrotron radiation ring. The high gradients provided by the relativistic klystron enables accelerator structure to be much shorter (typically 3 meters) than conventional injectors. This in turn enables manufacturers which utilize high energy, high intensity X-rays to produce various devices, such as computer chips, to do so on a cost effective basis.

Stable and unstable roots of ion temperature gradient driven mode using curvature modified plasma dispersion functions

NASA Astrophysics Data System (ADS)

Gültekin, Ö.; Gürcan, Ö. D.

2018-02-01

Basic, local kinetic theory of ion temperature gradient driven (ITG) mode, with adiabatic electrons is reconsidered. Standard unstable, purely oscillating as well as damped solutions of the local dispersion relation are obtained using a bracketing technique that uses the argument principle. This method requires computing the plasma dielectric function and its derivatives, which are implemented here using modified plasma dispersion functions with curvature and their derivatives, and allows bracketing/following the zeros of the plasma dielectric function which corresponds to different roots of the ITG dispersion relation. We provide an open source implementation of the derivatives of modified plasma dispersion functions with curvature, which are used in this formulation. Studying the local ITG dispersion, we find that near the threshold of instability the unstable branch is rather asymmetric with oscillating solutions towards lower wave numbers (i.e. drift waves), and damped solutions toward higher wave numbers. This suggests a process akin to inverse cascade by coupling to the oscillating branch towards lower wave numbers may play a role in the nonlinear evolution of the ITG, near the instability threshold. Also, using the algorithm, the linear wave diffusion is estimated for the marginally stable ITG mode.

Comparison of Microinstability Properties for Stellarator Magnetic Geometries

DOE Office of Scientific and Technical Information (OSTI.GOV)

G. Rewoldt; L.-P. Ku; W.M. Tang

2005-06-16

The microinstability properties of seven distinct magnetic geometries corresponding to different operating and planned stellarators with differing symmetry properties are compared. Specifically, the kinetic stability properties (linear growth rates and real frequencies) of toroidal microinstabilities (driven by ion temperature gradients and trapped-electron dynamics) are compared, as parameters are varied. The familiar ballooning representation is used to enable efficient treatment of the spatial variations along the equilibrium magnetic field lines. These studies provide useful insights for understanding the differences in the relative strengths of the instabilities caused by the differing localizations of good and bad magnetic curvature and of the presencemore » of trapped particles. The associated differences in growth rates due to magnetic geometry are large for small values of the temperature gradient parameter n identical to d ln T/d ln n, whereas for large values of n, the mode is strongly unstable for all of the different magnetic geometries.« less

Main-ion intrinsic toroidal rotation profile driven by residual stress torque from ion temperature gradient turbulence in the DIII-D tokamak

DOE PAGES

Grierson, B. A.; Wang, W. X.; Ethier, S.; ...

2017-01-06

Intrinsic toroidal rotation of the deuterium main ions in the core of the DIII-D tokamak is observed to transition from flat to hollow, forming an off-axis peak, above a threshold level of direct electron heating. Nonlinear gyrokinetic simulations show that the residual stress associated with electrostatic ion temperature gradient turbulence possesses the correct radial location and stress structure to cause the observed hollow rotation profile. Residual stress momentum flux in the gyrokinetic simulations is balanced by turbulent momentum diffusion, with negligible contributions from turbulent pinch. Finally, the prediction of the velocity profile by integrating the momentum balance equation produces amore » rotation profile that qualitatively and quantitatively agrees with the measured main-ion profile, demonstrating that fluctuation-induced residual stress can drive the observed intrinsic velocity profile.« less

Thermocapillary reorientation of Janus drops

NASA Astrophysics Data System (ADS)

Rosales, Rodolfo; Saenz, Pedro

2017-11-01

Janus drops, named after the Ancient Roman two-faced god, are liquid drops formed from two immiscible fluids. Experimental observations indicate that a Janus drop may re-orientate in response to an applied external thermal gradient due to the Marangoni effect. Depending on the angle between the interior interface and the direction of the temperature gradient, disparities in the physical properties of the constituent liquids may lead to asymmetries in the thermocapillary flow. As a result, the drop will move along a curved path until a torque-free configuration is achieved, point after which it will continue on a straight trajectory. Here, we present the results of a theoretical investigation of this realignment phenomenon in the Stokes regime and in the limit of non-deformable interfaces. A 3D semi-analytical method in terms of polar spherical harmonics is developed to characterize and rationalize the hydrodynamic response (forces and torques), flow (velocity and temperature distribution) and trajectory of a Janus drop moving during the temperature-driven reorientation process. Furthermore, we discuss how this phenomenon may be exploited to develop dynamically reconfigurable micro-lenses. This work was partially supported by the US National Science Foundation through Grants DMS-1614043 and DMS-1719637.

Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

NASA Astrophysics Data System (ADS)

Duff, James; Sarff, John; Ding, Weixing; Brower, David; Parke, Eli; Chapman, Brett; Terry, Paul; Pueschel, M. J.; Williams, Zach

2017-10-01

Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM). Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking, which are suppressed via inductive control for this work. The improved confinement is associated with an increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have f 50 kHz, kϕρs < 0.14 , and propagate in the electron drift direction. Their spectral emergence coincides with a sharp decrease in global tearing mode associated fluctuations, their amplitude increases with local density gradient, and they exhibit a density-gradient threshold at R /Ln 15 . The GENE code, modified for the RFP, predicts the onset of density-gradient-driven TEM for these strong-gradient plasma conditions. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations, comparable to experimental magnetic fluctuations, causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Work supported by US DOE.

Electro-diffusion in a plasma with two ion species

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kagan, Grigory; Tang Xianzhu

2012-08-15

Electric field is a thermodynamic force that can drive collisional inter-ion-species transport in a multicomponent plasma. In an inertial confinement fusion capsule, such transport causes fuel ion separation even with a target initially prepared to have equal number densities for the two fuel ion species. Unlike the baro-diffusion driven by ion pressure gradient and the thermo-diffusion driven by ion and electron temperature gradients, electro-diffusion has a critical dependence on the charge-to-mass ratio of the ion species. Specifically, it is shown here that electro-diffusion vanishes if the ion species have the same charge-to-mass ratio. An explicit expression for the electro-diffusion ratiomore » is obtained and used to investigate the relative importance of electro- and baro-diffusion mechanisms. In particular, it is found that electro-diffusion reinforces baro-diffusion in the deuterium and tritium mix, but tends to cancel it in the deuterium and helium-3 mix.« less

Development of High-Gradient Dielectric Laser-Driven Particle Accelerator Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Byer, Robert L.

2013-11-07

The thrust of Stanford's program is to conduct research on high-gradient dielectric accelerator structures driven with high repetition-rate, tabletop infrared lasers. The close collaboration between Stanford and SLAC (Stanford Linear Accelerator Center) is critical to the success of this project, because it provides a unique environment where prototype dielectric accelerator structures can be rapidly fabricated and tested with a relativistic electron beam.

Temperature-gradient-induced

NASA Astrophysics Data System (ADS)

Park, Cheol; Glaser, Matt; Maclennan, Joe; Clark, Noel; Trittel, Torsten; Stannarius, Ralf

Freely-suspended smectic films of sub-micrometer thickness and lateral extensions of several millimeters were used to study thermally driven migration and convection in the film plane. Film experiments were performed during the 6 minute microgravity phase of a TEXUS suborbital rocket flight (Texus 52, launched April 27, 2015). We have found an attraction of the smectic material towards the cold edge of the film in a temperature gradient, similar to the Soret effect. This process is reversed when this edge is heated up again. Thermal convection driven by two thermocontacts in the film is practically absent, even at temperature gradients up to 10 K/mm, with thermally driven convection only setting in when the hot post reaches the transition temperature to the nematic phase. The Observation and Analysis of Smectic Islands in Space (OASIS) flight hardware was launched on SpaceX-6 in April 2015 and experiments on smectic bubbles were carried out on the International Space Station using four different smectic A and C liquid crystal materials in separate sample chambers. We observed that smectic islands on the surface of the bubbles migrated towards the colder part of the bubble in a temperature gradient. This work was supported by NASA Grant No. NNX-13AQ81G, by the Soft Materials Research Center under NSF MRSEC Grants No. DMR-0820579 and No. DMR-1420736, and by DLR Grants 50WM1127 and 50WM1430.

Tecuamburro Volcano, Guatemala: exploration geothermal gradient drilling and results

USGS Publications Warehouse

Goff, S.J.; Goff, F.; Janik, C.J.

1992-01-01

Results of geological, volcanological, hydrogeochemical, and geophysical field studies conducted in 1988 and 1989 at the Tecuamburro geothermal site, Guatemala, indicate that there is a substantial shallow heat source beneath the area of youngest volcanism. Gases from acid-sulfate springs near Laguna Ixpaco consistently yield maximum estimated subsurface temperatures of 300??C. To obtain information on subsurface temperatures and temperature gradients, stratigraphy, fracturing, hydrothermal alteration, and hydrothermal fluids, a geothermal gradient core hole (TCB-1) was drilled to 808 m low on the northern flank of the Tecuamburro Volcano complex. The hole is located 300 m south of a 300m-diameter phreatic crater. Laguna Ixpaco, dated at 2910 years. TCB-1 temperature logs do not indicate isothermal conditions at depth and the calculated thermal gradient from 500-800 m is 230??C/km. Bottom hole temperature is close to 240??C. Calculated heat flow values are around 350-400 mW/m2. Fluid-inclusion and secondary-alteration studies indicate that veins and secondary minerals were formed at temperatures equal to or slightly less than present temperatures; thus, the Tecuamburro geothermal system may still be heating up. The integration of results from the TCB-1 gradient core hole with results from field studies provides strong evidence that the Tecuamburro area holds great promise for geothermal resource development. ?? 1992.

Instabilities and transport in Hall plasmas with ExB drift

NASA Astrophysics Data System (ADS)

Smolyakov, Andrei

2016-10-01

Low temperature plasma with moderate magnetic field, where the ions are not or just weakly magnetized, i.e. the ion Larmor radius being larger or comparable to the characteristic length scale of interest (e.g. the size ofthe system), have distinctly different properties from strongly magnetized plasmas such as that for fusion applications. Such parameters regimes are generally defined here as Hall plasmas. The natural scale separation between the ion and electron Larmor radii in Hall plasma, further exploited by the application of the external electric field, offers unique applications in various plasma devices for material processing and electric propulsion. Plasmas in such devices are in strongly non-equilibrium state making it prone to a number of instabilities. This talk presents physics description of the dominant unstable modes in ExB Hall plasmas resulting in highly turbulent state with nonlinear coherent structures and anomalous electron current. Since ions are un-magnetized, fundamental instabilities operating in low temperature Hall plasmas are very different from much studied gradients (density, temperature and magnetic field) driven drift-wave turbulence in strongly magnetized plasmas for fusion applications. As a result the nonlinear saturation mechanisms, role of the ExB shear flows are also markedly different in such plasmas. We review the basic instabilities in these plasmas which are related to the ion-sound, low-hybrid and anti-drift modes, discuss nonlinear saturation and anomalous transport mechanisms. The advanced nonlinear fluid model for such plasmas and results of nonlinear simulations of turbulence and anomalous transport performed within a modified BOUT++ framework will be presented. Research supported by NSERC Canada and US AFOSR FA9550-15-1-0226.

The Effect of Gravity on the Combustion Synthesis of Porous Ceramics and Metal Matrix Composites

NASA Technical Reports Server (NTRS)

Moore, J. J.; Woodger, T. C.; Wolanski, T.; Yi, H. C.; Guigne, J. Y.

1997-01-01

Combustion synthesis (self propagating, high temperature synthesis-SHS) is a novel technique that is capable of producing many advanced materials. The ignition temperature (Tig) of such combustion synthesis reactions is often coincident with that of the lowest melting point reactant. The resultant liquid metal wets and spreads around the other solid reactant particles of higher melting points, thereby improving the reactant contact and kinetics, followed by formation of the required compounds. This ignition initiates a combustion propagating wave whose narrow reaction front rapidly travels through the reactants. Since this process is highly exothermic, the heat released by combustion often melts the reactant particles ahead of the combustion front and ignites the adjacent reactant layer, resulting in a self-sustaining reaction. Whenever a fluid phase (liquid or gas) is generated by the reaction system, gravity-driven phenomena can occur. Such phenomena include convective flows of fluid by conventional or unstable convection and settling of the higher density phases. A combustion process is often associated with various kinds of fluid flow. For instance, if the SHS reaction is carried out under inert or reactive gas atmospheres, or a volatile, e.g., B2O3, is deliberately introduced as a reactant, convective flows of the gas will occur due to a temperature gradient existing in the atmosphere when a combustion wave is initiated. The increased gas flow will produce a porous (or expanded) SHS product. Owing to the highly exothermic nature of many SHS reactions, liquid phase(s) can also form before, at, or after the combustion front. The huge temperature gradient at the combustion front can induce convective flows (conventional or unstable) of the liquid phase. Each of these types of convective fluid flow can change the combustion behavior of the synthesizing reaction, and, therefore, the resultant product microstructure. In addition, when two or more phases of different density are produced at or ahead of the propagating combustion front settling of the higher density phase will occur resulting in a non-uniform product microstructure and properties.

Temporal gradients in shear stimulate osteoblastic proliferation via ERK1/2 and retinoblastoma protein

NASA Technical Reports Server (NTRS)

Jiang, Guang-Liang; White, Charles R.; Stevens, Hazel Y.; Frangos, John A.

2002-01-01

Bone cells are subject to interstitial fluid flow (IFF) driven by venous pressure and mechanical loading. Rapid dynamic changes in mechanical loading cause transient gradients in IFF. The effects of pulsatile flow (temporal gradients in fluid shear) on rat UMR106 cells and rat primary osteoblastic cells were studied. Pulsatile flow induced a 95% increase in S-phase UMR106 cells compared with static controls. In contrast, ramped steady flow stimulated only a 3% increase. Similar patterns of S-phase induction were also observed in rat primary osteoblastic cells. Pulsatile flow significantly increased relative UMR106 cell number by 37 and 62% at 1.5 and 24 h, respectively. Pulsatile flow also significantly increased extracellular signal-regulated kinase (ERK1/2) phosphorylation by 418%, whereas ramped steady flow reduced ERK1/2 activation to 17% of control. Correspondingly, retinoblastoma protein was significantly phosphorylated by pulsatile fluid flow. Inhibition of mitogen-activated protein (MAP)/ERK kinase (MEK)1/2 by U0126 (a specific MEK1/2 inhibitor) reduced shear-induced ERK1/2 phosphorylation and cell proliferation. These findings suggest that temporal gradients in fluid shear stress are potent stimuli of bone cell proliferation.

Resolving the Mystery of Transport Within Internal Transport Barriers

NASA Astrophysics Data System (ADS)

Staebler, G. M.

2013-10-01

The Trapped Gyro-Landau Fluid (TGLF) quasilinear model, which is calibrated to approximate non-linear gyro-kinetic turbulence simulations, is now able to predict the electron density, electron and ion temperatures and ion toroidal rotation simultaneously for internal transport barrier (ITB) discharges in excellent agreement with data from the DIII-D tokamak. This is a strong validation of gyro-kinetic theory of ITBs, requiring multiple instabilities responsible for transport in different channels at different scales. Inside the ITB, the ion energy transport is observed to be reduced to the neoclassical level which is consistent with the theory of turbulence suppression by E × B velocity shear acting on low wavenumber turbulence. The electron energy transport is observed to be far above the neoclassical level which is consistent with electron energy transport due to high wavenumber electron temperature gradient (ETG) modes. Since the ETG modes do not produce particle and ion momentum transport, and low wavenumber modes are suppressed, these channels are expected to be reduced to the neoclassical level in striking disagreement with experimental measurements. A possible resolution of this conundrum was found in 2005 when gyro-kinetic turbulence simulations showed that the parallel velocity shear driven Kelvin-Helmholtz (KH) mode can arrest the suppression of transport by the shear in the E × B velocity Doppler shift at high toroidal flow shear. The success of TGLF in predicting ITB transport is due to the inclusion of ion gyro-radius scale modes that become dominant at high E × B shear and to recent improvements to TGLF that allow the KH mode to be faithfully modeled. The resolution of this long-standing mystery of the missing particle and momentum transport in an ITB is the result of the steady advances in gyro-kinetic simulations and quasilinear modeling. Supported by the US Department of Energy under DE-FG02-95ER54309.

Cooling beyond the boundary value in supercritical fluids under vibration

NASA Astrophysics Data System (ADS)

Sharma, D.; Erriguible, A.; Amiroudine, S.

2017-12-01

Supercritical fluids when subjected to simultaneous quench and vibration have been known to cause various intriguing flow phenomena and instabilities depending on the relative direction of temperature gradient and vibration. Here we describe a surprising and interesting phenomenon wherein temperature in the fluid falls below the imposed boundary value when the walls are quenched and the direction of vibration is normal to the temperature gradient. We define these regions in the fluid as sink zones, because they act like sink for heat within the fluid domain. The formation of these zones is first explained using a one-dimensional (1D) analysis with acceleration in constant direction. Subsequently, the effect of various boundary conditions and the relative direction of the temperature gradient to acceleration are analyzed, highlighting the necessary conditions for the formation of sink zones. It is found that the effect of high compressibility and the action of self-weight (due to high acceleration) causes the temperature to change in the bulk besides the usual action of piston effect. This subsequently affects the overall temperature profile thereby leading to the formation of sink zones. Though the examined 1D cases differ from the current two-dimensional (2D) cases, owing to the direction of acceleration being normal as compared to parallel in case of former, the explanations pertaining to 1D cases are judiciously utilized to elucidate the formation of sink zones in 2D supercritical fluids subjected to thermal quench and vibrational acceleration. The appearance of sink zones is found to be dependent on several factors such as proximity to the critical point and acceleration. A surface three-dimensional plot illustrating the effect of these parameters on onset time of sink zones is presented to further substantiate these arguments.

The Effect of Temperature on Moisture Transport in Concrete.

PubMed

Wang, Yao; Xi, Yunping

2017-08-09

Most concrete structures and buildings are under temperature and moisture variations simultaneously. Thus, the moisture transport in concrete is driven by the moisture gradient as well as the temperature gradient. This paper presents an experimental approach for determining the effect of different temperature gradients on moisture distribution profiles in concrete. The effect of elevated temperatures under isothermal conditions on the moisture transport was also evaluated, and found not to be significant. The non-isothermal tests show that the temperature gradient accelerates the moisture transport in concrete. The part of increased moisture transfer due to the temperature gradient can be quantified by a coupling parameter D HT , which can be determined by the present test data. The test results indicated that D HT is not a constant but increases linearly with the temperature variation. A material model was developed for D HT based on the experimental results obtained in this study.

The Effect of Temperature on Moisture Transport in Concrete

PubMed Central

Wang, Yao; Xi, Yunping

2017-01-01

Most concrete structures and buildings are under temperature and moisture variations simultaneously. Thus, the moisture transport in concrete is driven by the moisture gradient as well as the temperature gradient. This paper presents an experimental approach for determining the effect of different temperature gradients on moisture distribution profiles in concrete. The effect of elevated temperatures under isothermal conditions on the moisture transport was also evaluated, and found not to be significant. The non-isothermal tests show that the temperature gradient accelerates the moisture transport in concrete. The part of increased moisture transfer due to the temperature gradient can be quantified by a coupling parameter DHT, which can be determined by the present test data. The test results indicated that DHT is not a constant but increases linearly with the temperature variation. A material model was developed for DHT based on the experimental results obtained in this study. PMID:28792460

Poloidal asymmetries in edge transport barriersa)

NASA Astrophysics Data System (ADS)

Churchill, R. M.; Theiler, C.; Lipschultz, B.; Hutchinson, I. H.; Reinke, M. L.; Whyte, D.; Hughes, J. W.; Catto, P.; Landreman, M.; Ernst, D.; Chang, C. S.; Hager, R.; Hubbard, A.; Ennever, P.; Walk, J. R.

2015-05-01

Measurements of impurities in Alcator C-Mod indicate that in the pedestal region, significant poloidal asymmetries can exist in the impurity density, ion temperature, and main ion density. In light of the observation that ion temperature and electrostatic potential are not constant on a flux surface [Theiler et al., Nucl. Fusion 54, 083017 (2014)], a technique based on total pressure conservation to align profiles measured at separate poloidal locations is presented and applied. Gyrokinetic neoclassical simulations with XGCa support the observed large poloidal variations in ion temperature and density, and that the total pressure is approximately constant on a flux surface. With the updated alignment technique, the observed in-out asymmetry in impurity density is reduced from previous publishing [Churchill et al., Nucl. Fusion 53, 122002 (2013)], but remains substantial ( n z , H / n z , L ˜ 6 ). Candidate asymmetry drivers are explored, showing that neither non-uniform impurity sources nor localized fluctuation-driven transport are able to explain satisfactorily the impurity density asymmetry. Since impurity density asymmetries are only present in plasmas with strong electron density gradients, and radial transport timescales become comparable to parallel transport timescales in the pedestal region, it is suggested that global transport effects relating to the strong electron density gradients in the pedestal are the main driver for the pedestal in-out impurity density asymmetry.

Heat pipe systems using new working fluids

NASA Technical Reports Server (NTRS)

Chao, David F. (Inventor); Zhang, Nengli (Inventor)

2004-01-01

The performance of a heat pipe system is greatly improved by the use of a dilute aqueous solution of about 0.0005 and about 0.005 moles per liter of a long chain alcohol as the working fluid. The surface tension-temperature gradient of the long-chain alcohol solutions turns positive as the temperature exceeds a certain value, for example about 40.degree. C. for n-heptanol solutions. Consequently, the Marangoni effect does not impede, but rather aids in bubble departure from the heating surface. Thus, the bubble size at departure is substantially reduced at higher frequencies and, therefore, increases the boiling limit of heat pipes. This feature is useful in microgravity conditions. In addition to microgravity applications, the heat pipe system may be used for commercial, residential and vehicular air conditioning systems, micro heat pipes for electronic devices, refrigeration and heat exchangers, and chemistry and cryogenics.

A Theoretical Study of Remobilizing Surfactant Retarded Fluid Particle Interfaces

NASA Technical Reports Server (NTRS)

Wang, Yanping; Papageorgiou, Dimitri; Maldarelli, Charles

1996-01-01

Microgravity processes must rely on mechanisms other than bouyancy to move bubbles or droplets from one region to another in a continuous liquid phase. One suggested method is thermocapillary migration in which a temperature gradient is applied to the continuous phase. When a fluid particle contacts this gradient, one pole of the particle becomes warmer than the opposing pole. The interfacial tension between the drop or bubble phase and the continuous phase usually decreases with temperature. Thus the cooler pole is of higher interfacial tension than the warmer pole, and the interface is tugged in the direction of the cooler end. This thermocapillary or thermally induced Marangoni surface stress causes a fluid streaming in the continuous phase from which develops a viscous shear traction and pressure gradient which together propel the particle in the direction of the warmer fluid. In this paper, we provide a theoretical basis for remobilizing surfactant retarded fluid particle interfaces in an effort to make viable the use of thermocapillary migrations for the management of bubbles and drops in microgravity,

Topological Phase Transitions in Zinc-Blende Semimetals Driven Exclusively by Electronic Temperature

NASA Astrophysics Data System (ADS)

Trushin, Egor; Görling, Andreas

2018-04-01

We show that electronic phase transitions in zinc-blende semimetals with quadratic band touching (QBT) at the center of the Brillouin zone, like GaBi, InBi, or HgTe, can occur exclusively due to a change of the electronic temperature without the need to involve structural transformations or electron-phonon coupling. The commonly used Kohn-Sham density-functional methods based on local and semilocal density functionals employing the local density approximation (LDA) or generalized gradient approximations (GGAs), however, are not capable of describing such phenomena because they lack an intrinsic temperature dependence and account for temperature only via the occupation of bands, which essentially leads only to a shift of the Fermi level without changing the shape or topology of bands. Kohn-Sham methods using the exact temperature-dependent exchange potential, not to be confused with the Hartree-Fock exchange potential, on the other hand, describe such phase transitions. A simple modeling of correlation effects can be achieved by screening of the exchange. In the considered zinc-blende compounds the QBT is unstable at low temperatures and a transition to electronic states without QBT takes place. In the case of HgTe and GaBi Weyl points of type I and type II, respectively, emerge during the transitions. This demonstrates that Kohn-Sham methods can describe such topological phase transitions provided they are based on functionals more accurate than those within the LDA or GGA. Moreover, the electronic temperature is identified as a handle to tune topological materials.

Non-modal theory of the kinetic ion temperature gradient driven instability of plasma shear flows across the magnetic field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mikhailenko, V. V., E-mail: vladimir@pusan.ac.kr; Mikhailenko, V. S.; Lee, Hae June, E-mail: haejune@pusan.ac.kr

2016-06-15

The temporal evolution of the kinetic ion temperature gradient driven instability and of the related anomalous transport of the ion thermal energy of plasma shear flow across the magnetic field is investigated analytically. This instability develops in a steady plasma due to the inverse ion Landau damping and has the growth rate of the order of the frequency when the ion temperature is equal to or above the electron temperature. The investigation is performed employing the non-modal methodology of the shearing modes which are the waves that have a static spatial structure in the frame of the background flow. Themore » solution of the governing linear integral equation for the perturbed potential displays that the instability experiences the non-modal temporal evolution in the shearing flow during which the unstable perturbation becomes very different from a canonical modal form. It transforms into the non-modal structure with vanishing frequency and growth rate with time. The obtained solution of the nonlinear integral equation, which accounts for the random scattering of the angle of the ion gyro-motion due to the interaction of ions with ensemble of shearing waves, reveals similar but accelerated process of the transformations of the perturbations into the zero frequency structures. It was obtained that in the shear flow the anomalous ion thermal conductivity decays with time. It is a strictly non-modal effect, which originates from the temporal evolution of the shearing modes turbulence.« less

The self-consistent parallel electric field due to electrostatic ion-cyclotron turbulence in downward auroral-current regions of the Earth's magnetosphere. IV

NASA Astrophysics Data System (ADS)

Jasperse, John R.; Basu, Bamandas; Lund, Eric J.; Grossbard, Neil

2010-06-01

The physical processes that determine the self-consistent electric field (E∥) parallel to the magnetic field have been an unresolved problem in magnetospheric physics for over 40 years. Recently, a new multimoment fluid theory was developed for inhomogeneous, nonuniformly magnetized plasma in the guiding-center and gyrotropic approximation that includes the effect of electrostatic, turbulent, wave-particle interactions (see Jasperse et al. [Phys. Plasmas 13, 072903 (2006); Jasperse et al., Phys. Plasmas13, 112902 (2006)]). In the present paper and its companion paper [Jasperse et al., Phys. Plasmas 17, 062903 (2010)], which are intended as sequels to the earlier work, a fundamental model for downward, magnetic field-aligned (Birkeland) currents for quasisteady conditions is presented. The model includes the production of electrostatic ion-cyclotron turbulence in the long-range potential region by an electron, bump-on-tail-driven ion-cyclotron instability. Anomalous momentum transfer (anomalous resistivity) by itself is found to produce a very small contribution to E∥; however, the presence of electrostatic, ion-cyclotron turbulence has a very large effect on the altitude dependence of the entire quasisteady solution. Anomalous energy transfer (anomalous heating and cooling) modifies the density, drift, and temperature altitude profiles and hence the generalized parallel-pressure gradients and mirror forces in the electron and ion momentum-balance equations. As a result, |E∥| is enhanced by nearly a factor of 40 compared to its value when turbulence is absent. The space-averaged potential increase associated with the strong double layer at the bottom of the downward-current sheet is estimated using the FAST satellite data and the multimoment fluid theory.

Progress in Ion Transport Membranes for Gas Separation Applications

NASA Astrophysics Data System (ADS)

Bose, Arun C.; Stiegel, Gary J.; Armstrong, Phillip A.; Halper, Barry J.; (Ted) Foster, E. P.

This chapter describes the evolution and advances of ion transport membranes for gas separation applications, especially separation of oxygen from air. In partnership with the US Department of Energy (DOE), Air Products and Chemicals, Inc. (Air Products) successfully developed a novel class of mixed ion-electron conducting materials and membrane architecture. These novel materials are referred to as ion transport membranes (ITM). Generically, ITMs consist of modified perovskite and brownmillerite oxide solid electrolytes and provide high oxygen anion and electron conduction typically at high temperatures driven by an oxygen potential gradient without the need for external power. The partial pressure ratio across the ITM layer creates the driving force for oxygen separation.

Benchmarking gyrokinetic simulations in a toroidal flux-tube

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Y.; Parker, S. E.; Wan, W.

2013-09-15

A flux-tube model is implemented in the global turbulence code GEM [Y. Chen and S. E. Parker, J. Comput. Phys. 220, 839 (2007)] in order to facilitate benchmarking with Eulerian codes. The global GEM assumes the magnetic equilibrium to be completely given. The initial flux-tube implementation simply selects a radial location as the center of the flux-tube and a radial size of the flux-tube, sets all equilibrium quantities (B, ∇B, etc.) to be equal to the values at the center of the flux-tube, and retains only a linear radial profile of the safety factor needed for boundary conditions. This implementationmore » shows disagreement with Eulerian codes in linear simulations. An alternative flux-tube model based on a complete local equilibrium solution of the Grad-Shafranov equation [J. Candy, Plasma Phys. Controlled Fusion 51, 105009 (2009)] is then implemented. This results in better agreement between Eulerian codes and the particle-in-cell (PIC) method. The PIC algorithm based on the v{sub ||}-formalism [J. Reynders, Ph.D. dissertation, Princeton University, 1992] and the gyrokinetic ion/fluid electron hybrid model with kinetic electron closure [Y. Chan and S. E. Parker, Phys. Plasmas 18, 055703 (2011)] are also implemented in the flux-tube geometry and compared with the direct method for both the ion temperature gradient driven modes and the kinetic ballooning modes.« less

Theory of ion Bernstein wave induced shear suppression of turbulence

NASA Astrophysics Data System (ADS)

Craddock, G. G.; Diamond, P. H.; Ono, M.; Biglari, H.

1994-06-01

The theory of radio frequency induced ion Bernstein wave- (IBW) driven shear flow in the edge is examined, with the goal of application of shear suppression of fluctuations. This work is motivated by the observed confinement improvement on IBW heated tokamaks [Phys. Fluids B 5, 241 (1993)], and by previous low-frequency work on RF-driven shear flows [Phys. Rev. Lett. 67, 1535 (1991)]. It is found that the poloidal shear flow is driven electrostatically by both Reynolds stress and a direct ion momentum source, analogous to the concepts of helicity injection and electron momentum input in current drive, respectively. Flow drive by the former does not necessarily require momentum input to the plasma to induce a shear flow. For IBW, the direct ion momentum can be represented by direct electron momentum input, and a charge separation induced stress that imparts little momentum to the plasma. The derived Er profile due to IBW predominantly points inward, with little possibility of direction change, unlike low-frequency Alfvénic RF drive. The profile scale is set by the edge density gradient and electron dissipation. Due to the electrostatic nature of ion Bernstein waves, the poloidal flow contribution dominates in Er. Finally, the necessary edge power absorbed for shear suppression on Princeton Beta Experiment-Modified (PBX-M) [9th Topical Conference on Radio Frequency Power in Plasmas, Charleston, SC, 1991 (American Institute of Physics, New York, 1991), p. 129] is estimated to be 100 kW distributed over 5 cm.

Threshold for the destabilisation of the ion-temperature-gradient mode in magnetically confined toroidal plasmas

NASA Astrophysics Data System (ADS)

Zocco, A.; Xanthopoulos, P.; Doerk, H.; Connor, J. W.; Helander, P.

2018-02-01

The threshold for the resonant destabilisation of ion-temperature-gradient (ITG) driven instabilities that render the modes ubiquitous in both tokamaks and stellarators is investigated. We discover remarkably similar results for both confinement concepts if care is taken in the analysis of the effect of the global shear . We revisit, analytically and by means of gyrokinetic simulations, accepted tokamak results and discover inadequacies of some aspects of their theoretical interpretation. In particular, for standard tokamak configurations, we find that global shear effects on the critical gradient cannot be attributed to the wave-particle resonance destabilising mechanism of Hahm & Tang (Phys. Plasmas, vol. 1, 1989, pp. 1185-1192), but are consistent with a stabilising contribution predicted by Biglari et al. (Phys. Plasmas, vol. 1, 1989, pp. 109-118). Extensive analytical and numerical investigations show that virtually no previous tokamak theoretical predictions capture the temperature dependence of the mode frequency at marginality, thus leading to incorrect instability thresholds. In the asymptotic limit , where is the rotational transform, and such a threshold should be solely determined by the resonant toroidal branch of the ITG mode, we discover a family of unstable solutions below the previously known threshold of instability. This is true for a tokamak case described by a local local equilibrium, and for the stellarator Wendelstein 7-X, where these unstable solutions are present even for configurations with a small trapped-particle population. We conjecture they are of the Floquet type and derive their properties from the Fourier analysis of toroidal drift modes of Connor & Taylor (Phys. Fluids, vol. 30, 1987, pp. 3180-3185), and to Hill's theory of the motion of the lunar perigee (Acta Math., vol. 8, 1886, pp. 1-36). The temperature dependence of the newly determined threshold is given for both confinement concepts. In the first case, the new temperature-gradient threshold is found to be rather insensitive to the temperature ratio i/Te$ , at least for i/Te\\lesssim 1$ , and to be a growing function of the density gradient scale for i/Te\\gtrsim 1$ . For Wendelstein 7-X, the new critical temperature gradient is a growing function of the temperature ratio. The importance of these findings for the assessment of turbulence in stellarators and low-shear tokamak configurations is discussed.

Standing shocks in a two-fluid solar wind

NASA Technical Reports Server (NTRS)

Habbal, Shadia R.; Hu, You Qiu; Esser, Ruth

1994-01-01

We present a numerical study of the formation of standing shocks in the solar wind using a two-fluid time-dependent model in the presence of Alfven waves. Included in this model is the adiabatic cooling and thermal conduction of both electrons and protons. In this study, standing shocks develop in the flow when additional critical points form as a result of either localized momentum addition or rapid expansion of the flow tube below the existing sonic point. While the flow speed and density exhibit the same characteristics as found in earlier studies of the formation of standing shocks, the inclusion of electron and proton heat conduction produces different signatures in the electron and proton temperature profiles across the shock layer. Owing to the strong heat conduction, the electron temperature is nearly continuous across the shock, but its gradient has a negative jump across it, thus producing a net heat flux out of the shock layer. The proton temperature exhibits the same characteristics for shocks produced by momentum addition but behaves differently when the shock is formed by the rapid divergence of the flow tube. The adiabatic cooling in a rapidly diverging flow tube reduces the proton temperature so substantially that the proton heat conduction becomes negligible in the vicinity of the shock. As a result, protons experience a positive jump in temperature across the shock. While Alfven waves do not affect the formation of standing shocks, they contribute to the change of the mmomentum and energy balance across them. We also find that for this solar wind model the inclusion of thermal conduction and adiabatic cooling for the elctrons and protons increases significantly the range of parameters characterizing the formation of standing shocks over those previously found for isothermal and polytropic models.

Nomogram Method as Means for Resource Potential Efficiency Predicative Aid of Petrothermal Energy

NASA Astrophysics Data System (ADS)

Gabdrakhmanova, K. F.; Izmailova, G. R.; Larin, P. A.; Vasilyeva, E. R.; Madjidov, M. A.; Marupov, S. R.

2018-05-01

The article describes the innovative approach when predicting the resource potential efficiency of petrothermal energy. Various geothermal gradients representative of Bashkortostan and Tatarstan republics regions were considered. With the help of nomograms, the authors analysed fluid temperature dependency graphs at the outlet and the thermal power versus fluid velocity along the wellbore. From the family of graphs plotted by us, velocities corresponding to specific temperature were found. Then, according to thermal power versus velocity curve, power levels corresponding to these velocities relative to the selected fluid temperature were found. On the basis of two dependencies obtained, nomograms were plotted. The result of determining the petrothermal energy production efficiency is a family of isocline lines that enables one to select the optimum temperature and injection rate to obtain the required amount of heat for a particular depth and geothermal gradient.

Effect of Refractive Index Variation on Two-Wavelength Interferometry for Fluid Measurements

NASA Technical Reports Server (NTRS)

Mercer, Carolyn R.

1998-01-01

Two wavelength interferometry can in principle be used to measure changes in both temperature and concentration in a fluid, but measurement errors may be large if the fluid dispersion is small. This paper quantifies the effects of uncertainties in dn/dT and dn/dC on the measured temperature and concentration when using the simple expression dn = (dn/dT)dT + (dn/dC)dC. For the data analyzed here, ammonium chloride in water from -5 to 10(exp infinity) C over a concentration range of 2-14% and for wavelengths 514.5 and 633 nm, it is shown that the gradients must be known to within 0.015% to produce a modest 10% uncertainty in the measured temperature and concentration. These results show that real care must be taken to ensure the accuracy of refractive index gradients when using two wavelength interferometry for the simultaneous measurement of temperature and concentration.

Nonequilibrium Interfacial Tension in Simple and Complex Fluids

NASA Astrophysics Data System (ADS)

Truzzolillo, Domenico; Mora, Serge; Dupas, Christelle; Cipelletti, Luca

2016-10-01

Interfacial tension between immiscible phases is a well-known phenomenon, which manifests itself in everyday life, from the shape of droplets and foam bubbles to the capillary rise of sap in plants or the locomotion of insects on a water surface. More than a century ago, Korteweg generalized this notion by arguing that stresses at the interface between two miscible fluids act transiently as an effective, nonequilibrium interfacial tension, before homogenization is eventually reached. In spite of its relevance in fields as diverse as geosciences, polymer physics, multiphase flows, and fluid removal, experiments and theoretical works on the interfacial tension of miscible systems are still scarce, and mostly restricted to molecular fluids. This leaves crucial questions unanswered, concerning the very existence of the effective interfacial tension, its stabilizing or destabilizing character, and its dependence on the fluid's composition and concentration gradients. We present an extensive set of measurements on miscible complex fluids that demonstrate the existence and the stabilizing character of the effective interfacial tension, unveil new regimes beyond Korteweg's predictions, and quantify its dependence on the nature of the fluids and the composition gradient at the interface. We introduce a simple yet general model that rationalizes nonequilibrium interfacial stresses to arbitrary mixtures, beyond Korteweg's small gradient regime, and show that the model captures remarkably well both our new measurements and literature data on molecular and polymer fluids. Finally, we briefly discuss the relevance of our model to a variety of interface-driven problems, from phase separation to fracture, which are not adequately captured by current approaches based on the assumption of small gradients.

A mixed pseudospectral/finite difference method for a thermally driven fluid in a nonuniform gravitational field

NASA Technical Reports Server (NTRS)

Macaraeg, M. G.

1985-01-01

A numerical study of the steady, axisymmetric flow in a heated, rotating spherical shell is conducted to model the Atmospheric General Circulation Experiment (AGCE) proposed to run aboard a later shuttle mission. The AGCE will consist of concentric rotating spheres confining a dielectric fluid. By imposing a dielectric field across the fluid a radial body force will be created. The numerical solution technique is based on the incompressible Navier-Stokes equations. In the method a pseudospectral technique is based on the incompressible Navier-Stokes equations. In the method a pseudospectral technique is used in the latitudinal direction, and a second-order accurate finite difference scheme discretizes time and radial derivatives. This paper discusses the development and performance of this numerical scheme for the AGCE which has been modelled in the past only by pure FD formulations. In addition, previous models have not investigated the effect of using a dielectric force to simulate terrestrial gravity. The effect of this dielectric force on the flow field is investigated as well as a parameter study of varying rotation rates and boundary temperatures. Among the effects noted are the production of larger velocities and enhanced reversals of radial temperature gradients for a body force generated by the electric field.

Experimental Study of Current-Driven Turbulence During Magnetic Reconnection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Porkolab, Miklos; Egedal-Pedersen, Jan; Fox, William

CMPD Final Report Experimental Study of Current-Driven Turbulence During Magnetic Reconnection Miklos Porkolab, PI, Jan Egedal, co-PI, William Fox, graduate student. This is the final report for Grant DE-FC02-04ER54786, MIT Participation in the Center for Multiscale Plasma Dynamics, which was active from 8/1/2004 to 7/31/2010. This Grant supported the thesis work of one MIT graduate student, William Fox, The thesis research consisted of an experimental study of the fluctuations arising during magnetic reconnection in plasmas on the Versatile Toroidal Facility (VTF) at MIT Plasma Science and Fusion Center (PSFC). The thesis was submitted and accepted by the MIT physics Department,.more » Fox, Experimental Study of Current-Driven Turbulence During Magnetic Reconnection, Ph.D. Thesis, MIT (2009). In the VTF experiment reconnection and current-sheet formation is driven by quickly changing currents in a specially arranged set of internal conductors. Previous work on this device [Egedal, et al, PRL 98, 015003, (2007)] identified a spontaneous reconnection regime. In this work fluctuations were studied using impedance-matched, high-bandwidth Langmuir probes. Strong, broadband fluctuations, with frequencies extending from near the lower-hybrid frequency [fLH = (fcefci)1/2] to the electron cyclotron frequency fce were found to arise during the reconnection events. Based on frequency and wavelength measurements, lower-hybrid waves and Trivelpiece-Gould waves were identified. The lower-hybrid waves are easiest to drive with strong perpendicular drifts or gradients which arise due to the reconnection events; an appealing possibility is strong temperature gradients. The Trivelpiece-Gould modes can result from kinetic, bump-on-tail instability of a runaway electron population energized by the reconnection events. We also observed that the turbulence is often spiky, consisting of discrete positive-potential spikes, which were identified as electron phase-space holes, a class of nonlinear solitary wave known to evolve from a strong beam-on-tail instability. We established that fast electrons were produced by magnetic reconnection. Overall, these instabilities were found to be a consequence of reconnection, specifically the strong energization of electrons, leading to steep gradients in both coordinate- and velocity-space. Estimates (using quasi-linear theory) of the anomalous resistivity due to these modes did not appear large enough to substantially impact the reconnection process. Relevant publications: W. Fox, M. Porkolab, et al, Phys. Rev. Lett. 101, 255003 (2008). W. Fox, M. Porkolab, et al, Phys. Plasmas 17, 072303, (2010).« less

Reversed magnetic shear suppression of electron-scale turbulence on NSTX

NASA Astrophysics Data System (ADS)

Yuh, Howard Y.; Levinton, F. M.; Bell, R. E.; Hosea, J. C.; Kaye, S. M.; Leblanc, B. P.; Mazzucato, E.; Smith, D. R.; Domier, C. W.; Luhmann, N. C.; Park, H. K.

2009-11-01

Electron thermal internal transport barriers (e-ITBs) are observed in reversed (negative) magnetic shear NSTX discharges^1. These e-ITBs can be created with either neutral beam heating or High Harmonic Fast Wave (HHFW) RF heating. The e-ITB location occurs at the location of minimum magnetic shear determined by Motional Stark Effect (MSE) constrained equilibria. Statistical studies show a threshold condition in magnetic shear for e-ITB formation. High-k fluctuation measurements at electron turbulence wavenumbers^3 have been made under several different transport regimes, including a bursty regime that limits temperature gradients at intermediate magnetic shear. The growth rate of fluctuations has been calculated immediately following a change in the local magnetic shear, resulting in electron temperature gradient relaxation. Linear gyrokinetic simulation results for NSTX show that while measured electron temperature gradients exceed critical linear thresholds for ETG instability, growth rates can remain low under reversed shear conditions up to high electron temperatures gradients. ^1H. Yuh, et. al., PoP 16, 056120 ^2D.R. Smith, E. Mazzucato et al., RSI 75, 3840 ^3E. Mazzucato, D.R. Smith et al., PRL 101, 075001

Electron critical gradient scale length measurements of ICRF heated L-mode plasmas at Alcator C-Mod tokamak

NASA Astrophysics Data System (ADS)

Houshmandyar, S.; Hatch, D. R.; Horton, C. W.; Liao, K. T.; Phillips, P. E.; Rowan, W. L.; Zhao, B.; Cao, N. M.; Ernst, D. R.; Greenwald, M.; Howard, N. T.; Hubbard, A. E.; Hughes, J. W.; Rice, J. E.

2018-04-01

A profile for the critical gradient scale length (Lc) has been measured in L-mode discharges at the Alcator C-Mod tokamak, where electrons were heated by an ion cyclotron range of frequency through minority heating with the intention of simultaneously varying the heat flux and changing the local gradient. The electron temperature gradient scale length (LTe-1 = |∇Te|/Te) profile was measured via the BT-jog technique [Houshmandyar et al., Rev. Sci. Instrum. 87, 11E101 (2016)] and it was compared with electron heat flux from power balance (TRANSP) analysis. The Te profiles were found to be very stiff and already above the critical values, however, the stiffness was found to be reduced near the q = 3/2 surface. The measured Lc profile is in agreement with electron temperature gradient (ETG) models which predict the dependence of Lc-1 on local Zeff, Te/Ti, and the ratio of the magnetic shear to the safety factor. The results from linear Gene gyrokinetic simulations suggest ETG to be the dominant mode of turbulence in the electron scale (k⊥ρs > 1), and ion temperature gradient/trapped electron mode modes in the ion scale (k⊥ρs < 1). The measured Lc profile is in agreement with the profile of ETG critical gradients deduced from Gene simulations.

Classical Heat-Flux Measurements in Coronal Plasmas from Collective Thomson-Scattering Spectra

NASA Astrophysics Data System (ADS)

Henchen, R. J.; Hu, S. X.; Katz, J.; Froula, D. H.; Rozmus, W.

2016-10-01

Collective Thomson scattering was used to measure heat flux in coronal plasmas. The relative amplitude of the Thomson-scattered power into the up- and downshifted electron plasma wave features was used to determine the flux of electrons moving along the temperature gradient at three to four times the electron thermal velocity. Simultaneously, the ion-acoustic wave features were measured. Their relative amplitude was used to measure the flux of the return-current electrons. The frequencies of these ion-acoustic and electron plasma wave features provide local measurements of the electron temperature and density. These spectra were obtained at five locations along the temperature gradient in a laser-produced blowoff plasma. These measurements of plasma parameters are used to infer the Spitzer-Härm flux (qSH = - κ∇Te ) and are in good agreement with the values of the heat flux measured from the scattering-feature asymmetries. Additional experiments probed plasma waves perpendicular to the temperature gradient. The data show small effects resulting from heat flux compared to probing waves along the temperature gradient. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Numerical simulation of exploding pusher targets

NASA Astrophysics Data System (ADS)

Atzeni, S.; Rosenberg, M. J.; Gatu Johnson, M.; Petrasso, R. D.

2017-10-01

Exploding pusher targets, i.e. gas-filled large aspect-ratio glass or plastic shells, driven by a strong laser-generated shock, are widely used as pulsed sources of neutrons and fast charged particles. Recent experiments on exploding pushers provided evidence for the transition from a purely fluid behavior to a kinetic one. Indeed, fluid models largely overpredict yield and temperature as the Knudsen number Kn (ratio of ion mean-free path to compressed gas radius) is comparable or larger than one. At Kn = 0.3 - 1, fluid codes reasonably estimate integral quantities as yield and neutron-averaged temperatures, but do not reproduce burn radii, burn profiles and DD/DHe3 yield ratio. This motivated a detailed simulation study of intermediate-Kn exploding pushers. We will show how simulation results depend on models for laser-interaction, electron conductivity (flux-limited local vs nonlocal), viscosity (physical vs artificial), and ion mixing. Work partially supported by Sapienza Project C26A15YTMA, Sapienza 2016 (n. 257584), and Eurofusion Project AWP17-ENR-IFE-CEA-01.

High-Beta Electromagnetic Turbulence in LAPD Plasmas

NASA Astrophysics Data System (ADS)

Rossi, G.; Carter, T. A.; Pueschel, M. J.; Jenko, F.; Told, D.; Terry, P. W.

2015-11-01

The introduction of a new LaB6 cathode plasma source in the Large Plasma Device has enabled the study of pressure-gradient-driven turbulence and transport variations at significantly higher plasma β. Density fluctuations are observed to decrease with increasing β while magnetic fluctuations increase. Furthermore, the perpendicular magnetic fluctuations are seen to saturate while parallel (compressional) magnetic fluctuations increase continuously with β. These observations are compared to linear and nonlinear simulations with the GENE code. The results are consistent with the linear excitation of a Gradient-driven Drift Coupling mode (GDC) which relies on grad-B drift due to parallel magnetic fluctuations and can be driven by density or temperature gradients.

Electrostatic stability of electron-positron plasmas in dipole geometry

NASA Astrophysics Data System (ADS)

Mishchenko, Alexey; Plunk, Gabriel G.; Helander, Per

2018-04-01

The electrostatic stability of electron-positron plasmas is investigated in the point-dipole and Z-pinch limits of dipole geometry. The kinetic dispersion relation for sub-bounce-frequency instabilities is derived and solved. For the zero-Debye-length case, the stability diagram is found to exhibit singular behaviour. However, when the Debye length is non-zero, a fluid mode appears, which resolves the observed singularity, and also demonstrates that both the temperature and density gradients can drive instability. It is concluded that a finite Debye length is necessary to determine the stability boundaries in parameter space. Landau damping is investigated at scales sufficiently smaller than the Debye length, where instability is absent.

The Low-Recycling Lithium Boundary and Implications for Plasma Transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Granstedt, Erik Michael

Pumping of incident hydrogen and impurity ions by lithium enables control of the particle inventory and fueling profile in magnetic-confined plasmas, and may raise the plasma temperature near the wall. As a result, the density gradient is expected to contribute substantially to the free-energy, affecting particle and thermal transport from micro-turbulence which is typically the dominant transport mechanism in high-temperature fusion experiments. Transport in gyrokinetic simulations of density-gradient-dominated profiles is characterized by a small linear critical gradient, large particle flux, and preferential diffusion of cold particles. As a result, the heat flux is below 5/2 or even 3/2 times themore » particle flux, usually assumed to be the minimum for convection. While surprising, this result is consistent with increasing entropy. Coupled TEM-ITG (ion-temperature- gradient) simulations using ηe = ηi find η = ∇T /∇n∼0.8 maximizes the linear critical pressure gradient, which suggests that experiments operating near marginal ITG stability with larger η would increase the linear critical pressure gradient by transferring free-energy from the temperature gradient to the density gradient. Simulations were performed with profiles predicted for the Lithium Tokamak Experiment (LTX) if ion thermal transport was neoclassical, while electron thermal transport and particle transport were a fixed ratio above the neoclassical level. A robust TEM instability was found for the outer half radius, while the ITG was found to be driven unstable as well during gas puff fueling. This suggests that TEM transport will be an important transport mechanism in high-temperature low-recycling fusion experiments, and in the absence of stabilizing mechanisms, may dominate over neoclassical transport. A diagnostic suite has been developed to measure hydrogen and impurity emission in LTX in order to determine the lower bound on recycling that can be achieved in a small tokamak using solid lithium coatings, assess its dependence on the operating condition of the lithium surface, and evaluate its impact on the discharge. Coatings on the close-fitting stainless-steel substrate produce a significant reduction in recyling, so that the effective particle confinement times are as low as 1 ms. Measurements of particle inventory in the plasma and hydrogen Lyman-α emission indicate that hydrogen recycling at the surface increases as subsequent discharges are performed; nevertheless, strong pumping of hydrogen is observed even after almost double the cumulative fueling is applied that should saturate the lithium coating to the penetration depth of hydrogen ions. Probe measurements show that when external fueling is terminated, the scrape-off-layer of discharges with fresh coatings decays to lower density and rises to higher electron temperature than for discharges with a partially-passivated surface, consistent with reduced edge cooling from recycled particles. Near the end of the discharge, higher plasma current correlates with reduced τp* and hydrogen emission, suggesting that discharges with fresh coatings achieve higher electron temperature in the core. A novel approach using neutral modeling was developed for the inverse problem of determining the distribution of recycled particle flux from PFC surfaces given a large number of emission measurements, revealing that extremely low levels of recycling (Rcore∼0.6 and Rplate∼0.8) have been achieved with solid lithium coatings. Together with impurity emission measurements, modeling suggests that during periods of particularly low electron density, influx of impurities from the walls contributes substantially to the global particle balance.« less

From Geochemistry to Biochemistry: Simulating Prebiotic Chemistry Driven by Geochemical Gradients in Alkaline Hydrothermal Vents

NASA Astrophysics Data System (ADS)

Barge, Laurie

2016-07-01

Planetary water-rock interfaces generate energy in the form of redox, pH, and thermal gradients, and these disequilibria are particularly focused in hydrothermal vent systems where the reducing, heated hydrothermal fluid feeds back into the more oxidizing ocean. Alkaline hydrothermal vents have been proposed as a likely location for the origin of life on the early Earth due to various factors: including the hydrothermal pH / Eh gradients that resemble the ubiquitous electrical / proton gradients in biology, the catalytic hydrothermal precipitates that resemble inorganic catalysts in enzymes, and the presence of electron donors and acceptors in hydrothermal systems (e.g. H2 + CH4 and CO2) that are thought to have been utilized in the earliest metabolisms. Of particular importance for the emergence of metabolism are the mineral "chimneys" that precipitate at the vent fluid / seawater interface. Hydrothermal chimneys are flow-through chemical reactors that form porous and permeable inorganic membranes transecting geochemical gradients; in some ways similar to biological membranes that transect proton / ion gradients and harness these disequilibria to drive metabolism. These emergent chimney structures in the far-from-equilibrium system of the alkaline vent have many properties of interest to the origin of life that can be simulated in the laboratory: for example, they can generate electrical energy and drive redox reactions, and produce catalytic minerals (in particular the metal sulfides and iron oxyhydroxides - "green rust") that can facilitate chemical reactions towards proto-metabolic cycles and biosynthesis. Many of the factors prompting interest in alkaline hydrothermal vents on Earth may also have been present on early Mars, or even presently within icy worlds such as Europa or Enceladus - thus, understanding the disequilibria and resulting prebiotic chemistry in these systems can be of great use in assessing the potential for other environments in the Solar System where life could have emerged.

Designing gradient coils with reduced hot spot temperatures.

PubMed

While, Peter T; Forbes, Larry K; Crozier, Stuart

2010-03-01

Gradient coil temperature is an important concern in the design and construction of MRI scanners. Closely spaced gradient coil windings cause temperature hot spots within the system as a result of Ohmic heating associated with large current being driven through resistive material, and can strongly affect the performance of the coils. In this paper, a model is presented for predicting the spatial temperature distribution of a gradient coil, including the location and extent of temperature hot spots. Subsequently, a method is described for designing gradient coils with improved temperature distributions and reduced hot spot temperatures. Maximum temperature represents a non-linear constraint and a relaxed fixed point iteration routine is proposed to adjust coil windings iteratively to minimise this coil feature. Several examples are considered that assume different thermal material properties and cooling mechanisms for the gradient system. Coil winding solutions are obtained for all cases considered that display a considerable drop in hot spot temperature (>20%) when compared to standard minimum power gradient coils with equivalent gradient homogeneity, efficiency and inductance. The method is semi-analytical in nature and can be adapted easily to consider other non-linear constraints in the design of gradient coils or similar systems. Crown Copyright (c) 2009. Published by Elsevier Inc. All rights reserved.

On the Onset of Thermocapillary Convection in a Liquid bridge

NASA Astrophysics Data System (ADS)

Shukla, Kedar

Thermo capillary convection refers to motion driven by the application of a temperature gradient along the interface. The temperature gradient may be large enough to cause oscillations in the basic state of the fluid. The vast majority of the liquid bridge investigations performed aboard on the sounding rockets or the space shuttles [1, 2] focused on the float zone processes because the process has been regarded as a candidate for the space based manufacturing of semiconductor materials. Although the buoyancy effect is avoided in the floating zone techniques during space operation, it experiences surface tension driven convection initiated by the temperature gradient along the free surface of the zone [3]. The appearance of the oscillatory thermo capillary convection couples with the solidification processes leads to the striations and results into the degradation of the crystals [4, 5]. The half zone consists of the liquid bridge held between two solid, planar end walls across which a temperature gradient is applied. Thus the basic state of thermo capillary convection consists of a single toroidal roll with the surface motion directed downwards from the hot upper disc to the cold lower one. Bennacer et al [6] studied how different axial profiles of the heat flux affect the flow patterns and transition from ax symmetric steady to ax symmetric oscillatory flow. The three dimensional instability of liquid bridges located between isothermal differentially heated disks were studied by several authors [7-14]. The interface deformation caused by the gravity jitters depends on the volume of the liquid bridge and cause changes in the physical properties of the liquid, which ultimately influence the basic state of the fluid [15-16]. The paper discusses Marangoni convection in a liquid bridge subject to g-jitters in a micro gravity environment. The parametric excitement of the liquid bridge with surface tension variation along with the free surface is considered. We will follow the method of Shukla [17] for Boussinesq flow to model the convective instability in an axisymmetric flow in the liquid bridge. The surface deformation caused by g-jitters and its effects on the onset of oscillatory flow will be examined. References: [1] Grodzka, P.G. and Bannister, T.C., Heat flow and convection demonstration experiments abord Appolo 14, Science (Washington, D.C.), Vol.176, May 1972, pp. 506-508. [2] Bannister, T C., etal, NASA, TMX-64772, 1973. [3] Shukla, K.N. Hydrodynamics of Diffusive Processes, Applied Mechanics Review, Vol.54, No.5, 2001, pp. 391-404. [4] Chen, G., Lizee, A., Roux, B.,, Bifurcation analysis of the thermo capillary convection in cylindrical liquid bridge, J Crystal growth, Vol. 180, 1997, pp.638-647. [5] Imaishi, N., Yasuhiro, S., Akiyama, Y and Yoda, S., Numerical simulation of oscillatory Marangoni flow in half zone liquid bridge of low Prandtl number fluid, J., Crystal Growth, Vol. 230, 2001, pp. 164-171. [6] Bennacer, R., Mohamad, A.A., Leonardi, E., The effect o heat flux distribution on thermo capillary convection in a sideheated liquid bridge, Numer. Heat transfer, Part A, vol. 41, 2002, pp. 657-671. [7] Kuhlmann, H C., Rath, H J., Hydrodynamic instabilities in Cylindrical thermocapillary liquid bridges, J Fluid Mech., Vol. 247,1993, pp. 247-274. [8] Wanshura, M., Shevtsova, V M, Kuhlmann, H C and Rath, H J., Convective instability in thermocapillary liquid bridges, Phys. Fluids, Vol. 7, 1995, pp. 912-925. [9] Kasperski, G., Batoul, A., Labrosse, G., Up to the unsteadiness of axisymmetric thermocapillary low in a laterally heated liquid bridge, Phys. Fluids, Vol. 12, 2000, pp. 103-119. [10] Lappa, M., Savino, R., Monti, R., Three dimensional numerical simulation of Marangoni instabilities in non cylindrical liquid bridges in microgravity, Int. J Heat Mass Transfer, Vol. 44, 2001, pp. 1983-2003 [11] Zeng, Z, Mizuseki, H., Simamura, K., Fukud, T. Higashino, K, Kawaazoe, Y., Three dimensional oscillatory thermocapillary convection in liquid bridgeunder microgravity, Int. J heat Mass Transf., Vol. 44, 2001, pp. 3765-3774. [12] Kamotani, Y., Wang, L, Hatta, S., Wang, A., Yoda, S., Free surface heat loss effect on Oscillatory thermocapillary flow in a liquid bridges of high Prandtl number fluids, Int. J heat Mass Transfer, Vol. 46, 2003, pp. 3211-3220.

Validation of buoyancy driven spectral tensor model using HATS data

NASA Astrophysics Data System (ADS)

Chougule, A.; Mann, J.; Kelly, M.; Larsen, G. C.

2016-09-01

We present a homogeneous spectral tensor model for wind velocity and temperature fluctuations, driven by mean vertical shear and mean temperature gradient. Results from the model, including one-dimensional velocity and temperature spectra and the associated co-spectra, are shown in this paper. The model also reproduces two-point statistics, such as coherence and phases, via cross-spectra between two points separated in space. Model results are compared with observations from the Horizontal Array Turbulence Study (HATS) field program (Horst et al. 2004). The spectral velocity tensor in the model is described via five parameters: the dissipation rate (ɛ), length scale of energy-containing eddies (L), a turbulence anisotropy parameter (Γ), gradient Richardson number (Ri) representing the atmospheric stability and the rate of destruction of temperature variance (ηθ).

Natural convection along a heated vertical plate immersed in a nonlinearly stratified medium: application to liquefied gas storage

NASA Astrophysics Data System (ADS)

Forestier, M.; Haldenwang, P.

We consider free convection driven by a heated vertical plate immersed in a nonlinearly stratified medium. The plate supplies a uniform horizontal heat flux to a fluid, the bulk of which has a stable stratification, characterized by a non-uniform vertical temperature gradient. This gradient is assumed to have a typical length scale of variation, denoted Z0, while 0, and the physical properties of the medium.We then apply the new theory to the natural convection affecting the vapour phase in a liquefied pure gas tank (e.g. the cryogenic storage of hydrogen). It is assumed that the cylindrical storage tank is subject to a constant uniform heat flux on its lateral and top walls. We are interested in the vapour motion above a residual layer of liquid in equilibrium with the vapour. High-precision axisymmetric numerical computations show that the flow remains steady for a large range of parameters, and that a bulk stratification characterized by a quadratic temperature profile is undoubtedly present. The application of the theory permits a comparison of the numerical and analytic results, showing that the theory satisfactorily predicts the primary dynamical and thermal properties of the storage tank.

Comparison of Alcator C data with the Rebut-Lallia-Watkins critical gradient scaling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hutchinson, I.H.

The critical temperature gradient model of Rebut, Lallia and Watkins is compared with data from Alcator C. The predicted central electron temperature is derived from the model, and a simple analytic formula is given. It is found to be in quite good agreement with the observed temperatures on Alcator C under ohmic heating conditions. However, the thermal diffusivity postulated in the model for gradients that exceed the critical is not consistent with the observed electron heating by Lower Hybrid waves.

Analysis of metallic impurity density profiles in low collisionality Joint European Torus H-mode and L-mode plasmas

NASA Astrophysics Data System (ADS)

Puiatti, M. E.; Valisa, M.; Angioni, C.; Garzotti, L.; Mantica, P.; Mattioli, M.; Carraro, L.; Coffey, I.; Sozzi, C.

2006-04-01

This paper describes the behavior of nickel in low confinement (L-mode) and high confinement (H-mode) Joint European Torus (JET) discharges [P. J. Lomas, Plasma Phys. Control. Fusion 31, 1481 (1989)] characterized by the application of radio-frequency (rf) power heating and featuring ITER (International Thermonuclear Experimental Reactor) relevant collisionality. The impurity transport is analyzed on the basis of perturbative experiments (laser blow off injection) and is compared with electron heat and deuterium transport. In the JET plasmas analyzed here, ion cyclotron resonance heating (ICRH) is applied either in mode conversion (MC) to heat the electrons or in minority heating (MH) to heat the ions. The two heating schemes have systematically different effects on nickel transport, yielding flat or slightly hollow nickel density profiles in the case of ICRH in MC and peaked nickel density profiles in the case of rf applied in MH. Accordingly, both diffusion coefficients and pinch velocities of nickel are found to be systematically different. Linear gyrokinetic calculations by means of the code GS2 [M. Kotschenreuther, G. Rewoldt, and W.M. Tang, Comput. Phys. Commun. 88, 128 (1995)] provide a possible explanation of such different behavior by exploring the effects produced by the different microinstabilities present in these plasmas. In particular, trapped electron modes driven by the stronger electron temperature gradients measured in the MC cases, although subdominant, produce a contribution to the impurity pinch directed outwards that is qualitatively in agreement with the pinch reversal found in the experiment. Particle and heat diffusivities appear to be decoupled in MH shots, with χe and DD≫DNi, and are instead quite similar in the MC ones. In the latter case, nickel transport appears to be driven by the same turbulence that drives the electron heat transport and is sensitive to the value of the electron temperature gradient length. These findings give ground to the idea that in ITER it should be possible to find conditions in which the risk of accumulation of metals such as nickel can be contained.

Ultrasound Thermal Imaging and its application to Rayleigh-Bénard convection in mercury

NASA Astrophysics Data System (ADS)

Xu, Hongzhou; Andereck, C. David

2003-11-01

We have developed Ultrasound Thermal Imaging (UTI), a non-intrusive ultrasound technique for internal temperature measurement of opaque fluids, and have applied UTI to low Rayleigh number buoyancy driven convection in mercury. UTI relies upon the variation of sound speed with temperature of the fluid. An array of ultrasound transducers scanned electronically along the sidewall of a convection cell with aspect ratio of 6 yields a map of the thermal field over the chamber. The chamber has stainless steel sidewalls and molybdenum covered copper plates at the top and bottom. As the Rayleigh number increases slowly from zero, the data reveal the formation of a roll cell pattern and transitions between different cellular states. Based on standard deviation distributions of the temperature profile at the cell's mid-depth, the critical temperature difference agrees well with the theoretically predicted value. The heat flux through the horizontal mercury layer was determined by thermistors mounted at the exit and entrance of the internal channel in each copper plate through which flows warm/cool constant temperature water. Nusselt numbers and other experimental results will also be presented.

Gyrokinetic theory of turbulent acceleration and momentum conservation in tokamak plasmas

NASA Astrophysics Data System (ADS)

Lu, WANG; Shuitao, PENG; P, H. DIAMOND

2018-07-01

Understanding the generation of intrinsic rotation in tokamak plasmas is crucial for future fusion reactors such as ITER. We proposed a new mechanism named turbulent acceleration for the origin of the intrinsic parallel rotation based on gyrokinetic theory. The turbulent acceleration acts as a local source or sink of parallel rotation, i.e., volume force, which is different from the divergence of residual stress, i.e., surface force. However, the order of magnitude of turbulent acceleration can be comparable to that of the divergence of residual stress for electrostatic ion temperature gradient (ITG) turbulence. A possible theoretical explanation for the experimental observation of electron cyclotron heating induced decrease of co-current rotation was also proposed via comparison between the turbulent acceleration driven by ITG turbulence and that driven by collisionless trapped electron mode turbulence. We also extended this theory to electromagnetic ITG turbulence and investigated the electromagnetic effects on intrinsic parallel rotation drive. Finally, we demonstrated that the presence of turbulent acceleration does not conflict with momentum conservation.

Numerical modeling of physical vapor transport under microgravity conditions: Effect of thermal creep and stress

NASA Technical Reports Server (NTRS)

Mackowski, Daniel W.; Knight, Roy W.

1993-01-01

One of the most promising applications of microgravity (micro-g) environments is the manufacture of exotic and high-quality crystals in closed cylindrical ampoules using physical vapor transport (PVT) processes. The quality enhancements are believed to be due to the absence of buoyant convection in the weightless environment - resulting in diffusion-limited transport of the vapor. In a typical experiment, solid-phase sample material is initially contained at one end of the ampoule. The sample is made to sublime into the vapor phase and deposit onto the opposite end by maintaining the source at an elevated temperature with respect to the deposit. Identification of the physical factors governing both the rates and uniformity of crystal growth, and the optimization of the micro-g technology, will require an accurate modeling of the vapor transport within the ampoule. Previous micro-g modeling efforts have approached the problem from a 'classical' convective/diffusion formulation, in which convection is driven by the action of buoyancy on thermal and solutal density differences. The general conclusion of these works have been that in low gravity environments the effect of buoyancy on vapor transport is negligible, and vapor transport occurs in a diffusion-limited mode. However, it has been recently recognized than in the non-isothermal (and often low total pressure) conditions encountered in ampoules, the commonly-assumed no-slip boundary condition to the differential equations governing fluid motion can be grossly unrepresentative of the actual situation. Specifically, the temperature gradients can give rise to thermal creep flows at the ampoule side walls. In addition, temperature gradients in the vapor itself can, through the action of thermal stress, lead to bulk fluid convection.

Particle simulation of electromagnetic emissions from electrostatic instability driven by an electron ring beam on the density gradient

NASA Astrophysics Data System (ADS)

Horký, Miroslav; Omura, Yoshiharu; Santolík, Ondřej

2018-04-01

This paper presents the wave mode conversion between electrostatic and electromagnetic waves on the plasma density gradient. We use 2-D electromagnetic code KEMPO2 implemented with the generation of density gradient to simulate such a conversion process. In the dense region, we use ring beam instability to generate electron Bernstein waves and we study the temporal evolution of wave spectra, velocity distributions, Poynting flux, and electric and magnetic energies to observe the wave mode conversion. Such a conversion process can be a source of electromagnetic emissions which are routinely measured by spacecraft on the plasmapause density gradient.

Temperature gradient scale length measurement: A high accuracy application of electron cyclotron emission without calibration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Houshmandyar, S., E-mail: houshmandyar@austin.utexas.edu; Phillips, P. E.; Rowan, W. L.

2016-11-15

Calibration is a crucial procedure in electron temperature (T{sub e}) inference from a typical electron cyclotron emission (ECE) diagnostic on tokamaks. Although the calibration provides an important multiplying factor for an individual ECE channel, the parameter ΔT{sub e}/T{sub e} is independent of any calibration. Since an ECE channel measures the cyclotron emission for a particular flux surface, a non-perturbing change in toroidal magnetic field changes the view of that channel. Hence the calibration-free parameter is a measure of T{sub e} gradient. B{sub T}-jog technique is presented here which employs the parameter and the raw ECE signals for direct measurement ofmore » electron temperature gradient scale length.« less

Fluid Flow Phenomena during Welding

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Wei

2011-01-01

MOLTEN WELD POOLS are dynamic. Liquid in the weld pool in acted on by several strong forces, which can result in high-velocity fluid motion. Fluid flow velocities exceeding 1 m/s (3.3 ft/s) have been observed in gas tungsten arc (GTA) welds under ordinary welding conditions, and higher velocities have been measured in submerged arc welds. Fluid flow is important because it affects weld shape and is related to the formation of a variety of weld defects. Moving liquid transports heat and often dominates heat transport in the weld pool. Because heat transport by mass flow depends on the direction andmore » speed of fluid motion, weld pool shape can differ dramatically from that predicted by conductive heat flow. Temperature gradients are also altered by fluid flow, which can affect weld microstructure. A number of defects in GTA welds have been attributed to fluid flow or changes in fluid flow, including lack of penetration, top bead roughness, humped beads, finger penetration, and undercutting. Instabilities in the liquid film around the keyhole in electron beam and laser welds are responsible for the uneven penetration (spiking) characteristic of these types of welds.« less

Effects of spatial gradients in thermophysical properties on the topology of turbulence in heated channel flow of supercritical fluids

NASA Astrophysics Data System (ADS)

Azih, Chukwudi; Yaras, Metin I.

2018-01-01

The current literature suggests that large spatial gradients of thermophysical properties, which occur in the vicinity of the pseudo-critical thermodynamic state, may result in significant variations in forced-convection heat transfer rates. Specifically, these property gradients induce inertia- and buoyancy-driven phenomena that may enhance or deteriorate the turbulence-dominated heat convection process. Through direct numerical simulations, the present study investigates the role of coherent flow structures in channel geometries for non-buoyant and buoyant flows of supercritical water, with buoyant configurations involving wall-normal oriented gravitational acceleration and downstream-oriented gravitational acceleration. This sequence of simulations enables the evaluation of the relative contributions of inertial and buoyancy phenomena to heat transfer variations. In these simulations, the state of the working fluid is in the vicinity of the pseudo-critical point. The uniform wall heat flux and the channel mass flux are specified such that the heat to mass flux ratio is 3 kJ/kg, with an inflow Reynolds number of 12 000 based on the channel hydraulic diameter, the area-averaged inflow velocity, and fluid properties evaluated at the bulk temperature and pressure of the inflow plane. In the absence of buoyancy forces, notable reductions in the density and viscosity in close proximity of the heated wall are observed to promote generation of small-scale vortices, with resultant breakdown into smaller scales as they interact with preexisting larger near-wall vortices. This interaction results in a reduction in the overall thermal mixing at particular wall-normal regions of the channel. Under the influence of wall-normal gravitational acceleration, the wall-normal density gradients are noted to enhance ejection motions due to baroclinic vorticity generation on the lower wall, thus providing additional wall-normal thermal mixing. Along the upper wall, the same mechanism generates streamwise vorticity of the opposing sense of rotation in the close vicinity to the respective legs of the hairpin vortices causing a net reduction in thermal mixing. Finally, in the case of downstream-oriented gravitational acceleration, baroclinic vorticity generation as per spanwise density gradients causes additional wall-normal thermal mixing by promoting larger-scale ejection and sweep motions.

Microturbulence studies of pulsed poloidal current drive discharges in the reversed field pinch

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carmody, D., E-mail: dcarmody@wisc.edu; Pueschel, M. J.; Anderson, J. K.

2015-01-15

Experimental discharges with pulsed poloidal current drive (PPCD) in the Madison Symmetric Torus reversed field pinch are investigated using a semi-analytic equilibrium model in the gyrokinetic turbulence code GENE. PPCD cases, with plasma currents of 500 kA and 200 kA, exhibit a density-gradient-driven trapped electron mode (TEM) and an ion temperature gradient mode, respectively. Relative to expectations of tokamak core plasmas, the critical gradients for the onset of these instabilities are found to be greater by roughly a factor of the aspect ratio. A significant upshift in the nonlinear TEM transport threshold, previously found for tokamaks, is confirmed in nonlinear reversed fieldmore » pinch simulations and is roughly three times the threshold for linear instability. The simulated heat fluxes can be brought in agreement with measured diffusivities by introducing a small, resonant magnetic perturbation, thus modeling the residual fluctuations from tearing modes. These fluctuations significantly enhance transport.« less

The study of the transition regime between slab and mixed slab-toroidal electron temperature gradient modes in a basic experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balbaky, Abed; Sokolov, Vladimir; Sen, Amiya K.

2015-05-15

Electron temperature gradient (ETG) modes are suspected sources of anomalous electron thermal transport in magnetically confined plasmas as in tokamaks. Prior work in the Columbia Linear Machine (CLM) has been able to produce and identify slab ETG modes in a slab geometry [Wei et al., Phys. Plasmas 17, 042108 (2010)]. Now by modifying CLM to introduce curvature to the confining axial magnetic field, we have excited mixed slab-toroidal modes. Linear theory predicts a transition between slab and toroidal ETG modes when (k{sub ∥}R{sub c})/(k{sub y}ρ) ∼1 [J. Kim and W. Horton, Phys. Fluids B 3, 1167 (1991)]. We observe changesmore » in the mode amplitude for levels of curvature R{sub c}{sup −1}≪(k{sub ∥,slab})/(k{sub ⊥}ρ) , which may be explained by reductions in k{sub ∥} in the transition from slab to mixed slab-toroidal modes, as also predicted by theory. We present mode amplitude scaling as a function of magnetic field curvature. Over the range of curvature available in CLM experimentally we find a modest increase in saturated ETG potential fluctuations (∼1.5×), and a substantial increase in the power density of individual mode peaks (∼4–5×)« less

Investigation of transition from thermal- to solutal-Marangoni flow in dilute alcohol/water mixtures using nano-plasmonic heaters

NASA Astrophysics Data System (ADS)

Namura, Kyoko; Nakajima, Kaoru; Suzuki, Motofumi

2018-02-01

We experimentally investigated Marangoni flows around a microbubble in diluted 1-butanol/water, 2-propanol/water, and ethanol/water mixtures using the thermoplasmonic effect of gold nanoisland film. A laser spot on the gold nanoisland film acted as a highly localized heat source that was utilized to generate stable air microbubbles with diameters of 32-48 μm in the fluid and to induce a steep temperature gradient on the bubble surface. The locally heated bubble has a flow along the bubble surface, with the flow direction showing a clear transition depending on the alcohol concentrations. The fluid is driven from the hot to cold regions when the alcohol concentration is lower than the transition concentration, whereas it is driven from the cold to hot regions when the concentration is higher than the transition concentration. In addition, the transition concentration increases as the carbon number of the alcohol decreases. The observed flow direction transition is explained by the balance of the thermal- and solutal-Marangoni forces that are cancelled out for the transition concentration. The selective evaporation of the alcohol at the locally heated surface allows us to generate stable and rapid thermoplasmonic solutal-Marangoni flows in the alcohol/water mixtures.

Comparison of kinetic and extended magnetohydrodynamics computational models for the linear ion temperature gradient instability in slab geometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schnack, D. D.; Department of Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706; Cheng, J.

We perform linear stability studies of the ion temperature gradient (ITG) instability in unsheared slab geometry using kinetic and extended magnetohydrodynamics (MHD) models, in the regime k{sub ∥}/k{sub ⊥}≪1. The ITG is a parallel (to B) sound wave that may be destabilized by finite ion Larmor radius (FLR) effects in the presence of a gradient in the equilibrium ion temperature. The ITG is stable in both ideal and resistive MHD; for a given temperature scale length L{sub Ti0}, instability requires that either k{sub ⊥}ρ{sub i} or ρ{sub i}/L{sub Ti0} be sufficiently large. Kinetic models capture FLR effects to all ordersmore » in either parameter. In the extended MHD model, these effects are captured only to lowest order by means of the Braginskii ion gyro-viscous stress tensor and the ion diamagnetic heat flux. We present the linear electrostatic dispersion relations for the ITG for both kinetic Vlasov and extended MHD (two-fluid) models in the local approximation. In the low frequency fluid regime, these reduce to the same cubic equation for the complex eigenvalue ω=ω{sub r}+iγ. An explicit solution is derived for the growth rate and real frequency in this regime. These are found to depend on a single non-dimensional parameter. We also compute the eigenvalues and the eigenfunctions with the extended MHD code NIMROD, and a hybrid kinetic δf code that assumes six-dimensional Vlasov ions and isothermal fluid electrons, as functions of k{sub ⊥}ρ{sub i} and ρ{sub i}/L{sub Ti0} using a spatially dependent equilibrium. These solutions are compared with each other, and with the predictions of the local kinetic and fluid dispersion relations. Kinetic and fluid calculations agree well at and near the marginal stability point, but diverge as k{sub ⊥}ρ{sub i} or ρ{sub i}/L{sub Ti0} increases. There is good qualitative agreement between the models for the shape of the unstable global eigenfunction for L{sub Ti0}/ρ{sub i}=30 and 20. The results quantify how far fluid calculations can be extended accurately into the kinetic regime. We conclude that for the linear ITG problem in slab geometry with unsheared magnetic field when k{sub ∥}/k{sub ⊥}≪1, the extended MHD model may be a reliable physical model for this problem when ρ{sub i}/L{sub Ti0}<10{sup −2} and k{sub ⊥}ρ{sub i}<0.2.« less

Probing plasma wakefields using electron bunches generated from a laser wakefield accelerator

NASA Astrophysics Data System (ADS)

Zhang, C. J.; Wan, Y.; Guo, B.; Hua, J. F.; Pai, C.-H.; Li, F.; Zhang, J.; Ma, Y.; Wu, Y. P.; Xu, X. L.; Mori, W. B.; Chu, H.-H.; Wang, J.; Lu, W.; Joshi, C.

2018-04-01

We show experimental results of probing the electric field structure of plasma wakes by using femtosecond relativistic electron bunches generated from a laser wakefield accelerator. Snapshots of laser-driven linear wakes in plasmas with different densities and density gradients are captured. The spatiotemporal evolution of the wake in a plasma density up-ramp is recorded. Two parallel wakes driven by a laser with a main spot and sidelobes are identified in the experiment and reproduced in simulations. The capability of this new method for capturing the electron- and positron-driven wakes is also shown via 3D particle-in-cell simulations.

Oxidation of Molecular Hydrogen by a Chemolithoautotrophic Beggiatoa Strain

PubMed Central

2016-01-01

ABSTRACT A chemolithoautotrophic strain of the family Beggiatoaceae, Beggiatoa sp. strain 35Flor, was found to oxidize molecular hydrogen when grown in a medium with diffusional gradients of oxygen, sulfide, and hydrogen. Microsensor profiles and rate measurements suggested that the strain oxidized hydrogen aerobically when oxygen was available, while hydrogen consumption under anoxic conditions was presumably driven by sulfur respiration. Beggiatoa sp. 35Flor reached significantly higher biomass in hydrogen-supplemented oxygen-sulfide gradient media, but hydrogen did not support growth of the strain in the absence of reduced sulfur compounds. Nevertheless, hydrogen oxidation can provide Beggiatoa sp. 35Flor with energy for maintenance and assimilatory purposes and may support the disposal of internally stored sulfur to prevent physical damage resulting from excessive sulfur accumulation. Our knowledge about the exposure of natural populations of Beggiatoaceae to hydrogen is very limited, but significant amounts of hydrogen could be provided by nitrogen fixation, fermentation, and geochemical processes in several of their typical habitats such as photosynthetic microbial mats and submarine sites of hydrothermal fluid flow. IMPORTANCE Reduced sulfur compounds are certainly the main electron donors for chemolithoautotrophic Beggiatoaceae, but the traditional focus on this topic has left other possible inorganic electron donors largely unexplored. In this paper, we provide evidence that hydrogen oxidation has the potential to strengthen the ecophysiological plasticity of Beggiatoaceae in several ways. Moreover, we show that hydrogen oxidation by members of this family can significantly influence biogeochemical gradients and therefore should be considered in environmental studies. PMID:26896131

Heat Transfer by Thermo-Capillary Convection. Sounding Rocket COMPERE Experiment SOURCE

NASA Astrophysics Data System (ADS)

Fuhrmann, Eckart; Dreyer, Michael

2009-08-01

This paper describes the results of a sounding rocket experiment which was partly dedicated to study the heat transfer from a hot wall to a cold liquid with a free surface. Natural or buoyancy-driven convection does not occur in the compensated gravity environment of a ballistic phase. Thermo-capillary convection driven by a temperature gradient along the free surface always occurs if a non-condensable gas is present. This convection increases the heat transfer compared to a pure conductive case. Heat transfer correlations are needed to predict temperature distributions in the tanks of cryogenic upper stages. Future upper stages of the European Ariane V rocket have mission scenarios with multiple ballistic phases. The aims of this paper and of the COMPERE group (French-German research group on propellant behavior in rocket tanks) in general are to provide basic knowledge, correlations and computer models to predict the thermo-fluid behavior of cryogenic propellants for future mission scenarios. Temperature and surface location data from the flight have been compared with numerical calculations to get the heat flux from the wall to the liquid. Since the heat flux measurements along the walls of the transparent test cell were not possible, the analysis of the heat transfer coefficient relies therefore on the numerical modeling which was validated with the flight data. The coincidence between experiment and simulation is fairly good and allows presenting the data in form of a Nusselt number which depends on a characteristic Reynolds number and the Prandtl number. The results are useful for further benchmarking of Computational Fluid Dynamics (CFD) codes such as FLOW-3D and FLUENT, and for the design of future upper stage propellant tanks.

Thermal liquid propulsion system using magnetic nanofluid

NASA Astrophysics Data System (ADS)

Dave, V. H.; Virpura, H. A.; Bhatnagar, S. P.

2018-05-01

In the present study, we have demonstrated the thermal liquid propulsion system using the idea of magnetocaloric energy generation system. Thermal sensitive magnetic nanofluid is used for this study. In presence of magnetic field and temperature gradient, the magnetic nanofluid loses its magnetization. Hot fluid replaced by the fluid which is at ambient temperature. Temperature profile of liquid propulsion was measured in a horizontal closed loop of glass assembly.

Electrostatic waves driven by electron beam in lunar wake plasma

NASA Astrophysics Data System (ADS)

Sreeraj, T.; Singh, S. V.; Lakhina, G. S.

2018-05-01

A linear analysis of electrostatic waves propagating parallel to the ambient field in a four component homogeneous, collisionless, magnetised plasma comprising fluid protons, fluid He++, electron beam, and suprathermal electrons following kappa distribution is presented. In the absence of electron beam streaming, numerical analysis of the dispersion relation shows six modes: two electron acoustic modes (modes 1 and 6), two fast ion acoustic modes (modes 2 and 5), and two slow ion acoustic modes (modes 3 and 4). The modes 1, 2 and 3 and modes 4, 5, and 6 have positive and negative phase speeds, respectively. With an increase in electron beam speed, the mode 6 gets affected the most and the phase speed turns positive from negative. The mode 6 thus starts to merge with modes 2 and 3 and generates the electron beam driven fast and slow ion acoustic waves unstable with a finite growth. The electron beam driven slow ion-acoustic waves occur at lower wavenumbers, whereas fast ion-acoustic waves occur at a large value of wavenumbers. The effect of various other parameters has also been studied. We have applied this analysis to the electrostatic waves observed in lunar wake during the first flyby of the ARTEMIS mission. The analysis shows that the low (high) frequency waves observed in the lunar wake could be the electron beam driven slow (fast) ion-acoustic modes.

System for cooling hybrid vehicle electronics, method for cooling hybrid vehicle electronics

DOEpatents

France, David M.; Yu, Wenhua; Singh, Dileep; Zhao, Weihuan

2017-11-21

The invention provides a single radiator cooling system for use in hybrid electric vehicles, the system comprising a surface in thermal communication with electronics, and subcooled boiling fluid contacting the surface. The invention also provides a single radiator method for simultaneously cooling electronics and an internal combustion engine in a hybrid electric vehicle, the method comprising separating a coolant fluid into a first portion and a second portion; directing the first portion to the electronics and the second portion to the internal combustion engine for a time sufficient to maintain the temperature of the electronics at or below 175.degree. C.; combining the first and second portion to reestablish the coolant fluid; and treating the reestablished coolant fluid to the single radiator for a time sufficient to decrease the temperature of the reestablished coolant fluid to the temperature it had before separation.

Observations of ionospheric electron beams in the plasma sheet.

PubMed

Zheng, H; Fu, S Y; Zong, Q G; Pu, Z Y; Wang, Y F; Parks, G K

2012-11-16

Electrons streaming along the magnetic field direction are frequently observed in the plasma sheet of Earth's geomagnetic tail. The impact of these field-aligned electrons on the dynamics of the geomagnetic tail is however not well understood. Here we report the first detection of field-aligned electrons with fluxes increasing at ~1 keV forming a "cool" beam just prior to the dissipation of energy in the current sheet. These field-aligned beams at ~15 R(E) in the plasma sheet are nearly identical to those commonly observed at auroral altitudes, suggesting the beams are auroral electrons accelerated upward by electric fields parallel (E([parallel])) to the geomagnetic field. The density of the beams relative to the ambient electron density is δn(b)/n(e)~5-13% and the current carried by the beams is ~10(-8)-10(-7) A m(-2). These beams in high β plasmas with large density and temperature gradients appear to satisfy the Bohm criteria to initiate current driven instabilities.

Fluid flow in solidifying monotectic alloys

NASA Technical Reports Server (NTRS)

Ecker, A.; Frazier, D. O.; Alexander, J. Iwan D.

1989-01-01

Use of a two-wavelength holographic technique results in a simultaneous determination of temperature and composition profiles during directional solidification in a system with a miscibility gap. The relationships among fluid flow, phase separation, and mass transport during the solidification of the monotectic alloy are discussed. The primary sources of fluid motion in this system are buoyancy and thermocapillary forces. These forces act together when phase separation results in the formation of droplets (this occurs at the solid-liquid interface and in the bulk melt). In the absence of phase separation, buoyancy results from density gradients related to temperature and compositional gradients in the single-phase bulk melt. The effects of buoyancy are especially evident in association with water- or ethanol-rich volumes created at the solid-liquid growth interface.

Interaction between neoclassical effects and ion temperature gradient turbulence in gradient- and flux-driven gyrokinetic simulations

NASA Astrophysics Data System (ADS)

Oberparleiter, M.; Jenko, F.; Told, D.; Doerk, H.; Görler, T.

2016-04-01

Neoclassical and turbulent transport in tokamaks has been studied extensively over the past decades, but their possible interaction remains largely an open question. The two are only truly independent if the length scales governing each of them are sufficiently separate, i.e., if the ratio ρ* between ion gyroradius and the pressure gradient scale length is small. This is not the case in particularly interesting regions such as transport barriers. Global simulations of a collisional ion-temperature-gradient-driven microturbulence performed with the nonlinear global gyrokinetic code Gene are presented. In particular, comparisons are made between systems with and without neoclassical effects. In fixed-gradient simulations, the modified radial electric field is shown to alter the zonal flow pattern such that a significant increase in turbulent transport is observed for ρ*≳1 /300 . Furthermore, the dependency of the flux on the collisionality changes. In simulations with fixed power input, we find that the presence of neoclassical effects decreases the frequency and amplitude of intermittent turbulent transport bursts (avalanches) and thus plays an important role for the self-organisation behaviour.

Stabilization of lower hybrid drift modes by finite parallel wavenumber and electron temperature gradients in field-reversed configurations

NASA Astrophysics Data System (ADS)

Farengo, R.; Guzdar, P. N.; Lee, Y. C.

1989-08-01

The effect of finite parallel wavenumber and electron temperature gradients on the lower hybrid drift instability is studied in the parameter regime corresponding to the TRX-2 device [Fusion Technol. 9, 48 (1986)]. Perturbations in the electrostatic potential and all three components of the vector potential are considered and finite beta electron orbit modifications are included. The electron temperature gradient decreases the growth rate of the instability but, for kz=0, unstable modes exist for ηe(=T'en0/Ten0)>6. Since finite kz effects completely stabilize the mode at small values of kz/ky(≂5×10-3), magnetic shear could be responsible for stabilizing the lower hybrid drift instability in field-reversed configurations.

Electron cyclotron heating can drastically alter reversed shear Alfvén eigenmode activity in DIII-D through finite pressure effects

NASA Astrophysics Data System (ADS)

Van Zeeland, M. A.; Heidbrink, W. W.; Sharapov, S. E.; Spong, D.; Cappa, A.; Chen, Xi; Collins, C.; García-Muñoz, M.; Gorelenkov, N. N.; Kramer, G. J.; Lauber, P.; Lin, Z.; Petty, C.

2016-11-01

A recent DIII-D experiment investigating the impact of electron cyclotron heating (ECH) on neutral beam driven reversed shear Alfvén eigenmode (RSAE) activity is presented. The experiment includes variations of ECH injection location and timing, current ramp rate, beam injection geometry (on/off-axis), and neutral beam power. Essentially all variations carried out in this experiment were observed to change the impact of ECH on AE activity significantly. In some cases, RSAEs were observed to be enhanced with ECH near the off-axis minimum in magnetic safety factor ({{q}\\min} ), in contrast to the original DIII-D experiments where the modes were absent when ECH was deposited near {{q}\\min} . It is found that during intervals when the geodesic acoustic mode (GAM) frequency at {{q}\\min} is elevated and the calculated RSAE minimum frequency, including contributions from thermal plasma gradients, is very near or above the nominal TAE frequency (f TAE), RSAE activity is not observed or RSAEs with a much reduced frequency sweep range are found. This condition is primarily brought about by ECH modification of the local electron temperature (T e) which can raise both the local T e at {{q}\\min} as well as its gradient. A q-evolution model that incorporates this reduction in RSAE frequency sweep range is in agreement with the observed spectra and appears to capture the relative balance of TAE or RSAE-like modes throughout the current ramp phase of over 38 DIII-D discharges. Detailed ideal MHD calculations using the NOVA code show both modification of plasma pressure and pressure gradient at {{q}\\min} play an important role in modifying the RSAE activity. Analysis of the ECH injection near the {{q}\\min} case where no frequency sweeping RSAEs are observed shows the typical RSAE is no longer an eigenmode of the system. What remains is an eigenmode with poloidal harmonic content reminiscent of the standard RSAE, but absent of the typical frequency sweeping behavior. The remaining eigenmode is also often strongly coupled to gap TAEs. Analysis with the non-perturbative gyro fluid code TAEFL confirms this change in RSAE activity and also shows a large drop in the resultant mode growth rates.

Electron cyclotron heating can drastically alter reversed shear Alfvén eigenmode activity in DIII-D through finite pressure effects

DOE PAGES

Van Zeeland, M. A.; Heidbrink, W. W.; Sharapov, S. E.; ...

2016-07-22

Here, a recent DIII-D experiment investigating the impact of electron cyclotron heating (ECH) on neutral beam driven reversed shear Alfvén eigenmode (RSAE) activity is presented. The experiment includes variations of ECH injection location and timing, current ramp rate, beam injection geometry (on/off-axis), and neutral beam power. Essentially all variations carried out in this experiment were observed to change the impact of ECH on AE activity significantly. In some cases, RSAEs were observed to be enhanced with ECH near the off-axis minimum in magnetic safety factor (more » $${{q}_{\\min}}$$ ), in contrast to the original DIII-D experiments where the modes were absent when ECH was deposited near $${{q}_{\\min}}$$ . It is found that during intervals when the geodesic acoustic mode (GAM) frequency at $${{q}_{\\min}}$$ is elevated and the calculated RSAE minimum frequency, including contributions from thermal plasma gradients, is very near or above the nominal TAE frequency (f TAE), RSAE activity is not observed or RSAEs with a much reduced frequency sweep range are found. This condition is primarily brought about by ECH modification of the local electron temperature (T e) which can raise both the local T e at $${{q}_{\\min}}$$ as well as its gradient. A q-evolution model that incorporates this reduction in RSAE frequency sweep range is in agreement with the observed spectra and appears to capture the relative balance of TAE or RSAE-like modes throughout the current ramp phase of over 38 DIII-D discharges. Detailed ideal MHD calculations using the NOVA code show both modification of plasma pressure and pressure gradient at $${{q}_{\\min}}$$ play an important role in modifying the RSAE activity. Analysis of the ECH injection near the $${{q}_{\\min}}$$ case where no frequency sweeping RSAEs are observed shows the typical RSAE is no longer an eigenmode of the system. What remains is an eigenmode with poloidal harmonic content reminiscent of the standard RSAE, but absent of the typical frequency sweeping behavior. The remaining eigenmode is also often strongly coupled to gap TAEs. Analysis with the non-perturbative gyro fluid code TAEFL confirms this change in RSAE activity and also shows a large drop in the resultant mode growth rates.« less

Preferential paths in yield stress fluid flow through a porous medium

NASA Astrophysics Data System (ADS)

Guasto, Jeffrey; Waisbord, Nicolas; Stoop, Norbert; Dunkel, Jörn

2016-11-01

A broad range of biological, geological, and industrial materials with complex rheological properties are subjected to flow through porous media in applications ranging from oil recovery to food manufacturing. In this experimental study, we examine the flow of a model yield stress fluid (Carbopol micro-gel) through a quasi-2D porous medium, fabricated in a microfluidic channel. The flow is driven by applying a precisely-controlled pressure gradient and measured by particle tracking velocimetry, and our observations are complemented by a pore-network model of the yield stress fluid flow. While remaining unyielded at small applied pressure, the micro-gel begins to yield at a critical pressure gradient, exhibiting a single preferential flow path that percolates through the porous medium. As the applied pressure gradient increases, we observe a subsequent coarsening and invasion of the yielded, fluidized network. An examination of both the yielded network topology and pore-scale flow reveal that two cooperative phenomena are involved in sculpting the preferential flow paths: (1) the geometry of the porous microstructure, and (2) the adhesive surface interactions between the micro-gel and substrate. NSF CBET-1511340.

Analysis of nanoscale two-phase flow of argon using molecular dynamics

NASA Astrophysics Data System (ADS)

Verma, Abhishek Kumar; Kumar, Rakesh

2014-12-01

Two phase flows through micro and nanochannels have attracted a lot of attention because of their immense applicability to many advanced fields such as MEMS/NEMS, electronic cooling, bioengineering etc. In this work, a molecular dynamics simulation method is employed to study the condensation process of superheated argon vapor force driven flow through a nanochannel combining fluid flow and heat transfer. A simple and effective particle insertion method is proposed to model phase change of argon based on non-periodic boundary conditions in the simulation domain. Starting from a crystalline solid wall of channel, the condensation process evolves from a transient unsteady state where we study the influence of different wall temperatures and fluid wall interactions on interfacial and heat transport properties of two phase flows. Subsequently, we analyzed transient temperature, density and velocity fields across the channel and their dependency on varying wall temperature and fluid wall interaction, after a dynamic equilibrium is achieved in phase transition. Quasi-steady nonequilibrium temperature profile, heat flux and interfacial thermal resistance were analyzed. The results demonstrate that the molecular dynamics method, with the proposed particle insertion method, effectively solves unsteady nonequilibrium two phase flows at nanoscale resolutions whose interphase between liquid and vapor phase is typically of the order of a few molecular diameters.

Electron Temperature Gradient Scale Measurements in ICRF Heated Plasmas at Alcator C-Mod

NASA Astrophysics Data System (ADS)

Houshmandyar, Saeid; Phillips, Perry E.; Rowan, William L.; Howard, Nathaniel T.; Greenwald, Martin

2016-10-01

It is generally believed that the temperature gradient is a driving mechanism for the turbulent transport in hot and magnetically confined plasmas. A feature of many anomalous transport models is the critical threshold value (LC) for the gradient scale length, above which both the turbulence and the heat transport increases. This threshold is also predicted by the recent multi-scale gyrokinetic simulations, which are focused on addressing the electron (and ion) heat transport in tokamaks. Recently, we have established an accurate technique (BT-jog) to directly measure the electron temperature gradient scale length (LTe =Te / ∇T) profile, using a high-spatial resolution radiometer-based electron cyclotron emission (ECE) diagnostic. For the work presented here, electrons are heated by ion cyclotron range of frequencies (ICRF) through minority heating in L-mode plasmas at different power levels, TRANSP runs determine the electron heat fluxes and the scale lengths are measured through the BT-jog technique. Furthermore, the experiment is extended for different plasma current and electron densities by which the parametric dependence of LC on magnetic shear, safety factor and density will be investigated. This work is supported by U.S. DoE OFES, under Award No. DE-FG03-96ER-54373.

Exact solution for the layered convection of a viscous incompressible fluid at specified temperature gradients and tangential forces on the free boundary

NASA Astrophysics Data System (ADS)

Burmasheva, N. V.; Prosviryakov, E. Yu.

2017-12-01

A new exact analytical solution of a system of thermal convection equations in the Boussinesq approximation describing layered flows in an incompressible viscous fluid is obtained. A fluid flow in an infinite layer is considered. Convection in the fluid is induced by tangential stresses specified on the upper non-deformable boundary. At the fixed lower boundary, the no-slip condition is satisfied. Temperature corrections are given on the both boundaries of the fluid layer. The possibility of physical field stratification is investigated.

A study of self organized criticality in ion temperature gradient mode driven gyrokinetic turbulence

NASA Astrophysics Data System (ADS)

Mavridis, M.; Isliker, H.; Vlahos, L.; Görler, T.; Jenko, F.; Told, D.

2014-10-01

An investigation on the characteristics of self organized criticality (Soc) in ITG mode driven turbulence is made, with the use of various statistical tools (histograms, power spectra, Hurst exponents estimated with the rescaled range analysis, and the structure function method). For this purpose, local non-linear gyrokinetic simulations of the cyclone base case scenario are performed with the GENE software package. Although most authors concentrate on global simulations, which seem to be a better choice for such an investigation, we use local simulations in an attempt to study the locally underlying mechanisms of Soc. We also study the structural properties of radially extended structures, with several tools (fractal dimension estimate, cluster analysis, and two dimensional autocorrelation function), in order to explore whether they can be characterized as avalanches. We find that, for large enough driving temperature gradients, the local simulations exhibit most of the features of Soc, with the exception of the probability distribution of observables, which show a tail, yet they are not of power-law form. The radial structures have the same radial extent at all temperature gradients examined; radial motion (transport) though appears only at large temperature gradients, in which case the radial structures can be interpreted as avalanches.

A study of self organized criticality in ion temperature gradient mode driven gyrokinetic turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mavridis, M.; Isliker, H.; Vlahos, L.

2014-10-15

An investigation on the characteristics of self organized criticality (Soc) in ITG mode driven turbulence is made, with the use of various statistical tools (histograms, power spectra, Hurst exponents estimated with the rescaled range analysis, and the structure function method). For this purpose, local non-linear gyrokinetic simulations of the cyclone base case scenario are performed with the GENE software package. Although most authors concentrate on global simulations, which seem to be a better choice for such an investigation, we use local simulations in an attempt to study the locally underlying mechanisms of Soc. We also study the structural properties ofmore » radially extended structures, with several tools (fractal dimension estimate, cluster analysis, and two dimensional autocorrelation function), in order to explore whether they can be characterized as avalanches. We find that, for large enough driving temperature gradients, the local simulations exhibit most of the features of Soc, with the exception of the probability distribution of observables, which show a tail, yet they are not of power-law form. The radial structures have the same radial extent at all temperature gradients examined; radial motion (transport) though appears only at large temperature gradients, in which case the radial structures can be interpreted as avalanches.« less

Investigations into dual-grating THz-driven accelerators

NASA Astrophysics Data System (ADS)

Wei, Y.; Ischebeck, R.; Dehler, M.; Ferrari, E.; Hiller, N.; Jamison, S.; Xia, G.; Hanahoe, K.; Li, Y.; Smith, J. D. A.; Welsch, C. P.

2018-01-01

Advanced acceleration technologies are receiving considerable interest in order to miniaturize future particle accelerators. One such technology is the dual-grating dielectric structures, which can support accelerating fields one to two orders of magnitude higher than the metal RF cavities in conventional accelerators. This opens up the possibility of enabling high accelerating gradients of up to several GV/m. This paper investigates numerically a quartz dual-grating structure which is driven by THz pulses to accelerate electrons. Geometry optimizations are carried out to achieve the trade-offs between accelerating gradient and vacuum channel gap. A realistic electron bunch available from the future Compact Linear Accelerator for Research and Applications (CLARA) is loaded into an optimized 100-period dual-grating structure for a detailed wakefield study. A THz pulse is then employed to interact with this CLARA bunch in the optimized structure. The computed beam quality is analyzed in terms of emittance, energy spread and loaded accelerating gradient. The simulations show that an accelerating gradient of 348 ± 12 MV/m with an emittance growth of 3.0% can be obtained.

Experimental observation of the thermocapillary driven motion of bubbles in a molten glass under low gravity conditions

NASA Technical Reports Server (NTRS)

Smith, H. D.; Mattox, D. M.; Wilcox, W. R.; Subramanian, R. S.; Meyyappan, M.

1982-01-01

An experiment was carried out on board a Space Processing Applications Rocket with the aim of demonstrating bubble migration in molten glass due to a temperature gradient under low gravity conditions. During the flight, a sample of a sodium borate melt with a specific bubble array, contained in a platinum/fused silica cell, was subjected to a well defined temperature gradient for more than 4 minutes. Photographs taken at one second intervals during the experiment clearly show that the bubbles move toward the hot spot on the platinum heater strip. This result is consistent with the predictions of the theory of thermocapillary driven bubble motion.

Density-Gradient-Driven trapped-electron-modes in improved-confinement RFP plasmas

NASA Astrophysics Data System (ADS)

Duff, James

2016-10-01

Short wavelength density fluctuations in improved-confinement MST plasmas exhibit multiple features characteristic of the trapped-electron-mode (TEM), strong evidence that drift wave turbulence emerges in RFP plasmas when transport associated with MHD tearing is reduced. Core transport in the RFP is normally governed by magnetic stochasticity stemming from long wavelength tearing modes that arise from current profile peaking. Using inductive control, the tearing modes are reduced and global confinement is increased to values expected for a comparable tokamak plasma. The improved confinement is associated with a large increase in the pressure gradient that can destabilize drift waves. The measured density fluctuations have frequencies >50 kHz, wavenumbers k_phi*rho_s<0.14, and propagate in the electron drift direction. Their spectral emergence coincides with a sharp decrease in fluctuations associated with global tearing modes. Their amplitude increases with the local density gradient, and they exhibit a density-gradient threshold at R/L_n 15, higher than in tokamak plasmas by R/a. the GENE code, modified for RFP equilibria, predicts the onset of microinstability for these strong-gradient plasma conditions. The density-gradient-driven TEM is the dominant instability in the region where the measured density fluctuations are largest, and the experimental threshold-gradient is close to the predicted critical gradient for linear stability. While nonlinear analysis shows a large Dimits shift associated with predicted strong zonal flows, the inclusion of residual magnetic fluctuations causes a collapse of the zonal flows and an increase in the predicted transport to a level close to the experimentally measured heat flux. Similar circumstances could occur in the edge region of tokamak plasmas when resonant magnetic perturbations are applied for the control of ELMs. Work supported by US DOE.

Numerical simulation and comparison of two ventilation methods for a restaurant - displacement vs mixed flow ventilation

NASA Astrophysics Data System (ADS)

Chitaru, George; Berville, Charles; Dogeanu, Angel

2018-02-01

This paper presents a comparison between a displacement ventilation method and a mixed flow ventilation method using computational fluid dynamics (CFD) approach. The paper analyses different aspects of the two systems, like the draft effect in certain areas, the air temperatureand velocity distribution in the occupied zone. The results highlighted that the displacement ventilation system presents an advantage for the current scenario, due to the increased buoyancy driven flows caused by the interior heat sources. For the displacement ventilation case the draft effect was less prone to appear in the occupied zone but the high heat emissions from the interior sources have increased the temperature gradient in the occupied zone. Both systems have been studied in similar conditions, concentrating only on the flow patterns for each case.

The behaviour of monazite at high temperature and high stress in the lower crust

NASA Astrophysics Data System (ADS)

Clark, Chris; Taylor, Richard; Erickson, Timmons; Reddy, Steven; Fougerouse, Denis; Fitzsimons, Ian; Hand, Martin

2017-04-01

Monazite is fast becoming the go to geochronometer for establishing the timing of metamorphic, deformational and hydrothermal events in crustal rocks. This is principally due to monazite forming in rocks that are petrologically useful (e.g. metapelites), it's susceptibility to recrystallization (both fluid and deformation driven) and the suite of trace elements it incorporates during growth. In dry conditions (i.e. the melt-depleted lower crust) monazite has a high closure temperature. It therefore has the ability to record the timing of prograde to peak metamorphic conditions. The reactivity of monazite in the presence of fluid allows the timing of post-peak fluid and melt crystallisation events to be constrained. Under high-stress monazite will recrystallise, forming new crystals that can be used to constrain the age of deformational events - this feature is particularly useful as high-grade reworking of lower crustal rocks often leave no geochronological record within other accessory minerals (e.g. zircon). However, it has long been recognised that monazite can record a cryptic range and/or distribution of ages that are difficult reconcile with how we traditionally believe the lower crust responds to deformational events - e.g. the anhydrous nature of lower crustal rocks and the preservation of granulite facies mineral assemblages. Here we present datasets collected by a suite of microanalytical techniques on monazite grains from lower-crustal rocks that have experienced deformation, fluid-rock interaction and ultrahigh temperature metamorphism. To better understand how monazite behaves in these environments we integrate electron probe, electron backscatter diffraction, laser ablation split stream petrochronology, transmission electron microscopy and Atom Probe Tomography datasets to image and quantify behaviour of key elements from the micro- to the nanoscale. When used sequentially, these techniques provide a detailed view of the processes that re-distribute U-Th-REE-Y-Pb at the nanoscale. Understanding how monazite behaves under different stress and thermal conditions is the key to using this geochronometer to develop and refine event chronologies in the lower crust.

Entropic anomaly and maximal efficiency of microscopic heat engines.

PubMed

Bo, Stefano; Celani, Antonio

2013-05-01

The efficiency of microscopic heat engines in a thermally heterogenous environment is considered. We show that-as a consequence of the recently discovered entropic anomaly-quasistatic engines, whose efficiency is maximal in a fluid at uniform temperature, have in fact vanishing efficiency in the presence of temperature gradients. For slow cycles the efficiency falls off as the inverse of the period. The maximum efficiency is reached at a finite value of the cycle period that is inversely proportional to the square root of the gradient intensity. The relative loss in maximal efficiency with respect to the thermally homogeneous case grows as the square root of the gradient. As an illustration of these general results, we construct an explicit, analytically solvable example of a Carnot stochastic engine. In this thought experiment, a Brownian particle is confined by a harmonic trap and immersed in a fluid with a linear temperature profile. This example may serve as a template for the design of real experiments in which the effect of the entropic anomaly can be measured.

Current Driven Instabilities and Anomalous Mobility in Hall-effect Thrusters

NASA Astrophysics Data System (ADS)

Tran, Jonathan; Eckhardt, Daniel; Martin, Robert

2017-10-01

Due to the extreme cost of fully resolving the Debye length and plasma frequency, hybrid plasma simulations utilizing kinetic ions and quasi-steady state fluid electrons have long been the principle workhorse methodology for Hall-effect thruster (HET) modeling. Plasma turbulence and the resulting anomalous electron transport in HETs is a promising candidate for developing predictive models for the observed anomalous transport. In this work, we investigate the implementation of an anomalous electron cross field transport model for hybrid HET simulations such a HPHall. A theory for anomalous transport in HETs and current driven instabilities has been recently studied by Lafleur et al. This work has shown collective electron-wave scattering due to large amplitude azimuthal fluctuations of the electric field. We will further adapt the previous results for related current driven instabilities to electric propulsion relevant mass ratios and conduct a preliminary study of resolving this instability with a modified hybrid (fluid electron and kinetic ion) simulation with the hope of integration with established hybrid HET simulations. This work is supported by the Air Force Office of Scientific Research award FA9950-17RQCOR465.

Study on the temperature gradient evolution of large size nonlinear crystal based on the fluid-solid coupling theory

NASA Astrophysics Data System (ADS)

Sun, F. Z.; Zhang, P.; Liang, Y. C.; Lu, L. H.

2014-09-01

In the non-critical phase-matching (NCPM) along the Θ =90° direction, ADP and DKDP crystals which have many advantages, including a large effective nonlinear optical coefficient, a small PM angular sensitivity and non beam walk-off, at the non-critical phase-matching become the competitive candidates in the inertial confinement fusion(ICF) facility, so the reasonable temperature control of crystals has become more and more important .In this paper, the fluid-solid coupling models of ADP crystal and DKDP crystal which both have anisotropic thermal conductivity in the states of vacuum and non-vacuum were established firstly, and then simulated using the fluid analysis software Fluent. The results through the analysis show that the crystal surface temperature distribution is a ring shape, the temperature gradients in the direction of the optical axis both the crystals are 0.02°C and 0.01°C due to the air, the lowest temperature points of the crystals are both at the center of surface, and the temperatures are lower than 0.09°C and 0.05°C compared in the vacuum and non-vacuum environment, then propose two designs for heating apparatus.

Heat-driven spin torques in antiferromagnets

NASA Astrophysics Data System (ADS)

Białek, Marcin; Bréchet, Sylvain; Ansermet, Jean-Philippe

2018-04-01

Heat-driven magnetization damping, which is a linear function of a temperature gradient, is predicted in antiferromagnets by considering the sublattice dynamics subjected to a heat-driven spin torque. This points to the possibility of achieving spin torque oscillator behavior. The model is based on the magnetic Seebeck effect acting on sublattices which are exchange coupled. The heat-driven spin torque is estimated and the feasibility of detecting this effect is discussed.

Convection induced by thermal gradients on thin reaction fronts

NASA Astrophysics Data System (ADS)

Ruelas Paredes, David R. A.; Vasquez, Desiderio A.

2017-09-01

We present a thin front model for the propagation of chemical reaction fronts in liquids inside a Hele-Shaw cell or porous media. In this model we take into account density gradients due to thermal and compositional changes across a thin interface. The front separating reacted from unreacted fluids evolves following an eikonal relation between the normal speed and the curvature. We carry out a linear stability analysis of convectionless flat fronts confined in a two-dimensional rectangular domain. We find that all fronts are stable to perturbations of short wavelength, but they become unstable for some wavelengths depending on the values of compositional and thermal gradients. If the effects of these gradients oppose each other, we observe a range of wavelengths that make the flat front unstable. Numerical solutions of the nonlinear model show curved fronts of steady shape with convection propagating faster than flat fronts. Exothermic fronts increase the temperature of the fluid as they propagate through the domain. This increment in temperature decreases with increasing speed.

Observations of reduced electron Gyroscale fluctuations in national spherical torus experiment H-mode plasmas with large ExB flow shear.

PubMed

Smith, D R; Kaye, S M; Lee, W; Mazzucato, E; Park, H K; Bell, R E; Domier, C W; Leblanc, B P; Levinton, F M; Luhmann, N C; Menard, J E; Yuh, H

2009-06-05

Electron gyroscale fluctuation measurements in National Spherical Torus Experiment H-mode plasmas with large toroidal rotation reveal fluctuations consistent with electron temperature gradient (ETG) turbulence. Large toroidal rotation in National Spherical Torus Experiment plasmas with neutral beam injection generates ExB flow shear rates comparable to ETG linear growth rates. Enhanced fluctuations occur when the electron temperature gradient is marginally stable with respect to the ETG linear critical gradient. Fluctuation amplitudes decrease when the ExB flow shear rate exceeds ETG linear growth rates. The observations indicate that ExB flow shear can be an effective suppression mechanism for ETG turbulence.

Inertial migration of elastic particles in a pressure-driven power-law fluid

NASA Astrophysics Data System (ADS)

Bowie, Samuel; Alexeev, Alexander

2016-11-01

Using three-dimensional computer simulations, we study the cross-stream migration of deformable particles in a channel filled with a non-Newtonian fluid driven by a pressure gradient. Our numerical approach integrates lattice Boltzmann method and lattice spring method in order to model fluid structural interactions of the elastic particle and the surrounding power fluid in the channel. The particles are modeled as elastic shells filled with a viscous fluid that are initially spherical. We focus on the regimes where the inertial effects cannot be neglected and cause cross-stream drift of particles. We probe the flow with different power law indexes including both the shear thickening and thinning fluids. We also examine migration of particles of with different elasticity and relative size. To isolate the non-Newtonian effects on particle migration, we compare the results with the inertial migration results found in the case where the channel is filled with a simple Newtonian fluid. The results can be useful for applications requiring high throughput separation, sorting, and focusing of both synthetic particles and biological cells in microfluidic devices. Financial support provided by National Science Foundation (NSF) Grant No. CMMI1538161.

Neutral Beam Driven Neoclassical Transport in NSTX

NASA Astrophysics Data System (ADS)

Houlberg, W. A.; Shaing, K. C.; Callen, J. D.

2002-11-01

We re-examine the particle and heat flows driven by neutral beam injection in tokamak plasmas. These appear as inward pinches for co-injection and outward for counter injection. We derive the parallel friction and heat friction forces exerted on the thermal species by the energetic beam ions by extending the early analysis of Callen, et al. [1], which are then used as external forces in the moments formulation of neoclassical transport in NCLASS [2]. NCLASS is based on the multiple species treatment of Hirshman and Sigmar [3]. Of particular interest is the ion energy flux driven by the heat friction term. It scales as the beam energy, while the particle and electron heat terms scale as the thermal plasma temperature. In NSTX the high beam energy to plasma temperature ratio may lead to a net negative ion heat flux with strong co-injection. Limtations to the theory, such as the large fast ion orbit size relative to the radius of the flux surface, are discussed. Comparisons are made with earlier works by Hinton and Kim [4] and Stacey [5], who evaluated only the beam-thermal friction. [1] J.D. Callen, et al, 5th IAEA, Tokyo (1974), Vol 1, 645 [2] W.A. Houlberg, K.C. Shaing, S.P. Hirshman, M.C. Zarnstorff, Phys. Plasmas 4 (1997) 3230 [3] S.P. Hirshman, D.J. Sigmar, Nucl. Fusion 21 (1981) 1079 [4] F.L. Hinton, Y.-B. Kim, Phys. Fluids B 5 (1993) 3012 [5] W.M. Stacey, Phys. Fluids B 5 (1993) 4505

Photo-Nernst current in graphene

NASA Astrophysics Data System (ADS)

Cao, Helin; Aivazian, Grant; Fei, Zaiyao; Ross, Jason; Cobden, David H.; Xu, Xiaodong

2016-03-01

Photocurrent measurements provide a powerful means of studying the spatially resolved optoelectronic and electrical properties of a material or device. Generally speaking there are two classes of mechanism for photocurrent generation: those involving separation of electrons and holes, and thermoelectric effects driven by electron temperature gradients. Here we introduce a new member in the latter class: the photo-Nernst effect. In graphene devices in a perpendicular magnetic field we observe photocurrent generated uniformly along the free edges, with opposite sign at opposite edges. The signal is antisymmetric in field, shows a peak versus gate voltage at the neutrality point flanked by wings of opposite sign at low fields, and exhibits quantum oscillations at higher fields. These features are all explained by the Nernst effect associated with laser-induced electron heating. This `photo-Nernst’ current provides a simple and clear demonstration of the Shockley-Ramo nature of long-range photocurrent generation in a gapless material.

Beam-driven acceleration in ultra-dense plasma media

DOE PAGES

Shin, Young-Min

2014-09-15

Accelerating parameters of beam-driven wakefield acceleration in an extremely dense plasma column has been analyzed with the dynamic framed particle-in-cell plasma simulator, and compared with analytic calculations. In the model, a witness beam undergoes a TeV/m scale alternating potential gradient excited by a micro-bunched drive beam in a 10 25 m -3 and 1.6 x 10 28 m -3 plasma column. The acceleration gradient, energy gain, and transformer ratio have been extensively studied in quasi-linear, linear-, and blowout-regimes. The simulation analysis indicated that in the beam-driven acceleration system a hollow plasma channel offers 20 % higher acceleration gradient by enlargingmore » the channel radius (r) from 0.2 Ap to 0.6 .Ap in a blowout regime. This paper suggests a feasibility of TeV/m scale acceleration with a hollow crystalline structure (e.g. nanotubes) of high electron plasma density.« less

Dual laser optical system and method for studying fluid flow

NASA Technical Reports Server (NTRS)

Owen, R. B.; Witherow, W. K. (Inventor)

1983-01-01

A dual laser optical system and method is disclosed for visualization of phenomena in transport substances which induce refractive index gradients such as fluid flow and pressure and temperature gradients in fluids and gases. Two images representing mutually perpendicular components of refractive index gradients may be viewed simultaneously on screen. Two lasers having wave lengths in the visible range but separated by about 1000 angstroms are utilized to provide beams which are collimated into a beam containing components of the different wave lengths. The collimated beam is passed through a test volume of the transparent substance. The collimated beam is then separated into components of the different wave lengths and focused onto a pair of knife edges arranged mutually perpendicular to produce and project images onto the screen.

Effects of Temperature, Oxygen Partial Pressure, and Materials Selection on Slag Infiltration into Porous Refractories for Entrained-Flow Gasifiers

NASA Astrophysics Data System (ADS)

Kaneko, Tetsuya Kenneth

The penetration rate of molten mineral contents (slag) from spent carbonaceous feedstock into porous ceramic-oxide refractory linings is a critical parameter in determining the lifecycle of integrated gasification combined cycle energy production plants. Refractory linings that withstand longer operation without interruption are desirable because they can mitigate consumable and maintenance costs. Although refractory degradation has been extensively studied for many other high-temperature industrial processes, this work focuses on the mechanisms that are unique to entrained-flow gasification systems. The use of unique feedstock mixtures, temperatures from 1450 °C to 1600 °C, and oxygen partial pressures from 10-7 atm to 10-9 atm pose engineering challenges in designing an optimal refractory material. Experimentation, characterization, and modeling show that gasifier slag infiltration into porous refractory is determined by interactions between the slag and the refractory that either form a physical barrier that impedes fluid flow or induce an increased fluid viscosity that decelerates the velocity of the fluid body. The viscosity of the slag is modified by the thermal profile of the refractory along the penetration direction as well as reactions between the slag and refractory that alter the chemistry, and thereby the thermo-physical properties of the fluid. Infiltration experiments reveal that the temperature gradient inherently present along the refractory lining limits penetration. A refractory in near-isothermal conditions demonstrates deeper slag penetration as compared to one that experiences a steeper thermal profile. The decrease in the local temperatures of the slag as it travels deeper into the refractory increases the viscosity of the fluid, which in turn slows the infiltration velocity of fluid body into the pores of the refractory microstructure. With feedstock mixtures that exhibit high iron-oxide concentrations, a transition-metal-oxide, the oxygen partial pressure of the operating atmosphere regulates the penetration of slag into refractory. The viscosity of the slag, which dictates its penetration rate, is influenced by the oxidation state of the Fe cation. Slag penetrations are shallower in oxidizing conditions than they are in reducing conditions because the iron-oxide from the slag solutions into the corundum-structured refractory and the slag is depleted of iron-oxide, increasing the viscosity of slags. Equally, the chemistries of both the refractory and slag materials dictate the course of penetration. Cr2O3-Al2O3 refractory limits mixed feedstock slag penetration through formation of a chromium spinel layer that functions as a physical obstacle against fluid flow. Al2O 3-SiO2 refractory limits eastern coal feedstock slag penetration as a result of refractory dissolution of SiO2, which increases the viscosity of slags. A physical model, which considers unidirectional fluid flow of slag through each pore of the porous microstructure of the refractory, sufficiently approximates the penetration depth of the slag into the refractory. Agreement between experiments and the physical model demonstrates that the slag is driven into the refractory by capillary pressure. Since the viscosity of the slag continuously changes as the slag travels through the inherent temperature gradient of the refractory lining, the model incorporates dynamic viscosities that are dependent on both temperature and composition to project depths that are unique to the experimental parameters. The significantly different length scales of the radial and penetration directions of the pores allows for the application of a lubrication approximation onto the momentum equation. This process produces an analytical solution that effectively envelopes the variable viscosity into a single term.

Prediction of gravity-driven fingering in porous media

NASA Astrophysics Data System (ADS)

Beljadid, Abdelaziz; Cueto-Felgueroso, Luis; Juanes, Ruben

2017-11-01

Gravity-driven displacement of one fluid by another in porous media is often subject to a hydrodynamic instability, whereby fluid invasion takes the form of preferential flow paths-examples include secondary oil migration in reservoir rocks, and infiltration of rainfall water in dry soil. Here, we develop a continuum model of gravity-driven two-phase flow in porous media within the phase-field framework (Cueto-Felgueroso and Juanes, 2008). We employ pore-scale physics arguments to design the free energy of the system, which notably includes a nonlinear formulation of the high-order (square-gradient) term based on equilibrium considerations in the direction orthogonal to gravity. This nonlocal term plays the role of a macroscopic surface tension, which exhibits a strong link with capillary pressure. Our theoretical analysis shows that the proposed model enforces that fluid saturations are bounded between 0 and 1 by construction, therefore overcoming a serious limitation of previous models. Our numerical simulations show that the proposed model also resolves the pinning behavior at the base of the infiltration front, and the asymmetric behavior of the fingers at material interfaces observed experimentally.

On axial temperature gradients due to large pressure drops in dense fluid chromatography.

PubMed

Colgate, Sam O; Berger, Terry A

2015-03-13

The effect of energy degradation (Degradation is the creation of net entropy resulting from irreversibility.) accompanying pressure drops across chromatographic columns is examined with regard to explaining axial temperature gradients in both high performance liquid chromatography (HPLC) and supercritical fluid chromatography (SFC). The observed effects of warming and cooling can be explained equally well in the language of thermodynamics or fluid dynamics. The necessary equivalence of these treatments is reviewed here to show the legitimacy of using whichever one supports the simpler determination of features of interest. The determination of temperature profiles in columns by direct application of the laws of thermodynamics is somewhat simpler than applying them indirectly by solving the Navier-Stokes (NS) equations. Both disciplines show that the preferred strategy for minimizing the reduction in peak quality caused by temperature gradients is to operate columns as nearly adiabatically as possible (i.e. as Joule-Thomson expansions). This useful fact, however, is not widely familiar or appreciated in the chromatography community due to some misunderstanding of the meaning of certain terms and expressions used in these disciplines. In fluid dynamics, the terms "resistive heating" or "frictional heating" have been widely used as synonyms for the dissipation function, Φ, in the NS energy equation. These terms have been widely used by chromatographers as well, but often misinterpreted as due to friction between the mobile phase and the column packing, when in fact Φ describes the increase in entropy of the system (dissipation, ∫TdSuniv>0) due to the irreversible decompression of the mobile phase. Two distinctly different contributions to the irreversibility are identified; (1) ΔSext, viscous dissipation of work done by the external surroundings driving the flow (the pump) contributing to its warming, and (2) ΔSint, entropy change accompanying decompression of fluid in the column, contributing either to warming or cooling depending on local density and temperature. The molecular basis for this variation is described. Sample calculations of dissipation and temperature profiles of several model fluids including carbon dioxide-methanol mixtures are presented, based on the NIST REFPROP program including select equations of state and property calculation software. Copyright © 2015 Elsevier B.V. All rights reserved.

The development and investigation of a strongly non-equilibrium model of heat transfer in fluid with allowance for the spatial and temporal non-locality and energy dissipation

NASA Astrophysics Data System (ADS)

Kudinov, V. A.; Eremin, A. V.; Kudinov, I. V.

2017-11-01

The differential equation of heat transfer with allowance for energy dissipation and spatial and temporal nonlocality has been derived by the relaxation of heat flux and temperature gradient in the Fourier law formula for the heat flux at the use of the heat balance equation. An investigation of the numerical solution of the heat-transfer problem at a laminar fluid flow in a plane duct has shown the impossibility of an instantaneous acceptance of the boundary condition of the first kind — the process of its settling at small values of relaxation coefficients takes a finite time interval the duration of which is determined by the thermophysical and relaxation properties of the fluid. At large values of relaxation coefficients, the use of the boundary condition of the first kind is possible only at Fo → ∞. The friction heat consideration leads to the alteration of temperature profiles, which is due to the rise of the intervals of elevated temperatures in the zone of the maximal velocity gradients. With increasing relaxation coefficients, the smoothing of temperature profiles occurs, and at their certain high values, the fluid cooling occurs at a gradientless temperature variation along the transverse spatial variable and, consequently, the temperature proves to be dependent only on time and on longitudinal coordinate.

Plasma transport in an Eulerian AMR code

DOE PAGES

Vold, E. L.; Rauenzahn, R. M.; Aldrich, C. H.; ...

2017-04-04

A plasma transport model has been implemented in an Eulerian AMR radiation-hydrodynamics code, xRage, which includes plasma viscosity in the momentum tensor, viscous dissipation in the energy equations, and binary species mixing with consistent species mass and energy fluxes driven by concentration gradients, ion and electron baro-diffusion terms and temperature gradient forces. The physics basis, computational issues, numeric options, and results from several test problems are discussed. The transport coefficients are found to be relatively insensitive to the kinetic correction factors when the concentrations are expressed with the molar fractions and the ion mass differences are large. The contributions tomore » flow dynamics from plasma viscosity and mass diffusion were found to increase significantly as scale lengths decrease in an inertial confinement fusion relevant Kelvin-Helmholtz instability mix layer. The mixing scale lengths in the test case are on the order of 100 μm and smaller for viscous effects to appear and 10 μm or less for significant ion species diffusion, evident over durations on the order of nanoseconds. The temperature gradient driven mass flux is seen to deplete a high Z tracer ion at the ion shock front. The plasma transport model provides the generation of the atomic mix per unit of interfacial area between two species with no free parameters. The evolution of the total atomic mix then depends also on an accurate resolution or estimate of the interfacial area between the species mixing by plasma transport. High resolution simulations or a more Lagrangian-like treatment of species interfaces may be required to distinguish plasma transport and numerical diffusion in an Eulerian computation of complex and dynamically evolving mix regions.« less

Plasma transport in an Eulerian AMR code

NASA Astrophysics Data System (ADS)

Vold, E. L.; Rauenzahn, R. M.; Aldrich, C. H.; Molvig, K.; Simakov, A. N.; Haines, B. M.

2017-04-01

A plasma transport model has been implemented in an Eulerian AMR radiation-hydrodynamics code, xRage, which includes plasma viscosity in the momentum tensor, viscous dissipation in the energy equations, and binary species mixing with consistent species mass and energy fluxes driven by concentration gradients, ion and electron baro-diffusion terms and temperature gradient forces. The physics basis, computational issues, numeric options, and results from several test problems are discussed. The transport coefficients are found to be relatively insensitive to the kinetic correction factors when the concentrations are expressed with the molar fractions and the ion mass differences are large. The contributions to flow dynamics from plasma viscosity and mass diffusion were found to increase significantly as scale lengths decrease in an inertial confinement fusion relevant Kelvin-Helmholtz instability mix layer. The mixing scale lengths in the test case are on the order of 100 μm and smaller for viscous effects to appear and 10 μm or less for significant ion species diffusion, evident over durations on the order of nanoseconds. The temperature gradient driven mass flux is seen to deplete a high Z tracer ion at the ion shock front. The plasma transport model provides the generation of the atomic mix per unit of interfacial area between two species with no free parameters. The evolution of the total atomic mix then depends also on an accurate resolution or estimate of the interfacial area between the species mixing by plasma transport. High resolution simulations or a more Lagrangian-like treatment of species interfaces may be required to distinguish plasma transport and numerical diffusion in an Eulerian computation of complex and dynamically evolving mix regions.

Stationary temperature profiles in a liquid nanochannel: Comparisons between molecular-dynamics simulation and classical hydrostatics

NASA Astrophysics Data System (ADS)

Okumura, Hisashi; Heyes, David M.

2006-12-01

We compare the results of three-dimensional molecular-dynamics (MD) simulations of a Lennard-Jones (LJ) liquid with a hydrostatic (HS) solution of a high temperature liquid channel which is surrounded by a fluid at lower temperature. The maximum temperature gradient, dT/dx , between the two temperature regions ranged from ∞ (step function) to dT/dx=0.1 (in the usual LJ units). Because the systems were in stationary-nonequilibrium states with no fluid flow, both MD simulation and the HS solution gave flat profiles for the normal pressure in all temperature-gradient cases. However, the other quantities showed differences between the two methods. The MD-derived density was found to oscillate over the length of ca. 8 LJ particle diameters from the boundary plane in the system with the infinite temperature gradient, while the HS-derived density showed simply a stepwise profile. The MD simulation also showed another anomaly near the boundary in potential energy. We have found systems in which the HS treatment works well and those where the HS approach breaks down, and therefore established the minimum length scale for the HS treatment to be valid. We also compare the kinetic temperature and the configurational temperature in these systems, and show that these can differ in the transition zone between the two temperatures.

Stationary temperature profiles in a liquid nanochannel: comparisons between molecular-dynamics simulation and classical hydrostatics.

PubMed

Okumura, Hisashi; Heyes, David M

2006-12-01

We compare the results of three-dimensional molecular-dynamics (MD) simulations of a Lennard-Jones (LJ) liquid with a hydrostatic (HS) solution of a high temperature liquid channel which is surrounded by a fluid at lower temperature. The maximum temperature gradient, dT/dx , between the two temperature regions ranged from infinity (step function) to dT/dx=0.1 (in the usual LJ units). Because the systems were in stationary-nonequilibrium states with no fluid flow, both MD simulation and the HS solution gave flat profiles for the normal pressure in all temperature-gradient cases. However, the other quantities showed differences between the two methods. The MD-derived density was found to oscillate over the length of ca. 8 LJ particle diameters from the boundary plane in the system with the infinite temperature gradient, while the HS-derived density showed simply a stepwise profile. The MD simulation also showed another anomaly near the boundary in potential energy. We have found systems in which the HS treatment works well and those where the HS approach breaks down, and therefore established the minimum length scale for the HS treatment to be valid. We also compare the kinetic temperature and the configurational temperature in these systems, and show that these can differ in the transition zone between the two temperatures.

Acceleration and heating of two-fluid solar wind by Alfven waves

NASA Technical Reports Server (NTRS)

Sandbaek, Ornulf; Leer, Egil

1994-01-01

Earlier model studies of solar wind driven by thermal pressure and Alfven waves have shown that wave amplitudes of 20-30 km/s at the coronal base are sufficient to accelerate the flow to the high speeds observed in quasi-steady streams emanating from large coronal holes. We focus on the energy balance in the proton gas and show that heat conduction from the region where the waves are dissipated may play an important role in determining the proton temperature at the orbit of Earth. In models with 'classical' heat conduction we find a correlation between high flow speed, high proton temperature, and low electron temperature at 1 AU. The effect of wave heating on the development of anisotropies in the solar wind proton gas pressure is also investigated in this study.

Fast ion stabilization of the ion temperature gradient driven modes in the Joint European Torus hybrid-scenario plasmas: a trigger mechanism for internal transport barrier formation

NASA Astrophysics Data System (ADS)

Romanelli, M.; Zocco, A.; Crisanti, F.; Contributors, JET-EFDA

2010-04-01

Understanding and modelling turbulent transport in thermonuclear fusion plasmas are crucial for designing and optimizing the operational scenarios of future fusion reactors. In this context, plasmas exhibiting state transitions, such as the formation of an internal transport barrier (ITB), are particularly interesting since they can shed light on transport physics and offer the opportunity to test different turbulence suppression models. In this paper, we focus on the modelling of ITB formation in the Joint European Torus (JET) [1] hybrid-scenario plasmas, where, due to the monotonic safety factor profile, magnetic shear stabilization cannot be invoked to explain the transition. The turbulence suppression mechanism investigated here relies on the increase in the plasma pressure gradient in the presence of a minority of energetic ions. Microstability analysis of the ion temperature gradient driven modes (ITG) in the presence of a fast-hydrogen minority shows that energetic ions accelerated by the ion cyclotron resonance heating (ICRH) system (hydrogen, nH,fast/nD,thermal up to 10%, TH,fast/TD,thermal up to 30) can increase the pressure gradient enough to stabilize the ITG modes driven by the gradient of the thermal ions (deuterium). Numerical analysis shows that, by increasing the temperature of the energetic ions, electrostatic ITG modes are gradually replaced by nearly electrostatic modes with tearing parity at progressively longer wavelengths. The growth rate of the microtearing modes is found to be lower than that of the ITG modes and comparable to the local E × B-velocity shearing rate. The above mechanism is proposed as a possible trigger for the formation of ITBs in this type of discharges.

Accumulation of Colloidal Particles in Flow Junctions Induced by Fluid Flow and Diffusiophoresis

NASA Astrophysics Data System (ADS)

Shin, Sangwoo; Ault, Jesse T.; Warren, Patrick B.; Stone, Howard A.

2017-10-01

The flow of solutions containing solutes and colloidal particles in porous media is widely found in systems including underground aquifers, hydraulic fractures, estuarine or coastal habitats, water filtration systems, etc. In such systems, solute gradients occur when there is a local change in the solute concentration. While the effects of solute gradients have been found to be important for many applications, we observe an unexpected colloidal behavior in porous media driven by the combination of solute gradients and the fluid flow. When two flows with different solute concentrations are in contact near a junction, a sharp solute gradient is formed at the interface, which may allow strong diffusiophoresis of the particles directed against the flow. Consequently, the particles accumulate near the pore entrance, rapidly approaching the packing limit. These colloidal dynamics have important implications for the clogging of a porous medium, where particles that are orders of magnitude smaller than the pore width can accumulate and block the pores within a short period of time. We also show that this effect can be exploited as a useful tool for preconcentrating biomolecules for rapid bioassays.

Ultrasound Thermal Field Imaging of Opaque Fluids

NASA Technical Reports Server (NTRS)

Andereck, C. David

1999-01-01

We have initiated an experimental program to develop an ultrasound system for non-intrusively imaging the thermal field in opaque fluids under an externally imposed temperature gradient. Many industrial processes involve opaque fluids, such as molten metals, semiconductors, and polymers, often in situations in which thermal gradients are important. For example, one may wish to understand semiconductor crystal growth dynamics in a Bridgman apparatus. Destructive testing of the crystal after the process is completed gives only indirect information about the fluid dynamics of the formation process. Knowledge of the coupled thermal and velocity fields during the growth process is then essential. Most techniques for non-intrusive velocity and temperature measurement in fluids are optical in nature, and hence the fluids studied must be transparent. In some cases (for example, LDV (laser Doppler velocimetry) and PIV (particle imaging velocimetry)) the velocities of small neutrally buoyant seed particles suspended in the fluid, are measured. Without particle seeding one can use the variation of the index of refraction of the fluid with temperature to visualize, through interferometric, Schlieren or shadowgraph techniques, the thermal field. The thermal field in turn gives a picture of the pattern existing in the fluid. If the object of study is opaque, non-optical techniques must be used. In this project we focus on the use of ultrasound, which propagates easily through opaque liquids and solids. To date ultrasound measurements have almost exclusively relied on the detection of sound scattered from density discontinuities inside the opaque material of interest. In most cases it has been used to visualize structural properties, but more recently the ultrasound Doppler velocimeter has become available. As in the optical case, it relies on seed particles that scatter Doppler shifted sound back to the detector. Doppler ultrasound techniques are, however, not useful for studying convective fluid flow in crystal growth, because particle seeding is unacceptable and flow velocities are typically too low to be resolved, and may be even lower in microgravity conditions where buoyancy forces are negligible. We will investigate a different use of ultrasound to probe the flows of opaque fluids non-intrusively and without the use of seed particles: our goal is to ultrasonically visualize the thermal field of opaque fluids with relatively high spatial resolution. The proposed technique relies upon the variation of sound speed with temperature of the fluid. A high frequency ultra-sound pulse passing through a fluid-filled chamber will traverse the chamber in a time determined by the relevant chamber dimension and the temperature of the fluid through which the pulse passes. With high time-resolution instrumentation that compares the excitation signal with the received pulse we can detect the influence of the fluid temperature on the pulse travel time. This is effectively an interferometric system, which in its optical form is an extremely sensitive approach to measuring thermal fields in fluids. Moreover, the temperature dependence of sound velocity in liquid metals is comparable to the temperature dependence of the speed of light required for accurate interferometric thermal images in transparent fluids. With an array of transducers scanned electronically a map of the thermal field over the chamber could be produced. An alternative approach would be to use the ultrasound analog of the shadowgraph technique. In the optical version, collimated light passes through the fluid, where it is focused or defocused locally by temperature field induced variations of the index of refraction. The resulting image reveals the thermal field through the spatial pattern of light intensity variations. By analogy, an ultrasound plane wave traversing an opaque fluid sample would be also locally focused or defocused depending on the speed of sound variations, giving rise to spatial variations in sound intensity that will reveal the thermal field pattern. These approaches could be applied to any situation in which temperature differences are expected to occur, and will rapidly provide information about the flow that simply cannot be obtained by any current intrusive or non-intrusive diagnostic technique. As materials processing in microgravity matures it will become increasingly important to have available simple and versatile diagnostic tools, such as we will develop, for studying the flows of opaque fluids under thermal forcing.

Theoretical transport modeling of Ohmic cold pulse experiments

NASA Astrophysics Data System (ADS)

Kinsey, J. E.; Waltz, R. E.; St. John, H. E.

1998-11-01

The response of several theory-based transport models in Ohmically heated tokamak discharges to rapid edge cooling due to trace impurity injection is studied. Results are presented for the Institute for Fusion Studies—Princeton Plasma Physics Laboratory (IFS/PPPL), gyro-Landau-fluid (GLF23), Multi-mode (MM), and the Itoh-Itoh-Fukuyama (IIF) transport models with an emphasis on results from the Texas Experimental Tokamak (TEXT) [K. W. Gentle, Nucl. Technol./Fusion 1, 479 (1981)]. It is found that critical gradient models containing a strong ion and electron temperature ratio dependence can exhibit behavior that is qualitatively consistent with experimental observation while depending solely on local parameters. The IFS/PPPL model yields the strongest response and demonstrates both rapid radial pulse propagation and a noticeable increase in the central electron temperature following a cold edge temperature pulse (amplitude reversal). Furthermore, the amplitude reversal effect is predicted to diminish with increasing electron density and auxiliary heating in agreement with experimental data. An Ohmic pulse heating effect due to rearrangement of the current profile is shown to contribute to the rise in the core electron temperature in TEXT, but not in the Joint European Tokamak (JET) [A. Tanga and the JET Team, in Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 65] and the Tokamak Fusion Test Reactor (TFTR) [R. J. Hawryluk, V. Arunsalam, M. G. Bell et al., in Plasma Physics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 51]. While this phenomenon is not necessarily a unique signature of a critical gradient, there is sufficient evidence suggesting that the apparent plasma response to edge cooling may not require any underlying nonlocal mechanism and may be explained within the context of the intrinsic properties of electrostatic drift wave-based models.

Superfluid helium sloshing dynamics induced oscillations and fluctuations of angular momentum, force and moment actuated on spacecraft driven by gravity gradient or jitter acceleration associated with slew motion

NASA Technical Reports Server (NTRS)

Hung, R. J.

1994-01-01

The generalized mathematical formulation of sloshing dynamics for partially filled liquid of cryogenic superfluid helium II in dewar containers driven by the gravity gradient and jitter accelerations associated with slew motion for the purpose to perform scientific observation during the normal spacecraft operation are investigated. An example is given with the Advanced X-Ray Astrophysics Facility-Spectroscopy (AXAF-S) for slew motion which is responsible for the sloshing dynamics. The jitter accelerations include slew motion, spinning motion, atmospheric drag on the spacecraft, spacecraft attitude motions arising from machinery vibrations, thruster firing, pointing control of spacecraft, crew motion, etc. Explicit mathematical expressions to cover these forces acting on the spacecraft fluid systems are derived. The numerical computation of sloshing dynamics is based on the non-inertia frame spacecraft bound coordinate, and solve time-dependent, three-dimensional formulations of partial differential equations subject to initial and boundary conditions. The explicit mathematical expressions of boundary conditions to cover capillary force effect on the liquid-vapor interface in microgravity environments are also derived. The formulations of fluid moment and angular moment fluctuations in fluid profiles induced by the sloshing dynamics, together with fluid stress and moment fluctuations exerted on the spacecraft dewar containers have also been derived. Examples are also given for cases applicable to the AXAF-S spacecraft sloshing dynamics associated with slew motion.

B2.5-Eirene modeling of radial transport in the MAGPIE linear plasma device

NASA Astrophysics Data System (ADS)

Owen, L. W.; Caneses, J. F.; Canik, J.; Lore, J. D.; Corr, C.; Blackwell, B.; Bonnin, X.; Rapp, J.

2017-05-01

Radial transport in helicon heated hydrogen plasmas in the MAGnetized Plasma Interaction Experiment (MAGPIE) is studied with the B2.5-Eirene (SOLPS5.0) code. Radial distributions of plasma density, temperature and ambipolar potential are computed for several magnetic field configurations and compared to double Langmuir probe measurements. Evidence for an unmagnetized ion population is seen in the requirement for a convective pinch term in the continuity equation in order to fit the centrally peaked density profile data. The measured slightly hollow electron temperature profiles are reproduced with combinations of on-axis and edge heating which can be interpreted as helicon and Trivelpiece-Gould wave absorption, respectively. Pressure gradient driven radial charged particle diffusion is chosen to describe the diffusive particle flux since the hollowness of the temperature profiles assists the establishment of on-axis density peaking.

Testing thermal gradient driving force for grain boundary migration using molecular dynamics simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bai, Xian-Ming; Zhang, Yongfeng; Tonks, Michael R.

2015-02-01

Strong thermal gradients in low-thermal-conductivity ceramics may drive extended defects, such as grain boundaries and voids, to migrate in preferential directions. In this work, molecular dynamics simulations are conducted to study thermal gradient driven grain boundary migration and to verify a previously proposed thermal gradient driving force equation, using uranium dioxide as a model system. It is found that a thermal gradient drives grain boundaries to migrate up the gradient and the migration velocity increases under a constant gradient owing to the increase in mobility with temperature. Different grain boundaries migrate at very different rates due to their different intrinsicmore » mobilities. The extracted mobilities from the thermal gradient driven simulations are compared with those calculated from two other well-established methods and good agreement between the three different methods is found, demonstrating that the theoretical equation of the thermal gradient driving force is valid, although a correction of one input parameter should be made. The discrepancy in the grain boundary mobilities between modeling and experiments is also discussed.« less

Rapid concentration of deoxyribonucleic acid via Joule heating induced temperature gradient focusing in poly-dimethylsiloxane microfluidic channel.

PubMed

Ge, Zhengwei; Wang, Wei; Yang, Chun

2015-02-09

This paper reports rapid microfluidic electrokinetic concentration of deoxyribonucleic acid (DNA) with the Joule heating induced temperature gradient focusing (TGF) by using our proposed combined AC and DC electric field technique. A peak of 480-fold concentration enhancement of DNA sample is achieved within 40s in a simple poly-dimethylsiloxane (PDMS) microfluidic channel of a sudden expansion in cross-section. Compared to a sole DC field, the introduction of an AC field can reduce DC field induced back-pressure and produce sufficient Joule heating effects, resulting in higher concentration enhancement. Within such microfluidic channel structure, negative charged DNA analytes can be concentrated at a location where the DNA electrophoretic motion is balanced with the bulk flow driven by DC electroosmosis under an appropriate temperature gradient field. A numerical model accounting for a combined AC and DC field and back-pressure driven flow effects is developed to describe the complex Joule heating induced TGF processes. The experimental observation of DNA concentration phenomena can be explained by the numerical model. Copyright © 2014 Elsevier B.V. All rights reserved.

Advanced computation for modeling fluid-solid dynamics in subduction zones

NASA Astrophysics Data System (ADS)

Spiegelman, Marc; Wilson, Cian; van Keken, Peter; Kelemen, Peter; Hacker, Bradley

2014-05-01

Arc volcanism associated with subduction is generally considered to occur by a process where hydrous fluids are released from the slab, interact with the overlying mantle wedge to produce silicate rich magmas which are then transported to the arc. However, the quantitative details of fluid release, migration, melt generation and transport in the wedge remain poorly understood. In particular, there are two fundamental observations that defy quantitative modeling. The first is the location of the volcanic front with respect to intermediate depth earthquakes (e.g. 100 ± 40 km). This observation is remarkably robust yet insensitive to subduction parameters. This contrasts with new estimates on the variability of fluid release in global subduction zones which suggest a significant sensitivity of fluid release to slab thermal conditions. Reconciling these results implies some mechanism for focusing fluids and/or melts toward the wedge corner. The second observation is the global existence of thermally hot erupted basalts and andesites that, if derived from flux melting of the mantle requires sub-arc mantle temperatures of 1300 degrees C over shallow pressures of 1-2 GPa comparable to P-T estimates for the dry solidus beneath mid-ocean ridges. These observations impose significant challenges for geodynamic models of subduction zones, and in particular for those that do not include the explicit transport of fluids and melts. We present a range of high-resolution models that include a more complete description of coupled fluid and solid mechanics (allowing the fluid to interact with solid rheological variations) together with rheologically consistent solution for temperature and solid flow. We discuss how successful these interactions are at focusing both fluids and hot solids to sub-arc regions worldwide. We also evaluate the efficacy of current wet melting parameterizations in these models. When driven by buoyancy alone, fluid migrates through the mantle wedge along nearly vertical trajectories. Only interactions with the solid flow at very low values of permeability or high values of fluid viscosity can cause deviations from this path. However, in a viscous, permeable medium, additional pressure gradients are generated by volumetric deformation due to variations in fluid flux. These pressure gradients can significantly modify the fluid flow paths. At shallow depths, compaction channels form along the rheological contrast with the overriding plate while in the mantle wedge itself porosity waves concentrate the fluid. When considering multiple, distributed sources of fluid, as predicted by thermodynamic models, interaction between layers in the slab itself can also cause significant focusing. As well as permeability, rheological controls and numerical regularizations place upper and lower bounds on the length-scales over which such interactions occur further modifying the degree of focusing seen. The wide range of behaviors described here is modeled using TerraFERMA (the Transparent Finite Element Rapid Model Assembler), which harnesses the advanced computational libraries FEniCS, PETSc and SPuD to provide the a flexible computational framework for exploring coupled multi-physics problems.

Advances in the simulation of toroidal gyro-Landau fluid model turbulence

NASA Astrophysics Data System (ADS)

Waltz, R. E.; Kerbel, G. D.; Milovich, J.; Hammett, G. W.

1995-06-01

The gyro-Landau fluid (GLF) model equations for toroidal geometry [R. E. Waltz, R. R. Dominguez, and G. W. Hammett, Phys. Fluids B 4, 3138 (1992)] have been recently applied to study ion temperature gradient (ITG) mode turbulence using the three-dimensional (3-D) nonlinear ballooning mode representation (BMR) outlined earlier [R. E. Waltz, G. D. Kerbel, and J. Milovich, Phys. Plasmas 1, 2229 (1994)]. The present paper extends this work by treating some unresolved issues concerning ITG turbulence with adiabatic electrons. Although eddies are highly elongated in the radial direction, long time radial correlation lengths are short and comparable to poloidal lengths. Although transport at vanishing shear is not particularly large, transport at reverse global shear, is significantly less. Electrostatic transport at moderate shear is not much affected by inclusion of local shear and average favorable curvature. Transport is suppressed when critical E×B rotational shear is comparable to the maximum linear growth rate with only a weak dependence on magnetic shear. Self-consistent turbulent transport of toroidal momentum can result in a transport bifurcation at sufficiently large r/(Rq). However, the main thrust of the new formulation in the paper deals with advances in the development of finite beta GLF models with trapped electrons and BMR numerical methods for treating the fast parallel field motion of the untrapped electrons.

Intra-slab COH fluid fluxes evidenced by fluid-mediated decarbonation of lawsonite eclogite-facies altered oceanic metabasalts

NASA Astrophysics Data System (ADS)

Vitale Brovarone, Alberto; Chu, Xu; Martin, Laure; Ague, Jay J.; Monié, Patrick; Groppo, Chiara; Martinez, Isabelle; Chaduteau, Carine

2018-04-01

The interplay between the processes controlling the mobility of H2O and C-bearing species during subduction zone metamorphism exerts a critical control on plate tectonics and global volatile recycling. Here we present the first study on fresh, carbonate-bearing, lawsonite eclogite-facies metabasalts from Alpine Corsica, France, which reached the critical depths at which important devolatilization reactions occur in subducting slabs. The studied samples indicate that the evolution of oceanic crustal sequences subducted under present-day thermal regimes is dominated by localized fluid-rock interactions that are strongly controlled by the nature and extent of inherited (sub)seafloor hydrothermal processes, and by the possibility of deep fluids to be channelized along inherited or newly-formed discontinuities. Fluid channelization along inherited discontinuities controlled local rehydration and dehydration/decarbonation reactions and the stability of carbonate and silicate minerals at the blueschist-eclogite transition. Fluid-mediated decarbonation was driven by upward, up-temperature fluid flow in the inverted geothermal gradient of a subducting oceanic slab, a process that has not been documented in natural samples to date. We estimate that the observed fluid-rock reactions released 20-60 kg CO2 per m3 of rock (i.e. 0.7-2.1 wt% CO2), which is in line with the values predicted from decarbonation of metabasalts in open systems at these depths. Conversely, the estimated time-integrated fluid fluxes (20-50 t/m2) indicate that the amount of carbon transported by channelized fluid flow within the volcanic part of subducting oceanic plates is potentially much higher than previous numerical estimates, testifying to the percolation of C-bearing fluids resulting from devolatilization/dissolution processes operative in large reservoirs.

Properties of two-fluid flowing equilibria observed in double-pulsing coaxial helicity injection on HIST

NASA Astrophysics Data System (ADS)

Kanki, T.; Nagata, M.

2013-10-01

Multi-pulsing coaxial helicity injection (M-CHI) method which aims to achieve both quasi-steady sustainment and good confinement has been proposed as a refluxing scenario of the CHI. To explore the usefulness of the M-CHI for spherical torus (ST) configurations, the double-pulsing operations have been carried out in the HIST, verifying the flux amplification and the formation of the closed flux surfaces after the second CHI pulse. The purpose of this study is to investigate the properties of the magnetic field and plasma flow structures during the sustainment by comparing the results of plasma flow, density, and magnetic fields measurements with those of two-fluid equilibrium calculations. The two-fluid flowing equilibrium model which is described by a pair of generalized Grad-Shafranov equations for ion and electron surface variables and Bernoulli equations for density is applied to reconstruct the ST configuration with poloidal flow shear observed in the HIST. Due to the negative steep density gradient in high field side, the toroidal field has a diamagnetic profile (volume average beta, < β > = 68 %) in the central open flux column region. The ion flow velocity with strong flow shear from the separatrix in the inboard side to the core region is the opposite direction to the electron flow velocity due to the diamagentic drift through the density gradient. The electric field is relatively small in the whole region, and thus the Lorentz force nearly balances with the two-fluid effect which is particularly significant in a region with the steep density gradient due to the ion and electron diamagnetic drifts.

Ion microprobe analysis of {sup 18}O/{sup 16}O in authigenic and detrital quartz in the St. Peter Sandstone, Michigan Basin and Wisconsin Arch, USA: Contrasting diagenetic histories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Graham, C.M.; Valley, J.W.; Winter, B.L.

1996-12-01

The oxygen isotopic compositions of authigenic quartz cements in sandstones provide a monitor of the temperatures, compositions, and origins of pore-occluding fluids during diagenesis, but quartz overgrowths are too fine-grained to be amenable to conventional isotopic analysis. We have used a Cameca ims-4f ion microprobe to determine oxygen isotopic variations in authigenic and detrital quartz in four samples of the Ordovician St. Peter Sandstone from the Michigan Basin and Wisconsin Arch, midwestern USA. Ion microprobe isotopic analyses have been successfully accomplished with an internal precision of {+-}1{per_thousand} (1{sigma}) and a spatial resolution of 20-30 {mu}m at low mass resolution usingmore » a high voltage offset technique. Repeated analyses of the quartz standard demonstrate a reproducibility of close to {+-}1{per_thousand} (1 sd) in good agreement with that expected from counting statistics. Conventional and ion microprobe analyses are mutually consistent, supporting the accuracy of the ion microprobe analyses. Within-sample isotopic variations of up to 13{per_thousand} and micro-scale isotopic variations of at least 4{per_thousand} over a distance of 100 {mu}m have been measured within quartz overgrowths in a sandstone from the Wisconsin Arch. Overgrowths are uniformly higher in {delta}{sup 18}O than detrital grains, and gradients of up to 25% exist across a few microns. {sup 18}O-enriched quartz overgrowths in sandstones from the Wisconsin Arch show complex CL zonation and reflect one of two possible processes: (1) low-temperature quartz precipitation during mixing of meteoric waters with upwelling basinal fluids; (2) higher temperature quartz precipitation during episodic gravity-driven upwelling of warm basinal fluids (of comparable isotopic composition to Michigan Basin fluids) from the Illinois Basin, related to evolution of Mississippi Valley type Pb-Zn ore-forming fluids. 59 refs., 7 figs., 4 tabs.« less

Modeling dynamic plasmas driven by ultraintense nano-focused x-ray laser pulses in solid iron targets

NASA Astrophysics Data System (ADS)

Royle, Ryan; Sentoku, Yasuhiko; Mancini, Roberto

2017-10-01

The hard x-ray free electron laser has proven to be a valuable tool for high energy density (HED) physics as it is able to produce well-characterized samples of HED matter at exactly solid density and homogeneous temperatures. However, if the x-ray pulses are focused to sub-micron spot sizes, where peak intensities can exceed 1020 W/cm2, the plasmas driven by sources of non-thermal photoelectrons and Auger electrons can be highly dynamic and so cannot be modeled by atomic kinetics or fluid codes. We apply the 2D/3D particle-in-cell code, PICLS-which has been extended with numerous physics models to enable the simulation of XFEL-driven plasmas-to the modeling of such dynamic plasmas driven by nano-focused XFEL pulses in solid iron targets. In the case of the smallest focal spot investigated of just 100 nm in diameter, keV plasmas induce strong radial E-fields that accelerate keV ions radially as well as sheath fields that accelerate surface ions to hundreds of keV. The heated spot, which is initially larger than the laser spot due to the kinetic nature of the fast Auger electrons, expands as ion and electron waves propagate radially, leaving a low density region along the laser axis. This research was supported by the US DOE-OFES under Grant No. DE-SC0008827, the DOE-NNSA under Grant No. DE-NA0002075, and the JSPS KAKENHI under Grant No. JP15K21767.

Perturbative tests of theoretical transport models using cold pulse and modulated electron cyclotron heating experiments

NASA Astrophysics Data System (ADS)

Kinsey, J. E.; Waltz, R. E.; DeBoo, J. C.

1999-05-01

It is difficult to discriminate between various tokamak transport models using standardized statistical measures to assess the goodness of fit with steady-state density and temperature profiles in tokamaks. This motivates consideration of transient transport experiments as a technique for testing the temporal response predicted by models. Results are presented comparing the predictions from the Institute for Fusion Studies—Princeton Plasma Physics Laboratory (IFS/PPPL), gyro-Landau-fluid (GLF23), Multi-mode (MM), Current Diffusive Ballooning Mode (CDBM), and Mixed-shear (MS) transport models against data from ohmic cold pulse and modulated electron cyclotron heating (ECH) experiments. In ohmically heated discharges with rapid edge cooling due to trace impurity injection, it is found that critical gradient models containing a strong temperature ratio (Ti/Te) dependence can exhibit behavior that is qualitatively consistent both spatially and temporally with experimental observation while depending solely on local parameters. On the DIII-D tokamak [J. L. Luxon and L. G. Davis, Fusion Technol. 8, 441 (1985)], off-axis modulated ECH experiments have been conducted in L-mode (low confinement mode) and the perturbed electron and ion temperature response to multiple heat pulses has been measured across the plasma core. Comparing the predicted Fourier phase of the temperature perturbations, it is found that no single model yielded agreement with both electron and ion phases for all cases. In general, it was found that the IFS/PPPL, GLF23, and MS models agreed well with the ion response, but not with the electron response. The CDBM and MM models agreed well with the electron response, but not with the ion response. For both types of transient experiments, temperature coupling between the electron and ion transport is found to be an essential feature needed in the models for reproducing the observed perturbative response.

Multiscale interaction between a large scale magnetic island and small scale turbulence

NASA Astrophysics Data System (ADS)

Choi, M. J.; Kim, J.; Kwon, J.-M.; Park, H. K.; In, Y.; Lee, W.; Lee, K. D.; Yun, G. S.; Lee, J.; Kim, M.; Ko, W.-H.; Lee, J. H.; Park, Y. S.; Na, Y.-S.; Luhmann, N. C., Jr.; Park, B. H.

2017-12-01

Multiscale interaction between the magnetic island and turbulence has been demonstrated through simultaneous two-dimensional measurements of turbulence and temperature and flow profiles. The magnetic island and turbulence can mutually interact via coupling between the electron temperature (T e ) gradient, the T e turbulence, and the poloidal flow. The T e gradient altered by the magnetic island steepens outside and flattens inside the island. The T e turbulence can appear in increased T e gradient regions. The combined effects of the T e gradient and the poloidal flow shear determines the two-dimensional distribution of the T e turbulence. When the poloidal vortex flow forms, it can maintain the steepest T e gradient and the magnetic island acts more like an electron heat transport barrier. Interestingly, when the T e gradient, the T e turbulence, and the vortex flow shear increase beyond critical levels, the magnetic island turns into a fast electron heat transport channel, which directly leads to the minor disruption.

Nonlinear responses of chiral fluids from kinetic theory

NASA Astrophysics Data System (ADS)

Hidaka, Yoshimasa; Pu, Shi; Yang, Di-Lun

2018-01-01

The second-order nonlinear responses of inviscid chiral fluids near local equilibrium are investigated by applying the chiral kinetic theory (CKT) incorporating side-jump effects. It is shown that the local equilibrium distribution function can be nontrivially introduced in a comoving frame with respect to the fluid velocity when the quantum corrections in collisions are involved. For the study of anomalous transport, contributions from both quantum corrections in anomalous hydrodynamic equations of motion and those from the CKT and Wigner functions are considered under the relaxation-time (RT) approximation, which result in anomalous charge Hall currents propagating along the cross product of the background electric field and the temperature (or chemical-potential) gradient and of the temperature and chemical-potential gradients. On the other hand, the nonlinear quantum correction on the charge density vanishes in the classical RT approximation, which in fact satisfies the matching condition given by the anomalous equation obtained from the CKT.

Electron temperature response to ECRH on FTU tokamak in transient conditions.

NASA Astrophysics Data System (ADS)

Jacchia, A.; Bruschi, A.; Cirant, S.; Granucci, G.; Sozzi, C.; de Luca, F.; Amadeo, P.; Bracco, G.; Tudisco, O.

2001-10-01

Steady-state electron heat transport analysis of FTU high density plasmas under Electron Cyclotron Heating (ECRH) shows "stiff" electron temperature profiles [1,2,3]. Plasma response to off-axis EC heating, in fact, exibits a lower limit to electron temperature gradient length, Lc , below which electron thermal conductivity switches to higher values. Stiffness, however, is attenuated in the plasma core of saw-tooth free discharges with flat-hollow temperature profile and during current ramp-up [3,4,5], in which cases the temperature gradient length can be brought to very low values by means of on-axis ECH. Steady and current ramp-up discharges probed by steady and modulated ECH are analyzed in terms of stiffnes. Critical gradient length dependence on local features of computed current density profile is discussed. [1] Sozzi, C. et al., Paper EXP5/13, Plasma Phys. Contr. Fus. Res., Proc.18th IAEA Conf., Sorrento, 2000. [2] Jacchia, A. et al. Topical Conference on Radio Frequency Power in Plasmas, Oxnard, USA, (2001). [3] Cirant, S. et al. Topical Conference on Radio Frequency Power in Plasmas, Oxnard, USA, (2001). [4] Sozzi, C. et al., EPS, Madeira 2001. [5] Bracco, G. et al.,Plasma Phys. Contr. Fus. Res., Proc.18th IAEA Conf., Sorrento, 2000.

Theoretical analysis of non-linear Joule heating effects over an electro-thermal patterned flow

NASA Astrophysics Data System (ADS)

Sanchez, Salvador; Ascanio, Gabriel; Mendez, Federico; Bautista, Oscar

2017-11-01

In this work, non-linear Joule heating effects for electro-thermal patterned flows driven inside of a slit microchannel are analyzed. Here, the movement of fluids is controlled by placing electro-thermal forces, which are generated through an imposed longitudinal electric field, E0, and the wall electric potential produced by electrodes inserted along the surface of the microchannel wall, ζ. For this analysis, viscosity and electrical conductivity of fluids are included as known functions, which depend on the temperature; therefore, in order to determine the flow, temperature and electric potential fields together with its simultaneous interactions, the equations of continuity, momentum, energy, charges distribution and electrical current have to be solved in a coupled manner. The main results obtained in the study reveal that with the presence of thermal gradients along of the microchannel, local electro-thermal forces, Fχ, are affected in a sensible manner, and consequently, the flow field is modified substantially, causing the interruption or intensification of recirculations along of the microchannel. This work was supported by the Fondo SEP-CONACYT through research Grants No. 220900 and 20171181 from SIP-IPN. F. Mendez acknowledges support from PAPIIT-UNAM under Contract Number IN112215. S. Sanchez thanks to DGAPA-UNAM for the postdoctoral fellowship.

Numerical Study of g-Jitter Induced Double-Diffusive Convection

NASA Technical Reports Server (NTRS)

Shu, Y.; Li, B. Q.; deGroh, Henry C.

2001-01-01

A finite element study is presented of double-diffusive convection driven by g-jitter in a microgravity environment. Mathematical formulations are presented and extensive simulations are carried out for g-jitter induced fluid flow, temperature distribution, and solutal transport in an alloy system under consideration for space flights. Computations include the use of idealized single-frequency and multi-frequency g-jitter as well as the real g-jitter data taken during an actual Space Shuttle fight. Little correlation is seen between these velocity components for the g-jitter components studied. The temperature field is basically undisturbed by convection because of a small Pr number for the fluid. The disturbance of the concentration field, however, is pronounced, and the local variation of the concentration follows the velocity oscillation in time. It is found that although the concentration field varies in both position and time, the local concentration gradient remains approximately constant in time. Numerical study further indicates that with an increase in g-jitter force (or amplitude), the nonlinear convective effects become much more obvious, which in turn drastically change the concentration fields. The simulated results computed using the g-jitter data taken during space flights show that both the velocity and concentration become random, following approximately the same pattern as the g-jitter perturbations.

Magnetic effect for electrochemically driven cellular convection.

PubMed

Nakabayashi, S; Inokuma, K; Karantonis, A

1999-06-01

Hydrodynamic instability analogous to Rayleigh-Bénard convection is observed in an electrolytic solution between two parallel copper wire electrodes. The laser interferometric technique can reveal the dissipation structure created by the motion of the fluid, which is controlled electrochemically. It is shown that under the presence of horizontal magnetic field the roll cells move horizontally along the electrodes. The electrochemically driven convection is simply controlled and monitored by setting and measuring the electrochemical parameters and forms many kinds of spatiotemporal patterns, especially under the magnetic field. The phenomenon is modeled by considering a Boussinesq fluid under a concentration gradient. The stability of the resulting equations is studied by linear stability analysis. The time dependent nonlinear system is investigated numerically and the main features of the experimental response are reproduced.

Marangoni-driven chemotaxis, chemotactic collapse, and the Keller-Segel equation

NASA Astrophysics Data System (ADS)

Shelley, Michael; Masoud, Hassan

2013-11-01

Almost by definition, chemotaxis involves the biased motion of motile particles along gradients of a chemical concentration field. Perhaps the most famous model for collective chemotaxis in mathematical biology is the Keller-Segel model, conceived to describe collective aggregation of slime mold colonies in response to an intrinsically produced, and diffusing, chemo-attractant. Heavily studied, particularly in 2D where the system is ``super-critical'', it has been proved that the KS model can develop finite-time singularities - so-called chemotactic collapse - of delta-function type. Here, we study the collective dynamics of immotile particles bound to a 2D interface above a 3D fluid. These particles are chemically active and produce a diffusing field that creates surface-tension gradients along the surface. The resultant Marangoni stresses create flows that carry the particles, possibly concentrating them. Remarkably, we show that this system involving 3D diffusion and fluid dynamics, exactly yields the 2D Keller-Segel model for the surface-flow of active particles. We discuss the consequences of collapse on the 3D fluid dynamics, and generalizations of the fluid-dynamical model.

The flow patterning capability of localized natural convection.

PubMed

Huang, Ling-Ting; Chao, Ling

2016-09-14

Controlling flow patterns to align materials can have various applications in optics, electronics, and biosciences. In this study, we developed a natural-convection-based method to create desirable spatial flow patterns by controlling the locations of heat sources. Fluid motion in natural convection is induced by the spatial fluid density gradient that is caused by the established spatial temperature gradient. To analyze the patterning resolution capability of this method, we used a mathematical model combined with nondimensionalization to correlate the flow patterning resolution with experimental operating conditions. The nondimensionalized model suggests that the flow pattern and resolution is only influenced by two dimensionless parameters, and , where Gr is the Grashof number, representing the ratio of buoyancy to the viscous force acting on a fluid, and Pr is the Prandtl number, representing the ratio of momentum diffusivity to thermal diffusivity. We used the model to examine all of the flow behaviors in a wide range of the two dimensionless parameter group and proposed a flow pattern state diagram which suggests a suitable range of operating conditions for flow patterning. In addition, we developed a heating wire with an angular configuration, which enabled us to efficiently examine the pattern resolution capability numerically and experimentally. Consistent resolutions were obtained between the experimental results and model predictions, suggesting that the state diagram and the identified operating range can be used for further application.

Trace Element Geochemistry of Magnetite and Accesory Phases from El Romeral Iron Oxide-Apatite Deposit, Northern Chile

NASA Astrophysics Data System (ADS)

Barra, F.; Rojas, P.; Reich, M.; Deditius, A.; Simon, A. C.

2017-12-01

Iron oxide-apatite (IOA) or "Kiruna-type" deposits are an important source of Fe, P, REE, among other essential elements for society. Three main hypotheses have been proposed to explain the genesis of these controversial deposits, which invoke liquid immiscibility, hydrothermal replacement or a magmatic-hydrothermal origin driven by flotation of magnetite-bubble pairs. Here we focus on the El Romeral, one of the largest IOA deposits located in the southernmost part of the Cretaceous Chilean Iron Belt. We combined SEM observations and EMPA analyses of magnetite, actinolite, pyrite, and apatite, with micro-Raman determinations of mineral inclusions within magnetite grains. Two textural types of magnetite were identified at El Romeral: (i) inclusion-rich magnetite (Mag I), and (ii) inclusion-poor magnetite (Mag II) that are commonly surrounding the inclusion-rich Mag I grains. Mag I is characterized by high V ( 2500-2800 ppm) and Ti (300-1000 ppm) contents with high-temperature mineral inclusions such as ilmenite, Ti-pargasite and clinochlore at depth, and quartz and phlogopite inclusions in shallower samples. These characteristics are consistent with a magmatic origin for Mag I. Inclusion-poor magnetite (Mag II) have high V (2400-2600 ppm) and lower Ti (70-200 ppm) contents than Mag I, which point to chemical changes of the mineralizing fluid(s). An increase in thermal gradient with depth is evidenced by the presence of high-temperature (low #Fe) actinolite, as well as F-rich apatite and pyrite with high Co:Ni (>1) in the deep zones. In contrast, lower Co:Ni ratios (<0.5) in pyrite and higher Cl contents in OH-rich apatite are detected in samples from shallower levels. This vertical chemical variation supports a magmatic-hydrothermal origin for the El Romeral deposit, and point to compositional changes driven by decompression of a magnetite-fluid suspension.

Base flow-driven shifts in tropical stream temperature regimes across a mean annual rainfall gradient

Treesearch

Ayron M. Strauch; Richard A. MacKenzie; Ralph W. Tingley

2017-01-01

Climate change is expected to affect air temperature and watershed hydrology, but the degree to which these concurrent changes affect stream temperature is not well documented in the tropics. How stream temperature varies over time under changing hydrologic conditions is difficult to isolate from seasonal changes in air temperature. Groundwater and bank storage...

The wavelength of supercritical surface tension driven Benard convection

NASA Technical Reports Server (NTRS)

Koschmieder, E. L.

1991-01-01

The size or the wavelength of moderately supercritical surface tension driven Benard convection has been investigated experimentally in a thin fluid layer of large aspect ratio. It has been found that the number of the hexagonal convection cells increases with increased temperature differences, up to 1.3 times the critical temperature difference. That means that the wavelength of surface tension driven convection decreases after onset of the instability for moderately nonlinear conditions. This result is in striking contrast to the well-known increase of the wavelength of buoyancy driven Rayleigh-Benard convection.

Analysis of Heat Transfer Phenomenon in Magnetohydrodynamic Casson Fluid Flow Through Cattaneo-Christov Heat Diffusion Theory

NASA Astrophysics Data System (ADS)

Ramesh, G. K.; Gireesha, B. J.; Shehzad, S. A.; Abbasi, F. M.

2017-07-01

Heat transport phenomenon of two-dimensional magnetohydrodynamic Casson fluid flow by employing Cattaneo-Christov heat diffusion theory is described in this work. The term of heat absorption/generation is incorporated in the mathematical modeling of present flow problem. The governing mathematical expressions are solved for velocity and temperature profiles using RKF 45 method along with shooting technique. The importance of arising nonlinear quantities namely velocity, temperature, skin-friction and temperature gradient are elaborated via plots. It is explored that the Casson parameter retarded the liquid velocity while it enhances the fluid temperature. Further, we noted that temperature and thickness of temperature boundary layer are weaker in case of Cattaneo-Christov heat diffusion model when matched with the profiles obtained for Fourier’s theory of heat flux.

Mixed convection of nanofluids in a lid-driven rough cavity

NASA Astrophysics Data System (ADS)

Guo, Zhimeng; Wang, Jinyu; Mozumder, Aloke K.; Das, Prodip K.

2017-06-01

Mixed convection heat transfer and fluid flow of air, water or oil in enclosures have been studied extensively using experimental and numerical means for many years due to their ever-increasing applications in many engineering fields. In comparison, little effort has been given to the problem of mixed convection of nanofluids in spite of several applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. Mixed convection of nanofluids is a challenging problem due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, mixed convection of nanofluids in a lid-driven square cavity with sinusoidal roughness elements at the bottom is studied numerically using the Navier-Stokes equations with the Boussinesq approximation. The numerical model is developed using commercial finite volume software ANSYS-FLUENT for Al2O3-water and CuO-water nanofluids inside a square cavity with various roughness elements. The effects of number and amplitude of roughness elements on the heat transfer and fluid flow are analysed for various volume concentrations of Al2O3 and CuO nanoparticles. The flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers. The outcome of this study provides some important insight into the heat transfer behaviour of Al2O3-water and CuO-water nanofluids inside a lid-driven rough cavity. This knowledge can be further used in developing novel geometries with enhanced and controlled heat transfer for solar collectors, electronic cooling, and food processing industries.

Thermally Driven Electronic Topological Transition in FeTi

NASA Astrophysics Data System (ADS)

Yang, F. C.; Muñoz, J. A.; Hellman, O.; Mauger, L.; Lucas, M. S.; Tracy, S. J.; Stone, M. B.; Abernathy, D. L.; Xiao, Yuming; Fultz, B.

2016-08-01

Ab initio molecular dynamics, supported by inelastic neutron scattering and nuclear resonant inelastic x-ray scattering, showed an anomalous thermal softening of the M5- phonon mode in B 2 -ordered FeTi that could not be explained by phonon-phonon interactions or electron-phonon interactions calculated at low temperatures. A computational investigation showed that the Fermi surface undergoes a novel thermally driven electronic topological transition, in which new features of the Fermi surface arise at elevated temperatures. The thermally induced electronic topological transition causes an increased electronic screening for the atom displacements in the M5- phonon mode and an adiabatic electron-phonon interaction with an unusual temperature dependence.

Double Diffusive Convection in Materials Processing

NASA Technical Reports Server (NTRS)

Ramachandra, Narayanan; Leslie, Fred W.

1999-01-01

A great number of crystals grown in space are plagued by convective motions which contribute to structural flaws. The character of these instabilities is not well understood but is associated with density variations in the presence of residual gravity (g-jitter). As a specific example, past HgCdTe crystal growth space experiments by Lehoczky and co-workers indicate radial compositional asymmetry in the grown crystals. In the case of HgCdTe the rejected component into the melt upon solidification is HgTe which is denser than the melt. The space grown crystals indicate the presence of three dimensional flow with the heavier HgTe-rich material clearly aligned with the residual gravity (0.55-1.55 micro g) vector. This flow stems from double-diffusive convection, namely, thermal and solutal buoyancy driven flow in the melt. The study of double-diffusive convection is multi-faceted and rather vast. In our investigation, we seek to focus on one specific aspect of this discipline that is of direct relevance to materials processing especially crystal growth, namely, the side ways heating regime. This problem has been widely studied, both experimentally and numerically, in the context of solar ponds wherein the system is characterized by a linear salt (solutal) gradient with an imposed lateral temperature gradient. The induced flow instabilities arise from the wide disparity between the fluid thermal diffusivity and the solute diffusivity. The extension of the analysis to practical crystal growth applications has however not been rigorously made and understood. One subtle but important difference in crystal growth systems is the fact that die system solute gradient is non-linear (typically exponential). Besides, the crystal growth problem has the added complexities of solidification, both lateral and longitudinal thermal gradients and segregation phenomena in systems where binary and ternary compounds are being grown. This paper treats the side ways heating problem alone in a model fluid system. Results from detailed numerical calculations, mainly two dimensional are provided. The interactions between a non-linear solute gradient and an imposed transverse thermal gradient are investigated. The buoyancy effects are treated in the traditional Boussinesq approximation and also in a more complete density formulation to address recent concerns of the first approach especially in simulations of the system response in a reduced gravity environment. Detailed flow, temperature and solute field plots along with heat and mass transfer results are presented in the paper. Implications to practical crystal growth systems as discerned from the modeling results are also explored and reported.

The effect of small temperature gradients on flow in a continuous flow electrophoresis chamber

NASA Technical Reports Server (NTRS)

Rhodes, P. H.; Snyder, R. S.

1982-01-01

Continuous flow electrophoresis employs an electric field to separate biological cells suspended in a flowing liquid buffer solution. Good separations based on differences in electrophoretic mobility are obtained only when a unidirectional flow is maintained. The desired flow has a parabolic structure in the narrow dimension of the chamber and is uniform acros the width, except near the edges where the no-slip condition prevails. However, because of buoyancy, very small laterall or axial temperature gradients deform the flow significantly. The results of experiments conducted with a specially instrumented chamber show the origin and structure of the buoyancy-driven perturbations. It is found that very small temperature gradients can disturb the flow significantly, as was predicted by earlier theoretical work.

Thermodiffusion in concentrated ferrofluids: A review and current experimental and numerical results on non-magnetic thermodiffusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sprenger, Lisa, E-mail: Lisa.Sprenger@tu-dresden.de; Lange, Adrian; Odenbach, Stefan

2013-12-15

Ferrofluids are colloidal suspensions consisting of magnetic nanoparticles dispersed in a carrier liquid. Their thermodiffusive behaviour is rather strong compared to molecular binary mixtures, leading to a Soret coefficient (S{sub T}) of 0.16 K{sup −1}. Former experiments with dilute magnetic fluids have been done with thermogravitational columns or horizontal thermodiffusion cells by different research groups. Considering the horizontal thermodiffusion cell, a former analytical approach has been used to solve the phenomenological diffusion equation in one dimension assuming a constant concentration gradient over the cell's height. The current experimental work is based on the horizontal separation cell and emphasises the comparison ofmore » the concentration development in different concentrated magnetic fluids and at different temperature gradients. The ferrofluid investigated is the kerosene-based EMG905 (Ferrotec) to be compared with the APG513A (Ferrotec), both containing magnetite nanoparticles. The experiments prove that the separation process linearly depends on the temperature gradient and that a constant concentration gradient develops in the setup due to the separation. Analytical one dimensional and numerical three dimensional approaches to solve the diffusion equation are derived to be compared with the solution used so far for dilute fluids to see if formerly made assumptions also hold for higher concentrated fluids. Both, the analytical and numerical solutions, either in a phenomenological or a thermodynamic description, are able to reproduce the separation signal gained from the experiments. The Soret coefficient can then be determined to 0.184 K{sup −1} in the analytical case and 0.29 K{sup −1} in the numerical case. Former theoretical approaches for dilute magnetic fluids underestimate the strength of the separation in the case of a concentrated ferrofluid.« less

Viscous effects on the Rayleigh-Taylor instability with background temperature gradient

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerashchenko, Sergiy; Livescu, Daniel

Here we studied the growth rate of the compressible Rayleigh-Taylor instability in the presence of a background temperature gradient, Θ, using a normal mode analysis. The effect of Θ variation is examined for three interface types corresponding to the combinations of the viscous properties of the fluids (inviscid-inviscid, viscous-viscous, and viscous-inviscid) at different Atwood numbers, At, and when at least one of the fluids' viscosity is non-zero, as a function of the Grashof number. For the general case, the resulting ordinary differential equations are solved numerically; however, dispersion relations for the growth rate are presented for several limiting cases. Anmore » analytical solution is found for the inviscid-inviscid interface and the corresponding dispersion equation for the growth rate is obtained in the limit of large Θ. For the viscous-inviscid case, a dispersion relation is derived in the incompressible limit and Θ=0. Compared to Θ=0 case, the role of Θ<0 (hotter light fluid) is destabilizing and becomes stabilizing when Θ>0 (colder light fluid). The most pronounced effect of Θ ≠ 0 is found at low At and/or at large perturbation wavelengths relative to the domain size for all interface types. On the other hand, at small perturbation wavelengths relative to the domain size, the growth rate for the Θ<0 case exceeds the infinite domain incompressible constant density result. The results are applied to two practical examples, using sets of parameters relevant to Inertial Confinement Fusion coasting stage and solar corona plumes. The role of viscosity on the growth rate reduction is discussed together with highlighting the range of wavenumbers most affected by viscosity. The viscous effects further increase in the presence of background temperature gradient, when the viscosity is temperature dependent.« less

Viscous effects on the Rayleigh-Taylor instability with background temperature gradient

DOE PAGES

Gerashchenko, Sergiy; Livescu, Daniel

2016-07-28

Here we studied the growth rate of the compressible Rayleigh-Taylor instability in the presence of a background temperature gradient, Θ, using a normal mode analysis. The effect of Θ variation is examined for three interface types corresponding to the combinations of the viscous properties of the fluids (inviscid-inviscid, viscous-viscous, and viscous-inviscid) at different Atwood numbers, At, and when at least one of the fluids' viscosity is non-zero, as a function of the Grashof number. For the general case, the resulting ordinary differential equations are solved numerically; however, dispersion relations for the growth rate are presented for several limiting cases. Anmore » analytical solution is found for the inviscid-inviscid interface and the corresponding dispersion equation for the growth rate is obtained in the limit of large Θ. For the viscous-inviscid case, a dispersion relation is derived in the incompressible limit and Θ=0. Compared to Θ=0 case, the role of Θ<0 (hotter light fluid) is destabilizing and becomes stabilizing when Θ>0 (colder light fluid). The most pronounced effect of Θ ≠ 0 is found at low At and/or at large perturbation wavelengths relative to the domain size for all interface types. On the other hand, at small perturbation wavelengths relative to the domain size, the growth rate for the Θ<0 case exceeds the infinite domain incompressible constant density result. The results are applied to two practical examples, using sets of parameters relevant to Inertial Confinement Fusion coasting stage and solar corona plumes. The role of viscosity on the growth rate reduction is discussed together with highlighting the range of wavenumbers most affected by viscosity. The viscous effects further increase in the presence of background temperature gradient, when the viscosity is temperature dependent.« less

A generalized two-fluid picture of non-driven collisionless reconnection and its relation to whistler waves

DOE PAGES

None, None

2017-05-05

A generalized, intuitive two-fluid picture of 2D non-driven collisionless magnetic reconnection is described using results from a full-3D numerical simulation. The relevant two-fluid equations simplify to the condition that the flux associated with canonical circulation Q=m e∇×u e+q eB is perfectly frozen into the electron fluid. In the reconnection geometry, flux tubes defined by Q are convected with the central electron current, effectively stretching the tubes and increasing the magnitude of Q exponentially. This, coupled with the fact that Q is a sum of two quantities, explains how the magnetic fields in the reconnection region reconnect and give rise tomore » strong electron acceleration. The Q motion provides an interpretation for other phenomena as well, such as spiked central electron current filaments. The simulated reconnection rate was found to agree with a previous analytical calculation having the same geometry. Energy analysis shows that the magnetic energy is converted and propagated mainly in the form of the Poynting flux, and helicity analysis shows that the canonical helicity ∫P·Q dV as a whole must be considered when analyzing reconnection. A mechanism for whistler wave generation and propagation is also described, with comparisons to recent spacecraft observations.« less

The wave numbers of supercritical surface tension driven Benard convection

NASA Technical Reports Server (NTRS)

Koschmieder, E. L.; Switzer, D. W.

1991-01-01

The cell size or the wave numbers of supercritical hexagonal convection cells in primarily surface tension driven convection on a uniformly heated plate was studied experimentally in thermal equilibrium in thin layers of silicone oil of large aspect ratio. It was found that the cell size decreases with increased temperature difference in the slightly supercritical range, and that the cell size is unique within the experimental error. It was also observed that the cell size reaches a minimum and begins to increase at larger temperature differences. This reversal of the rate of change of the wave number with temperature difference is attributed to influences of buoyancy on the fluid motion. The consequences of buoyancy were tested with three fluid layers of different depth.

The wavenumbers of supercritical surface-tension-driven Benard convection

NASA Technical Reports Server (NTRS)

Koschmieder, E. L.; Switzer, D. W.

1992-01-01

The cell size or the wavenumbers of supercritical hexagonal convection cells in primarily surface-tension-driven convection on a uniformly heated plate has been studied experimentally in thermal equilibrium in thin layers of silicone oil of large aspect ratio. It has been found that the cell size decreases with increased temperature difference in the slightly supercritical range, and that the cell size is unique within the experimental error. It has also been observed that the cell size reaches a minimum and begins to increase at larger temperature differences. This reversal of the rate of change of the wavenumber with temperature difference is attributed to influences of buoyancy on the fluid motion. The consequences of buoyancy have been tested with three fluid layers of different depth.

Reversible beam heater for suppression of microbunching instability by transverse gradient undulators

NASA Astrophysics Data System (ADS)

Liu, Tao; Qin, Weilun; Wang, Dong; Huang, Zhirong

2017-08-01

The microbunching instability driven by beam collective effects in a linear accelerator of a free-electron laser (FEL) facility significantly degrades the electron beam quality and FEL performance. A conventional method to suppress this instability is to introduce an additional uncorrelated energy spread by laser-electron interaction, which has been successfully operated in the Linac Coherent Light Source and Fermi@Elettra, etc. Some other ideas are recently proposed to suppress the instability without increasing energy spread, which could benefit the seeded FEL schemes. In this paper, we propose a reversible electron beam heater using two transverse gradient undulators to suppress the microbunching instability. This scheme introduces both an energy spread increase and a transverse-to-longitudinal phase space coupling, which suppress the microbunching instabilities driven by both longitudinal space charge and coherent synchrotron radiation before and within the system. Finally the induced energy spread increase and emittance growth are reversed. Theoretical analysis and numerical simulations are presented to verify the feasibility of the scheme and indicate the capability to improve the seeded FEL radiation performance.

Reversible beam heater for suppression of microbunching instability by transverse gradient undulators

DOE PAGES

Liu, Tao; Qin, Weilun; Wang, Dong; ...

2017-08-02

The microbunching instability driven by beam collective effects in a linear accelerator of a free-electron laser (FEL) facility significantly degrades the electron beam quality and FEL performance. A conventional method to suppress this instability is to introduce an additional uncorrelated energy spread by laser-electron interaction, which has been successfully operated in the Linac Coherent Light Source and Fermi@Elettra, etc. Some other ideas are recently proposed to suppress the instability without increasing energy spread, which could benefit the seeded FEL schemes. In this paper, we propose a reversible electron beam heater using two transverse gradient undulators to suppress the microbunching instability.more » This scheme introduces both an energy spread increase and a transverse-to-longitudinal phase space coupling, which suppress the microbunching instabilities driven by both longitudinal space charge and coherent synchrotron radiation before and within the system. Finally the induced energy spread increase and emittance growth are reversed. In conclusion, theoretical analysis and numerical simulations are presented to verify the feasibility of the scheme and indicate the capability to improve the seeded FEL radiation performance.« less

Gradient Theory simulations of pure fluid interfaces using a generalized expression for influence parameters and a Helmholtz energy equation of state for fundamentally consistent two-phase calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahms, Rainer N.

2014-12-31

The fidelity of Gradient Theory simulations depends on the accuracy of saturation properties and influence parameters, and require equations of state (EoS) which exhibit a fundamentally consistent behavior in the two-phase regime. Widely applied multi-parameter EoS, however, are generally invalid inside this region. Hence, they may not be fully suitable for application in concert with Gradient Theory despite their ability to accurately predict saturation properties. The commonly assumed temperature-dependence of pure component influence parameters usually restricts their validity to subcritical temperature regimes. This may distort predictions for general multi-component interfaces where temperatures often exceed the critical temperature of vapor phasemore » components. Then, the calculation of influence parameters is not well defined. In this paper, one of the first studies is presented in which Gradient Theory is combined with a next-generation Helmholtz energy EoS which facilitates fundamentally consistent calculations over the entire two-phase regime. Illustrated on pentafluoroethane as an example, reference simulations using this method are performed. They demonstrate the significance of such high-accuracy and fundamentally consistent calculations for the computation of interfacial properties. These reference simulations are compared to corresponding results from cubic PR EoS, widely-applied in combination with Gradient Theory, and mBWR EoS. The analysis reveals that neither of those two methods succeeds to consistently capture the qualitative distribution of obtained key thermodynamic properties in Gradient Theory. Furthermore, a generalized expression of the pure component influence parameter is presented. This development is informed by its fundamental definition based on the direct correlation function of the homogeneous fluid and by presented high-fidelity simulations of interfacial density profiles. As a result, the new model preserves the accuracy of previous temperature-dependent expressions, remains well-defined at supercritical temperatures, and is fully suitable for calculations of general multi-component two-phase interfaces.« less

Aspects of wellbore heat transfer during two-phase flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hasan, A.R.; Kabir, C.S.

1994-08-01

Wellbore fluid temperature is governed by the rate of heat loss from the wellbore to the surrounding formation, which in turn is a function of depth and production/injection time. The authors present an approach to estimate wellbore fluid temperature during steady-state two-phase flow. The method incorporates a new solution of the thermal diffusivity equation and the effect of both conductive and convective heat transport for the wellbore/formation system. For the multiphase flow in the wellbore, the Hasan-Kabir model has been adapted, although other mechanistic models may be used. A field example is used to illustrate the fluid temperature calculation proceduremore » and shows the importance of accounting for convection in the tubing/casing annulus. A sensitivity study shows that significant differences exist between the predicted wellhead temperature and the formation surface temperature and that the fluid temperature gradient is nonlinear. This study further shows that increased free gas lowers the wellhead temperature as a result of the Joule-Thompson effect. In such cases, the expression for fluid temperature developed earlier for single-phase flow should not be applied when multiphase flow is encountered. An appropriate expression is presented in this work for wellbores producing multiphase fluids.« less

Morphometric traits capture the climatically driven species turnover of 10 spruce taxa across China.

PubMed

Li, He; Wang, GuoHong; Zhang, Yun; Zhang, WeiKang

2016-02-01

This study explored the relative roles of climate and phylogenetic background in driving morphometric trait variation in 10 spruce taxa in China. The study further addressed the hypothesis that these variations are consistent with species turnover on climatic gradients. Nine morphometric traits of leaves, seed cones, and seeds for the 10 studied spruce taxa were measured at 504 sites. These data were analyzed in combination with species DNA sequences from NCBI GenBank. We detected the effects of phylogeny and climate through trait-variation-based K statistics and phylogenetic eigenvector regression (PVR) analyses. Multivariate analyses were performed to detect trait variation along climatic gradients with species replacement. The estimated K-values for the nine studied morphometric traits ranged from 0.19 to 0.68, and the studied environmental variables explained 39-83% of the total trait variation. Trait variation tended to be determined largely by a temperature gradient varying from wet-cool climates to dry-warm summers and, additionally, by a moisture gradient. As the climate became wetter and cooler, spruce species tended to be replaced by other spruces with smaller needle leaves and seeds but larger cones and seed scales. A regression analysis showed that spruce species tended to be successively replaced by other species, along the gradient, although the trends observed within species were not necessarily consistent with the overall trend. The climatically driven replacement of the spruces in question could be well indicated by the between-species variation in morphometric traits that carry lower phylogenetic signal. Between-species variation in these traits is driven primarily by climatic factors. These species demonstrate a narrower ecological amplitude in temperature but wider ranges on the moisture gradient.

Regarding the influence of heating and the Soret effect on a magnetic fluid seal

NASA Astrophysics Data System (ADS)

Krakov, M. S.; Nikiforov, I. V.

2017-06-01

The influence of a temperature gradient and the Soret effect on the distribution of particles in a magnetic fluid seal (MFS) is studied. The heating of the MFS is found to be an effective method of homogenizing the magnetic fluid in the seal; in addition, the influence of the Soret effect on this process is found to be essential.

Experimental studies of high-confinement mode plasma response to non-axisymmetric magnetic perturbations in ASDEX Upgrade

DOE PAGES

Suttrop, Wolfgang; Kirk, A.; Nazikian, R.; ...

2016-11-22

Here, the interaction of externally applied small non-axisymmetric magnetic perturbations (MP) with tokamak high-confinement mode (H-mode) plasmas is reviewed and illustrated by recent experiments in ASDEX Upgrade. The plasma response to the vacuum MP field is amplified by stable ideal kink modes with low toroidal mode number n driven by the H-mode edge pressure gradient (and associated bootstrap current) which is experimentally evidenced by an observable shift of the poloidal mode number m away from field alignment (m = qn, with q being the safety factor) at the response maximum. A torque scan experiment demonstrates the importance of the perpendicular electron flow for shielding of the resonant magnetic perturbation, as expected from a two-fluid MHD picture. Two significant effects of MP occur in H-mode plasmas at low pedestal collisionality,more » $$\

Experimental verification of the role of electron pressure in fast magnetic reconnection with a guide field

DOE PAGES

Fox, W.; Sciortino, F.; v. Stechow, A.; ...

2017-03-21

We report detailed laboratory observations of the structure of a reconnection current sheet in a two-fluid plasma regime with a guide magnetic field. We observe and quantitatively analyze the quadrupolar electron pressure variation in the ion-diffusion region, as originally predicted by extended magnetohydrodynamics simulations. The projection of the electron pressure gradient parallel to the magnetic field contributes significantly to balancing the parallel electric field, and the resulting cross-field electron jets in the reconnection layer are diamagnetic in origin. Furthermore, these results demonstrate how parallel and perpendicular force balance are coupled in guide field reconnection and confirm basic theoretical models ofmore » the importance of electron pressure gradients for obtaining fast magnetic reconnection.« less

Relationships between heat flow, thermal and pressure fields in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Husson, L.; Henry, P.; Le Pichon, X.

2004-12-01

The thermal field of the Gulf of Mexico (GoM) is restored from a comprehensive temperature-depth database. A striking feature is the systematic sharp gradient increase between 2500 and 4000 m. The analysis of the pressure (fracturation tests and mud weights) indicates a systematic correlation between the pressure and temperature fields, as well as with the thickness of Plio-Pleistocene sedimentary layer, and is interpreted as the fact of cooling from fluid flow in the upper, almost hydrostatically pressured layer. The Nusselt number, that we characterize by the ratio between the near high-P gradient over low-P gradient varies spatially and is correlated to the structural pattern of the GoM; this observation outlines the complex relationships between heat and fluid flows, structure and sedimentation. The deep thermal signal is restored in terms of gradient and heat flow density from a statistical analysis of the thermal data combined to the thermal modelling of about 175 wells. At a regional scale, although the sedimentary cover is warmer in Texas than in Louisiana in terms of temperature, the steady state basal heat flow is higher in Louisiana. In addition, beneath the Corsair Fault, which lay offshore parallel to the Texan coast, the high heat flow suggests a zone of Tertiary lithospheric thinning.

Investigation of the Temperature Fluctuation of Single-Phase Fluid Based Microchannel Heat Sink.

PubMed

Wang, Tao; Wang, Jiejun; He, Jian; Wu, Chuangui; Luo, Wenbo; Shuai, Yao; Zhang, Wanli; Lee, Chengkuo

2018-05-10

The temperature fluctuation in a single-phase microchannel heat sink (MCHS) is investigated using the integrated temperature sensors with deionized water as the coolant. Results show that the temperature fluctuation in single phase is not negligible. The causes of the temperature fluctuation are revealed based on both simulation and experiment. It is found that the inlet temperature fluctuation and the gas bubbles separated out from coolant are the main causes. The effect of the inlet temperature fluctuation is global, where the temperatures at different locations change simultaneously. Meanwhile, the gas bubble effect is localized where the temperature changes at different locations are not synchronized. In addition, the relation between temperature fluctuation and temperature gradient is established. The temperature fluctuation increases with the temperature gradient accordingly.

An Investigation Into: I) Active Flow Control for Cold-Start Performance Enhancement of a Pump-Assisted, Capillary-Driven, Two-Phase Cooling Loop II) Surface Tension of n-Pentanol + Water, a Self-Rewetting Working Fluid, From 25 °C to 85 °C

NASA Astrophysics Data System (ADS)

Bejarano, Roberto Villa

Cold-start performance enhancement of a pump-assisted, capillary-driven, two-phase cooling loop was attained using proportional integral and fuzzy logic controls to manage the boiling condition inside the evaporator. The surface tension of aqueous solutions of n-Pentanol, a self-rewetting fluid, was also investigated for enhancing heat transfer performance of capillary driven (passive) thermal devices was also studied. A proportional-integral control algorithm was used to regulate the boiling condition (from pool boiling to thin-film boiling) and backpressure in the evaporator during cold-start and low heat input conditions. Active flow control improved the thermal resistance at low heat inputs by 50% compared to the baseline (constant flow rate) case, while realizing a total pumping power savings of 56%. Temperature overshoot at start-up was mitigated combining fuzzy-logic with a proportional-integral controller. A constant evaporator surface temperature of 60°C with a variation of +/-8°C during start-up was attained with evaporator thermal resistances as low as 0.10 cm2--K/W. The surface tension of aqueous solutions of n-Pentanol, a self-rewetting working fluid, as a function of concentration and temperature were also investigated. Self-rewetting working fluids are promising in two-phase heat transfer applications because they have the ability to passively drive additional working fluid towards the heated surface; thereby increasing the dryout limitations of the thermal device. Very little data is available in literature regarding the surface tension of these fluids due to the complexity involved in fluid handling, heating, and experimentation. Careful experiments were performed to investigate the surface tension of n-Pentanol + water. The concentration and temperature range investigated were from 0.25%wt. to1.8%wt and 25°C to 85°C, respectively.

The neoclassical ``Electron Root'' feature in the Wendelstein-7-AS stellarator

NASA Astrophysics Data System (ADS)

Maaßberg, H.; Beidler, C. D.; Gasparino, U.; Romé, M.; Dyabilin, K. S.; Marushchenko, N. B.; Murakami, S.

2000-01-01

The neoclassical prediction of the "electron root," i.e., a strongly positive radial electric field, Er (being the solution of the ambipolarity condition of the particle fluxes), is analyzed for low-density discharges in Wendelstein-7-AS [G. Grieger, W. Lotz, P. Merkel, et al., Phys. Fluids B 4, 2081 (1992)]. In these electron cyclotron resonance heated (ECRH) discharges with highly localized central power deposition, peaked Te profiles [with Te(0) up to 6 keV and with Ti≪Te] and strongly positive Er in the central region are measured. It is shown that this "electron root" feature at W7-AS is driven by ripple-trapped suprathermal electrons generated by the ECRH. The fraction of ripple-trapped particles in the ECRH launching plane, which can be varied at W7-AS, is found to be the most important. After switching off the heating the "electron root" feature disappears nearly immediately, i.e., two different time scales for the electron temperature decay in the central region are observed. Monte Carlo simulations in five-dimensional phase space are presented, clearly indicating that the additional "convective" electron fluxes driven by the ECRH are of the same order as the ambipolar neoclassical prediction for the "ion root" at much lower Er. For the predicted "electron root," the ion fluxes calculated based on the traditional neoclassical ordering are much too small; shortcomings of the usual approach are indentified and a new ordering scheme is proposed.

Diffusion-driven fluid dynamics in ideal gases and plasmas

NASA Astrophysics Data System (ADS)

Vold, E. L.; Yin, L.; Taitano, W.; Molvig, K.; Albright, B. J.

2018-06-01

The classical transport theory based on Chapman-Enskog methods provides self-consistent approximations for the kinetic flux of mass, heat, and momentum in a fluid limit characterized with a small Knudsen number. The species mass fluxes relative to the center of mass, or "diffusive fluxes," are expressed as functions of known gradient quantities with kinetic coefficients evaluated using similar analyses for mixtures of gases or plasma components. The sum over species of the diffusive mass fluxes is constrained to be zero in the Lagrange frame, and thus results in a non-zero molar flux leading to a pressure perturbation. At an interface between two species initially in pressure equilibrium, the pressure perturbation driven by the diffusive molar flux induces a center of mass velocity directed from the species of greater atomic mass towards the lighter atomic mass species. As the ratio of the species particle masses increases, this center of mass velocity carries an increasingly greater portion of the mass across the interface and for a particle mass ratio greater than about two, the center of mass velocity carries more mass than the gradient driven diffusion flux. Early time transients across an interface between two species in a 1D plasma regime and initially in equilibrium are compared using three methods; a fluid code with closure in a classical transport approximation, a particle in cell simulation, and an implicit Fokker-Planck solver for the particle distribution functions. The early time transient phenomenology is shown to be similar in each of the computational simulation methods, including a pressure perturbation associated with the stationary "induced" component of the center of mass velocity which decays to pressure equilibrium during diffusion. At early times, the diffusive process generates pressure and velocity waves which propagate outward from the interface and are required to maintain momentum conservation. The energy in the outgoing waves dissipates as heat in viscous regions, and it is hypothesized that these diffusion driven waves may sustain fluctuations in less viscid finite domains after reflections from the boundaries. These fluid dynamic phenomena are similar in gases or plasmas and occur in flow transients with a moderate Knudsen number. The analysis and simulation results show how the kinetic flux, represented in the fluid transport closure, directly modifies the mass averaged flow described with the Euler equations.

Numerical simulation of the hydrodynamical combustion to strange quark matter in the trapped neutrino regime

NASA Astrophysics Data System (ADS)

Ouyed, Amir; Ouyed, Rachid; Jaikumar, Prashanth

2018-02-01

We simulate and study the microphysics of combustion (flame burning) of two flavored quark matter (u,d) to three flavored quark matter (u,d,s) in a trapped neutrino regime applicable to conditions prevailing in a hot proto-neutron star. The reaction-diffusion-advection equations for (u,d) to (u,d,s) combustion are coupled with neutrino transport, which is modeled through a flux-limited diffusion scheme. The flame speed is proportional to initial lepton fraction because of the release of electron chemical potential as heat, and reaches a steady-state burning speed of (0.001-0.008)c. We find that the burning speed is ultimately driven by the neutrino pressure gradient, given that the pressure gradient induced by quarks is opposed by the pressure gradients induced by electrons. This suggests, somewhat counter-intuitively, that the pressure gradients that drive the interface are controlled primarily by leptonic weak decays rather than by the quark Equation of State (EOS). In other words, the effects of the leptonic weak interaction, including the corresponding weak decay rates and the EOS of electrons and neutrinos, are at least as important as the uncertainties related to the EOS of high density matter. We find that for baryon number densities nB ≤ 0.35 fm-3, strong pressure gradients induced by leptonic weak decays drastically slow down the burning speed, which is thereafter controlled by the much slower burning process driven by backflowing downstream matter. We discuss the implications of our findings to proto-neutron stars.

Thermally driven ratchet motion of a skyrmion microcrystal and topological magnon Hall effect

NASA Astrophysics Data System (ADS)

Mochizuki, M.; Yu, X. Z.; Seki, S.; Kanazawa, N.; Koshibae, W.; Zang, J.; Mostovoy, M.; Tokura, Y.; Nagaosa, N.

2014-03-01

Spontaneously emergent chirality is an issue of fundamental importance across the natural sciences. It has been argued that a unidirectional (chiral) rotation of a mechanical ratchet is forbidden in thermal equilibrium, but becomes possible in systems out of equilibrium. Here we report our finding that a topologically nontrivial spin texture known as a skyrmion—a particle-like object in which spins point in all directions to wrap a sphere—constitutes such a ratchet. By means of Lorentz transmission electron microscopy we show that micrometre-sized crystals of skyrmions in thin films of Cu2OSeO3 and MnSi exhibit a unidirectional rotation motion. Our numerical simulations based on a stochastic Landau-Lifshitz-Gilbert equation suggest that this rotation is driven solely by thermal fluctuations in the presence of a temperature gradient, whereas in thermal equilibrium it is forbidden by the Bohr-van Leeuwen theorem. We show that the rotational flow of magnons driven by the effective magnetic field of skyrmions gives rise to the skyrmion rotation, therefore suggesting that magnons can be used to control the motion of these spin textures.

Thermo-Rotational Instability in Plasma Disks Around Compact Objects*

NASA Astrophysics Data System (ADS)

Coppi, Bruno

2008-04-01

Differentially rotating plasma disks, around compact objects, that are imbedded in a ``seed'' magnetic field are shown to develop vertically localized ballooning modes that are driven by the combined radial gradient of the rotation frequency and the vertical gradients of the plasma density and temperature [1]. When the electron mean free path is shorter than the disk height and the (vertical) thermal conductivity can be neglected, the vertical particle flows produced by of these modes have the effect to drive the density and temperature profiles toward the ``adiabatic condition'' where ηT≡(dlnT/dz/(dlnn/dz)=2/3. Here T is the plasma temperature and n the particle density. The faster growth rates correspond to steeper temperature profiles (ηT>2/3) such as those produced by an internal (e.g. viscous) heating process. In the end, ballooning modes excited for various values of ηT can lead to the evolution of the disk into a different current carrying configuration such as a sequence of plasma rings[2].*Sponsored in part by the U.S. Department of Energy[1]B. Coppi, M.I.T. (LNS) Report HEP, 07/02, Cambridge, MA (2007), Invited Paper at the International Symposium on ``Momentum Transport in Jets, Disks and Laboratory Plasmas'', Alba, Piedmont, September 2007, to be published in Europhysical Letters (EPL, IOP)[2]B. Coppi andF. Rousseau, Ap. J., 641, 458, (2006)

Effect of electromigration-induced back stress gradient on nanoindentation marker movement in SnAgCu solder joints

NASA Astrophysics Data System (ADS)

Xu, Luhua; Pang, John H. L.; Tu, K. N.

2006-11-01

The electromigration-induced back stress in Pb-free SnAgCu solder was studied by an area array of nanoindentation markers on the cross section of a solder joint. The marker movements driven by combined electron wind force and electromigration-induced back stress gradient were measured at different locations. The back stress gradient was determined from the observation of marker motion using the proposed model. With the applied current density of 104A/cm2 at 125°C, the stress gradient near the anode is 97kPa/μm.

Plasma interpenetration study on the Omega laser facility

NASA Astrophysics Data System (ADS)

Le Pape, Sebastien; Divol, Laurent; Ross, Steven; Wilks, Scott; Amendt, Peter; Berzak Hopkins, Laura; Huser, Gael; Moody, John; MacKinnon, Andy; Meezan, Nathan

2016-10-01

The Near Vacuum Campaign on the National Ignition Facility has sparked an interest on the nature of the gold/carbon interface at high velocity, high electron temperature, low-electron density. Indeed radiation-hydrodynamic simulations have been unable to accurately reproduce the experimental shape of the hot spot resulting from implosion driven in Near Vacuum Holhraum. The experimental data are suggesting that the inner beams are freely propagating to the waist of the hohlraum when simulations predict that a density ridge at the gold/carbon interface blocks the inner beams. The discrepancy between experimental data and simulation might be explained by the fluid description of the plasma interface in a rad-hydro code which is probably not valid in when two plasma at high velocity, high temperature are meeting. To test our assumption, we went to the Omega laser facility to study gold/carbon interface in the relevant regime. Time resolved images of the self-emission as well as Thomson scattering data will be presented. For the first time, a transition from a multifluid to a single fluid is observed as plasmas are interacting. This work was performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.

Four-fluid MHD simulations of the plasma and neutral gas environment of comet 67P/Churyumov-Gerasimenko near perihelion

NASA Astrophysics Data System (ADS)

Huang, Zhenguang; Tóth, Gábor; Gombosi, Tamas I.; Jia, Xianzhe; Rubin, Martin; Fougere, Nicolas; Tenishev, Valeriy; Combi, Michael R.; Bieler, Andre; Hansen, Kenneth C.; Shou, Yinsi; Altwegg, Kathrin

2016-05-01

The neutral and plasma environment is critical in understanding the interaction of the solar wind and comet 67P/Churyumov-Gerasimenko (CG), the target of the European Space Agency's Rosetta mission. To serve this need and support the Rosetta mission, we have developed a 3-D four-fluid model, which is based on BATS-R-US (Block-Adaptive Tree Solarwind Roe-type Upwind Scheme) within SWMF (Space Weather Modeling Framework) that solves the governing multifluid MHD equations and the Euler equations for the neutral gas fluid. These equations describe the behavior and interactions of the cometary heavy ions, the solar wind protons, the electrons, and the neutrals. This model incorporates different mass loading processes, including photoionization and electron impact ionization, charge exchange, dissociative ion-electron recombination, and collisional interactions between different fluids. We simulated the plasma and neutral gas environment near perihelion in three different cases: an idealized comet with a spherical body and uniform neutral gas outflow, an idealized comet with a spherical body and illumination-driven neutral gas outflow, and comet CG with a realistic shape model and illumination-driven neutral gas outflow. We compared the results of the three cases and showed that the simulations with illumination-driven neutral gas outflow have magnetic reconnection, a magnetic pileup region and nucleus directed plasma flow inside the nightside reconnection region, which have not been reported in the literature.

Accumulation of Colloidal Particles in Flow Junctions Induced by Fluid Flow and Diffusiophoresis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shin, Sangwoo; Ault, Jesse T.; Warren, Patrick B.

The flow of solutions containing solutes and colloidal particles in porous media is widely found in systems including underground aquifers, hydraulic fractures, estuarine or coastal habitats, water filtration systems, etc. In such systems, solute gradients occur when there is a local change in the solute concentration. While the effects of solute gradients have been found to be important for many applications, we observe an unexpected colloidal behavior in porous media driven by the combination of solute gradients and the fluid flow. When two flows with different solute concentrations are in contact near a junction, a sharp solute gradient is formedmore » at the interface, which may allow strong diffusiophoresis of the particles directed against the flow. Consequently, the particles accumulate near the pore entrance, rapidly approaching the packing limit. These colloidal dynamics have important implications for the clogging of a porous medium, where particles that are orders of magnitude smaller than the pore width can accumulate and block the pores within a short period of time. As a result, we also show that this effect can be exploited as a useful tool for preconcentrating biomolecules for rapid bioassays.« less

Accumulation of Colloidal Particles in Flow Junctions Induced by Fluid Flow and Diffusiophoresis

DOE PAGES

Shin, Sangwoo; Ault, Jesse T.; Warren, Patrick B.; ...

2017-11-16

The flow of solutions containing solutes and colloidal particles in porous media is widely found in systems including underground aquifers, hydraulic fractures, estuarine or coastal habitats, water filtration systems, etc. In such systems, solute gradients occur when there is a local change in the solute concentration. While the effects of solute gradients have been found to be important for many applications, we observe an unexpected colloidal behavior in porous media driven by the combination of solute gradients and the fluid flow. When two flows with different solute concentrations are in contact near a junction, a sharp solute gradient is formedmore » at the interface, which may allow strong diffusiophoresis of the particles directed against the flow. Consequently, the particles accumulate near the pore entrance, rapidly approaching the packing limit. These colloidal dynamics have important implications for the clogging of a porous medium, where particles that are orders of magnitude smaller than the pore width can accumulate and block the pores within a short period of time. As a result, we also show that this effect can be exploited as a useful tool for preconcentrating biomolecules for rapid bioassays.« less

Overview of results from the MST reversed field pinch experiment

NASA Astrophysics Data System (ADS)

Sarff, J. S.; Almagri, A. F.; Anderson, J. K.; Borchardt, M.; Carmody, D.; Caspary, K.; Chapman, B. E.; Den Hartog, D. J.; Duff, J.; Eilerman, S.; Falkowski, A.; Forest, C. B.; Goetz, J. A.; Holly, D. J.; Kim, J.-H.; King, J.; Ko, J.; Koliner, J.; Kumar, S.; Lee, J. D.; Liu, D.; Magee, R.; McCollam, K. J.; McGarry, M.; Mirnov, V. V.; Nornberg, M. D.; Nonn, P. D.; Oliva, S. P.; Parke, E.; Reusch, J. A.; Sauppe, J. P.; Seltzman, A.; Sovinec, C. R.; Stephens, H.; Stone, D.; Theucks, D.; Thomas, M.; Triana, J.; Terry, P. W.; Waksman, J.; Bergerson, W. F.; Brower, D. L.; Ding, W. X.; Lin, L.; Demers, D. R.; Fimognari, P.; Titus, J.; Auriemma, F.; Cappello, S.; Franz, P.; Innocente, P.; Lorenzini, R.; Martines, E.; Momo, B.; Piovesan, P.; Puiatti, M.; Spolaore, M.; Terranova, D.; Zanca, P.; Belykh, V.; Davydenko, V. I.; Deichuli, P.; Ivanov, A. A.; Polosatkin, S.; Stupishin, N. V.; Spong, D.; Craig, D.; Harvey, R. W.; Cianciosa, M.; Hanson, J. D.

2013-10-01

An overview of recent results from the MST programme on physics important for the advancement of the reversed field pinch (RFP) as well as for improved understanding of toroidal magnetic confinement more generally is reported. Evidence for the classical confinement of ions in the RFP is provided by analysis of impurity ions and energetic ions created by 1 MW neutral beam injection (NBI). The first appearance of energetic-particle-driven modes by NBI in a RFP plasma is described. MST plasmas robustly access the quasi-single-helicity state that has commonalities to the stellarator and ‘snake’ formation in tokamaks. In MST the dominant mode grows to 8% of the axisymmetric field strength, while the remaining modes are reduced. Predictive capability for tearing mode behaviour has been improved through nonlinear, 3D, resistive magnetohydrodynamic computation using the measured resistivity profile and Lundquist number, which reproduces the sawtooth cycle dynamics. Experimental evidence and computational analysis indicates two-fluid effects, e.g., Hall physics and gyro-viscosity, are needed to understand the coupling of parallel momentum transport and current profile relaxation. Large Reynolds and Maxwell stresses, plus separately measured kinetic stress, indicate an intricate momentum balance and a possible origin for MST's intrinsic plasma rotation. Gyrokinetic analysis indicates that micro-tearing modes can be unstable at high beta, with a critical gradient for the electron temperature that is larger than for tokamak plasmas by roughly the aspect ratio.

Wave propagation in fluid-conveying viscoelastic carbon nanotubes under longitudinal magnetic field with thermal and surface effect via nonlocal strain gradient theory

NASA Astrophysics Data System (ADS)

Zhen, Yaxin; Zhou, Lin

2017-03-01

Based on nonlocal strain gradient theory, wave propagation in fluid-conveying viscoelastic single-walled carbon nanotubes (SWCNTs) is studied in this paper. With consideration of thermal effect and surface effect, wave equation is derived for fluid-conveying viscoelastic SWCNTs under longitudinal magnetic field utilizing Euler-Bernoulli beam theory. The closed-form expressions are derived for the frequency and phase velocity of the wave motion. The influences of fluid flow velocity, structural damping coefficient, temperature change, magnetic flux and surface effect are discussed in detail. SWCNTs’ viscoelasticity reduces the wave frequency of the system and the influence gets remarkable with the increase of wave number. The fluid in SWCNTs decreases the frequency of wave propagation to a certain extent. The frequency (phase velocity) gets larger due to the existence of surface effect, especially when the diameters of SWCNTs and the wave number decrease. The wave frequency increases with the increase of the longitudinal magnetic field, while decreases with the increase of the temperature change. The results may be helpful for better understanding the potential applications of SWCNTs in nanotechnology.

Thermally Driven Electronic Topological Transition in FeTi

DOE PAGES

Yang, F. C.; Muñoz, J. A.; Hellman, O.; ...

2016-08-08

In this paper, ab initio molecular dynamics, supported by inelastic neutron scattering and nuclear resonant inelastic x-ray scattering, showed an anomalous thermal softening of the M 5 - phonon mode in B2-ordered FeTi that could not be explained by phonon-phonon interactions or electron-phonon interactions calculated at low temperatures. A computational investigation showed that the Fermi surface undergoes a novel thermally driven electronic topological transition, in which new features of the Fermi surface arise at elevated temperatures. Finally, the thermally induced electronic topological transition causes an increased electronic screening for the atom displacements in the M 5 - phonon mode andmore » an adiabatic electron-phonon interaction with an unusual temperature dependence.« less

Heat flow in the flanks of the Oceanographer-Hayes segment of the Mid-Atlantic Ridge

NASA Astrophysics Data System (ADS)

Le Gal, V.; Lucazeau, F.; Cannat, M.; Battani, A.; Poort, J.; Guichet, X.; Monnin, C.; Fontaine, F. J.; Leroy, S. D.

2016-12-01

It is currently estimated that a third of the oceanic heat loss is due to fluid circulation in the oceanic crust. Besides high and low temperature fluid discharge at ridge axis, off-axis low temperature fluid circulations can affect large volumes of the oceanic crust. Long term investigations of the Eastern Juan de Fuca ridge flank (Hutnak et al.2006) have established a circulation pattern where hydrothermal discharge and recharge occur at basement outcrops and where sediment is mostly impermeable. Here, we present results from the recent Oceanograflu cruise (2013), on the Oceanographer-Hayes segment ridge flanks of the Mid-Atlantic ridge in crust 5 and 12 myrs in age. On both flanks, we obtained 185 temperature gradients and conductivities in-situ, 30 Küllenberg cores (3 to 5 meters long) coupled with temperature gradients in-situ and conductivity measurements onboard. These data are interpreted in terms of heat flow values and are generally lower than the conductive cooling model. Several temperature-depth profiles don't show linear gradients, but rather sigmoid shapes or inverse gradients suggesting superficial circulations through the first meters of sediments. The corresponding heat flow pattern is not similar to the one observed at Juan de Fuca. No systematic links have been observed between basement outcrops and lower or higher heat flow which would point to discharge or recharge sites. Instead, the pattern recalls studies in the North Pond area (Langseth et al.1992), with a clear predominance of low heat flow values over the site. We propose that the North Pond circulation model is applicable to large portions of slow-spreading ridge flanks such as the Atlantic. In this model, seawater cools the uppermost crust below sediments in basins that are typically tens of kms wide, reducing the surface heat flow under cooling model values. Based on subsidence rates, these shallow hydrothermal circulations have a minor impact on the cooling of the diverging plates.

Thermal transpiration: A molecular dynamics study

NASA Astrophysics Data System (ADS)

T, Joe Francis; Sathian, Sarith P.

2014-12-01

Thermal transpiration is a phenomenon where fluid molecules move from the cold end towards the hot end of a channel under the influence of longitudinal temperature gradient alone. Although the phenomenon of thermal transpiration is observed at rarefied gas conditions in macro systems, the phenomenon can occur at atmospheric pressure if the characteristic dimensions of the channel is less than 100 nm. The flow through these nanosized channels is characterized by the free molecular flow regimes and continuum theory is inadequate to describe the flow. Thus a non-continuum method like molecular dynamics (MD) is necessary to study such phenomenon. In the present work, MD simulations were carried out to investigate the occurance of thermal transpiration in copper and platinum nanochannels at atmospheric pressure conditions. The mean pressure of argon gas confined inside the nano channels was maintained around 1 bar. The channel height is maintained at 2nm. The argon atoms interact with each other and with the wall atoms through the Lennard-Jones potential. The wall atoms are modelled using an EAM potential. Further, separate simulations were carried out where a Harmonic potential is used for the atom-atom interaction in the platinum channel. A thermally insulating wall was introduced between the low and high temperature regions and those wall atoms interact with fluid atoms through a repulsive potential. A reduced cut off radius were used to achieve this. Thermal creep is induced by applying a temperature gradient along the channel wall. It was found that flow developed in the direction of the increasing temperature gradient of the wall. An increase in the volumetric flux was observed as the length of the cold and the hot regions of the wall were increased. The effect of temperature gradient and the wall-fluid interaction strength on the flow parameters have been studied to understand the phenomenon better.

Turbulent Heat Transfer from a Thermally Forced Boundary in a Stratified Fluid

NASA Astrophysics Data System (ADS)

Burns, K. J.; Wells, A.; Flierl, G.

2017-12-01

When a marine-terminating glacier melts into a stratified ocean, a buoyancy-driven flow develops along the ice surface. The resulting turbulent heat and salt fluxes provide a key feedback on the ice melting rate. To build insight into such flows, we consider direct numerical simulations of an analogue problem with convection driven by a thermally forced sidewall in a stably stratified Boussinesq fluid. Our model considers vertical and inclined periodic channels in 2D with a constant background buoyancy gradient. When the lateral or upper boundary is given a sufficient thermal perturbation relative to the ambient, a confined and homogeneous turbulent plume emerges along the heated wall. We present a scaling analysis for the resulting heat transport across the plume, and compare it to simulations over a range of Rayleigh numbers, Prandtl numbers, and wall-inclination angles.

Turbulence, transport, and zonal flows in the Madison symmetric torus reversed-field pinch

NASA Astrophysics Data System (ADS)

Williams, Z. R.; Pueschel, M. J.; Terry, P. W.; Hauff, T.

2017-12-01

The robustness and the effect of zonal flows in trapped electron mode (TEM) turbulence and Ion Temperature Gradient (ITG) turbulence in the reversed-field pinch (RFP) are investigated from numerical solutions of the gyrokinetic equations with and without magnetic external perturbations introduced to model tearing modes. For simulations without external magnetic field perturbations, zonal flows produce a much larger reduction of transport for the density-gradient-driven TEM turbulence than they do for the ITG turbulence. Zonal flows are studied in detail to understand the nature of their strong excitation in the RFP and to gain insight into the key differences between the TEM- and ITG-driven regimes. The zonal flow residuals are significantly larger in the RFP than in tokamak geometry due to the low safety factor. Collisionality is seen to play a significant role in the TEM zonal flow regulation through the different responses of the linear growth rate and the size of the Dimits shift to collisionality, while affecting the ITG only minimally. A secondary instability analysis reveals that the TEM turbulence drives zonal flows at a rate that is twice that of the ITG turbulence. In addition to interfering with zonal flows, the magnetic perturbations are found to obviate an energy scaling relation for fast particles.

Accelerating gradient improvement using shape-tailor laser front in radiation pressure acceleration progress

NASA Astrophysics Data System (ADS)

Wang, W. P.; Shen, B. F.; Xu, Z. Z.

2017-05-01

The accelerating gradient of a proton beam is crucial for stable radiation pressure acceleration (RPA) because the multi-dimensional instabilities increase γ times slower in the relativistic region. In this paper, a shape-tailored laser is proposed to significantly accelerate the ions in a controllable high accelerating gradient. In this method, the fastest ions initially rest in the middle of the foil are controlled to catch the compressed electron layer at the end of the hole-boring stage, thus the light-sail stage can start as soon as possible. Then the compressed electron layer is accelerated tightly together with the fastest ions by the shaped laser intensity, which further increases the accelerating gradient in the light-sail stage. Such tailored pulse may be beneficial for the RPA driven by the 10-fs 10 petawatt laser in the future.

Experiments on Electron-Plasma Vortex Motion Driven by a Background Vorticity Gradient.

NASA Astrophysics Data System (ADS)

Kabantsev, A. A.; Driscoll, C. F.

2000-10-01

The interaction of self-trapped vortices with a background vorticity gradient plays an important role in 2D hydrodynamics, including various aspects of relaxation and self-organization of 2D turbulence. In the present experiments, electron plasma columns with monotonically decreasing density profiles provide a vorticity background with (negative) shear in the rotational flow. Clumps of extra electrons are then retrograde vortices, rotating against the background shear; and regions with a deficit of electrons (holes) are prograde vortices. Theory predicts that clumps move up the background gradient, and holes move down the gradient, with velocities which depend differently on the ratio of the vortex trapping length to vortex radius, l / r_v. The present experiments show quantitative agreement with recent theory and simulations,(D.A. Schecter and D.H.E. Dubin, Phys. Rev. Lett. 83), 2191 (1999). for the accessible regime of 0.2 < l/rv < 2. The experiments also show that moving clumps leave a spiral density wake, and that instability of these wakes results in a large number of long-lived holes.

Thermal transport dynamics in the quasi-single helicity state

NASA Astrophysics Data System (ADS)

McKinney, I. J.; Terry, P. W.

2017-06-01

A dynamical model describing oscillations between multiple and single helicity configurations in the quasi-single helicity (QSH) state of the reversed field pinch [P. W. Terry and G. G. Whelan, Plasma Phys. Controlled Fusion 56, 094003 (2014)] is extended to include electron temperature profile dynamics. It is shown that QSH dynamics is linked to the electron temperature profile because the suppression of mode coupling between tearing modes proposed to underlie QSH also suppresses magnetic-fluctuation-induced thermal transport. Above the threshold of dominant-mode shear that marks the transition to QSH, the model produces temperature-gradient steepening in the strong shear region. Oscillations of the dominant and secondary mode amplitudes give rise to oscillations of the temperature gradient. The phasing and amplitude of temperature gradient oscillations relative to those of the dominant mode are in agreement with experiment. This provides further evidence that the model, while heuristic, captures key physical aspects of the QSH state.

Trapped electron mode turbulence driven intrinsic rotation in Tokamak plasmas.

PubMed

Wang, W X; Hahm, T S; Ethier, S; Zakharov, L E; Diamond, P H

2011-02-25

Progress from global gyrokinetic simulations in understanding the origin of intrinsic rotation in toroidal plasmas is reported. The turbulence-driven intrinsic torque associated with nonlinear residual stress generation due to zonal flow shear induced asymmetry in the parallel wave number spectrum is shown to scale close to linearly with plasma gradients and the inverse of the plasma current, qualitatively reproducing experimental empirical scalings of intrinsic rotation. The origin of current scaling is found to be enhanced k(∥) symmetry breaking induced by the increased radial variation of the safety factor as the current decreases. The intrinsic torque is proportional to the pressure gradient because both turbulence intensity and zonal flow shear, which are two key ingredients for driving residual stress, increase with turbulence drive, which is R/L(T(e)) and R/L(n(e)) for the trapped electron mode. © 2011 American Physical Society

Thermally induced delay and reversal of liquid film dewetting on chemically patterned surfaces.

PubMed

Kalpathy, Sreeram K; Francis, Lorraine F; Kumar, Satish

2013-10-15

A thin liquid film resting on a solid substrate that is heated or cooled from below experiences surface tension gradients, which lead to Marangoni flows. We explore the behavior of such a film on a chemically patterned substrate which drives film dewetting in order to determine how surface patterning and applied temperature gradients can be designed to influence the behavior of thin-film coatings. A nonlinear partial differential equation for the film height based on lubrication theory is solved numerically for a broad range of problem parameters. Uniform cooling of the substrate is found to significantly delay dewetting that is driven by wettability gradients. Uniform heating speeds up dewetting but can destroy the near-perfect templating imposed by the surface patterning. However, localized heating and cooling together can accelerate dewetting while maintaining templating quality. Localized heating and cooling can also be used to drive liquid onto areas that it would dewet from in the absence of heating. Overall, these results indicate that applied temperature gradients can significantly influence dewetting driven by surface patterning, and suggest strategies for the creation of spatially patterned thin-film coatings and flow control in microfluidic devices. Copyright © 2013 Elsevier Inc. All rights reserved.

Hydrodynamic and thermal modeling of two-dimensional microdroplet arrays for digitized heat transfer

NASA Astrophysics Data System (ADS)

Baird, Eric S.

This document describes hydrodynamic and thermal modeling of two-dimensional microdroplet arrays for use in digitized heat transfer (DHT), a novel active thermal management technique for high power density electronics and integrated microsystems. In DHT, thermal energy is transported by a discrete array of electrostatically activated microdroplets of liquid metals, alloys or aqueous solutions with the potential of supporting significantly higher heat transfer rates than classical air-cooled heat sinks. Actuation methods for dispensing and transporting individual fluid slugs with a high degree of precision and programmability are described, with simple approximate formulae for net forces for steady state and transient velocities in terms of known parameters. A modified cavity flow solver is developed to provide details on the internal flow properties of a translating microdroplet and used to detail the effects of droplet curvature, internal mixing, Peclet number and other parameters on the heat transfer capabilities of a discretized liquid flow. The concept of Nusselt number is generalized to an individual fluid slug and shown to oscillate with a period equal to the droplet's mixing rate. In whole, DHT is demonstrated to be a viable new alternative for achieving the most important objectives of electronic cooling (i.e., minimization of the maximum substrate temperature, reduction of the substrate temperature gradient and removal of substrate hot spots) and a sound fundamental description of the method's electro-, hydro- and thermodynamics is provided.

Regional geothermal exploration in Egypt

NASA Technical Reports Server (NTRS)

Morgan, P.; Boulos, F. K.; Swanberg, C. A.

1983-01-01

A study is presented of the evaluation of the potential geothermal resources of Egypt using a thermal gradient/heat flow technique and a groundwater temperature/chemistry technique. Existing oil well bottom-hole temperature data, as well as subsurface temperature measurements in existing boreholes, were employed for the thermal gradient/heat flow investigation before special thermal gradient holes were drilled. The geographic range of the direct subsurface thermal measurements was extended by employing groundwater temperature and chemistry data. Results show the presence of a regional thermal high along the eastern margin of Egypt with a local thermal anomaly in this zone. It is suggested that the sandstones of the Nubian Formation may be a suitable reservoir for geothermal fluids. These findings indicate that temperatures of 150 C or higher may be found in this reservoir in the Gulf of Suez and Red Sea coastal zones where it lies at a depth of 4 km and deeper.

Effect of electron beam on the properties of electron-acoustic rogue waves

NASA Astrophysics Data System (ADS)

El-Shewy, E. K.; Elwakil, S. A.; El-Hanbaly, A. M.; Kassem, A. I.

2015-04-01

The properties of nonlinear electron-acoustic rogue waves have been investigated in an unmagnetized collisionless four-component plasma system consisting of a cold electron fluid, Maxwellian hot electrons, an electron beam and stationary ions. It is found that the basic set of fluid equations is reduced to a nonlinear Schrodinger equation. The dependence of rogue wave profiles and the associated electric field on the carrier wave number, normalized density of hot electron and electron beam, relative cold electron temperature and relative beam temperature are discussed. The results of the present investigation may be applicable in auroral zone plasma.

Aspect ratio effects on limited scrape-off layer plasma turbulence

NASA Astrophysics Data System (ADS)

Jolliet, Sébastien; Halpern, Federico D.; Loizu, Joaquim; Mosetto, Annamaria; Ricci, Paolo

2014-02-01

The drift-reduced Braginskii model describing turbulence in the tokamak scrape-off layer is written for a general magnetic configuration with a limiter. The equilibrium is then specified for a circular concentric magnetic geometry retaining aspect ratio effects. Simulations are then carried out with the help of the global, flux-driven fluid three-dimensional code GBS [Ricci et al., Plasma Phys. Controlled Fusion 54, 124047 (2012)]. Linearly, both simulations and simplified analytical models reveal a stabilization of ballooning modes. Nonlinearly, flux-driven nonlinear simulations give a pressure characteristic length whose trends are correctly captured by the gradient removal theory [Ricci and Rogers, Phys. Plasmas 20, 010702 (2013)], that assumes the profile flattening from the linear modes as the saturation mechanism. More specifically, the linear stabilization of ballooning modes is reflected by a 15% increase in the steady-state pressure gradient obtained from GBS nonlinear simulations when going from an infinite to a realistic aspect ratio.

Controls on the Migration of Fluids in Subduction Zones

NASA Astrophysics Data System (ADS)

Wilson, C. R.; Spiegelman, M. W.; Van Keken, P. E.; Kelemen, P. B.; Hacker, B. R.

2013-12-01

Arc volcanism associated with subduction is generally considered to be caused by the transport in the slab of hydrated minerals to sub-arc depths. In a qualitative sense it appears clear that progressive dehydration reactions in the down-going slab release fluids to the hot overlying mantle wedge, causing flux melting and the migration of melts to the volcanic front. However, the quantitative details of fluid release, migration, melt generation and transport in the wedge remain poorly understood. In particular, there are two fundamental observations that defy quantitative modeling. The first is the location of the volcanic front with respect to intermediate depth earthquakes (e.g. 100+/-40 km; England et al., 2004, Syracuse and Abers, 2006) which is remarkably robust yet insensitive to subduction parameters. This is particularly surprising given new estimates on the variability of fluid release in global subduction zones (e.g. van Keken et al. 2011) which show great sensitivity of fluid release to slab thermal conditions. Reconciling these results implies some robust mechanism for focusing fluids and/or melts toward the wedge corner. The second observation is the global existence of thermally hot erupted basalts and andesites that, if derived from flux melting of the mantle requires sub-arc mantle temperatures of 1300 degrees C over shallow pressures of 1-2 GPa which are not that different from mid-ocean ridge conditions. These observations impose significant challenges for geodynamic models of subduction zones, and in particular for those that do not include the explicit transport of fluids and melts. We present a range of high-resolution models that include a more complete description of coupled fluid and solid mechanics (allowing the fluid to interact with solid rheological variations) together with rheologically consistent solution for temperature and solid flow. Focusing on end-members of a global suite of arc geometries and thermal histories we discuss how successful these interactions are at focusing both fluids and hot solids to sub-arc regions worldwide. We will also evaluate the efficacy of current wet melting parameterizations in these models. When driven by buoyancy alone, fluid migrates through the mantle wedge along a near vertical trajectory. Only interactions with the solid flow at very low values of permeability or high values of fluid viscosity can cause deviations from this path. However, in a viscous, permeable medium, additional pressure gradients are generated by volumetric deformation due to variations in fluid flux. These pressure gradients can significantly modify the fluid flow paths. At shallow depths, compaction channels form along the rheological contrast with the overriding plate while in the mantle wedge itself porosity waves concentrate the fluid. When considering multiple, distributed sources of fluid, interaction between layers in the slab itself can also cause significant focusing. As well as permeability, rheological controls and numerical regularizations place upper and lower bounds on the length-scales over which such interactions occur further modifying the degree of focusing seen. The wide range of behaviors described here is modeled using TerraFERMA (the Transparent Finite Element Rapid Model Assembler), which harnesses the advanced computational libraries FEniCS, PETSc and SPuD to provide the required numerical flexibility.

Towards the Identification of the Keeper Erosion Cause(s): Numerical Simulations of the Plasma and Neutral Gas Using the Global Cathode Model OrCa2D-II

NASA Technical Reports Server (NTRS)

Mikellides, Ioannis G.; Katz, Ira; Goebel, Dan M.; Jameson, Kristina K.

2006-01-01

Numerical simulations with the time-dependent Orificed Cathode (OrCa2D-II) computer code show that classical enhancements of the plasma resistivity can not account for the elevated electron temperatures and steep plasma potential gradients measured in the plume of a 25-27.5 A discharge hollow cathode. The cathode, which employs a 0.11-in diameter orifice, was operated at 5.5 sccm without an applied magnetic field using two different anode geometries. It is found that anomalous resistivity based on electron-driven instabilities improves the comparison between theory and experiment. It is also estimated that other effects such as the Hall-effect from the self-induced magnetic field, not presently included in OrCa2D-II, may contribute to the constriction of the current density streamlines thus explaining the higher plasma densities observed along the centerline.

Lagrangian fluid description with simple applications in compressible plasma and gas dynamics

NASA Astrophysics Data System (ADS)

Schamel, Hans

2004-03-01

The Lagrangian fluid description, in which the dynamics of fluids is formulated in terms of trajectories of fluid elements, not only presents an alternative to the more common Eulerian description but has its own merits and advantages. This aspect, which seems to be not fully explored yet, is getting increasing attention in fluid dynamics and related areas as Lagrangian codes and experimental techniques are developed utilizing the Lagrangian point of view with the ultimate goal of a deeper understanding of flow dynamics. In this tutorial review we report on recent progress made in the analysis of compressible, more or less perfect flows such as plasmas and dilute gases. The equations of motion are exploited to get further insight into the formation and evolution of coherent structures, which often exhibit a singular or collapse type behavior occurring in finite time. It is argued that this technique of solution has a broad applicability due to the simplicity and generality of equations used. The focus is on four different topics, the physics of which being governed by simple fluid equations subject to initial and/or boundary conditions. Whenever possible also experimental results are mentioned. In the expansion of a semi-infinite plasma into a vacuum the energetic ion peak propagating supersonically towards the vacuum-as seen in laboratory experiments-is interpreted by means of the Lagrangian fluid description as a relic of a wave breaking scenario of the corresponding inviscid ion dynamics. The inclusion of viscosity is shown numerically to stabilize the associated density collapse giving rise to a well defined fast ion peak reminiscent of adhesive matter. In purely convection driven flows the Lagrangian flow velocity is given by its initial value and hence the Lagrangian velocity gradient tensor can be evaluated accurately to find out the appearance of singularities in density and vorticity and the emergence of new structures such as wavelets in one-dimension (1D). In cosmology referring to the pancake model of Zel'dovich and the adhesion model of Gurbatov and Saichev, both assuming a clumping of matter at the intersection points of fluid particle trajectories (i.e. at the caustics), the foam-like large-scale structure of our Universe observed recently by Chandra X-ray observatory may be explained by the 3D convection of weakly interacting dark matter. Recent developments in plasma and nanotechnology-the miniaturization and fabrication of nanoelectronic devices being one example-have reinforced the interest in the quasi-ballistic electron transport in diodes and triodes, a field which turns out to be best treated by the Lagrangian fluid description. It is shown that the well-known space-charge-limited flow given by Child-Langmuir turns out to be incorrect in cases of finite electron injection velocities at the emitting electrode. In that case it is an intrinsic bifurcation scenario which is responsible for current limitation rather than electron reflection at the virtual cathode as intuitively assumed by Langmuir. The inclusion of a Drude friction term in the electron momentum equation can be handled solely by the Lagrangian fluid description. Exploiting the formula in case of field emission it is possible to bridge ballistic and drift-dominated transport. Furthermore, the transient processes in the electron transport triggered by the switching of the anode potential are shown to be perfectly accounted for by means of the Lagrangian fluid description. Finally, by use of the Lagrangian ion fluid equations in case of a two component, current driven plasma we derive a system of two coupled scalar wave equations which involve the specific volume of ions and electrons, respectively. It has a small amplitude strange soliton solution with unusual scaling properties. In case of charge neutrality the existence of two types of collapses are predicted, one being associated with a density excavation, the other one with a density clumping as in the laser induced ion expansion problem and in the cosmic sticking matter problem. However, only the latter will survive charge separation and hence be observable. In summary, the Lagrangian method of solving fluid equations turns out to be a powerful tool for compressible media in general. It offers new perspectives and addresses to a broad audience of physicists with interest in fields such as plasma and fluid dynamics, semiconductor- and astrophysics, to mention few of them.

Intraspecific Adaptations to Thermal Gradients in a Cosmopolitan Coccolithophore

NASA Astrophysics Data System (ADS)

Matson, P. G.; Ladd, T. M.; Iglesias-Rodriguez, D.

2016-02-01

The species concept in marine phytoplankton has enormous biological complexity. Differences in genomic, morphological, physiological, biogeochemical, and ecological/biogeographic properties between strains of the same species can be comparable or even exceed those between species. This complexity is particularly pronounced in the cosmopolitan coccolithophore species Emiliania huxleyi. This bloom-forming species is found at nearly every latitude in a variety of environments including upwelling regions, and exposed to large temperature gradients. We present results from experiments using two strains of E. huxleyi isolated from different latitudes and environmental conditions. Tests involved semi-continuous culturing in lab manipulation experiments to determine how carbon fixation, growth, and morphology respond to temperature-driven alterations in physico-chemical conditions. This talk will discuss the observed differences in physiology within an ecological context and the implications of these biogeochemical differences in modeling carbon fluxes driven by phytoplankton.

Simultaneous use of camera and probe diagnostics to unambiguously identify and study the dynamics of multiple underlying instabilities during the route to plasma turbulence.

PubMed

Thakur, S C; Brandt, C; Light, A; Cui, L; Gosselin, J J; Tynan, G R

2014-11-01

We use multiple-tip Langmuir probes and fast imaging to unambiguously identify and study the dynamics of underlying instabilities during the controlled route to fully-developed plasma turbulence in a linear magnetized helicon plasma device. Langmuir probes measure radial profiles of electron temperature, plasma density and potential; from which we compute linear growth rates of instabilities, cross-phase between density and potential fluctuations, Reynold's stress, particle flux, vorticity, time-delay estimated velocity, etc. Fast imaging complements the 1D probe measurements by providing temporally and spatially resolved 2D details of plasma structures associated with the instabilities. We find that three radially separated plasma instabilities exist simultaneously. Density gradient driven resistive drift waves propagating in the electron diamagnetic drift direction separate the plasma into an edge region dominated by strong, velocity shear driven Kelvin-Helmholtz instabilities and a central core region which shows coherent Rayleigh-Taylor modes propagating in the ion diamagnetic drift direction. The simultaneous, complementary use of both probes and camera was crucial to identify the instabilities and understand the details of the very rich plasma dynamics.

Dynamical Defects in Rotating Magnetic Skyrmion Lattices

NASA Astrophysics Data System (ADS)

Pöllath, S.; Wild, J.; Heinen, L.; Meier, T. N. G.; Kronseder, M.; Tutsch, L.; Bauer, A.; Berger, H.; Pfleiderer, C.; Zweck, J.; Rosch, A.; Back, C. H.

2017-05-01

The chiral magnet Cu2 OSeO3 hosts a Skyrmion lattice that may be equivalently described as a superposition of plane waves or a lattice of particlelike topological objects. A thermal gradient may break up the Skyrmion lattice and induce rotating domains, raising the question of which of these scenarios better describes the violent dynamics at the domain boundaries. Here, we show that in an inhomogeneous temperature gradient caused by illumination in a Lorentz transmission electron microscope different parts of the Skyrmion lattice can be set into motion with different angular velocities. Tracking the time dependence, we show that the constant rearrangement of domain walls is governed by dynamic 5-7 defects arranging into lines. An analysis of the associated defect density is described by Frank's equation and agrees well with classical 2D Monte Carlo simulations. Fluctuations of boundaries show a surgelike rearrangement of Skyrmion clusters driven by defect rearrangement consistent with simulations treating Skyrmions as point particles. Our findings underline the particle character of the Skyrmion.

Inertial Currents in Isotropic Plasma

NASA Technical Reports Server (NTRS)

Heinemann, M.; Erickson, G. M.; Pontius, D. H., Jr.

1993-01-01

The magnetospheric convection electric field contributes to Birkeland currents. The effects of the field are to polarize the plasma by displacing the bounce paths of the ions from those of electrons, to redistribute the pressure so that it is not constant along magnetic field lines, and to enhance the pressure gradient by the gradient of the bulk speed. Changes in the polarization charge during the convection of the plasma are neutralized by electrons in the form of field-aligned currents that close through the ionosphere. The pressure drives field-aligned currents through its gradient in the same manner as in quasi-static plasma, but with modifications that are important if the bulk speed is of the order of the ion thermal speed; the variations in the pressure along field lines are maintained by a weak parallel potential drop. These effects are described in terms of the field-aligned currents in steady state, isotropic, MED plasma. Solutions are developed by taking the MHD limit of two-fluid solutions and illustrated in the special case of Maxwellian plasma for which the temperature is constant along magnetic field lines. The expression for the Birkeland current density is a generalization of Vasyliunas' expression for the field-aligned current density in quasi-static plasma and provides a unifying expression when both pressure gradients and ion inertia operate simultaneously as sources of field-aligned currents. It contains a full account of different aspects of the ion flow (parallel and perpendicular velocity and vorticity) that contribute to the currents. Contributions of ion inertia to field-aligned currents will occur in regions of strong velocity shear, electric field reversal, or large gradients in the parallel velocity or number density, and may be important in the low-latitude boundary layer, plasma sheet boundary layer, and the inner edge region of the plasma sheet.

Inertial currents in isotropic plasma

NASA Technical Reports Server (NTRS)

Heinemann, M.; Erickson, G. M.; Pontius, D. H. JR.

1994-01-01

The magnetospheric convection electric field contributes to Birkeland currents. The effects of the field are to polarize the plasma by displacing the bounce paths of the ions from those of electrons, to redistribute the pressure so that it is not constant along magnetic field lines, and to enhance the pressure gradient by the gradient of the bulk speed. Changes in the polarization charge during the convection of the plasma are neutralized by electrons in the form of field-aligned currents that close through the ionosphere. The pressure drives field-aligned currents through its gradient in the same manner as in quasi-static plasma, but with modifications that are important if the bulk speed is of the order of the ion thermal speed; the variations in the pressure along field lines are maintained by a weak parallel potential drop. These effects are described in terms of the field-aligned currents in steady state, isotropic, magnetohyrodynamic (MHD) plasma. Solutions are developed by taking the MHD limit of two-fluid solutions and illustrated in the special case of Maxwellian plasma for which the temperature is constant along magnetic field lines. The expression for the Birkeland current density is a generalization of Vasyliunas' expression for the field-aligned current density in quasi-static plasma and provides a unifying expression when both pressure gradients and ion inertia operate simultaneously as sources of field-aligned currents. It contains a full account of different aspects of the ion flow (parallel and perpendicular velocity and vorticity) that contribute to the currents. Contributions of ion inertia to field-aligned currents will occur in regions of strong velocity shear, electric field reversal, or large gradients in the parallel velocity or number density, and may be important in the low-latitude boundary layer, plasma sheet boundary layer, and the inner edge region of the plasma sheet.

Inertial currents in isotropic plasma

NASA Technical Reports Server (NTRS)

Heinemann, M.; Erickson, G. M.; Pontius, D. H., Jr.

1994-01-01

The magnetospheric convection electric field contributes to Birkeland currents. The effects of the field are to polarize the plasma by displacing the bounce paths of the ions from those of electrons, to redistribute the pressure so that it is not constant along magnetic field lines, and to enhance the pressure gradient by the gradient of the bulk speed. Changes in the polarization charge during the convection of the plasma are neutralized by electrons in the form of field-aligned currents that close through the ionosphere. The pressure drives field-aligned currents through its gradient in the same manner as in quasi-static plasmas, but with modifications that are important if the bulk speed is of the order of the ion thermal speed; the variations in the pressure along field lines are maintained by a weak parallel potential drop. These effects are described in terms of the field-aligned currents in steady state, isotropic, MHD plasma. Solutions are developed by taking the MHD limit ot two-fluid solutions and illustrated in the special case of Maxwellian plasma for which the temperature is constant along magnetic field lines. The expression for the Birkeland current density is a generalization of Vasyliunas' expression for the field-aligned current density in quasi-static plasma and provides a unifying expression when both pressure gradients and ion inertia operate simultaneously as sources of field-aligned currents. It contains a full account of different aspects of the ion flow (parallel and perpendicular velocity and vorticity) that contribute to the currents. Contributions of ion inertia to field-aligned currents will occur in regions of strong velocity shear, electric field reversal, or large gradients in the parallel velocity or number density, and may be important in the low-latitude boundary layer, plasma sheet boundary layer, and the inner edge region of the plasma sheet.

Novel Applications of Magnetic Fields for Fluid Flow Control and for Simulating Variable Gravity Conditions

NASA Technical Reports Server (NTRS)

Ramachandran, N.

2005-01-01

Static and dynamic magnetic fields have been used to control convection in many materials processing applications. In most of the applications, convection control (damping or enhancement) is achieved through the Lorentz force that can be tailored to counteract/assist dominant system flows. This technique has been successfully applied to liquids that are electrically conducting, such as high temperature melts of semiconductors, metals and alloys, etc. In liquids with low electrical conductivity such as ionic solutions of salts in water, the Lorentz force is weak and hence not very effective and alternate ways of flow control are necessary. If the salt in solution is paramagnetic then the variation of magnetic susceptibility with temperature and/or concentration can be used for flow control. For thermal buoyancy driven flows this can be accomplished in a temperature range below the Curie point of the salt. The magnetic force is proportional to the magnetic susceptibility and the product of the magnetic field and its gradient. By suitably positioning the experiment cell in the magnet, system flows can be assisted or countered, as desired. A similar approach can be extended to diamagnetic substances and fluids but the required magnetic force is considerably larger than that required for paramagnetic substances. The presentation will provide an overview of work to date on a NASA fluid physics sponsored project that aims to test the hypothesis of convective flow control using strong magnetic fields in protein crystal growth. The objective is to understand the nature of the various forces that come into play, delineate causative factors for fluid flow and to quantify them through experiments, analysis, and numerical modeling. The seminar will report specifically on the experimental results using paramagnetic salts and solutions in magnetic fields and compare them to analytical predictions. Applications of the concept to protein crystallization studies will be discussed. The use of strong magnetic fields for terrestrially simulating variable gravity environments and applications supporting the NASA Exploration Initiative will also be briefly discussed.

Permeability evolution during non-linear viscous creep of porous calcite rocks

NASA Astrophysics Data System (ADS)

Xiao, X.; Evans, B.; Bernabe, Y.

2005-12-01

Below the brittle-ductile transition, permeability might be exceedingly small, due to compaction facilitated by intracrystalline plasticity or viscous creep. The ductile lower crust may consist of depth intervals or isolated domains of relatively high permeability, where the fluid pressures are at or near lithostatic values. Fluid escape from metamorphic rocks likely involves episodic hydrofracturing or porosity-wave propagation driven by the difference between the gradients of fluid and rock pressure. Although it is generally agreed that fluid flow in ductile porous rocks is critically dependent on the interplay between the fluid properties and the rheology of the rock matrix, more experimental work is needed to elucidate the ways that permeability and porosity change during deformation at elevated temperature and pressures. Triaxial tests of synthetic calcite marbles containing 10, 20, or 30 wt% quartz and up to 9% residual porosity done at temperature up to 873K, reported earlier (Xiao and Evans, 2003), indicate that shear-enhanced compaction occurs under triaxial conditions, roughly consistent with a model of void collapse by viscous creep (Budiansky et al., 1982). In this study, we report the effect of viscous creep on the permeability of those porous rocks during both isostatic and conventional triaxial loading. The tests were performed at confining pressure of 300 MPa, pore pressures between 50 to 290 MPa, temperatures from 673 to 873K and strain rates of 3.0× 10-5 s-1. Argon gas was used as the pore fluid. Under isostatic loading conditions, permeability, k, is nonlinearly related to porosity, Φ. Over small changes in porosity, the two parameters are approximately related as k~Φn. The exponent n progressively increases as the porosity decreases to a finite value, suggesting a percolation porosity. When subjected to triaxial deformation, the calcite-quartz aggregates exhibit a shear-enhanced compaction, but permeability does not decrease as rapidly as it does during isostatic conditions; the exponent n varies between 2 and 3. Non-isostatic deformation seems to reduce the percolation threshold, and, in fact, enhances the permeability relative to that at the same porosity during isostatic compaction. Our data provide constraints on the governing parameters of the compaction theory, and may have far-reaching implications for melt extraction from partially molten rocks, for the expulsion of sedimentary fluids, and for fluid flow during deformation and metamorphism.

Modeling of Propagation of Interacting Cracks Under Hydraulic Pressure Gradient

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Hai; Mattson, Earl Douglas; Podgorney, Robert Karl

A robust and reliable numerical model for fracture initiation and propagation, which includes the interactions among propagating fractures and the coupling between deformation, fracturing and fluid flow in fracture apertures and in the permeable rock matrix, would be an important tool for developing a better understanding of fracturing behaviors of crystalline brittle rocks driven by thermal and (or) hydraulic pressure gradients. In this paper, we present a physics-based hydraulic fracturing simulator based on coupling a quasi-static discrete element model (DEM) for deformation and fracturing with conjugate lattice network flow model for fluid flow in both fractures and porous matrix. Fracturingmore » is represented explicitly by removing broken bonds from the network to represent microcracks. Initiation of new microfractures and growth and coalescence of the microcracks leads to the formation of macroscopic fractures when external and/or internal loads are applied. The coupled DEM-network flow model reproduces realistic growth pattern of hydraulic fractures. In particular, simulation results of perforated horizontal wellbore clearly demonstrate that elastic interactions among multiple propagating fractures, fluid viscosity, strong coupling between fluid pressure fluctuations within fractures and fracturing, and lower length scale heterogeneities, collectively lead to complicated fracturing patterns.« less

Profile modifications in laser-driven temperature fronts using flux-limiters and delocalization models

NASA Astrophysics Data System (ADS)

Colombant, Denis; Manheimer, Wallace; Busquet, Michel

2004-11-01

A simple steady-state model using flux-limiters by Day et al [1] showed that temperature profiles could formally be double-valued. Stability of temperature profiles in laser-driven temperature fronts using delocalization models was also discussed by Prasad and Kershaw [2]. We have observed steepening of the front and flattening of the maximum temperature in laser-driven implosions [3]. Following the simple model first proposed in [1], we solve for a two-boundary value steady-state heat flow problem for various non-local heat transport models. For the more complicated models [4,5], we obtain the steady-state solution as the asymptotic limit of the time-dependent solution. Solutions will be shown and compared for these various models. 1.M.Day, B.Merriman, F.Najmabadi and R.W.Conn, Contrib. Plasma Phys. 36, 419 (1996) 2.M.K.Prasad and D.S.Kershaw, Phys. Fluids B3, 3087 (1991) 3.D.Colombant, W.Manheimer and M.Busquet, Bull. Amer. Phys. Soc. 48, 326 (2003) 4.E.M.Epperlein and R.W.Short, Phys. Fluids B3, 3092 (1991) 5.W.Manheimer and D.Colombant, Phys. Plasmas 11, 260 (2004)

Designing a Dielectric Laser Accelerator on a Chip

NASA Astrophysics Data System (ADS)

Niedermayer, Uwe; Boine-Frankenheim, Oliver; Egenolf, Thilo

2017-07-01

Dielectric Laser Acceleration (DLA) achieves gradients of more than 1GeV/m, which are among the highest in non-plasma accelerators. The long-term goal of the ACHIP collaboration is to provide relativistic (>1 MeV) electrons by means of a laser driven microchip accelerator. Examples of ’’slightly resonant” dielectric structures showing gradients in the range of 70% of the incident laser field (1 GV/m) for electrons with beta=0.32 and 200% for beta=0.91 are presented. We demonstrate the bunching and acceleration of low energy electrons in dedicated ballistic buncher and velocity matched grating structures. However, the design gradient of 500 MeV/m leads to rapid defocusing. Therefore we present a scheme to bunch the beam in stages, which does not only reduce the energy spread, but also the transverse defocusing. The designs are made with a dedicated homemade 6D particle tracking code.

The Future with Cryogenic Fluid Dynamics

NASA Astrophysics Data System (ADS)

Scurlock, R. G.

The applications of cryogenic systems have expanded over the past 50 years into many areas of our lives. During this time, the impact of the common features of Cryogenic Fluid Dynamics, CryoFD, on the economic design of these cryogenic systems, has grown out of a long series of experimental studies carried out by teams of postgraduate students at Southampton University.These studies have sought to understand the heat transfer and convective behavior of cryogenic liquids and vapors, but they have only skimmed over the many findings made, on the strong convective motions of fluids at low temperatures. The convection takes place in temperature gradients up to 10,000 K per meter, and density gradients of 1000% per meter and more, with rapid temperature and spatially dependent changes in physical properties like viscosity and surface tension, making software development and empirical correlations almost impossible to achieve. These temperature and density gradients are far larger than those met in other convecting systems at ambient temperatures, and there is little similarity. The paper will discuss the likely impact of CryoFD on future cryogenic systems, and hopefully inspire further research to support and expand the use of existing findings, and to improve the economy of present-day systems even more effectively. Particular examples to be mentioned include the following. Doubling the cooling power of cryo-coolers by a simple use of CryoFD. Reducing the boil-off rate of liquid helium stored at the South Pole, such that liquid helium availability is now all-the-year-round. Helping to develop the 15 kA current leads for the LHC superconducting magnets at CERN, with much reduced refrigeration loads. Improving the heat transfer capability of boiling heat transfer surfaces by 10 to 100 fold. This paper is an edited text of an invited plenary presentation at ICEC25/ICMC2014 by Professor Scurlock on the occasion of his being presented with the ICEC Mendelssohn Award for his many contributions to Cryogenics. As long ago as 1992, he first proposed in his "History and Origins of Cryogenics" that the temperature range for Cryogenics should be extended up to the ice-point at 273K. This paper expands on this proposal with the implicit assumption that Cryogenic Fluid Dynamics can provide a universal basis for modelling heat transfer and convective fluid behaviour of all fluids, at all temperatures, below the ice-point at 273K; or below 250K if you wish to exclude refrigeration engineering."

High-quality electron beam generation in a proton-driven hollow plasma wakefield accelerator

NASA Astrophysics Data System (ADS)

Li, Y.; Xia, G.; Lotov, K. V.; Sosedkin, A. P.; Hanahoe, K.; Mete-Apsimon, O.

2017-10-01

Simulations of proton-driven plasma wakefield accelerators have demonstrated substantially higher accelerating gradients compared to conventional accelerators and the viability of accelerating electrons to the energy frontier in a single plasma stage. However, due to the strong intrinsic transverse fields varying both radially and in time, the witness beam quality is still far from suitable for practical application in future colliders. Here we demonstrate the efficient acceleration of electrons in proton-driven wakefields in a hollow plasma channel. In this regime, the witness bunch is positioned in the region with a strong accelerating field, free from plasma electrons and ions. We show that the electron beam carrying the charge of about 10% of 1 TeV proton driver charge can be accelerated to 0.6 TeV with a preserved normalized emittance in a single channel of 700 m. This high-quality and high-charge beam may pave the way for the development of future plasma-based energy frontier colliders.

Gyrokinetic Particle Simulations of Neoclassical Transport

NASA Astrophysics Data System (ADS)

Lin, Zhihong

A time varying weighting (delta f) scheme based on the small gyro-radius ordering is developed and applied to a steady state, multi-species gyrokinetic particle simulation of neoclassical transport. Accurate collision operators conserving momentum and energy are developed and implemented. Benchmark simulation results using these operators are found to agree very well with neoclassical theory. For example, it is dynamically demonstrated that like-particle collisions produce no particle flux and that the neoclassical fluxes are ambipolar for an ion -electron plasma. An important physics feature of the present scheme is the introduction of toroidal flow to the simulations. In agreement with the existing analytical neoclassical theory, ion energy flux is enhanced by the toroidal mass flow and the neoclassical viscosity is a Pfirsch-Schluter factor times the classical viscosity in the banana regime. In addition, the poloidal electric field associated with toroidal mass flow is found to enhance density gradient driven electron particle flux and the bootstrap current while reducing temperature gradient driven flux and current. Modifications of the neoclassical transport by the orbit squeezing effects due to the radial electric field associated with sheared toroidal flow are studied. Simulation results indicate a reduction of both ion thermal flux and neoclassical toroidal rotation. Neoclassical theory in the steep gradient profile regime, where conventional neoclassical theory fails, is examined by taking into account finite banana width effects. The relevance of these studies to interesting experimental conditions in tokamaks is discussed. Finally, the present numerical scheme is extended to general geometry equilibrium. This new formulation will be valuable for the development of new capabilities to address complex equilibria such as advanced stellarator configurations and possibly other alternate concepts for the magnetic confinement of plasmas. In general, the present work demonstrates a valuable new capability for studying important aspects of neoclassical transport inaccessible by conventional analytical calculation processes.

Design of a high-pressure circulating pump for viscous liquids.

PubMed

Seifried, Bernhard; Temelli, Feral

2009-07-01

The design of a reciprocating dual action piston pump capable of circulating viscous fluids at pressures of up to 34 MPa (5000 psi) and temperatures up to 80 degrees C is described. The piston of this pump is driven by a pair of solenoids energized alternatively by a 12 V direct current power supply controlled by an electronic controller facilitating continuously adjustable flow rates. The body of this seal-less pump is constructed using off-the-shelf parts eliminating the need for custom made parts. Both the electronic controller and the pump can be assembled relatively easily. Pump performance has been evaluated at room temperature (22 degrees C) and atmospheric pressure using liquids with low and moderately high viscosities, such as ethanol and corn oil, respectively. At ambient conditions, the pump delivered continuous flow of ethanol and corn oil at a flow rate of up to 170 and 17 cm3/min, respectively. For pumping viscous fluids comparable to corn oil, an optimum reciprocation frequency was ascertained to maximize flow rate. For low viscosity liquids such as ethanol, a linear relationship between the flow rate and reciprocation frequency was determined up to the maximum reciprocation frequency of the pump. Since its fabrication, the pump has been used in our laboratory for circulating triglycerides in contact with supercritical carbon dioxide at pressures of up to 25 MPa (3600 psi) and temperatures up to 70 degrees C on a daily basis for a total of more than 1500 h of operation functioning trouble free.

Stabilization of electron-scale turbulence by electron density gradient in national spherical torus experiment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ruiz Ruiz, J.; White, A. E.; Ren, Y.

2015-12-15

Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the electron gyro-scale, k{sub ⊥}ρ{sub e} ≲ 1, can be responsible for anomalous electron thermal transport in NSTX. Electron scale (high-k) turbulence is diagnosed in NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report on stabilization effects of the electron density gradient on electron-scale density fluctuations in a set of neutral beam injection heated H-mode plasmas. We found that the absence of high-k density fluctuations from measurements is correlated with large equilibrium density gradient, which ismore » shown to be consistent with linear stabilization of ETG modes due to the density gradient using the analytical ETG linear threshold in F. Jenko et al. [Phys. Plasmas 8, 4096 (2001)] and linear gyrokinetic simulations with GS2 [M. Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1995)]. We also found that the observed power of electron-scale turbulence (when it exists) is anti-correlated with the equilibrium density gradient, suggesting density gradient as a nonlinear stabilizing mechanism. Higher density gradients give rise to lower values of the plasma frame frequency, calculated based on the Doppler shift of the measured density fluctuations. Linear gyrokinetic simulations show that higher values of the electron density gradient reduce the value of the real frequency, in agreement with experimental observation. Nonlinear electron-scale gyrokinetic simulations show that high electron density gradient reduces electron heat flux and stiffness, and increases the ETG nonlinear threshold, consistent with experimental observations.« less

Chemical environments of submarine hydrothermal systems. [supporting abiogenetic theory

NASA Technical Reports Server (NTRS)

Shock, Everett L.

1992-01-01

The paper synthesizes diverse information about the inorganic geochemistry of submarine hydrothermal systems, provides a description of the fundamental physical and chemical properties of these systems, and examines the implications of high-temperature, fluid-driven processes for organic synthesis. Emphasis is on a few general features, i.e., pressure, temperature, oxidation states, fluid composition, and mineral alteration, because these features will control whether organic synthesis can occur in hydrothermal systems.

Nonlinear resistivity for magnetohydrodynamical models

DOE PAGES

Lingam, M.; Hirvijoki, E.; Pfefferlé, D.; ...

2017-04-20

A new formulation of the plasma resistivity that stems from the collisional momentum-transfer rate between electrons and ions is presented. The resistivity computed herein is shown to depend not only on the temperature and density but also on all other polynomial velocity-space moments of the distribution function, such as the pressure tensor and heat flux vector. The full expression for the collisional momentum-transfer rate is determined and is used to formulate the nonlinear anisotropic resistivity. The new formalism recovers the Spitzer resistivity, as well as the concept of thermal force if the heat flux is assumed to be proportional tomore » a temperature gradient. Furthermore, if the pressure tensor is related to viscous stress, the latter enters the expression for the resistivity. The relative importance of the nonlinear term(s) with respect to the well-established electron inertia and Hall terms is also examined. Lastly, the subtle implications of the nonlinear resistivity, and its dependence on the fluid variables, are discussed in the context of magnetized plasma environments and phenomena such as magnetic reconnection.« less

Room Temperature Deposition Processes Mediated By Ultrafast Photo-Excited Hot Electrons

DTIC Science & Technology

2014-01-30

mechanical through resonant energy transfer. The average electron temperature (Tel) during τ2 evolves as energy is lost through optical and acoustic ...through ballistic collisions and acoustic phonons. The large difference in heat capacities between electrons and the substrate leads to negligible...temperature pyrometer indicated only a ~30oC temperature gradient between the thermocouple location and the topside of the sample which faced the

Reconfigurable Full-Page Braille Displays

NASA Technical Reports Server (NTRS)

Garner, H. Douglas

1994-01-01

Electrically actuated braille display cells of proposed type arrayed together to form full-page braille displays. Like other braille display cells, these provide changeable patterns of bumps driven by digitally recorded text stored on magnetic tapes or in solid-state electronic memories. Proposed cells contain electrorheological fluid. Viscosity of such fluid increases in strong electrostatic field.

MRI temperature and velocity measurements in a fluid layer with heat transfer

NASA Astrophysics Data System (ADS)

Leclerc, S.; Métivier, C.

2018-02-01

Magnetic resonance thermometry (MRT) is an innovative technique which can provide 2D and 3D temperature measurements using magnetic resonance imaging (MRI). Despite the powerful advantages of MRT, this technique is sparcely developed and used in the engineering sciences. In this paper, we investigate the possibility to measure temperatures with MRI in a fluid layer submitted to heat transfer. By imposing a vertical temperature gradient, we study the temperature fields in both conductive and convective regimes. The temperature fields are obtained by measuring the transverse relaxation time T_2 in glycerol, a Newtonian fluid. The MRT protocol is described in detail and the results are presented. We show that for a conductive regime, temperature measurements are in very good agreement with the theoretical profile. In the convective regime, when comparing the temperature and velocity fields obtained by MRI, we get an excellent agreement in terms of flow structure. Temperature uncertainties are found to be less than 1°C for all our results.

Giant osmotic energy conversion measured in a single transmembrane boron nitride nanotube.

PubMed

Siria, Alessandro; Poncharal, Philippe; Biance, Anne-Laure; Fulcrand, Rémy; Blase, Xavier; Purcell, Stephen T; Bocquet, Lydéric

2013-02-28

New models of fluid transport are expected to emerge from the confinement of liquids at the nanoscale, with potential applications in ultrafiltration, desalination and energy conversion. Nevertheless, advancing our fundamental understanding of fluid transport on the smallest scales requires mass and ion dynamics to be ultimately characterized across an individual channel to avoid averaging over many pores. A major challenge for nanofluidics thus lies in building distinct and well-controlled nanochannels, amenable to the systematic exploration of their properties. Here we describe the fabrication and use of a hierarchical nanofluidic device made of a boron nitride nanotube that pierces an ultrathin membrane and connects two fluid reservoirs. Such a transmembrane geometry allows the detailed study of fluidic transport through a single nanotube under diverse forces, including electric fields, pressure drops and chemical gradients. Using this device, we discover very large, osmotically induced electric currents generated by salinity gradients, exceeding by two orders of magnitude their pressure-driven counterpart. We show that this result originates in the anomalously high surface charge carried by the nanotube's internal surface in water at large pH, which we independently quantify in conductance measurements. The nano-assembly route using nanostructures as building blocks opens the way to studying fluid, ionic and molecule transport on the nanoscale, and may lead to biomimetic functionalities. Our results furthermore suggest that boron nitride nanotubes could be used as membranes for osmotic power harvesting under salinity gradients.

On the physics of the pressure and temperature gradients in the edge of tokamak plasmas

NASA Astrophysics Data System (ADS)

Stacey, Weston M.

2018-04-01

An extended plasma fluid theory including atomic physics, radiation, electromagnetic and themodynamic forces, external sources of particles, momentum and energy, and kinetic ion orbit loss is employed to derive theoretical expressions that display the role of the various factors involved in the determination of the pressure and temperature gradients in the edge of tokamak plasmas. Calculations for current experiments are presented to illustrate the magnitudes of various effects including strong radiative and atomic physics edge cooling effects and strong reduction in ion particle and energy fluxes due to ion orbit loss in the plasma edge. An important new insight is the strong relation between rotation and the edge pressure gradient.

Effect of fluid-colloid interactions on the mobility of a thermophoretic microswimmer in non-ideal fluids.

PubMed

Fedosov, Dmitry A; Sengupta, Ankush; Gompper, Gerhard

2015-09-07

Janus colloids propelled by light, e.g., thermophoretic particles, offer promising prospects as artificial microswimmers. However, their swimming behavior and its dependence on fluid properties and fluid-colloid interactions remain poorly understood. Here, we investigate the behavior of a thermophoretic Janus colloid in its own temperature gradient using numerical simulations. The dissipative particle dynamics method with energy conservation is used to investigate the behavior in non-ideal and ideal-gas like fluids for different fluid-colloid interactions, boundary conditions, and temperature-controlling strategies. The fluid-colloid interactions appear to have a strong effect on the colloid behavior, since they directly affect heat exchange between the colloid surface and the fluid. The simulation results show that a reduction of the heat exchange at the fluid-colloid interface leads to an enhancement of colloid's thermophoretic mobility. The colloid behavior is found to be different in non-ideal and ideal fluids, suggesting that fluid compressibility plays a significant role. The flow field around the colloid surface is found to be dominated by a source-dipole, in agreement with the recent theoretical and simulation predictions. Finally, different temperature-control strategies do not appear to have a strong effect on the colloid's swimming velocity.

Interactions between solidification and compositional convection in mushy layers

NASA Technical Reports Server (NTRS)

Worster, M. Grae

1994-01-01

Mushy layers are ubiquitous during the solidification of alloys. They are regions of mixed phase wherein solid crystals are bathed in the melt from which they grew. The matrix of crystals forms a porous medium through which the melt can flow, driven either by external forces or by its own buoyancy in a gravitational field. Buoyancy-driven convection of the melt depends both on temperature gradients, which are necessary for solidification, and on compositional gradients, which are generated as certain components of the alloy are preferentially incorporated in the solid phase and the remaining components are expelled into the melt. In fully liquid regions, the combined action of temperature and concentration on the density of the liquid can cause various forms of double-diffusive convection. However, in the interior of mushy regions the temperature and concentration are thermodynamically coupled so only single-diffusive convection can occur. Typically, the effect of composition on the buoyancy of the melt is much greater than the effect of temperature, and thus convection in mushy layers in driven primarily by the computational gradients within them. The rising interstitial liquid is relatively dilute, having come from colder regions of the mushy layer, where the liquidus concentration is lower, and can dissolve the crystal matrix through which it flows. This is the fundamental process by which chimneys are formed. It is a nonlinear process that requires the convective velocities to be sufficiently large, so fully fledged chimneys (narrow channels) might be avoided by means that weaken the flow. Better still would be to prevent convection altogether, since even weak convection will cause lateral, compositional inhomogeneities in castings. This report outlines three studies that examine the onset of convection within mushy layers.

Analytic Energy Gradients for Variational Two-Electron Reduced-Density-Matrix-Driven Complete Active Space Self-Consistent Field Theory.

PubMed

Maradzike, Elvis; Gidofalvi, Gergely; Turney, Justin M; Schaefer, Henry F; DePrince, A Eugene

2017-09-12

Analytic energy gradients are presented for a variational two-electron reduced-density-matrix (2-RDM)-driven complete active space self-consistent field (CASSCF) method. The active-space 2-RDM is determined using a semidefinite programing (SDP) algorithm built upon an augmented Lagrangian formalism. Expressions for analytic gradients are simplified by the fact that the Lagrangian is stationary with respect to variations in both the primal and the dual solutions to the SDP problem. Orbital response contributions to the gradient are identical to those that arise in conventional CASSCF methods in which the electronic structure of the active space is described by a full configuration interaction (CI) wave function. We explore the relative performance of variational 2-RDM (v2RDM)- and CI-driven CASSCF for the equilibrium geometries of 20 small molecules. When enforcing two-particle N-representability conditions, full-valence v2RDM-CASSCF-optimized bond lengths display a mean unsigned error of 0.0060 Å and a maximum unsigned error of 0.0265 Å, relative to those obtained from full-valence CI-CASSCF. When enforcing partial three-particle N-representability conditions, the mean and maximum unsigned errors are reduced to only 0.0006 and 0.0054 Å, respectively. For these same molecules, full-valence v2RDM-CASSCF bond lengths computed in the cc-pVQZ basis set deviate from experimentally determined ones on average by 0.017 and 0.011 Å when enforcing two- and three-particle conditions, respectively, whereas CI-CASSCF displays an average deviation of 0.010 Å. The v2RDM-CASSCF approach with two-particle conditions is also applied to the equilibrium geometry of pentacene; optimized bond lengths deviate from those derived from experiment, on average, by 0.015 Å when using a cc-pVDZ basis set and a (22e,22o) active space.

Key parameters controlling the performance of catalytic motors.

PubMed

Esplandiu, Maria J; Afshar Farniya, Ali; Reguera, David

2016-03-28

The development of autonomous micro/nanomotors driven by self-generated chemical gradients is a topic of high interest given their potential impact in medicine and environmental remediation. Although impressive functionalities of these devices have been demonstrated, a detailed understanding of the propulsion mechanism is still lacking. In this work, we perform a comprehensive numerical analysis of the key parameters governing the actuation of bimetallic catalytic micropumps. We show that the fluid motion is driven by self-generated electro-osmosis where the electric field originates by a proton current rather than by a lateral charge asymmetry inside the double layer. Hence, the surface potential and the electric field are the key parameters for setting the pumping strength and directionality. The proton flux that generates the electric field stems from the proton gradient induced by the electrochemical reactions taken place at the pump. Surprisingly the electric field and consequently the fluid flow are mainly controlled by the ionic strength and not by the conductivity of the solution, as one could have expected. We have also analyzed the influence of the chemical fuel concentration, electrochemical reaction rates, and size of the metallic structures for an optimized pump performance. Our findings cast light on the complex chemomechanical actuation of catalytic motors and provide important clues for the search, design, and optimization of novel catalytic actuators.

Advances in electrophoretic separations

NASA Technical Reports Server (NTRS)

Snyder, R. S.; Rhodes, P. H.

1984-01-01

Free fluid electrophoresis is described using laboratory and space experiments combined with extensive mathematical modeling. Buoyancy driven convective flows due to thermal and concentration gradients are absent in the reduced gravity environment of space. The elimination of convection in weightlessness offers possible improvements in electrophoresis and other separation methods which occur in fluid media. The mathematical modeling suggests new ways of doing electrophoresis in space and explains various phenomena observed during past experiments. The extent to which ground based separation techniques are limited by gravity induced convection is investigated and space experiments are designed to evaluate specific characteristics of the fluid/particle environment. A series of experiments are proposed that require weightlessness and apparatus is developed that can be used to carry out these experiments in the near future.

Low-gravity fluid flows

NASA Technical Reports Server (NTRS)

Ostrach, S.

1982-01-01

The behavior of fluids in micro-gravity conditions is examined, with particular regard to applications in the growth of single crystals. The effects of gravity on fluid behavior are reviewed, and the advent of Shuttle flights are noted to offer extended time for experimentation and processing in a null-gravity environment, with accelerations resulting solely from maneuvering rockets. Buoyancy driven flows are considered for the cases stable-, unstable-, and mixed-mode convection. Further discussion is presented on g-jitter, surface-tension gradient, thermoacoustic, and phase-change convection. All the flows are present in both gravity and null gravity conditions, although the effects of buoyancy and g-jitter convection usually overshadow the other effects while in a gravity field. Further work is recommended on critical-state and sedimentation processes in microgravity conditions.

Ion distribution in the hot spot of an inertial confinement fusion plasma

NASA Astrophysics Data System (ADS)

Tang, Xianzhu; Guo, Zehua; Berk, Herb

2012-10-01

Maximizing the fusion gain of inertial confinement fusion (ICF) for inertial fusion energy (IFE) applications leads to the standard scenario of central hot spot ignition followed by propagating burn wave through the cold/dense assembled fuel. The fact that the hot spot is surrounded by cold but dense fuel layer introduces subtle plasma physics which requires a kinetic description. Here we perform Fokker-Planck calculations and kinetic PIC simulations for an ICF plasma initially in pressure balance but having large temperature gradient over a narrow transition layer. The loss of the fast ion tail from the hot spot, which is important for fusion reactivity, is quantified by Fokker-Planck models. The role of electron energy transport and the ambipolar electric field is investigated via kinetic simulations and the fluid moment models. The net effect on both hot spot ion temperature and the ion tail distribution, and hence the fusion reactivity, is elucidated.

Electron temperature gradient scale at collisionless shocks.

PubMed

Schwartz, Steven J; Henley, Edmund; Mitchell, Jeremy; Krasnoselskikh, Vladimir

2011-11-18

Shock waves are ubiquitous in space and astrophysics. They transform directed flow energy into thermal energy and accelerate energetic particles. The energy repartition is a multiscale process related to the spatial and temporal structure of the electromagnetic fields within the shock layer. While large scale features of ion heating are known, the electron heating and smaller scale fields remain poorly understood. We determine for the first time the scale of the electron temperature gradient via electron distributions measured in situ by the Cluster spacecraft. Half of the electron heating coincides with a narrow layer several electron inertial lengths (c/ω(pe)) thick. Consequently, the nonlinear steepening is limited by wave dispersion. The dc electric field must also vary over these small scales, strongly influencing the efficiency of shocks as cosmic ray accelerators.

Behavior of a wave-driven buoyant surface jet on a coral reef

USGS Publications Warehouse

Herdman, Liv; Hench, James L.; Fringer, Oliver; Monismith, Stephen G.

2017-01-01

A wave-driven surface buoyant jet exiting a coral reef was studied in order to quantify the amount of water re-entrained over the reef crest. Both moored observations and Lagrangian drifters were used to study the fate of the buoyant jet. To investigate in detail the effects of buoyancy and along-shore flow variations, we developed an idealized numerical model of the system. Consistent with previous work, the ratio of along-shore velocity to jet-velocity and the jet internal Froude number were found to be important determinants of the fate of the jet. In the absence of buoyancy, the entrainment of fluid at the reef crest, creates a significant amount of retention, keeping 60% of water in the reef system. However, when the jet is lighter than the ambient ocean-water, the net effect of buoyancy is to enhance the separation of the jet from shore, leading to a greater export of reef water. Matching observations, our modeling predicts that buoyancy limits retention to 30% of the jet flow for conditions existing on the Moorea reef. Overall, the combination of observations and modeling we present here shows that reef-ocean temperature gradients can play an important role in reef-ocean exchanges.

Behavior of a wave-driven buoyant surface jet on a coral reef

NASA Astrophysics Data System (ADS)

Herdman, Liv M. M.; Hench, James L.; Fringer, Oliver; Monismith, Stephen G.

2017-05-01

A wave-driven surface-buoyant jet exiting a coral reef was studied in order to quantify the amount of water reentrained over the reef crest. Both moored observations and Lagrangian drifters were used to study the fate of the buoyant jet. To investigate in detail the effects of buoyancy and alongshore flow variations, we developed an idealized numerical model of the system. Consistent with previous work, the ratio of alongshore velocity to jet velocity and the jet internal Froude number were found to be important determinants of the fate of the jet. In the absence of buoyancy, the entrainment of fluid at the reef crest creates a significant amount of retention, keeping 60% of water in the reef system. However, when the jet is lighter than the ambient ocean water, the net effect of buoyancy is to enhance the separation of the jet from shore, leading to a greater export of reef water. Matching observations, our modeling predicts that buoyancy limits retention to 30% of the jet flow for conditions existing on the Moorea reef. Overall, the combination of observations and modeling we present here shows that reef-ocean temperature gradients can play an important role in reef-ocean exchanges.

Small-scale plasma, magnetic, and neutral density fluctuations in the nightside Venus ionosphere

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hoegy, W.R.; Brace, L.H.; Kasprazak, W.T.

1990-04-01

Pioneer Venus orbiter measurements have shown that coherent small-scale waves exist in the electron density, the electron temperature, and the magnetic field in the lower ionosphere of Venus just downstream of the solar terminator (Brace et al., 1983). The waves become less regular and less coherent at larger solar zenith angles, and Brace et al. suggested that these structures may have evolved from the terminator waves as they are convected into the nightside ionosphere, driven by the day-to-night plasma pressure gradient. In this paper the authors describe the changes in wave characteristics with solar zenith angle and show that themore » neutral gas also has related wave characteristics, probably because of atmospheric gravity waves. The plasma pressure exceeds the magnetic pressure in the nightside ionosphere at these altitudes, and thus the magnetic field is carried along and controlled by the turbulent motion of the plasma, but the wavelike nature of the thermosphere may also be coupled to the plasma and magnetic structure. They show that there is a significant coherence between the ionosphere, thermosphere, and magnetic parameters at altitudes below about 185 km, a coherence which weakens in the antisolar region. The electron temperature and density are approximately 180{degree} out of phase and consistently exhibit the highest correlation of any pair of variables. Waves in the electron and neutral densities are moderately correlated on most orbits, but with a phase difference that varies within each orbit. The average electron temperature is higher when the average magnetic field is more horizontal; however, the correlation between temperature and dip angle does not extend to individual wave structures observed within a satellite pass, particularly in the antisolar region.« less

Magneto-thermal reconnection processes, related mode momentum and formation of high energy particle populations

DOE PAGES

Coppi, B.; Basu, B.; Fletcher, A.

2017-05-31

In the context of a two-fluid theory of magnetic reconnection, when the longitudinal electron thermal conductivity is relatively large, the perturbed electron temperature tends to become singular in the presence of a reconnected field component and an electron temperature gradient. A finite transverse thermal diffusivity removes this singularity while a finite ‘inductivity’ can remove the singularity of the relevant plasma displacement. Then (i) a new ‘magneto-thermal’ reconnection producing mode, is found with characteristic widths of the reconnection layer remaining significant even when the macroscopic distances involved are very large; (ii) the mode phase velocities can be both in the directionmore » of the electron diamagnetic velocity as well in the opposite (ion) direction. A numerical solution of the complete set of equations has been carried out with a simplified analytical reformulation of the problem. A sequence of processes is analyzed to point out that high-energy particle populations can be produced as a result of reconnection events. These processes involve mode-particle resonances transferring energy of the reconnecting mode to a superthermal ion population and the excitation of lower hybrid waves that can lead to a significant superthermal electron population. The same modes excited in axisymmetric (e.g. toroidal) confinement configurations can extract angular momentum from the main body of the plasma column and thereby sustain a local ‘spontaneous rotation’ of it.« less

A Generalized Electron Heat Flow Relation and its Connection to the Thermal Force and the Solar Wind Parallel Electric Field

NASA Astrophysics Data System (ADS)

Scudder, J. D.

2017-12-01

Enroute to a new formulation of the heat law for the solar wind plasma the role of the invariably neglected, but omnipresent, thermal force for the multi-fluid physics of the corona and solar wind expansion will be discussed. This force (a) controls the size of the collisional ion electron energy exchange, favoring the thermal vs supra thermal electrons; (b) occurs whenever heat flux occurs; (c) remains after the electron and ion fluids come to a no slip, zero parallel current, equilibrium; (d) enhances the equilibrium parallel electric field; but (e) has a size that is theoretically independent of the electron collision frequency - allowing its importance to persist far up into the corona where collisions are invariably ignored in first approximation. The constituent parts of the thermal force allow the derivation of a new generalized electron heat flow relation that will be presented. It depends on the separate field aligned divergences of electron and ion pressures and the gradients of the ion gravitational potential and parallel flow energies and is based upon a multi-component electron distribution function. The new terms in this heat law explicitly incorporate the astrophysical context of gradients, acceleration and external forces that make demands on the parallel electric field and quasi-neutrality; essentially all of these effects are missing in traditional formulations.

Surface Tension Driven Convection Experiment (STDCE)

NASA Technical Reports Server (NTRS)

Ostrach, S.; Kamotani, Y.

1996-01-01

This document reports the results obtained from the Surface Tension Driven Convection Experiment (STDCE) conducted aboard the USML-1 Spacelab in 1992. The experiments used 10 cSt silicone oil placed in an open circular container that was 10 cm wide and 5 cm deep. Thermocapillary flow was induced by using either a cylindrical heater placed along the container centerline or by a CO2 laser. The tests were conducted under various power settings, laser beam diameters, and free surface shapes. Thermistors located at various positions in the test section recorded the temperature of the fluid, heater, walls, and air. An infrared imager was used to measure the free surface temperature. The flow field was studied by flow visualization and the data was analyzed by a PTV technique. The results from the flow visualization and the temperature measurements are compared with the numerical analysis that was conducted in conjunction with the experiment. The compared results include the experimental and numerical velocity vector plots, the streamline plots, the fluid temperature, and the surface temperature distribution.

Generation of Electron Whistler Waves at the Mirror Mode Magnetic Holes: MMS Observations and PIC Simulation

NASA Astrophysics Data System (ADS)

Ahmadi, N.; Wilder, F. D.; Usanova, M.; Ergun, R.; Argall, M. R.; Goodrich, K.; Eriksson, S.; Germaschewski, K.; Torbert, R. B.; Lindqvist, P. A.; Le Contel, O.; Khotyaintsev, Y. V.; Strangeway, R. J.; Schwartz, S. J.; Giles, B. L.; Burch, J.

2017-12-01

The Magnetospheric Multiscale (MMS) mission observed electron whistler waves at the center and at the gradients of magnetic holes on the dayside magnetosheath. The magnetic holes are nonlinear mirror structures which are anti-correlated with particle density. We used expanding box Particle-in-cell simulations and produced the mirror instability magnetic holes. We show that the electron whistler waves can be generated at the gradients and the center of magnetic holes in our simulations which is in agreement with MMS observations. At the nonlinear regime of mirror instability, the proton and electron temperature anisotropy are anti-correlated with the magnetic hole. The plasma is unstable to electron whistler waves at the minimum of the magnetic field structures. In the saturation regime of mirror instability, when magnetic holes are dominant, electron temperature anisotropy develops at the edges of the magnetic holes and electrons become isotropic at the magnetic field minimum. We investigate the possible mechanism for enhancing the electron temperature anisotropy and analyze the electron pitch angle distributions and electron distribution functions in our simulations and compare it with MMS observations.

Brownian motion and entropic torque driven motion of domain walls in antiferromagnets

NASA Astrophysics Data System (ADS)

Yan, Zhengren; Chen, Zhiyuan; Qin, Minghui; Lu, Xubing; Gao, Xingsen; Liu, Junming

2018-02-01

We study the spin dynamics in antiferromagnetic nanowire under an applied temperature gradient using micromagnetic simulations on a classical spin model with a uniaxial anisotropy. The entropic torque driven domain-wall motion and the Brownian motion are discussed in detail, and their competition determines the antiferromagnetic wall motion towards the hotter or colder region. Furthermore, the spin dynamics in an antiferromagnet can be well tuned by the anisotropy and the temperature gradient. Thus, this paper not only strengthens the main conclusions obtained in earlier works [Kim et al., Phys. Rev. B 92, 020402(R) (2015), 10.1103/PhysRevB.92.020402; Selzer et al., Phys. Rev. Lett. 117, 107201 (2016), 10.1103/PhysRevLett.117.107201], but more importantly gives the concrete conditions under which these conclusions apply, respectively. Our results may provide useful information on the antiferromagnetic spintronics for future experiments and storage device design.

Bifurcation Theory of the Transition to Collisionless Ion-temperature-gradient-driven Plasma Turbulence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kolesnikov, R.A.; Krommes, J.A.

The collisionless limit of the transition to ion-temperature-gradient-driven plasma turbulence is considered with a dynamical-systems approach. The importance of systematic analysis for understanding the differences in the bifurcations and dynamics of linearly damped and undamped systems is emphasized. A model with ten degrees of freedom is studied as a concrete example. A four-dimensional center manifold (CM) is analyzed, and fixed points of its dynamics are identified and used to predict a ''Dimits shift'' of the threshold for turbulence due to the excitation of zonal flows. The exact value of that shift in terms of physical parameters is established for themore » model; the effects of higher-order truncations on the dynamics are noted. Multiple-scale analysis of the CM equations is used to discuss possible effects of modulational instability on scenarios for the transition to turbulence in both collisional and collisionless cases.« less

Data-driven gradient algorithm for high-precision quantum control

NASA Astrophysics Data System (ADS)

Wu, Re-Bing; Chu, Bing; Owens, David H.; Rabitz, Herschel

2018-04-01

In the quest to achieve scalable quantum information processing technologies, gradient-based optimal control algorithms (e.g., grape) are broadly used for implementing high-precision quantum gates, but their performance is often hindered by deterministic or random errors in the system model and the control electronics. In this paper, we show that grape can be taught to be more effective by jointly learning from the design model and the experimental data obtained from process tomography. The resulting data-driven gradient optimization algorithm (d-grape) can in principle correct all deterministic gate errors, with a mild efficiency loss. The d-grape algorithm may become more powerful with broadband controls that involve a large number of control parameters, while other algorithms usually slow down due to the increased size of the search space. These advantages are demonstrated by simulating the implementation of a two-qubit controlled-not gate.

Numerical modeling of heat transfer in molten silicon during directional solidification process

DOE Office of Scientific and Technical Information (OSTI.GOV)

Srinivasan, M.; Ramasamy, P., E-mail: ramasamyp@ssn.edu.in

2015-06-24

Numerical investigation is performed for some of the thermal and fluid flow properties of silicon melt during directional solidification by numerical modeling. Dimensionless numbers are extremely useful to understand the heat and mass transfer of fluid flow on Si melt and control the flow patterns during crystal growth processes. The average grain size of whole crystal would increase when the melt flow is laminar. In the silicon growth process, the melt flow is mainly driven by the buoyancy force resulting from the horizontal temperature gradient. The thermal and flow pattern influences the quality of the crystal through the convective heatmore » and mass transport. The computations are carried out in a 2D axisymmetric model using the finite-element technique. The buoyancy effect is observed in the melt domain for a constant Rayleigh number and for different Prandtl numbers. The convective heat flux and Reynolds numbers are studied in the five parallel horizontal cross section of melt silicon region. And also, velocity field is simulated for whole melt domain with limited thermal boundaries. The results indicate that buoyancy forces have a dramatic effect on the most of melt region except central part.« less

Micro-structured heat exchanger for cryogenic mixed refrigerant cycles

NASA Astrophysics Data System (ADS)

Gomse, D.; Reiner, A.; Rabsch, G.; Gietzelt, T.; Brandner, J. J.; Grohmann, S.

2017-12-01

Mixed refrigerant cycles (MRCs) offer a cost- and energy-efficient cooling method for the temperature range between 80 and 200 K. The performance of MRCs is strongly influenced by entropy production in the main heat exchanger. High efficiencies thus require small temperature gradients among the fluid streams, as well as limited pressure drop and axial conduction. As temperature gradients scale with heat flux, large heat transfer areas are necessary. This is best achieved with micro-structured heat exchangers, where high volumetric heat transfer areas can be realized. The reliable design of MRC heat exchangers is challenging, since two-phase heat transfer and pressure drop in both fluid streams have to be considered simultaneously. Furthermore, only few data on the convective boiling and condensation kinetics of zeotropic mixtures is available in literature. This paper presents a micro-structured heat exchanger designed with a newly developed numerical model, followed by experimental results on the single-phase pressure drop and their implications on the hydraulic diameter.

Instability of a shear layer between multicomponent fluids at supercritical pressure

NASA Astrophysics Data System (ADS)

Fu, Qing-fei; Zhang, Yun-xiao; Mo, Chao-jie; Yang, Li-jun

2018-04-01

The temporal instability of a thin shear layer lying between streams of two components of fluids has been studied. The effects of density profile of the layer on the instability behavior were mainly considered. The detailed density profile was obtained through Linear Gradient Theory. The eigenvalue problem was calculated, and the temporal instability curves were obtained for the thermodynamic parameters, e.g. pressure and temperature. The results show that, increase of pressure leads to the increase of the maximum growth rate. However, increasing pressure has opposite effects on the disturbances with small and large wave length. The increase of temperature causes the decrease of disturbance growth rate. The instability behavior of the shear layers was determined mainly by the interval between the inflections of the velocity and density profiles, and the maximum density gradient. The total effects, determined by coupling density stratification, and interval between the inflections of the velocity and density profiles, were quite distinct for different ranges of temperature and pressure.

The unidirectional motion of two heat-conducting liquids in a flat channel

NASA Astrophysics Data System (ADS)

Andreev, V. K.; Cheremnykh, E. N.

2017-10-01

The unidirectional motion of two viscous incompressible liquids in a flat channel is studied. Liquids contact on a flat interface. External boundaries are fixed solid walls, on which the non-stationary temperature gradients are given. The motion is induced by a joint action of thermogravitational and thermocapillary forces and given total non - stationary fluid flow rate in layers. The corresponding initial boundary value problem is conjugate and inverse because the pressure gradients along axes channel have to be determined together with the velocity and temperature field. For this problem the exact stationary solution is found and a priori estimates of non - stationary solutions are obtained. In Laplace images the solution of the non - stationary problem is found in quadratures. It is proved, that the solution converges to a steady regime with time, if the temperature on the walls and the fluid flow rate are stabilized. The numerical calculations for specific liquid media good agree with the theoretical results.

Suppression of Electron Thermal Conduction by Whistler Turbulence in a Sustained Thermal Gradient

NASA Astrophysics Data System (ADS)

Roberg-Clark, G. T.; Drake, J. F.; Reynolds, C. S.; Swisdak, M.

2018-01-01

The dynamics of weakly magnetized collisionless plasmas in the presence of an imposed temperature gradient along an ambient magnetic field is explored with particle-in-cell simulations and modeling. Two thermal reservoirs at different temperatures drive an electron heat flux that destabilizes off-angle whistler-type modes. The whistlers grow to large amplitude, δ B /B0≃1 , and resonantly scatter the electrons, significantly reducing the heat flux. Surprisingly, the resulting steady-state heat flux is largely independent of the thermal gradient. The rate of thermal conduction is instead controlled by the finite propagation speed of the whistlers, which act as mobile scattering centers that convect the thermal energy of the hot reservoir. The results are relevant to thermal transport in high-β astrophysical plasmas such as hot accretion flows and the intracluster medium of galaxy clusters.

Viscous effects on the Rayleigh-Taylor instability with background temperature gradient

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerashchenko, S.; Livescu, D., E-mail: livescu@lanl.gov

The growth rate of the compressible Rayleigh-Taylor instability is studied in the presence of a background temperature gradient, Θ, using a normal mode analysis. The effect of Θ variation is examined for three interface types corresponding to the combinations of the viscous properties of the fluids (inviscid-inviscid, viscous-viscous, and viscous-inviscid) at different Atwood numbers, At, and when at least one of the fluids' viscosity is non-zero, as a function of the Grashof number. For the general case, the resulting ordinary differential equations are solved numerically; however, dispersion relations for the growth rate are presented for several limiting cases. An analyticalmore » solution is found for the inviscid-inviscid interface and the corresponding dispersion equation for the growth rate is obtained in the limit of large Θ. For the viscous-inviscid case, a dispersion relation is derived in the incompressible limit and Θ = 0. Compared to Θ = 0 case, the role of Θ < 0 (hotter light fluid) is destabilizing and becomes stabilizing when Θ > 0 (colder light fluid). The most pronounced effect of Θ ≠ 0 is found at low At and/or at large perturbation wavelengths relative to the domain size for all interface types. On the other hand, at small perturbation wavelengths relative to the domain size, the growth rate for the Θ < 0 case exceeds the infinite domain incompressible constant density result. The results are applied to two practical examples, using sets of parameters relevant to Inertial Confinement Fusion coasting stage and solar corona plumes. The role of viscosity on the growth rate reduction is discussed together with highlighting the range of wavenumbers most affected by viscosity. The viscous effects further increase in the presence of background temperature gradient, when the viscosity is temperature dependent.« less

Effects of heavy ions on electron temperatures in the solar corona and solar wind

NASA Technical Reports Server (NTRS)

Nakada, M. P.

1972-01-01

The effects of the reduction in the thermal conductivity due to heavy ions on electron temperatures in the solar corona and solar wind are examined. Large enhancements of heavy ions in the corona appear to be necessary to give appreciable changes in the thermal gradient of the electrons.

Thermal Field Imaging Using Ultrasound

NASA Technical Reports Server (NTRS)

Andereck, D.; Rahal, S.; Fife, S.

2000-01-01

It is often desirable to be able to determine the temperature field in the interiors of opaque fluids forced into convection by externally imposed temperature gradients. To measure the temperature at a point in an opaque fluid in the usual fashion requires insertion of a probe, and to determine the full field therefore requires either the ability to move this probe or the introduction of multiple probes. Neither of these solutions is particularly satisfactory, although they can lead to quite accurate measurements. As an alternative we have investigated the use of ultrasound as a relatively non-intrusive probe of the temperature field in convecting opaque fluids. The temperature dependence of the sound velocity can be sufficiently great to permit a determination of the temperature from timing the traversal of an ultrasound pulse across a chamber. In this paper we will present our results on convecting flows of transparent and opaque fluids. Our experimental cells consist of relatively narrow rectangular cavities made of thermally insulating materials on the sides, and metal top and bottom plates. The ultrasound transducer is powered by a pulser/receiver, the signal output of which goes to a very high speed signal averager. The average of several hundred to several thousand signals is then sent to a computer for storage and analysis. The experimental procedure is to establish a convective flow by imposing a vertical temperature gradient on the chamber, and then to measure, at several regularly spaced locations, the transit time for an ultrasound pulse to traverse the chamber horizontally (parallel to the convecting rolls) and return to the transducer. The transit time is related to the temperature of the fluid through which the sound pulse travels. Knowing the relationship between transit time and temperature (determined in a separate experiment), we can extract the average temperature across the chamber at that location. By changing the location of the transducer it is then possible to find the average temperature at different locations along the chamber, thereby determining the temperature profile along the system. (In the future we will construct an array of transducers. This will give us the capability to determine the temperature profile much more rapidly than at present, an important consideration if time-dependent phenomena are to be studied.) To validate our procedure we introduced encapsulated liquid crystal particles into glycerol. The liquid crystal particles' color varies depending on the temperature of the fluid. A photograph of the fluid through transparent sidewalls therefore gives a picture of the temperature field of the convecting fluid, independent of our ultrasound imaging. A representative result is shown in the Figure 1, which reveals a very satisfying correspondence between the two techniques. Therefore we have a great deal of confidence that the ultrasound imaging approach is indeed measuring the actual temperature profile of the fluid. The technique has also been applied to convecting liquid metal flows, and representative data will be presented from those experiments as well.

Development of Electric Power Units Driven by Waste Heat

NASA Astrophysics Data System (ADS)

Inoue, Naoyuki; Takeuchi, Takao; Kaneko, Atsushi; Uchimura, Tomoyuki; Irie, Kiichi; Watanabe, Hiroyoshi

For the development of a simple and compact power generator driven by waste heat, working fluids and an expander were studied, then a practical electric power unit was put to test. Many working fluids were calculated with the low temperature power cycle (evaporated at 77°C, condensed at 42°C),and TFE,R123,R245fa were selected to be suitable for the cycle. TFE(Trifluoroethanol CF3CH2OH) was adopted to the actual power generator which was tested. A radial turbine was adopted as an expander, and was newly designed and manufactured for working fluid TFE. The equipment was driven by hot water as heat source and cooling water as cooling source, and generated power was connected with electric utility. Characteristics of the power generating cycle and characteristics of the turbine were obtained experimentally.

Generalized two-temperature model for coupled phonon-magnon diffusion.

PubMed

Liao, Bolin; Zhou, Jiawei; Chen, Gang

2014-07-11

We generalize the two-temperature model [Sanders and Walton, Phys. Rev. B 15, 1489 (1977)] for coupled phonon-magnon diffusion to include the effect of the concurrent magnetization flow, with a particular emphasis on the thermal consequence of the magnon flow driven by a nonuniform magnetic field. Working within the framework of the Boltzmann transport equation, we derive the constitutive equations for coupled phonon-magnon transport driven by gradients of both temperature and external magnetic fields, and the corresponding conservation laws. Our equations reduce to the original Sanders-Walton two-temperature model under a uniform external field, but predict a new magnon cooling effect driven by a nonuniform magnetic field in a homogeneous single-domain ferromagnet. We estimate the magnitude of the cooling effect in an yttrium iron garnet, and show it is within current experimental reach. With properly optimized materials, the predicted cooling effect can potentially supplement the conventional magnetocaloric effect in cryogenic applications in the future.

Guiding of relativistic electron beams in dense matter by laser-driven magnetostatic fields.

PubMed

Bailly-Grandvaux, M; Santos, J J; Bellei, C; Forestier-Colleoni, P; Fujioka, S; Giuffrida, L; Honrubia, J J; Batani, D; Bouillaud, R; Chevrot, M; Cross, J E; Crowston, R; Dorard, S; Dubois, J-L; Ehret, M; Gregori, G; Hulin, S; Kojima, S; Loyez, E; Marquès, J-R; Morace, A; Nicolaï, Ph; Roth, M; Sakata, S; Schaumann, G; Serres, F; Servel, J; Tikhonchuk, V T; Woolsey, N; Zhang, Z

2018-01-09

Intense lasers interacting with dense targets accelerate relativistic electron beams, which transport part of the laser energy into the target depth. However, the overall laser-to-target energy coupling efficiency is impaired by the large divergence of the electron beam, intrinsic to the laser-plasma interaction. Here we demonstrate that an efficient guiding of MeV electrons with about 30 MA current in solid matter is obtained by imposing a laser-driven longitudinal magnetostatic field of 600 T. In the magnetized conditions the transported energy density and the peak background electron temperature at the 60-μm-thick target's rear surface rise by about a factor of five, as unfolded from benchmarked simulations. Such an improvement of energy-density flux through dense matter paves the ground for advances in laser-driven intense sources of energetic particles and radiation, driving matter to extreme temperatures, reaching states relevant for planetary or stellar science as yet inaccessible at the laboratory scale and achieving high-gain laser-driven thermonuclear fusion.

3D Global Fluid Simulations of Turbulence in LAPD

NASA Astrophysics Data System (ADS)

Rogers, Barrett; Ricci, Paolo; Li, Bo

2009-05-01

We present 3D global fluid simulations of the UCLA upgraded Large Plasma Device (LAPD). This device confines an 18-m-long, cylindrically symmetric plasma with a uniform magnetic field. The plasma in the simulations is generated by density and temperature sources inside the computational domain, and sheath boundary conditions are applied at the ends of the plasma column. In 3D simulations of the entire plasma, we observe strong, rotating intermittent density and temperature fluctuations driven by resistive driftwave turbulence with finite parallel wavenumbers. Analogous simulations carried out in the 2D limit (that is, assuming that the motions are purely interchange-like) display much weaker mode activity driven a Kelvin-Helmholtz instability. The properties and scaling of the turbulence and transport will be discussed.

Energy Options for Wireless Sensor Nodes.

PubMed

Knight, Chris; Davidson, Joshua; Behrens, Sam

2008-12-08

Reduction in size and power consumption of consumer electronics has opened up many opportunities for low power wireless sensor networks. One of the major challenges is in supporting battery operated devices as the number of nodes in a network grows. The two main alternatives are to utilize higher energy density sources of stored energy, or to generate power at the node from local forms of energy. This paper reviews the state-of-the art technology in the field of both energy storage and energy harvesting for sensor nodes. The options discussed for energy storage include batteries, capacitors, fuel cells, heat engines and betavoltaic systems. The field of energy harvesting is discussed with reference to photovoltaics, temperature gradients, fluid flow, pressure variations and vibration harvesting.

Energy Options for Wireless Sensor Nodes

PubMed Central

Knight, Chris; Davidson, Joshua; Behrens, Sam

2008-01-01

Reduction in size and power consumption of consumer electronics has opened up many opportunities for low power wireless sensor networks. One of the major challenges is in supporting battery operated devices as the number of nodes in a network grows. The two main alternatives are to utilize higher energy density sources of stored energy, or to generate power at the node from local forms of energy. This paper reviews the state-of-the art technology in the field of both energy storage and energy harvesting for sensor nodes. The options discussed for energy storage include batteries, capacitors, fuel cells, heat engines and betavoltaic systems. The field of energy harvesting is discussed with reference to photovoltaics, temperature gradients, fluid flow, pressure variations and vibration harvesting. PMID:27873975

A Two-Fluid, MHD Coronal Model

NASA Technical Reports Server (NTRS)

Suess, Steven T.; Wang, A.-H.; Wu, S. T.; Poletto, G.; McComas, D. J.

1998-01-01

We describe first results from a numerical two-fluid MHD model of the global structure of the solar corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and momentum sources are required to produce high speed wind from coronal holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature in the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UVCS, and with the Ulysses/SWOOPS proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 solar radii and 5 solar radii (2RS and 5RS) is similar to the density reported from SPARTAN 201-01 measurements by Fisher and Guhathakurta. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer, the temperature and density are similar to those reported empirically by Li et al and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub s), as it is in all other MHD coronal streamer models.

Heat-Flux Measurements from Collective Thomson-Scattering Spectra

NASA Astrophysics Data System (ADS)

Henchen, R. J.; Hu, S. X.; Katz, J.; Froula, D. H.; Rozmus, W.

2015-11-01

Collective Thomson scattering was used to measure heat flux in coronal plasmas. The relative amplitude of the Thomson-scattered power into the up- and downshifted electron plasma wave features was used to determine the flux of electrons moving along the temperature gradient at three to four times the electron thermal velocity. Simultaneously, the ion-acoustic wave features were measured. Their relative amplitude is used to measure the flux of the return-current electrons. The frequencies of these ion-acoustic and electron plasma wave features provide local measurements of the electron temperature and density. These spectra were obtained at five locations along the temperature gradient in a laser-produced blowoff plasma. These measurements of plasma parameters are used to infer the Spitzer -Härm flux qSH = - κ∇Te and are in good agreement with the values of the heat flux measured from the scattering-feature asymmetries. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Thermoelectrically cooled temperature-gradient apparatus for comparative cell and virus temperature studies.

PubMed

Clark, H F; Kaminski, F; Karzon, D T

1970-05-01

Establishment of a near-linear temperature gradient in an incubator has been accomplished by the application of heat to one terminus of a conducting body, normally a metal bar, and the removal of heat from the other terminus of the conducting body. Such incubators have been complex and unwieldy because of the need for mechanical refrigeration. We have described a simplified temperature gradient incubator which uses thermoelectric module cooling coupled with electric heating. Along the gradient, 20 stations in two parallel rows of 10, each accommodating a 30-ml plastic cell culture flask, were continually monitored by an electronic thermometer, and the temperatures were recorded. By manipulation of two simple potentiometer controls, any temperature gradient between 0 and 50 C could be obtained. Minor deviations which occurred between theoretically perfect and obtained temperature gradients were reproducible and readily measured. The gradient incubator was particularly applicable to (i) simultaneously studying a given biological activity over the entire temperature range supporting the growth of a given cell, virus, or microorganism, or (ii) precisely defining the upper or lower temperature limits of a biological system by 10-point determinations. Preliminary experiments have demonstrated the usefulness of the apparatus in characterizing the temperature limits for growth in vitro of cells of reptilian cell lines. The gradient incubator was also successfully utilized for the characterization of the effect of temperature on the efficiency of plating of amphibian viruses and possible temperature variants of those viruses.

Peristaltic transport of copper-water nanofluid saturating porous medium

NASA Astrophysics Data System (ADS)

Abbasi, F. M.; Hayat, T.; Ahmad, B.

2015-03-01

Prime goal of present study is to model the problem for peristaltic transport of copper-water nanofluid in an asymmetric channel. The fluid fills porous space. Analysis is carried out in the presence of mixed conviction, viscous dissipation and heat generation/absorption. Long wavelength and low Reynolds number approximations are utilized in problem formulation. Numerical computations are presented for the axial velocity, pressure gradient, streamlines, temperature and heat transfer rate at the boundary. Graphical analysis is carried out to examine the effects of sundry parameters on flow quantities of interest. Results revealed that the axial velocity of copper-water nanofluid decreases with an increase in the nanoparticle volume fraction. Copper nanoparticles prove effective coolant since they sufficiently reduce the fluid temperature and show increase in the heat transfer between the fluid and solid boundary. Moreover temperature of the fluid decreases by increasing the permeability of porous medium.

Interaction of an ultrarelativistic electron bunch train with a W-band accelerating structure: High power and high gradient

DOE PAGES

Wang, D.; Antipov, S.; Jing, C.; ...

2016-02-05

Electron beam interaction with high frequency structures (beyond microwave regime) has a great impact on future high energy frontier machines. We report on the generation of multimegawatt pulsed rf power at 91 GHz in a planar metallic accelerating structure driven by an ultrarelativistic electron bunch train. This slow-wave wakefield device can also be used for high gradient acceleration of electrons with a stable rf phase and amplitude which are controlled by manipulation of the bunch train. To achieve precise control of the rf pulse properties, a two-beam wakefield interferometry method was developed in which the rf pulse, due to themore » interference of the wakefields from the two bunches, was measured as a function of bunch separation. As a result, measurements of the energy change of a trailing electron bunch as a function of the bunch separation confirmed the interferometry method.« less

Effect of electric field and temperature gradient on orientational dynamics of nematics encapsulated in a hallow cylindrical cavity

NASA Astrophysics Data System (ADS)

Zakharov, A. V.; Maslennikov, P. V.

2018-05-01

We have considered a homogeneously oriented liquid crystal (HOLC) microvolume, confined between two infinitely long horizontal coaxial cylinders subjected to both a temperature gradient ∇T and a radially applied electric field E . We have investigated dynamic field pumping, i.e. studied the interactions between director, velocity, electric fields, as well as a radially applied temperature gradient, where the inner cylinder is kept at a lower temperature than the outer one. In order to elucidate the role of ∇T and E in producing hydrodynamic flow, we have carried out a numerical study of a system of hydrodynamic equations including director reorientation, fluid flow, and temperature redistribution across the HOLC cavity. Calculations show that, under the effect of the named perturbations and at high curvature of the inner cylinder, the HOLC microvolume settles down to a nonstandard pumping regime with maximum flow in the vicinity of the cooler inner cylinder.

Direct numerical simulation of variable surface tension flows using a Volume-of-Fluid method

NASA Astrophysics Data System (ADS)

Seric, Ivana; Afkhami, Shahriar; Kondic, Lou

2018-01-01

We develop a general methodology for the inclusion of a variable surface tension coefficient into a Volume-of-Fluid based Navier-Stokes solver. This new numerical model provides a robust and accurate method for computing the surface gradients directly by finding the tangent directions on the interface using height functions. The implementation is applicable to both temperature and concentration dependent surface tension coefficient, along with the setups involving a large jump in the temperature between the fluid and its surrounding, as well as the situations where the concentration should be strictly confined to the fluid domain, such as the mixing of fluids with different surface tension coefficients. We demonstrate the applicability of our method to the thermocapillary migration of bubbles and the coalescence of drops characterized by a different surface tension coefficient.

Direct measurement of asperity contact growth in quartz at hydrothermal conditions

USGS Publications Warehouse

Beeler, Nicholas M.; Hickman, Stephen H.

2015-01-01

Earthquake recurrence requires interseismic fault restrengthening which results from solid state deformation in room-temperature friction and indentation experiments. In contrast exhumed fault zones show solution-transport processes such as pressure solution and contact overgrowths influence fault zone properties . In the absence of fluid flow, overgrowths are driven by gradients in surface curvature where material is dissolved, diffuses, and precipitates at the contact without convergence normal to the contact. To determine the rate of overgrowth for quartz, we conducted single contact experiments in an externally heated pressure vessel. Convergence was continuously monitored using reflected-light interferometry through a long-working-distance microscope. Contact normal force was constant with an initial effective normal stress of 1.7 MPa, temperature was between 350 and 530{degree sign}C, and water pressure was constant at 150 MPa. Two control experiments were conducted: one dry at 425{degree sign}C and one bi-material (sapphire) at 425{degree sign}C and 150 MPa water pressure. No contact growth or convergence was observed in the controls. For wet single-phase contacts, growth was initially rapid and then decreased with time. No convergence was observed. Fluid inclusions indicate that the contact is not uniformly wetted. The contact is bounded by small regions of high aperture, reflecting local free-face dissolution as the source for the overgrowth. The apparent activation energy is ~125 kJ/mol. Extrapolation predicts rates of contact area increase orders of magnitude faster than in dry, room-temperature and hydrothermal friction experiments, suggesting that natural strength recovery near the base of the seismogenic zone could be dominated by contact overgrowth.

Effect of Interface Shape and Magnetic Field on the Microstructure of Bulk Ge:Ga

NASA Technical Reports Server (NTRS)

Cobb, S. D.; Szofran, F. R.; Volz, M. P.

1999-01-01

Thermal and compositional gradients induced during the growth process contribute significantly to the development of defects in the solidified boule. Thermal gradients and the solid-liquid interface shape can be greatly effected by ampoule material. Compositional gradients are strongly influenced by interface curvature and convective flow in the liquid. Results of this investigation illustrate the combined influences of interface shape and convective fluid flow. An applied magnetic field was used to reduce the effects of convective fluid flow in the electrically conductive melt during directional solidification. Several 8 mm diameter boules of Ga-doped Ge were grown at different field strengths, up to 5 Tesla, in four different ampoule materials. Compositional profiles indicate mass transfer conditions ranged from completely mixed to diffusion controlled. The influence of convection in the melt on the developing crystal microstructure and defect density was investigated as a function of field strength and ampoule material. Chemical etching and electron backscattered electron diffraction were used to map the crystal structure of each boule along the center plane. Dislocation etch pit densities were measured for each boule. Results show the influence of magnetic field strength and ampoule material on overall crystal quality.

Temperature gradient effects on vapor diffusion in partially-saturated porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Webb, S.W.

1999-07-01

Vapor diffusion in porous media in the presence of its own liquid may be enhanced due to pore-scale processes, such as condensation and evaporation across isolated liquid islands. Webb and Ho (1997) developed one-and two-dimensional mechanistic pore-scale models of these processes in an ideal porous medium. For isothermal and isobaric boundary conditions with a concentration gradient, the vapor diffusion rate was significantly enhanced by these liquid island processes compared to a dry porous media. The influence of a temperature gradient on the enhanced vapor diffusion rate is considered in this paper. The two-dimensional pore network model which is used inmore » the present study is shown. For partially-saturated conditions, a liquid island is introduced into the top center pore. Boundary conditions on the left and right sides of the model are specified to give the desired concentration and temperature gradients. Vapor condenses on one side of the liquid island and evaporates off the other side due to local vapor pressure lowering caused by the interface curvature, even without a temperature gradient. Rather than acting as an impediment to vapor diffusion, the liquid island actually enhances the vapor diffusion rate. The enhancement of the vapor diffusion rate can be significant depending on the liquid saturation. Vapor diffusion is enhanced by up to 40% for this single liquid island compared to a dry porous medium; enhancement factors of up to an order of magnitude have been calculated for other conditions by Webb and Ho (1997). The dominant effect on the enhancement factor is the concentration gradient; the influence of the temperature gradient is smaller. The significance of these results, which need to be confirmed by experiments, is that the dominant model of enhanced vapor diffusion (EVD) by Philip and deVries (1957) predicts that temperature gradients must exist for EVD to occur. If there is no temperature gradient, there is no enhancement. The present results indicate that EVD is predominantly driven by concentration gradients; temperature gradients are less important. Therefore, the EVD model of Philip and deVries may need to be modified to reflect these results.« less

Perpetual Motion with Maxwell's Demon

NASA Astrophysics Data System (ADS)

Gordon, Lyndsay G. M.

2002-11-01

A method for producing a temperature gradient by Brownian motion in an equilibrated isolated system composed of two fluid compartments and a separating adiabatic membrane is discussed. This method requires globular protein molecules, partially embedded in the membrane, to alternate between two conformations which lie on opposite sides of the membrane. The greater part of each conformer is bathed by one of the fluids and rotates in Brownian motion around its axis, perpendicular to the membrane. Rotational energy is transferred through the membrane during conformational changes. Angular momentum is conserved during the transitions. The energy flow becomes asymmetrical when the conformational changes of the protein are sterically hindered by two of its side-chains, the positions of which are affected by the angular velocity of the rotor. The heat flow increases the temperature gradient in contravention of the Second Law. A second hypothetical model which illustrates solute transfer at variance with the Second Law is also discussed.

Experimental Study of Instantaneous Evolution of A Scalar Gradient With Small-scale Anisotropic Injection In A 2d, Periodic Flow

NASA Astrophysics Data System (ADS)

Godard, G.; Paranthoen, P.; Gonzalez, M.

Anisotropic small-scale injection of a scalar (e.g. heat) in a turbulent medium can be performed by means of a small-diameter line source as already done in a turbulent plane jet and a turbulent boundary layer (Rosset et al., Phys. Fluids 13, 3729, 2001). In such conditions, however, experiment is revealed delicate especially, as regard to temperature gradient measurements in the near-field of the source. In the present study, we get rid of previous difficulties by setting up the heated line source in a simpler flow namely, a Bénard-von Kármán street. Under this situation, owing to a phase reference, the history of the instantaneous temperature gradient can be scrutinized from the vicinity of the source. Gradient statistics (second-order mo- ments, skewness, kurtosis ...) is derived which allows us to follow the evolution of anisotropy downstream of the line source. Alignment of temperature gradient with respect to strain principal axes is also analyzed. This experiment provides a precise knowledge of the way in which a scalar gradient evolves under the combined actions of strain, vorticity and molecular diffusion.

Kinetics of liquid-mediated crystallization of amorphous Ge from multi-frame dynamic transmission electron microscopy

DOE PAGES

Santala, M. K.; Raoux, S.; Campbell, G. H.

2015-12-24

The kinetics of laser-induced, liquid-mediated crystallization of amorphous Ge thin films were studied using multi-frame dynamic transmission electron microscopy (DTEM), a nanosecond-scale photo-emission transmission electron microscopy technique. In these experiments, high temperature gradients are established in thin amorphous Ge films with a 12-ns laser pulse with a Gaussian spatial profile. The hottest region at the center of the laser spot crystallizes in ~100 ns and becomes nano-crystalline. Over the next several hundred nanoseconds crystallization continues radially outward from the nano-crystalline region forming elongated grains, some many microns long. The growth rate during the formation of these radial grains is measuredmore » with time-resolved imaging experiments. Crystal growth rates exceed 10 m/s, which are consistent with crystallization mediated by a very thin, undercooled transient liquid layer, rather than a purely solid-state transformation mechanism. The kinetics of this growth mode have been studied in detail under steady-state conditions, but here we provide a detailed study of liquid-mediated growth in high temperature gradients. Unexpectedly, the propagation rate of the crystallization front was observed to remain constant during this growth mode even when passing through large local temperature gradients, in stark contrast to other similar studies that suggested the growth rate changed dramatically. As a result, the high throughput of multi-frame DTEM provides gives a more complete picture of the role of temperature and temperature gradient on laser crystallization than previous DTEM experiments.« less

Kinetics of liquid-mediated crystallization of amorphous Ge from multi-frame dynamic transmission electron microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Santala, M. K., E-mail: melissa.santala@oregonstate.edu; Campbell, G. H.; Raoux, S.

2015-12-21

The kinetics of laser-induced, liquid-mediated crystallization of amorphous Ge thin films were studied using multi-frame dynamic transmission electron microscopy (DTEM), a nanosecond-scale photo-emission transmission electron microscopy technique. In these experiments, high temperature gradients are established in thin amorphous Ge films with a 12-ns laser pulse with a Gaussian spatial profile. The hottest region at the center of the laser spot crystallizes in ∼100 ns and becomes nano-crystalline. Over the next several hundred nanoseconds crystallization continues radially outward from the nano-crystalline region forming elongated grains, some many microns long. The growth rate during the formation of these radial grains is measured withmore » time-resolved imaging experiments. Crystal growth rates exceed 10 m/s, which are consistent with crystallization mediated by a very thin, undercooled transient liquid layer, rather than a purely solid-state transformation mechanism. The kinetics of this growth mode have been studied in detail under steady-state conditions, but here we provide a detailed study of liquid-mediated growth in high temperature gradients. Unexpectedly, the propagation rate of the crystallization front was observed to remain constant during this growth mode even when passing through large local temperature gradients, in stark contrast to other similar studies that suggested the growth rate changed dramatically. The high throughput of multi-frame DTEM provides gives a more complete picture of the role of temperature and temperature gradient on laser crystallization than previous DTEM experiments.« less

Mathematical Development of the Spill Assessment Model (SAM) for Hydrazine and Similar Acting Materials in Water Bodies.

DTIC Science & Technology

1980-02-01

migration of the chemical mass in the fluid volume according to two entirely different means, yet governed by the same form of the equation: molecular ...pressure or temperature gradients, gravitational or other body forces, or bulk fluid motion, is observed as molecular diffusion. In general, the...need be made at this stage as to whether the diffusion of a released mass in the fluid is molecular or turbulent in nature. The general form of the one

Solvent coarsening around colloids driven by temperature gradients

NASA Astrophysics Data System (ADS)

Roy, Sutapa; Dietrich, Siegfried; Maciolek, Anna

2018-04-01

Using mesoscopic numerical simulations and analytical theory, we investigate the coarsening of the solvent structure around a colloidal particle emerging after a temperature quench of the colloid surface. Qualitative differences in the coarsening mechanisms are found, depending on the composition of the binary liquid mixture forming the solvent and on the adsorption preferences of the colloid. For an adsorptionwise neutral colloid, the phase next to its surface alternates as a function of time. This behavior sets in on the scale of the relaxation time of the solvent and is absent for colloids with strong adsorption preferences. A Janus colloid, with a small temperature difference between its two hemispheres, reveals an asymmetric structure formation and surface enrichment around it, even if the solvent is within its one-phase region and if the temperature of the colloid is above the critical demixing temperature Tc of the solvent. Our phenomenological model turns out to capture recent experimental findings according to which, upon laser illumination of a Janus colloid and due to the ensuing temperature gradient between its two hemispheres, the surrounding binary liquid mixture develops a concentration gradient.

Low-Temperature Alteration of the Seafloor: Impacts on Ocean Chemistry

NASA Astrophysics Data System (ADS)

Coogan, Laurence A.; Gillis, Kathryn M.

2018-05-01

Over 50% of Earth is covered by oceanic crust, the uppermost portion of which is a high-permeability layer of basaltic lavas through which seawater continuously circulates. Fluid flow is driven by heat lost from the oceanic lithosphere; the global fluid flux is dependent on plate creation rates and the thickness and distribution of overlying sediment, which acts as a low-permeability layer impeding seawater access to the crust. Fluid-rock reactions in the crust, and global chemical fluxes, depend on the average temperature in the aquifer, the fluid flux, and the composition of seawater. The average temperature in the aquifer depends largely on bottom water temperature and, to a lesser extent, on the average seafloor sediment thickness. Feedbacks between off-axis chemical fluxes and their controls may play an important role in modulating ocean chemistry and planetary climate on long timescales, but more work is needed to quantify these feedbacks.

Transition to subcritical turbulence in a tokamak plasma

NASA Astrophysics Data System (ADS)

van Wyk, F.; Highcock, E. G.; Schekochihin, A. A.; Roach, C. M.; Field, A. R.; Dorland, W.

2016-12-01

Tokamak turbulence, driven by the ion-temperature gradient and occurring in the presence of flow shear, is investigated by means of local, ion-scale, electrostatic gyrokinetic simulations (with both kinetic ions and electrons) of the conditions in the outer core of the Mega-Ampere Spherical Tokamak (MAST). A parameter scan in the local values of the ion-temperature gradient and flow shear is performed. It is demonstrated that the experimentally observed state is near the stability threshold and that this stability threshold is nonlinear: sheared turbulence is subcritical, i.e. the system is formally stable to small perturbations, but, given a large enough initial perturbation, it transitions to a turbulent state. A scenario for such a transition is proposed and supported by numerical results: close to threshold, the nonlinear saturated state and the associated anomalous heat transport are dominated by long-lived coherent structures, which drift across the domain, have finite amplitudes, but are not volume filling; as the system is taken away from the threshold into the more unstable regime, the number of these structures increases until they overlap and a more conventional chaotic state emerges. Whereas this appears to represent a new scenario for transition to turbulence in tokamak plasmas, it is reminiscent of the behaviour of other subcritically turbulent systems, e.g. pipe flows and Keplerian magnetorotational accretion flows.

Thermally driven microfluidic pumping via reversible shape memory polymers

NASA Astrophysics Data System (ADS)

Robertson, J. M.; Rodriguez, R. X.; Holmes, L. R., Jr.; Mather, P. T.; Wetzel, E. D.

2016-08-01

The need exists for autonomous microfluidic pumping systems that utilize environmental cues to transport fluid within a network of channels for such purposes as heat distribution, self-healing, or optical reconfiguration. Here, we report on reversible thermally driven microfluidic pumping enabled by two-way shape memory polymers. After developing a suitable shape memory polymer (SMP) through variation in the crosslink density, thin and flexible microfluidic devices were constructed by lamination of plastic films with channels defined by laser-cutting of double-sided adhesive film. SMP blisters integrated into the devices provide thermally driven pumping, while opposing elastic blisters are used to generate backpressure for reversible operation. Thermal cycling of the device was found to drive reversible fluid flow: upon heating to 60 °C, the SMP rapidly contracted to fill the surface channels with a transparent fluid, and upon cooling to 8 °C the flow reversed and the channel re-filled with black ink. Combined with a metallized backing layer, this device results in refection of incident light at high temperatures and absorption of light (at the portions covered with channels) at low temperatures. We discuss power-free, autonomous applications ranging from thermal regulation of structures to thermal indication via color change.

Scrape-off layer tokamak plasma turbulence

NASA Astrophysics Data System (ADS)

Bisai, N.; Singh, R.; Kaw, P. K.

2012-05-01

Two-dimensional (2D) interchange turbulence in the scrape-off layer of tokamak plasmas and their subsequent contribution to anomalous plasma transport has been studied in recent years using electron continuity, current balance, and electron energy equations. In this paper, numerically it is demonstrated that the inclusion of ion energy equation in the simulation changes the nature of plasma turbulence. Finite ion temperature reduces floating potential by about 15% compared with the cold ion temperature approximation and also reduces the radial electric field. Rotation of plasma blobs at an angular velocity about 1.5×105 rad/s has been observed. It is found that blob rotation keeps plasma blob charge separation at an angular position with respect to the vertical direction that gives a generation of radial electric field. Plasma blobs with high electron temperature gradients can align the charge separation almost in the radial direction. Influence of high ion temperature and its gradient has been presented.

Anomalous metastability in a temperature-driven transition

NASA Astrophysics Data System (ADS)

Ibáñez Berganza, M.; Coletti, P.; Petri, A.

2014-06-01

The Langer theory of metastability provides a description of the lifetime and properties of the metastable phase of the Ising model field-driven transition, describing the magnetic-field-driven transition in ferromagnets and the chemical-potential-driven transition of fluids. An immediate further step is to apply it to the study of a transition driven by the temperature, as the one exhibited by the two-dimensional Potts model. For this model, a study based on the analytical continuation of the free energy (Meunier J. L. and Morel A., Eur. Phys. J. B, 13 (2000) 341) predicts the anomalous vanishing of the metastable temperature range in the large-system-size limit, an issue that has been controversial since the eighties. By a GPU algorithm we compare the Monte Carlo dynamics with the theory. For temperatures close to the transition we obtain agreement and characterize the dependence on the system size, which is essentially different with respect to the Ising case. For smaller temperatures, we observe the onset of stationary states with non-Boltzmann statistics, not predicted by the theory.

The stochastic thermodynamics of a rotating Brownian particle in a gradient flow

PubMed Central

Lan, Yueheng; Aurell, Erik

2015-01-01

We compute the entropy production engendered in the environment from a single Brownian particle which moves in a gradient flow, and show that it corresponds in expectation to classical near-equilibrium entropy production in the surrounding fluid with specific mesoscopic transport coefficients. With temperature gradient, extra terms are found which result from the nonlinear interaction between the particle and the non-equilibrated environment. The calculations are based on the fluctuation relations which relate entropy production to the probabilities of stochastic paths and carried out in a multi-time formalism. PMID:26194015

Experimental Nanofluidics in an individual Nanotube

NASA Astrophysics Data System (ADS)

Siria, Alessandro; Poncharal, Philippe; Biance, Anne Laure; Fulcrand, Remy; Purcell, Stephen; Bocquet, Lyderic

2012-11-01

Building new devices that benefit from the strange transport behavior of fluids at nanoscales is an open and worthy challenge that may lead to new scientific and technological paradigms. We present here a new class of nanofluidic device, made of individual Boron-Nitride (BN) nanotube inserted in a pierced membrane and connecting two macroscopic reservoirs. We explore fluidic transport inside a single BN nanotube under electric fields, pressure drops, chemical gradients, and combinations of these. We show that in this transmembrane geometry, the pressure-driven streaming current is voltage gated, with an apparent electro-osmotic zeta potential raising up to one volt. Further, we measured the current induced by ion concentration gradients and show its dependency on the surface charge.

The effect of magnetic islands on Ion Temperature Gradient turbulence driven transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hill, P., E-mail: peter.hill@york.ac.uk; York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD; Hariri, F.

2015-04-15

In this work, we address the question of the influence of magnetic islands on the perpendicular transport due to steady-state ITG turbulence on the energy transport time scale. We demonstrate that turbulence can cross the separatrix and enhance the perpendicular transport across magnetic islands. As the perpendicular transport in the interior of the island sets the critical island size needed for growth of neoclassical tearing modes, this increased transport leads to a critical island size larger than that predicted from considering collisional conductivities, but smaller than that using anomalous effective conductivities. We find that on Bohm time scales, the turbulencemore » is able to re-establish the temperature gradient across the island for islands widths w ≲ λ{sub turb}, the turbulence correlation length. The reduction in the island flattening is estimated by comparison with simulations retaining only the perpendicular temperature and no turbulence. At intermediate island widths, comparable to λ{sub turb}, turbulence is able to maintain finite temperature gradients across the island.« less

Tide-driven fluid mud transport in the Ems estuary

NASA Astrophysics Data System (ADS)

Becker, Marius; Maushake, Christian; Winter, Christian

2014-05-01

The Ems estuary, located at the border between The Netherlands and Germany, experienced a significant change of the hydrodynamic regime during the past decades, as a result of extensive river engineering. With the net sediment transport now being flood-oriented, suspended sediment concentrations have increased dramatically, inducing siltation and formation of fluid mud layers, which, in turn, influence hydraulic flow properties, such as turbulence and the apparent bed roughness. Here, the process-based understanding of fluid mud is essential to model and predict mud accumulation, not only regarding the anthropogenic impact, but also in view of the expected changes of environmental boundary conditions, i.e., sea level rise. In the recent past, substantial progress has been made concerning the understanding of estuarine circulation and influence of tidal asymmetry on upstream sediment accumulation. While associated sediment transport formulations have been implemented in the framework of numerical modelling systems, in-situ data of fluid mud are scarce. This study presents results on tide-driven fluid mud dynamics, measured during four tidal cycles aside the navigation channel in the Ems estuary. Lutoclines, i.e., strong vertical density gradients, were detected by sediment echo sounder (SES). Acoustic Doppler current profiles (ADCP) of different acoustic frequencies were used to determine hydrodynamic parameters and the vertical distribution of suspended sediment concentrations in the upper part of the water column. These continuous profiling measurements were complemented by CTD, ADV, and OBS casts. SES and ADCP profiles show cycles of fluid mud entrainment during accelerating flow, and subsequent settling, and the reformation of a lutocline during decelerating flow and slack water. Significant differences are revealed between flood and ebb phase. Highest entrainment rates are measured at the beginning of the flood phase, associated with strong current shear and rapid vertical mixing, inducing the highest instantaneous suspended sediment flux measured during the tidal cycle. During decelerating flood currents a lutocline is again established at a certain distance above the consolidated river bed. During slack water after the flood phase the concentration gradient increases and the thickness of the fluid mud layer below is constant, also during a significant part of the ebb phase. As water depth decreases during ebb, entrainment occurs only at the upper part of the fluid mud layer. The suspended sediment flux is low compared to the flood phase. These observations are further elaborated using turbulence parameters obtained from ADV and ADCP, explaining the difference between ebb and flood concerning the vertical location of the maximum concentration gradient. This study is funded through DFG-Research Center / Excellence Cluster "The Ocean in the Earth System". The Senckenberg Institute and the Federal Waterways Engineering and Research Institute are acknowledged for technical support.

Nature of fluid flows in differentially heated cylindrical container filled with a stratified solution

NASA Technical Reports Server (NTRS)

Wang, Jai-Ching

1992-01-01

Semiconductor crystals such as Hg(1-x)Cd(x)Te grown by unidirectional solidification Bridgmann method have shown compositional segregations in both the axial and radial directions. Due to the wide separation between the liquidus and the solidus of its pseudobinary phase diagram, there is a diffusion layer of higher HgTe content built up in the melt near the melt-solid interface which gives a solute concentration gradient in the axial direction. Because of the higher thermal conductivity in the melt than that in the crystal there is a thermal leakage through the fused silica crucible wall near the melt-solid interface. This gives a thermal gradient in the radial direction. Hart (1971), Thorpe, Hutt and Soulsby (1969) have shown that under such condition a fluid will become convectively unstable as a result of different diffusivities of temperature and solute. It is quite important to understand the effects of this thermosolute convection on the compositional segregation in the unidirectionally solidified crystals. To reach this goal, we start with a simplified problem. We study the nature of fluid flows of a stratified solution in a cylindrical container with a radial temperature gradient. The cylindrical container wall is considered to be maintained at a higher temperature than that at the center of the solution and the solution in the lower gravitational direction has higher solute concentration which decrease linearly to a lower concentration and then remain constant to the top of the solution. The sample solution is taken to be salt water.

Identification of new turbulence contributions to plasma transport and confinement in spherical tokamak regime

NASA Astrophysics Data System (ADS)

Wang, W. X.; Ethier, S.; Ren, Y.; Kaye, S.; Chen, J.; Startsev, E.; Lu, Z.; Li, Z. Q.

2015-10-01

Highly distinct features of spherical tokamaks (ST), such as National Spherical Torus eXperiment (NSTX) and NSTX-U, result in a different fusion plasma regime with unique physics properties compared to conventional tokamaks. Nonlinear global gyrokinetic simulations critical for addressing turbulence and transport physics in the ST regime have led to new insights. The drift wave Kelvin-Helmholtz (KH) instability characterized by intrinsic mode asymmetry is identified in strongly rotating NSTX L-mode plasmas. While the strong E ×B shear associated with the rotation leads to a reduction in KH/ion temperature gradient turbulence, the remaining fluctuations can produce a significant ion thermal transport that is comparable to the experimental level in the outer core region (with no "transport shortfall"). The other new, important turbulence source identified in NSTX is the dissipative trapped electron mode (DTEM), which is believed to play little role in conventional tokamak regime. Due to the high fraction of trapped electrons, long wavelength DTEMs peaking around kθρs˜0.1 are destabilized in NSTX collisionality regime by electron density and temperature gradients achieved there. Surprisingly, the E ×B shear stabilization effect on DTEM is remarkably weak, which makes it a major turbulence source in the ST regime dominant over collisionless TEM (CTEM). The latter, on the other hand, is subject to strong collisional and E ×B shear suppression in NSTX. DTEM is shown to produce significant particle, energy and toroidal momentum transport, in agreement with experimental levels in NSTX H-modes. Moreover, DTEM-driven transport in NSTX parametric regime is found to increase with electron collision frequency, providing one possible source for the scaling of confinement time observed in NSTX H-modes. Most interestingly, the existence of a turbulence-free regime in the collision-induced CTEM to DTEM transition, corresponding to a minimum plasma transport in advanced ST collisionality regime, is predicted.

Identification of new turbulence contributions to plasma transport and confinement in spherical tokamak regime

DOE PAGES

Wang, W. X.; Ethier, S.; Ren, Y.; ...

2015-10-15

Highly distinct features of spherical tokamaks (ST), such as National Spherical Torus eXperiment (NSTX) and NSTX-U, result in a different fusion plasma regime with unique physics properties compared to conventional tokamaks. Nonlinear global gyrokinetic simulations critical for addressing turbulence and transport physics in the ST regime have led to new insights. The drift wave Kelvin-Helmholtz (KH) instability characterized by intrinsic mode asymmetry is identified in strongly rotating NSTX L-mode plasmas. While the strong E x B shear associated with the rotation leads to a reduction in KH/ion temperature gradient turbulence, the remaining fluctuations can produce a significant ion thermal transportmore » that is comparable to the experimental level in the outer core region (with no "transport shortfall"). The other new, important turbulence source identified in NSTX is the dissipative trapped electron mode (DTEM), which is believed to play little role in conventional tokamak regime. Due to the high fraction of trapped electrons, long wavelength DTEMs peaking around k θρs ~ 0.1 are destabilized in NSTX collisionality regime by electron density and temperature gradients achieved there. Surprisingly, the E x B shear stabilization effect on DTEM is remarkably weak, which makes it a major turbulence source in the ST regime dominant over collisionless TEM (CTEM). The latter, on the other hand, is subject to strong collisional and E x B shear suppression in NSTX. DTEM is shown to produce significant particle, energy and toroidal momentum transport, in agreement with experimental levels in NSTX H-modes. Furthermore, DTEM-driven transport in NSTX parametric regime is found to increase with electron collision frequency, providing one possible source for the scaling of confinement time observed in NSTX H-modes. Most interestingly, the existence of a turbulence-free regime in the collision-induced CTEM to DTEM transition, corresponding to a minimum plasma transport in advanced ST collisionality regime, is predicted.« less

Ion heating and characteristics of ST plasma used by double-pulsing CHI on HIST

NASA Astrophysics Data System (ADS)

Hanao, Takafumi; Hirono, Hidetoshi; Hyobu, Takahiro; Ito, Kengo; Matsumoto, Keisuke; Nakayama, Takashi; Oki, Nobuharu; Kikuchi, Yusuke; Fukumoto, Naoyuki; Nagata, Masayoshi

2013-10-01

Multi-pulsing Coaxial Helicity Injection (M-CHI) is an efficient current drive and sustainment method used in spheromak and spherical torus (ST). We have observed plasma current/flux amplification by double pulsing CHI. Poloidal ion temperature measured by Ion Doppler Spectrometer (IDS) has a peak at plasma core region. In this region, radial electric field has a negative peak. At more inboard side that is called separatrix between closed flux region and inner open flux region, poloidal flow has a large shear and radial electric field changes the polarity. After the second CHI pulse, we observed sharp and rapid ion heating at plasma core region and separatrix. In this region, the poloidal ion temperature is selective heating because electron temperature is almost uniform. At this time, flow shear become larger and radial electric field is amplified at separatorix. These effects produce direct heating of ion through the viscous flow damping. Furthermore, we observed decrease of electron density at separatrix. Decreased density makes Hall dynamo electric field as two-fluid effect. When the ion temperature is increasing, dynamo electric field is observed at separatrix. It may have influence with the ion heating. We will discuss characteristic of double pulsing CHI driven ST plasmas and correlation of direct heating of ion with dynamo electric field and any other parameters.

A self-organized criticality model for ion temperature gradient mode driven turbulence in confined plasma

NASA Astrophysics Data System (ADS)

Isliker, H.; Pisokas, Th.; Strintzi, D.; Vlahos, L.

2010-08-01

A new self-organized criticality (SOC) model is introduced in the form of a cellular automaton (CA) for ion temperature gradient (ITG) mode driven turbulence in fusion plasmas. Main characteristics of the model are that it is constructed in terms of the actual physical variable, the ion temperature, and that the temporal evolution of the CA, which necessarily is in the form of rules, mimics actual physical processes as they are considered to be active in the system, i.e., a heating process and a local diffusive process that sets on if a threshold in the normalized ITG R /LT is exceeded. The model reaches the SOC state and yields ion temperature profiles of exponential shape, which exhibit very high stiffness, in that they basically are independent of the loading pattern applied. This implies that there is anomalous heat transport present in the system, despite the fact that diffusion at the local level is imposed to be of a normal kind. The distributions of the heat fluxes in the system and of the heat out-fluxes are of power-law shape. The basic properties of the model are in good qualitative agreement with experimental results.

Determination of Critical Parameters Based on the Intensity of Transmitted Light Around Gas-Liquid Interface: Critical Parameters of CO

NASA Astrophysics Data System (ADS)

Nakayama, Masaki; Katano, Hiroaki; Sato, Haruki

2014-05-01

A precise determination of the critical temperature and density for technically important fluids would be possible on the basis of the digital image for the visual observation of the phase boundary in the vicinity of the critical point since the sensitivity and resolution are higher than those of naked eyes. In addition, the digital image can avoid the personal uncertainty of an observer. A strong density gradient occurs in a sample cell at the critical point due to gravity. It was carefully assessed to determine the critical density, where the density profile in the sample cell can be observed from the luminance profile of a digital image. The density-gradient profile becomes symmetric at the critical point. One of the best fluids, whose thermodynamic properties have been measured with the highest reliability among technically important fluids, would be carbon dioxide. In order to confirm the reliability of the proposed method, the critical temperature and density of carbon dioxide were determined using the digital image. The critical temperature and density values of carbon dioxide are ( and ( kg m, respectively. The critical temperature and density values agree with the existing best values within estimated uncertainties. The reliability of the method was confirmed. The critical pressure, 7.3795 MPa, corresponding to the determined critical temperature of 304.143 K is also proposed. A new set of parameters for the vapor-pressure equation is also provided.

Laboratory observation of resistive electron tearing in a two-fluid reconnecting current sheet

DOE PAGES

Jara-Almonte, Jonathan; Ji, Hantao; Yamada, Masaaki; ...

2016-08-25

The spontaneous formation of plasmoids via the resistive electron tearing of a reconnecting current sheet is observed in the laboratory. These experiments are performed during driven, antiparallel reconnection in the two-fluid regime within the Magnetic Reconnection Experiment. It is found that plasmoids are present even at a very low Lundquist number, and the number of plasmoids scales with both the current sheet aspect ratio and the Lundquist number. Furthermore, the reconnection electric field increases when plasmoids are formed, leading to an enhanced reconnection rate.

Effects of low central fuelling on density and ion temperature profiles in reversed shear plasmas on JT-60U

NASA Astrophysics Data System (ADS)

Takenaga, H.; Ide, S.; Sakamoto, Y.; Fujita, T.; JT-60 Team

2008-07-01

Effects of low central fuelling on density and ion temperature profiles have been investigated using negative ion based neutral beam injection and electron cyclotron heating (ECH) in reversed shear plasmas on JT-60U. Strong internal transport barrier (ITB) was maintained in density and ion temperature profiles, when central fuelling was decreased by switching positive ion based neutral beam injection to ECH after the strong ITB formation. Similar density and ion temperature ITBs were formed for the low and high central fuelling cases during the plasma current ramp-up phase. Strong correlation between the density gradient and the ion temperature gradient was observed, indicating that particle transport and ion thermal transport are strongly coupled or the density gradient assists the ion temperature ITB formation through suppression of drift wave instabilities such as ion temperature gradient mode. These results support that the density and ion temperature ITBs can be formed under reactor relevant conditions.

Tunable mega-ampere electron current propagation in solids by dynamic control of lattice melt

DOE PAGES

MacLellan, D.  A.; Carroll, D.  C.; Gray, R.  J.; ...

2014-10-31

The influence of lattice-melt-induced resistivity gradients on the transport of mega-ampere currents of fast electrons in solids is investigated numerically and experimentally using laser-accelerated protons to induce isochoric heating. Tailoring the heating profile enables the resistive magnetic fields which strongly influence the current propagation to be manipulated. This tunable laser-driven process enables important fast electron beam properties, including the beam divergence, profile, and symmetry to be actively tailored, and without recourse to complex target manufacture.

Cell Blebbing in Confined Microfluidic Environments

PubMed Central

Ibo, Markela; Srivastava, Vasudha; Robinson, Douglas N.; Gagnon, Zachary R.

2016-01-01

Migrating cells can extend their leading edge by forming myosin-driven blebs and F-actin-driven pseudopods. When coerced to migrate in resistive environments, Dictyostelium cells switch from using predominately pseudopods to blebs. Bleb formation has been shown to be chemotactic and can be influenced by the direction of the chemotactic gradient. In this study, we determine the blebbing responses of developed cells of Dictyostelium discoideum to cAMP gradients of varying steepness produced in microfluidic channels with different confining heights, ranging between 1.7 μm and 3.8 μm. We show that microfluidic confinement height, gradient steepness, buffer osmolarity and Myosin II activity are important factors in determining whether cells migrate with blebs or with pseudopods. Dictyostelium cells were observed migrating within the confines of microfluidic gradient channels. When the cAMP gradient steepness is increased from 0.7 nM/μm to 20 nM/μm, cells switch from moving with a mixture of blebs and pseudopods to moving only using blebs when chemotaxing in channels with confinement heights less than 2.4 μm. Furthermore, the size of the blebs increases with gradient steepness and correlates with increases in myosin-II localization at the cell cortex. Reduction of intracellular pressure by high osmolarity buffer or inhibition of myosin-II by blebbistatin leads to a decrease in bleb formation and bleb size. Together, our data reveal that the protrusion type formed by migrating cells can be influenced by the channel height and the steepness of the cAMP gradient, and suggests that a combination of confinement-induced myosin-II localization and cAMP-regulated cortical contraction leads to increased intracellular fluid pressure and bleb formation. PMID:27706201

Phoresis in fluids.

PubMed

Brenner, Howard

2011-12-01

This paper presents a unified theory of phoretic phenomena in single-component fluids. Simple formulas are given for the phoretic velocities of small inert force-free non-Brownian particles migrating through otherwise quiescent single-component gases and liquids and animated by a gradient in the fluid's temperature (thermophoresis), pressure (barophoresis), density (pycnophoresis), or any combination thereof. The ansatz builds upon a recent paper [Phys. Rev. E 84, 046309 (2011)] concerned with slip of the fluid's mass velocity at solid surfaces--that is, with phenomena arising from violations of the classical no-slip fluid-mechanical boundary condition. Experimental and other data are cited in support of the phoretic model developed herein.

Key parameters controlling the performance of catalytic motors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Esplandiu, Maria J.; Afshar Farniya, Ali; Reguera, David, E-mail: dreguera@ub.edu

2016-03-28

The development of autonomous micro/nanomotors driven by self-generated chemical gradients is a topic of high interest given their potential impact in medicine and environmental remediation. Although impressive functionalities of these devices have been demonstrated, a detailed understanding of the propulsion mechanism is still lacking. In this work, we perform a comprehensive numerical analysis of the key parameters governing the actuation of bimetallic catalytic micropumps. We show that the fluid motion is driven by self-generated electro-osmosis where the electric field originates by a proton current rather than by a lateral charge asymmetry inside the double layer. Hence, the surface potential andmore » the electric field are the key parameters for setting the pumping strength and directionality. The proton flux that generates the electric field stems from the proton gradient induced by the electrochemical reactions taken place at the pump. Surprisingly the electric field and consequently the fluid flow are mainly controlled by the ionic strength and not by the conductivity of the solution, as one could have expected. We have also analyzed the influence of the chemical fuel concentration, electrochemical reaction rates, and size of the metallic structures for an optimized pump performance. Our findings cast light on the complex chemomechanical actuation of catalytic motors and provide important clues for the search, design, and optimization of novel catalytic actuators.« less

3D theory of a high-gain free-electron laser based on a transverse gradient undulator

NASA Astrophysics Data System (ADS)

Baxevanis, Panagiotis; Ding, Yuantao; Huang, Zhirong; Ruth, Ronald

2014-02-01

The performance of a free-electron laser (FEL) depends significantly on the various parameters of the driving electron beam. In particular, a large energy spread in the beam results in a substantial reduction of the FEL gain, an effect which is especially relevant when one considers FELs driven by plasma accelerators or ultimate storage rings. For such cases, one possible solution is to use a transverse gradient undulator (TGU). In this concept, the energy spread problem is mitigated by properly dispersing the electron beam and introducing a linear, transverse field dependence in the undulator. This paper presents a self-consistent theoretical analysis of a TGU-based, high-gain FEL which takes into account three-dimensional (3D) effects, including beam size variations along the undulator. The results of our theory compare favorably with simulation and are used in fast optimization studies of various x-ray FEL configurations.

NIMROD calculations of energetic particle driven toroidal Alfvén eigenmodes

NASA Astrophysics Data System (ADS)

Hou, Yawei; Zhu, Ping; Kim, Charlson C.; Hu, Zhaoqing; Zou, Zhihui; Wang, Zhengxiong; Nimrod Team

2018-01-01

Toroidal Alfvén eigenmodes (TAEs) are gap modes induced by the toroidicity of tokamak plasmas in the absence of continuum damping. They can be excited by energetic particles (EPs) when the EP drive exceeds other dampings, such as electron and ion Landau damping, and collisional and radiative damping. A TAE benchmark case, which was proposed by the International Tokamak Physics Activity group, is studied in this work. The numerical calculations of linear growth of TAEs driven by EPs in a circular-shaped, large aspect ratio tokamak have been performed using the Hybrid Kinetic-MHD (HK-MHD) model implemented in the NIMROD code. This HK-MHD model couples a δf particle-in-cell representation of EPs with the 3D MHD representation of the bulk plasma through moment closure for the momentum conservation equation. Both the excitation of TAEs and their transition to energetic particle modes (EPMs) have been observed. The influence of EP density, temperature, density gradient, and position of the maximum relative density gradient, on the frequency and the growth rate of TAEs are obtained, which are consistent with those from the eigen-analysis calculations, kinetic-MHD, and gyrokinetic simulations for an initial Maxwellian distribution of EPs. The relative pressure gradient of EP at the radial location of the TAE gap, which represents the drive strength of EPs, can strongly affect the growth rate of TAEs. It is demonstrated that the mode transition due to EP drive variation leads to not only the change of frequency but also the change of the mode structure. This mechanism can be helpful in understanding the nonlinear physics of TAE/EPM, such as frequency chirping.

Heat and mass transfer analogy for condensation of humid air in a vertical channel

NASA Astrophysics Data System (ADS)

Desrayaud, G.; Lauriat, G.

This study examines energy transport associated with liquid film condensation in natural convection flows driven by differences in density due to temperature and concentration gradients. The condensation problem is based on the thin-film assumptions. The most common compositional gradient, which is encountered in humid air at ambient temperature is considered. A steady laminar Boussinesq flow of an ideal gas-vapor mixture is studied for the case of a vertical parallel plate channel. New correlations for the latent and sensible Nusselt numbers are established, and the heat and mass transfer analogy between the sensible Nusselt number and Sherwood number is demonstrated.

Stability of magnetohydrodynamic Dean Flow as applied to centrifugally confined plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hassam, A.B.

1999-10-01

Dean Flow is the azimuthal flow of fluid between static concentric cylinders. In a magnetized plasma, there may also be radial stratification of the pressure. The ideal magnetohydrodynamic stability of such a flow in the presence of a strong axial magnetic field and an added radial gravitational force is examined. It is shown that both the Kelvin{endash}Helmholtz instability and pressure-gradient-driven interchanges can be stabilized if the flow is driven by a unidirectional external force and if the plasma annulus is sufficiently thin (large aspect ratio). These results find application in schemes using centrifugal confinement of plasma for fusion. {copyright} {italmore » 1999 American Institute of Physics.}« less

Hotspot: the Snake River Geothermal Drilling Project--initial report

USGS Publications Warehouse

Shervais, J.W.; Nielson, D.; Lachmar, T.; Christiansen, E.H.; Morgan, L.; Shanks, Wayne C.; Delahunty, C.; Schmitt, D.R.; Liberty, L.M.; Blackwell, D.D.; Glen, J.M.; Kessler, J.A.; Potter, K.E.; Jean, M.M.; Sant, C.J.; Freeman, T.

2012-01-01

The Snake River volcanic province (SRP) overlies a thermal anomaly that extends deep into the mantle; it represents one of the highest heat flow provinces in North America. The primary goal of this project is to evaluate geothermal potential in three distinct settings: (1) Kimama site: inferred high sub-aquifer geothermal gradient associated with the intrusion of mafic magmas, (2) Kimberly site: a valley-margin setting where surface heat flow may be driven by the up-flow of hot fluids along buried caldera ringfault complexes, and (3) Mountain Home site: a more traditional fault-bounded basin with thick sedimentary cover. The Kimama hole, on the axial volcanic zone, penetrated 1912 m of basalt with minor intercalated sediment; no rhyolite basement was encountered. Temperatures are isothermal through the aquifer (to 960 m), then rise steeply on a super-conductive gradient to an estimated bottom hole temperature of ~98°C. The Kimberly hole is on the inferred margin of a buried rhyolite eruptive center, penetrated rhyolite with intercalated basalt and sediment to a TD of 1958 m. Temperatures are isothermal at 55-60°C below 400 m, suggesting an immense passive geothermal resource. The Mountain Home hole is located above the margin of a buried gravity high in the western SRP. It penetrates a thick section of basalt and lacustrine sediment overlying altered basalt flows, hyaloclastites, and volcanic sediments, with a TD of 1821 m. Artesian flow of geothermal water from 1745 m depth documents a power-grade resource that is now being explored in more detail. In-depth studies continue at all three sites, complemented by high-resolution gravity, magnetic, and seismic surveys, and by downhole geophysical logging.

Salinity-gradient energy driven microbial electrosynthesis of value-added chemicals from CO2 reduction.

PubMed

Li, Xiaohu; Angelidaki, Irini; Zhang, Yifeng

2018-06-14

Biological conversion of CO 2 to value-added chemicals and biofuels has emerged as an attractive strategy to address the energy and environmental concerns caused by the over-reliance on fossil fuels. In this study, an innovative microbial reverse-electrodialysis electrolysis cell (MREC), which combines the strengths of reverse electrodialysis (RED) and microbial electrosynthesis technology platforms, was developed to achieve efficient CO 2 -to-value chemicals bioconversion by using the salinity gradient energy as driven energy sources. In the MREC, maximum acetate and ethanol concentrations of 477.5 ± 33.2 and 46.2 ± 8.2 mg L -1 were obtained at the cathode, catalyzed by Sporomusa ovata with production rates of 165.79 ± 11.52 and 25.11 ± 4.46 mmol m -2 d -1 , respectively. Electron balance analysis indicates that 94.4 ± 3.9% of the electrons derived from wastewater and salinity gradient were recovered in acetate and ethanol. This work for the first time proved the potential of innovative MREC configuration has the potential as an efficient technology platform for simultaneous CO 2 capture and electrosynthesis of valuable chemicals. Copyright © 2018 Elsevier Ltd. All rights reserved.

Effect of ion beam on the characteristics of ion acoustic Gardner solitons and double layers in a multicomponent superthermal plasma

NASA Astrophysics Data System (ADS)

Kaur, Nimardeep; Singh, Kuldeep; Saini, N. S.

2017-09-01

The nonlinear propagation of ion acoustic solitary waves (IASWs) is investigated in an unmagnetized plasma composed of a positive warm ion fluid, two temperature electrons obeying kappa type distribution and penetrated by a positive ion beam. The reductive perturbation method is used to derive the nonlinear equations, namely, Korteweg-de Vries (KdV), modified KdV (mKdV), and Gardner equations. The characteristic features of both compressive and rarefactive nonlinear excitations from the solution of these equations are studied and compared in the context with the observation of the He+ beam in the polar cap region near solar maximum by the Dynamics Explorer 1 satellite. It is observed that the superthermality and density of cold electrons, number density, and temperature of the positive ion beam crucially modify the basic properties of compressive and rarefactive IASWs in the KdV and mKdV regimes. It is further analyzed that the amplitude and width of Gardner solitons are appreciably affected by different plasma parameters. The characteristics of double layers are also studied in detail below the critical density of cold electrons. The theoretical results may be useful for the observation of nonlinear excitations in laboratory and ion beam driven plasmas in the polar cap region near solar maximum and polar ionosphere as well in Saturn's magnetosphere, solar wind, pulsar magnetosphere, etc., where the population of two temperature superthermal electrons is present.

Cooling system with automated seasonal freeze protection

DOEpatents

Campbell, Levi A.; Chu, Richard C.; David, Milnes P.; Ellsworth, Jr., Michael J.; Iyengar, Madhusudan K.; Simons, Robert E.; Singh, Prabjit; Zhang, Jing

2016-05-24

An automated multi-fluid cooling system and method are provided for cooling an electronic component(s). The cooling system includes a coolant loop, a coolant tank, multiple valves, and a controller. The coolant loop is at least partially exposed to outdoor ambient air temperature(s) during normal operation, and the coolant tank includes first and second reservoirs containing first and second fluids, respectively. The first fluid freezes at a lower temperature than the second, the second fluid has superior cooling properties compared with the first, and the two fluids are soluble. The multiple valves are controllable to selectively couple the first or second fluid into the coolant in the coolant loop, wherein the coolant includes at least the second fluid. The controller automatically controls the valves to vary first fluid concentration level in the coolant loop based on historical, current, or anticipated outdoor air ambient temperature(s) for a time of year.

Cooling method with automated seasonal freeze protection

DOEpatents

Cambell, Levi; Chu, Richard; David, Milnes; Ellsworth, Jr, Michael; Iyengar, Madhusudan; Simons, Robert; Singh, Prabjit; Zhang, Jing

2016-05-31

An automated multi-fluid cooling method is provided for cooling an electronic component(s). The method includes obtaining a coolant loop, and providing a coolant tank, multiple valves, and a controller. The coolant loop is at least partially exposed to outdoor ambient air temperature(s) during normal operation, and the coolant tank includes first and second reservoirs containing first and second fluids, respectively. The first fluid freezes at a lower temperature than the second, the second fluid has superior cooling properties compared with the first, and the two fluids are soluble. The multiple valves are controllable to selectively couple the first or second fluid into the coolant in the coolant loop, wherein the coolant includes at least the second fluid. The controller automatically controls the valves to vary first fluid concentration level in the coolant loop based on historical, current, or anticipated outdoor air ambient temperature(s) for a time of year.

Features of a SINDA/FLUINT model of a liquid oxygen supply line

NASA Astrophysics Data System (ADS)

Simmonds, Boris G.

1993-11-01

The modeling features used in a steady-state heat transfer problem using SINDA/FLUINT are described. The problem modeled is a 125 feet long, 3 inch diameter pipe, filled with liquid oxygen flow driven by a given pressure gradient. The pipe is fully insulated in five sections. Three sections of 1 inch thick spray-on foam and two sections of vacuum jacket. The model evaluates friction, turns losses and convection heat transfer between the fluid and the pipe wall. There is conduction through the foam insulation with temperature dependent thermal conductivity. The vacuum space is modeled with radiation and gas molecular conduction, if present, in the annular gap. Heat is transferred between the outer surface and surrounding ambient by natural convection and radiation; and, by axial conduction along the pipe and through the vacuum jacket spacers and welded seal flanges. The model makes extensive use of SINDA/FLUINT basic capabilities such as the GEN option for nodes and conductors (to generate groups of nodes or conductors), the SIV option (to generate single, temperature varying conductors), the SIM option (for multiple, temperature varying conductors) and the M HX macros for fluids (to generate strings of lumps, paths, and ties representing a diabatic duct). It calls subroutine CONTRN (returns the relative location in the G-array of a network conductor, given an actual conductor number) enabling an extensive manipulation of conductor (calculates an assignment of their values) with DO loops. Models like this illustrate to the new and even to the old SINDA/FLUINT user, features of the program that are not so obvious or known, and that are extremely handy when trying to take advantage of both, the automation of the DATA headers and make surgical modifications to specific parameters of the thermal or fluid elements in the OPERATIONS portion of the model.

Features of a SINDA/FLUINT model of a liquid oxygen supply line

NASA Technical Reports Server (NTRS)

Simmonds, Boris G.

1993-01-01

The modeling features used in a steady-state heat transfer problem using SINDA/FLUINT are described. The problem modeled is a 125 feet long, 3 inch diameter pipe, filled with liquid oxygen flow driven by a given pressure gradient. The pipe is fully insulated in five sections. Three sections of 1 inch thick spray-on foam and two sections of vacuum jacket. The model evaluates friction, turns losses and convection heat transfer between the fluid and the pipe wall. There is conduction through the foam insulation with temperature dependent thermal conductivity. The vacuum space is modeled with radiation and gas molecular conduction, if present, in the annular gap. Heat is transferred between the outer surface and surrounding ambient by natural convection and radiation; and, by axial conduction along the pipe and through the vacuum jacket spacers and welded seal flanges. The model makes extensive use of SINDA/FLUINT basic capabilities such as the GEN option for nodes and conductors (to generate groups of nodes or conductors), the SIV option (to generate single, temperature varying conductors), the SIM option (for multiple, temperature varying conductors) and the M HX macros for fluids (to generate strings of lumps, paths, and ties representing a diabatic duct). It calls subroutine CONTRN (returns the relative location in the G-array of a network conductor, given an actual conductor number) enabling an extensive manipulation of conductor (calculates an assignment of their values) with DO loops. Models like this illustrate to the new and even to the old SINDA/FLUINT user, features of the program that are not so obvious or known, and that are extremely handy when trying to take advantage of both, the automation of the DATA headers and make surgical modifications to specific parameters of the thermal or fluid elements in the OPERATIONS portion of the model.

CVB: the Constrained Vapor Bubble Capillary Experiment on the International Space Station MARANGONI FLOW REGION

NASA Technical Reports Server (NTRS)

Wayner, Peter C., Jr.; Kundan, Akshay; Plawsky, Joel

2014-01-01

The Constrained Vapor Bubble (CVB) is a wickless, grooved heat pipe and we report on a full- scale fluids experiment flown on the International Space Station (ISS). The CVB system consists of a relatively simple setup a quartz cuvette with sharp corners partially filled with either pentane or an ideal mixture of pentane and isohexane as the working fluids. Along with temperature and pressure measurements, the two-dimensional thickness profile of the menisci formed at the corners of the quartz cuvette was determined using the Light Microscopy Module (LMM). Even with the large, millimeter dimensions of the CVB, interfacial forces dominate in these exceedingly small Bond Number systems. The experiments were carried out at various power inputs. Although conceptually simple, the transport processes were found to be very complex with many different regions. At the heated end of the CVB, due to a high temperature gradient, we observed Marangoni flow at some power inputs. This region from the heated end to the central drop region is defined as a Marangoni dominated region. We present a simple analysis based on interfacial phenomena using only measurements from the ISS experiments that lead to a predictive equation for the thickness of the film near the heated end of the CVB. The average pressure gradient for flow in the film is assumed due to the measured capillary pressure at the two ends of the liquid film and that the pressure stress gradient due to cohesion self adjusts to a constant value over a distance L. The boundary conditions are the no slip condition at the wall interface and an interfacial shear stress at the liquid- vapor interface due to the Marangoni stress, which is due to the high temperature gradient. Although the heated end is extremely complex, since it includes three- dimensional variations in radiation, conduction, evaporation, condensation, fluid flow and interfacial forces, we find that using the above simplifying assumptions, a simple successful model can be developed.

Suppression/Reversal of Natural Convection by Exploiting the Temperature/Composition Dependence of Magnetic Susceptibility

NASA Technical Reports Server (NTRS)

Seybert, C. D.; Evans, J. W.; Leslie, F.; Jones, W. K., Jr.

2000-01-01

Natural convection, driven by temperature-or concentration gradients or both, is an inherent phenomenon during solidification of materials on Earth. This convection has practical consequences (e.g effecting macrosegregation) but also renders difficult the scientific examination of diffusive/conductive phenomena during solidification. It is possible to halt, or even reverse, natural convection by exploiting the variation (with temperature, for example) of the susceptibility of a material. If the material is placed in a vertical magnetic field gradient, a buoyancy force of magnetic origin arises and, at a critical field gradient, can balance the normal buoyancy forces to halt convection. At higher field gradients the convection can be reversed. The effect has been demonstrated in experiments at Marshall Space Flight Center where flow was measured by PIV in MnCl2 solution in a superconducting magnet. In auxiliary experiments the field in the magnet and the properties of the solution were measured. Computations of the natural convection, its halting and reversal, using the commercial software FLUENT were in good agreement with the measurements.

Bio-inspired Polymer Composite Actuator and Generator Driven by Water Gradients

PubMed Central

Ma, Mingming; Guo, Liang; Anderson, Daniel G.; Langer, Robert

2013-01-01

Here we describe the development of a water-responsive polymer film; combining both a rigid matrix (polypyrrole) and a dynamic network (polyol-borate), strong and flexible polymer films were developed that can exchange water with the environment to induce film expansion and contraction, resulting in rapid and continuous locomotion. The film actuator can generate contractile stress up to 27 MPa, lift objects 380 times heavier than itself, and transport cargo 10 times heavier than itself. We have assembled a generator by associating this actuator with a piezoelectric element. Driven by water gradients, this generator outputs alternating electricity at ∼0.3 Hz, with a peak voltage of ∼1.0 V. The electrical energy is stored in capacitors that could power micro- and nano-electronic devices. PMID:23307738

Cooperative inter- and intra-layer lattice dynamics of photoexcited multi-walled carbon nanotubes studied by ultrafast electron diffraction.

PubMed

Sun, Shuaishuai; Li, Zhongwen; Li, Zi-An; Xiao, Ruijuan; Zhang, Ming; Tian, Huanfang; Yang, Huaixin; Li, Jianqi

2018-04-26

Optical tuning and probing ultrafast structural response of nanomaterials driven by electronic excitation constitute a challenging but promising approach for understanding microscopic mechanisms and applications in microelectromechanical systems and optoelectrical devices. Here we use pulsed electron diffraction in a transmission electron microscope to investigate laser-induced tubular lattice dynamics of multi-walled carbon nanotubes (MWCNTs) with varying laser fluence and initial specimen temperature. Our photoexcitation experiments demonstrate cooperative and inverse collective atomic motions in intralayer and interlayer directions, whose strengths and rates depend on pump fluence. The electron-driven and thermally driven structural responses with opposite amplitudes cause a crossover between intralayer and interlayer directions. Our ab initio calculations support these findings and reveal that electrons excited from π to π* orbitals in a carbon tube weaken the intralayer bonds while strengthening the interlayer bonds along the radial direction. Moreover, by probing the structural dynamics of MWCNTs at initial temperatures of 300 and 100 K, we uncover the concomitance of thermal and nonthermal dynamical processes and their mutual influence in MWCNTs. Our results illustrate the nature of electron-driven nonthermal process and electron-phonon thermalization in the MWCNTs, and bear implications for the intricate energy conversion and transfer in materials at the nanoscale.

Low- to moderate-temperature geothermal resource assessment for Nevada: area specific studies, Pumpernickel Valley, Carlin and Moana. Final report June 1, 1981-July 31, 1982

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trexler, D.T.; Flynn, T.; Koenig, B.A.

1982-01-01

Geological, geophysical and geochemical surveys were used in conjunction with temperature gradient hole drilling to assess the geothermal resources in Pumpernickel Valley and Carlin, Nevada. This program is based on a statewide assessment of geothermal resources that was completed in 1979. The exploration techniques are based on previous federally-funded assessment programs that were completed in six other areas in Nevada and include: literature search and compilation of existing data, geologic reconnaissance, chemical sampling of thermal and non-thermal fluids, interpretation of satellite imagery, interpretation of low-sun angle aerial photographs, two-meter depth temperature probe survey, gravity survey, seismic survey, soil-mercury survey, andmore » temperature gradient drilling.« less

Thermal Imaging of Convecting Opaque Fluids using Ultrasound

NASA Technical Reports Server (NTRS)

Xu, Hongzhou; Fife, Sean; Andereck, C. David

2002-01-01

An ultrasound technique has been developed to non-intrusively image temperature fields in small-scale systems of opaque fluids undergoing convection. Fluids such as molten metals, semiconductors, and polymers are central to many industrial processes, and are often found in situations where natural convection occurs, or where thermal gradients are otherwise important. However, typical thermal and velocimetric diagnostic techniques rely upon transparency of the fluid and container, or require the addition of seed particles, or require mounting probes inside the fluid, all of which either fail altogether in opaque fluids, or necessitate significant invasion of the flow and/or modification of the walls of the container to allow access to the fluid. The idea behind our work is to use the temperature dependence of sound velocity, and the ease of propagation of ultrasound through fluids and solids, to probe the thermal fields of convecting opaque fluids non-intrusively and without the use of seed particles. The technique involves the timing of the return echoes from ultrasound pulses, a variation on an approach used previously in large-scale systems.

A Fluid Pulse on the Hikurangi Subduction Margin: Evidence From a Heat Flux Transect Across the Upper Limit of Gas Hydrate Stability

NASA Astrophysics Data System (ADS)

Pecher, I. A.; Villinger, H.; Kaul, N.; Crutchley, G. J.; Mountjoy, J. J.; Huhn, K.; Kukowski, N.; Henrys, S. A.; Rose, P. S.; Coffin, R. B.

2017-12-01

A transect of seafloor heat probe measurements on the Hikurangi Margin shows a significant increase of thermal gradients upslope of the updip limit of gas hydrate stability at the seafloor. We interpret these anomalously high thermal gradients as evidence for a fluid pulse leading to advective heat flux, while endothermic cooling from gas hydrate dissociation depresses temperatures in the hydrate stability field. Previous studies predict a seamount on the subducting Pacific Plate to cause significant overpressure beneath our study area, which may be the source of the fluid pulse. Double-bottom simulating reflections are present in our study area and likely caused by uplift based on gas hydrate phase boundary considerations, although we cannot exclude a thermogenic origin. We suggest that uplift may be associated with the leading edge of the subducting seamount. Our results provide further evidence for the transient nature of fluid expulsion in subduction zones.

Thermocapillary Migration and Interactions of Bubbles and Drops

NASA Technical Reports Server (NTRS)

Balasubramaniam, R.; Lacy, Claud E.; Wozniak, Guenter; Subramanian, R. Shankar

1996-01-01

When a drop or bubble is placed in another fluid and subjected to the action of a temperature gradient, the drop will move. Such motion is a direct consequence of the variation of interfacial tension with temperature, and is termed thermocapillary migration. This paper discusses results from experiments conducted in reduced gravity on the thermocapillary motion of bubbles and drops.

Compact and tunable focusing device for plasma wakefield acceleration

NASA Astrophysics Data System (ADS)

Pompili, R.; Anania, M. P.; Chiadroni, E.; Cianchi, A.; Ferrario, M.; Lollo, V.; Notargiacomo, A.; Picardi, L.; Ronsivalle, C.; Rosenzweig, J. B.; Shpakov, V.; Vannozzi, A.

2018-03-01

Plasma wakefield acceleration, either driven by ultra-short laser pulses or electron bunches, represents one of the most promising techniques able to overcome the limits of conventional RF technology and allows the development of compact accelerators. In the particle beam-driven scenario, ultra-short bunches with tiny spot sizes are required to enhance the accelerating gradient and preserve the emittance and energy spread of the accelerated bunch. To achieve such tight transverse beam sizes, a focusing system with short focal length is mandatory. Here we discuss the development of a compact and tunable system consisting of three small-bore permanent-magnet quadrupoles with 520 T/m field gradient. The device has been designed in view of the plasma acceleration experiments planned at the SPARC_LAB test-facility. Being the field gradient fixed, the focusing is adjusted by tuning the relative position of the three magnets with nanometer resolution. Details about its magnetic design, beam-dynamics simulations, and preliminary results are examined in the paper.

The deep atmosphere of Venus and the possible role of density-driven separation of CO2 and N2

NASA Astrophysics Data System (ADS)

Lebonnois, Sebastien; Schubert, Gerald

2017-07-01

With temperatures around 700 K and pressures of around 75 bar, the deepest 12 km of the atmosphere of Venus are so hot and dense that the atmosphere behaves like a supercritical fluid. The Soviet VeGa-2 probe descended through the atmosphere in 1985 and obtained the only reliable temperature profile for the deep Venusian atmosphere thus far. In this temperature profile, the atmosphere appears to be highly unstable at altitudes below 7 km, contrary to expectations. We argue that the VeGa-2 temperature profile could be explained by a change in the atmospheric gas composition, and thus molecular mass, with depth. We propose that the deep atmosphere consists of a non-homogeneous layer in which the abundance of N2--the second most abundant constituent of the Venusian atmosphere after CO2--gradually decreases to near-zero at the surface. It is difficult to explain a decline in N2 towards the surface with known nitrogen sources and sinks for Venus. Instead we suggest, partly based on experiments on supercritical fluids, that density-driven separation of N2 from CO2 can occur under the high pressures of Venus's deep atmosphere, possibly by molecular diffusion, or by natural density-driven convection. If so, the amount of nitrogen in the atmosphere of Venus is 15% lower than commonly assumed. We suggest that similar density-driven separation could occur in other massive planetary atmospheres.

Detailed energy distributions in laser-produced plasmas of solid gold and foam gold planar targets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dong, Yunsong; Department of Engineering Physics, Tsinghua University, Beijing 100084; Zhang, Lu

Foam gold was proposed to increase the laser to x-ray conversion efficiency due to its important applications. To understand the mechanism of x-ray enhancement, the detailed energy distributions and plasma profiles for laser-irradiated solid gold and foam gold targets were studied comparatively by hydrodynamic simulations using the code Multi-1D. It is confirmed that the radiation heat wave is subsonic for the normal solid gold target, while supersonic for the foam gold target. The shock wave, which is behind the supersonic radiation heat wave for the foam gold target, generates a plasma temperature gradient with high temperature near the shock wavemore » front to produce an additional net outward radiation for enhancement of the x-ray emission. Much larger inward plasma velocity is also driven by the shock wave as an initial plasma velocity for the laser deposition and electron thermal conduct zone, which decreases the expanding plasma kinetic energy loss and helps to increase the x-ray radiation.« less

Design for a spin-Seebeck diode based on two-dimensional materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Hua-Hua; Wu, Dan-Dan; Gu, Lei

2015-07-01

Studies of the spin-Seebeck effect (SSE) are very important for the development of fundamental science and novel low-power-consumption technologies. The spin-Seebeck diode (SSD), in which the spin current can be driven by a forward temperature gradient but not by a reverse temperature gradient, is a key unit in spin caloritronic devices. Here, we propose a SSD design using two-dimensional (2D) materials such as silicene and phosphorene nanoribbons as the source and drain. Due to their unique band structures and magnetic states, thermally driven spin-up and spin-down currents flow in opposite directions. This mechanism is different from that of the previousmore » one, which uses two permalloy circular disks [Phys. Rev. Lett. 112, 047203 (2014)], and the SSD in our design can be easily integrated with gate voltage control. Since the concept of this design is rather general and applicable to many 2D materials, it is promising for the realization and exploitation of SSDs in nanodevices.« less

Seebeck coefficient of one electron

DOE Office of Scientific and Technical Information (OSTI.GOV)

Durrani, Zahid A. K., E-mail: z.durrani@imperial.ac.uk

2014-03-07

The Seebeck coefficient of one electron, driven thermally into a semiconductor single-electron box, is investigated theoretically. With a finite temperature difference ΔT between the source and charging island, a single electron can charge the island in equilibrium, directly generating a Seebeck effect. Seebeck coefficients for small and finite ΔT are calculated and a thermally driven Coulomb staircase is predicted. Single-electron Seebeck oscillations occur with increasing ΔT, as one electron at a time charges the box. A method is proposed for experimental verification of these effects.

Plasma density characterization at SPARC_LAB through Stark broadening of Hydrogen spectral lines

NASA Astrophysics Data System (ADS)

Filippi, F.; Anania, M. P.; Bellaveglia, M.; Biagioni, A.; Chiadroni, E.; Cianchi, A.; Di Giovenale, D.; Di Pirro, G.; Ferrario, M.; Mostacci, A.; Palumbo, L.; Pompili, R.; Shpakov, V.; Vaccarezza, C.; Villa, F.; Zigler, A.

2016-09-01

Plasma-based acceleration techniques are of great interest for future, compact accelerators due to their high accelerating gradient. Both particle-driven and laser-driven Plasma Wakefield Acceleration experiments are foreseen at the SPARC_LAB Test Facility (INFN National Laboratories of Frascati, Italy), with the aim to accelerate high-brightness electron beams. In order to optimize the efficiency of the acceleration in the plasma and preserve the quality of the accelerated beam, the knowledge of the plasma electron density is mandatory. The Stark broadening of the Hydrogen spectral lines is one of the candidates used to characterize plasma density. The implementation of this diagnostic for plasma-based experiments at SPARC_LAB is presented.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borovsky, Joseph E; Cayton, Thomas E; Denton, Michael H

Electron flux measurements from 7 satellites in geosynchronous orbit from 1990-2007 are fit with relativistic bi-Maxwellians, yielding a number density n and temperature T description of the outer electron radiation belt. For 54.5 spacecraft years of measurements the median value ofn is 3.7x10-4 cm-3 and the median value ofT is 142 keY. General statistical properties of n, T, and the 1.1-1.5 MeV flux J are investigated, including local-time and solar-cycle dependencies. Using superposed-epoch analysis triggered on storm onset, the evolution of the outer electron radiation belt through high-speed-steam-driven storms is investigated. The number density decay during the calm before themore » storm is seen, relativistic-electron dropouts and recoveries from dropout are investigated, and the heating of the outer electron radiation belt during storms is examined. Using four different triggers (SSCs, southward-IMF CME sheaths, southward-IMF magnetic clouds, and minimum Dst), CME-driven storms are analyzed with superposed-epoch techniques. For CME-driven storms an absence of a density decay prior to storm onset is found, the compression of the outer electron radiation belt at time of SSC is analyzed, the number-density increase and temperature decrease during storm main phase is seen, and the increase in density and temperature during storm recovery phase is observed. Differences are found between the density-temperature and the flux descriptions, with more information for analysis being available in the density-temperature description.« less

Resilience of quasi-isodynamic stellarators against trapped-particle instabilities.

PubMed

Proll, J H E; Helander, P; Connor, J W; Plunk, G G

2012-06-15

It is shown that in perfectly quasi-isodynamic stellarators, trapped particles with a bounce frequency much higher than the frequency of the instability are stabilizing in the electrostatic and collisionless limit. The collisionless trapped-particle instability is therefore stable as well as the ordinary electron-density-gradient-driven trapped-electron mode. This result follows from the energy balance of electrostatic instabilities and is thus independent of all other details of the magnetic geometry.

Misfit strain driven cation inter-diffusion across an epitaxial multiferroic thin film interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sankara Rama Krishnan, P. S.; Munroe, Paul; Nagarajan, V.

Cation intermixing at functional oxide interfaces remains a highly controversial area directly relevant to interface-driven nanoelectronic device properties. Here, we systematically explore the cation intermixing in epitaxial (001) oriented multiferroic bismuth ferrite (BFO) grown on a (001) lanthanum aluminate (LAO) substrate. Aberration corrected dedicated scanning transmission electron microscopy and electron energy loss spectroscopy reveal that the interface is not chemically sharp, but with an intermixing of ∼2 nm. The driving force for this process is identified as misfit-driven elastic strain. Landau-Ginzburg-Devonshire-based phenomenological theory was combined with the Sheldon and Shenoy formula in order to understand the influence of boundary conditions andmore » depolarizing fields arising from misfit strain between the LAO substrate and BFO film. The theory predicts the presence of a strong potential gradient at the interface, which decays on moving into the bulk of the film. This potential gradient is significant enough to drive the cation migration across the interface, thereby mitigating the misfit strain. Our results offer new insights on how chemical roughening at oxide interfaces can be effective in stabilizing the structural integrity of the interface without the need for misfit dislocations. These findings offer a general formalism for understanding cation intermixing at highly strained oxide interfaces that are used in nanoelectronic devices.« less

Heat Flux and Fluid Flow in the Terrebonne Basin, Northern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Meazell, K.; Flemings, P. B.

2016-12-01

We use a three-dimensional seismic survey to map the gas hydrate stability zone within a mid-slope salt-withdrawal minibasin in the northern Gulf of Mexico and identify anomalous regions within the basin where fluids may modify the hydrate stability zone. A discontinuous bottom-simulating reflector (BSR) marks the base of the hydrate stability zone and suggests an average geothermal gradient of 18.1 C/km based on the calculated temperature at the BSR assuming seawater salinity, hydrostatic pressure, and a seafloor temperature of 4 C. When compared to our model of the predicted base of gas hydrate stability assuming a basin-wide geothermal gradient of 18.1 C, two anomalies are found where the BSR is observed significantly shallower than expected. The southern anomaly has a lateral influence of 1500 m from the salt, and a maximum shoaling of 800 m. This anomaly is likely the result of increased salinity or heat from a rising salt diapir along the flank of the basin. A local geothermal gradient of 67.31 C/km or a salinity of 17.5 wt % can explain the observed position of the BSR at the southern anomaly. The northern anomaly is associated with active cold seep vents. In this area, the pluming BSR is crescent shaped, which we interpret as the result of warm and or salty fluids migrating up through a fault. This anomaly has a lateral influence of 1500 m, and a maximum shoaling of 600 m above the predicted base of gas hydrate stability. A local geothermal gradient of 35.45 C/km or a salinity of 14.7 wt % is required to adjust the position of the BSR to that which is observed at the northern anomaly. Active fluid migration suggests a combination of both heat and salinity is responsible for the altered position of the BSR.

A blended continuous–discontinuous finite element method for solving the multi-fluid plasma model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sousa, E.M., E-mail: sousae@uw.edu; Shumlak, U., E-mail: shumlak@uw.edu

The multi-fluid plasma model represents electrons, multiple ion species, and multiple neutral species as separate fluids that interact through short-range collisions and long-range electromagnetic fields. The model spans a large range of temporal and spatial scales, which renders the model stiff and presents numerical challenges. To address the large range of timescales, a blended continuous and discontinuous Galerkin method is proposed, where the massive ion and neutral species are modeled using an explicit discontinuous Galerkin method while the electrons and electromagnetic fields are modeled using an implicit continuous Galerkin method. This approach is able to capture large-gradient ion and neutralmore » physics like shock formation, while resolving high-frequency electron dynamics in a computationally efficient manner. The details of the Blended Finite Element Method (BFEM) are presented. The numerical method is benchmarked for accuracy and tested using two-fluid one-dimensional soliton problem and electromagnetic shock problem. The results are compared to conventional finite volume and finite element methods, and demonstrate that the BFEM is particularly effective in resolving physics in stiff problems involving realistic physical parameters, including realistic electron mass and speed of light. The benefit is illustrated by computing a three-fluid plasma application that demonstrates species separation in multi-component plasmas.« less

Thermally Actuated Hydraulic Pumps

NASA Technical Reports Server (NTRS)

Jones, Jack; Ross, Ronald; Chao, Yi

2008-01-01

Thermally actuated hydraulic pumps have been proposed for diverse applications in which direct electrical or mechanical actuation is undesirable and the relative slowness of thermal actuation can be tolerated. The proposed pumps would not contain any sliding (wearing) parts in their compressors and, hence, could have long operational lifetimes. The basic principle of a pump according to the proposal is to utilize the thermal expansion and contraction of a wax or other phase-change material in contact with a hydraulic fluid in a rigid chamber. Heating the chamber and its contents from below to above the melting temperature of the phase-change material would cause the material to expand significantly, thus causing a substantial increase in hydraulic pressure and/or a substantial displacement of hydraulic fluid out of the chamber. Similarly, cooling the chamber and its contents from above to below the melting temperature of the phase-change material would cause the material to contract significantly, thus causing a substantial decrease in hydraulic pressure and/or a substantial displacement of hydraulic fluid into the chamber. The displacement of the hydraulic fluid could be used to drive a piston. The figure illustrates a simple example of a hydraulic jack driven by a thermally actuated hydraulic pump. The pump chamber would be a cylinder containing encapsulated wax pellets and containing radial fins to facilitate transfer of heat to and from the wax. The plastic encapsulation would serve as an oil/wax barrier and the remaining interior space could be filled with hydraulic oil. A filter would retain the encapsulated wax particles in the pump chamber while allowing the hydraulic oil to flow into and out of the chamber. In one important class of potential applications, thermally actuated hydraulic pumps, exploiting vertical ocean temperature gradients for heating and cooling as needed, would be used to vary hydraulic pressures to control buoyancy in undersea research vessels. Heretofore, electrically actuated hydraulic pumps have been used for this purpose. By eliminating the demand for electrical energy for pumping, the use of the thermally actuated hydraulic pumps could prolong the intervals between battery charges, thus making it possible to greatly increase the durations of undersea exploratory missions.

Electron transfer across a thermal gradient

PubMed Central

Craven, Galen T.

2016-01-01

Charge transfer is a fundamental process that underlies a multitude of phenomena in chemistry and biology. Recent advances in observing and manipulating charge and heat transport at the nanoscale, and recently developed techniques for monitoring temperature at high temporal and spatial resolution, imply the need for considering electron transfer across thermal gradients. Here, a theory is developed for the rate of electron transfer and the associated heat transport between donor–acceptor pairs located at sites of different temperatures. To this end, through application of a generalized multidimensional transition state theory, the traditional Arrhenius picture of activation energy as a single point on a free energy surface is replaced with a bithermal property that is derived from statistical weighting over all configurations where the reactant and product states are equienergetic. The flow of energy associated with the electron transfer process is also examined, leading to relations between the rate of heat exchange among the donor and acceptor sites as functions of the temperature difference and the electronic driving bias. In particular, we find that an open electron transfer channel contributes to enhanced heat transport between sites even when they are in electronic equilibrium. The presented results provide a unified theory for charge transport and the associated heat conduction between sites at different temperatures. PMID:27450086

Control of topography gradients on residence time distributions, mixing dynamics and reactive hotspot development

NASA Astrophysics Data System (ADS)

Bandopadhyay, Aditya; Le Borgne, Tanguy; Davy, Philippe

2017-04-01

Topography-driven subsurface flows are thought to play a central role in determining solute turnover and biogeochemical processes at different scales in the critical zone, including river-hyporheic zone exchanges, hillslope solute transport and reactions, and catchment biogeochemical cycles. Hydraulic head gradients, induced by topography gradients at different scales, generate a distribution of streamlines at depth, dictating the spatial distribution of redox sensitive species, the magnitude of surface water - ground water exchanges and ultimately the source/sink function of the subsurface. Flow velocities generally decrease with depth, leading to broad residence time distributions, which have been shown to affect river chemistry and geochemical reactions in catchments. In this presentation, we discuss the impact of topography-driven flows on mixing processes and the formation of localized reactive hotspots. For this, we solve analytically the coupled flow, mixing and reaction equations in two-dimensional vertical cross-sections of subsurface domains with different topography gradients. For a given topography gradient, we derive the spatial distribution of subsurface velocities, the rates of solute mixing accross streamlines and the induced kinetics of redox, precipitation and dissolution reactions using a Lagrangian approach (Le Borgne et al. 2014). We demonstrate that vertical velocity profiles driven by topography variations, act effectively as shear flows, hence stretching continuously the mixing fronts between recently infiltrated and resident water (Bandopadhyay et al. 2017). We thus derive analytical expressions for residence time distributions, mixing rates and kinetics of chemical reactions as a function of the topography gradients. We show that the rates dissolution and precipitation reactions are significantly enhanced by the existence of vertical velocity gradients and that reaction rates reach a maximum in a localized subsurface reactive layer, whose location and intensity depends on topography gradients. As a consequence of these findings, we discuss the links between topography variations, subsurface velocity gradients and biogeochemical processes in the critical zone. References: Bandopadhyay A., T. Le Borgne, Y. Méheust and M. Dentz (2017) Enhanced reaction kinetics and reactive mixing scale dynamics in mixing fronts under shear flow for arbitrary Damkohler numbers, Adv. in Water Resour. Vol. 100, p. 78-95 Le Borgne T., T. Ginn and M. Dentz (2014) Impact of Fluid Deformation on Mixing-Induced Chemical Reactions in Heterogeneous Flows, Geophys. Res. Lett., Vol. 41, 22, p. 7898-790

A Two-Fluid, MHD Coronal Model

NASA Technical Reports Server (NTRS)

Suess, S. T.; Wang, A.-H.; Wu, S. T.; Poletto, G.; McComas, D. J.

1999-01-01

We describe first results from a numerical two-fluid MHD model of the global structure of the solar Corona. The model is two-fluid in the sense that it accounts for the collisional energy exchange between protons and electrons. As in our single-fluid model, volumetric heat and Momentum sources are required to produce high speed wind from Corona] holes, low speed wind above streamers, and mass fluxes similar to the empirical solar wind. By specifying different proton and electron heating functions we obtain a high proton temperature in the coronal hole and a relatively low proton temperature above the streamer (in comparison with the electron temperature). This is consistent with inferences from SOHO/UltraViolet Coronagraph Spectrometer instrument (UVCS), and with the Ulysses/Solar Wind Observations Over the Poles of the Sun instrument (SWOOPS) proton and electron temperature measurements which we show from the fast latitude scan. The density in the coronal hole between 2 and 5 solar radii (2 and 5 R(sub S)) is similar to the density reported from SPARTAN 201.-01 measurements by Fisher and Guhathakurta [19941. The proton mass flux scaled to 1 AU is 2.4 x 10(exp 8)/sq cm s, which is consistent with Ulysses observations. Inside the closed field region, the density is sufficiently high so that the simulation gives equal proton and electron temperatures due to the high collision rate. In open field regions (in the coronal hole and above the streamer) the proton and electron temperatures differ by varying amounts. In the streamer the temperature and density are similar to those reported empirically by Li et al. [1998], and the plasma beta is larger than unity everywhere above approx. 1.5 R(sub S), as it is in all other MHD coronal streamer models [e.g., Steinolfson et al., 1982; also G. A. Gary and D. Alexander, Constructing the coronal magnetic field, submitted to Solar Physics, 1998].

Katherine E. Weimer Award: X-ray light sources from laser-plasma and laser-electron interaction: development and applications

NASA Astrophysics Data System (ADS)

Albert, Felicie

2017-10-01

Bright sources of x-rays, such as synchrotrons and x-ray free electron lasers (XFEL) are transformational tools for many fields of science. They are used for biology, material science, medicine, or industry. Such sources rely on conventional particle accelerators, where electrons are accelerated to gigaelectronvolts (GeV) energies. The accelerated particles are wiggled in magnetic structures to emit x-ray radiation that is commonly used for molecular crystallography, fluorescence studies, chemical analysis, medical imaging, and many other applications. One of the drawbacks of these machines is their size and cost, because electric field gradients are limited to about 100 V/M in conventional accelerators. Particle acceleration in laser-driven plasmas is an alternative to generate x-rays via betatron emission, Compton scattering, or bremsstrahlung. A plasma can sustain electrical fields many orders of magnitude higher than that in conventional radiofrequency accelerator structures. When short, intense laser pulses are focused into a gas, it produces electron plasma waves in which electrons can be trapped and accelerated to GeV energies. X-ray sources, driven by electrons from laser-wakefield acceleration, have unique properties that are analogous to synchrotron radiation, with a 1000-fold shorter pulse. An important use of x-rays from laser plasma accelerators is in High Energy Density (HED) science, which requires laser and XFEL facilities to create in the laboratory extreme conditions of temperatures and pressures that are usually found in the interiors of stars and planets. To diagnose such extreme states of matter, the development of efficient, versatile and fast (sub-picosecond scale) x-ray probes has become essential. In these experiments, x-ray photons can pass through dense material, and absorption of the x-rays can be directly measured, via spectroscopy or imaging, to inform scientists about the temperature and density of the targets being studied. Performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344, supported by the LLNL LDRD program (16ERD024), and by the DOE Office Science Early Career Research Program (SCW1575).

Texturing of high T(sub c) superconducting polycrystalline fibers/wires by laser-driven directional solidification in an thermal gradient

NASA Technical Reports Server (NTRS)

Varshney, Usha; Eichelberger, B. Davis, III

1995-01-01

This paper summarizes the technique of laser-driven directional solidification in a controlled thermal gradient of yttria stabilized zirconia core coated Y-Ba-Cu-O materials to produce textured high T(sub c) superconducting polycrystalline fibers/wires with improved critical current densities in the extended range of magnetic fields at temperatures greater than 77 K. The approach involves laser heating to minimize phase segregation by heating very rapidly through the two-phase incongruent melt region to the single phase melt region and directionally solidifying in a controlled thermal gradient to achieve highly textured grains in the fiber axis direction. The technique offers a higher grain growth rate and a lower thermal budget compared with a conventional thermal gradient and is amenable as a continuous process for improving the J(sub c) of high T(sub c) superconducting polycrystalline fibers/wires. The technique has the advantage of suppressing weak-link behavior by orientation of crystals, formation of dense structures with enhanced connectivity, formation of fewer and cleaner grain boundaries, and minimization of phase segregation in the incongruent melt region.

An improved molecular dynamics algorithm to study thermodiffusion in binary hydrocarbon mixtures

NASA Astrophysics Data System (ADS)

Antoun, Sylvie; Saghir, M. Ziad; Srinivasan, Seshasai

2018-03-01

In multicomponent liquid mixtures, the diffusion flow of chemical species can be induced by temperature gradients, which leads to a separation of the constituent components. This cross effect between temperature and concentration is known as thermodiffusion or the Ludwig-Soret effect. The performance of boundary driven non-equilibrium molecular dynamics along with the enhanced heat exchange (eHEX) algorithm was studied by assessing the thermodiffusion process in n-pentane/n-decane (nC5-nC10) binary mixtures. The eHEX algorithm consists of an extended version of the HEX algorithm with an improved energy conservation property. In addition to this, the transferable potentials for phase equilibria-united atom force field were employed in all molecular dynamics (MD) simulations to precisely model the molecular interactions in the fluid. The Soret coefficients of the n-pentane/n-decane (nC5-nC10) mixture for three different compositions (at 300.15 K and 0.1 MPa) were calculated and compared with the experimental data and other MD results available in the literature. Results of our newly employed MD algorithm showed great agreement with experimental data and a better accuracy compared to other MD procedures.

Thermally developing MHD peristaltic transport of nanofluids with velocity and thermal slip effects

NASA Astrophysics Data System (ADS)

Sher Akbar, Noreen; Bintul Huda, A.; Tripathi, D.

2016-09-01

We investigate the velocity slip and thermal slip effects on peristaltically driven thermal transport of nanofluids through the vertical parallel plates under the influence of transverse magnetic field. The wall surface is propagating with sinusoidal wave velocity c. The flow characteristics are governed by the mass, momentum and energy conservation principle. Low Reynolds number and large wavelength approximations are taken into consideration to simplify the non-linear terms. Analytical solutions for axial velocity, temperature field, pressure gradient and stream function are obtained under certain physical boundary conditions. Two types of nanoparticles, SiO2 and Ag, are considered for analysis with water as base fluid. This is the first article in the literature that discusses the SiO2 and Ag nanoparticles for a peristaltic flow with variable viscosity. The effects of physical parameters on velocity, temperature, pressure and trapping are discussed. A comparative study of SiO2 nanofluid, Ag nanofluid and pure water is also presented. This model is applicable in biomedical engineering to make thermal peristaltic pumps and other pumping devices like syringe pumps, etc. It is observed that pressure for pure water is maximum and pressure for Ag nanofluid is minimum.

Joule-Thomson effect and internal convection heat transfer in turbulent He II flow

NASA Technical Reports Server (NTRS)

Walstrom, P. L.

1988-01-01

The temperature rise in highly turbulent He II flowing in tubing was measured in the temperature range 1.6-2.1 K. The effect of internal convection heat transport on the predicted temperature profiles is calculated from the two-fluid model with mutual friction. The model predictions are in good agreement with the measurements, provided that the pressure gradient term is retained in the expression for internal convection heat flow.

Compensated geothermal gradient: new map of old data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ibrahim, M.W.

1986-05-01

Bottom-hole temperature measurement is one of the oldest forms of downhole information acquired by the oil industry. Old and new geothermal maps that are based on these measurements have invariably been drawn with an assumed constant or average ground surface temperature over the mapped areas. However, near ground-surface equilibrium temperature is a variable rather than a constant over any region; therefore, old and current geothermal gradient mapping methods give a false impression of the true thermal level of subsurface strata, and may lead to erroneous results of temperature-based calculations, such as the TTI. In this paper, a geothermal mapping methodmore » is presented in which extrapolated surface temperature is coupled with the corresponding geothermal gradient over the mapped area. The method was tested on areas in the Middle East and Africa. Results indicate that it is especially effective in delineating loci of vertical geothermal heat flux carried upwards by ascending subsurface fluids; such areas are preferential sites for hydrocarbon entrapment, especially in young sedimentary basins where migration is still in progress.« less

Nonlocal electron energy transport and flux inhibition in laser produced plasmas in one and two dimensions

NASA Astrophysics Data System (ADS)

Manheimer, Wallace

2011-10-01

As the mean free path of the heat conducting electrons in laser produced plasmas can, at certain points, be greater than the temperature gradient scale length, the classical, local model can be invalid. More energetic electrons can advance ahead of the main heat front and preheat the fusion target. Also, experiments show that the main heat front does not propagate as rapidly as classical theory would predict, so there is heat flux inhibition. This latter effect is usually treated by limiting the flux to some arbitrary fraction f of the free streaming flux; f's have ranged from 0.03 to 0.3. However the choice of flux limit is arbitrary and the choice affects plasma temperature, which in turn affects thresholds for laser plasma instabilities; too low a limit has given too high a temperature and false optimism regarding instability threshold. We have developed a velocity dependent Krook model for nonlocal electron energy transport. It shows preheat and flux limitation are not separate effects, but are two sides of the same coin. The model gives an analytic solution for the nonlocal electron energy flux, and it is relatively simple and inexpensive to incorporate in a fluid simulation run at the ion time scale. It shows that in some sense, preheat is subtracted from the main electron energy flux, thereby giving rise to flux limitation. We have developed the theory and compared it with Fokker Planck simulations of simple configurations. We have incorporated the model into our code FAST2D and used it to model foil acceleration and evaluate and compare a number of competing physical effects in one and two dimensions, and compared with experiments. We have investigated the effect on spherical implosions, especially the effect on corona temperature, pressure, fuel adiabat and preheat, and ultimately gain. Supported by ONR and NNSA/DoE.

Femtosecond-laser induced dynamics of CO on Ru(0001): Deep insights from a hot-electron friction model including surface motion

NASA Astrophysics Data System (ADS)

Scholz, Robert; Floß, Gereon; Saalfrank, Peter; Füchsel, Gernot; Lončarić, Ivor; Juaristi, J. I.

2016-10-01

A Langevin model accounting for all six molecular degrees of freedom is applied to femtosecond-laser induced, hot-electron driven dynamics of Ru(0001)(2 ×2 ):CO. In our molecular dynamics with electronic friction approach, a recently developed potential energy surface based on gradient-corrected density functional theory accounting for van der Waals interactions is adopted. Electronic friction due to the coupling of molecular degrees of freedom to electron-hole pairs in the metal are included via a local density friction approximation, and surface phonons by a generalized Langevin oscillator model. The action of ultrashort laser pulses enters through a substrate-mediated, hot-electron mechanism via a time-dependent electronic temperature (derived from a two-temperature model), causing random forces acting on the molecule. The model is applied to laser induced lateral diffusion of CO on the surface, "hot adsorbate" formation, and laser induced desorption. Reaction probabilities are strongly enhanced compared to purely thermal processes, both for diffusion and desorption. Reaction yields depend in a characteristic (nonlinear) fashion on the applied laser fluence, as well as branching ratios for various reaction channels. Computed two-pulse correlation traces for desorption and other indicators suggest that aside from electron-hole pairs, phonons play a non-negligible role for laser induced dynamics in this system, acting on a surprisingly short time scale. Our simulations on precomputed potentials allow for good statistics and the treatment of long-time dynamics (300 ps), giving insight into this system which hitherto has not been reached. We find generally good agreement with experimental data where available and make predictions in addition. A recently proposed laser induced population of physisorbed precursor states could not be observed with the present low-coverage model.

Electrothermal enrichment of submicron particles in an insulator-based dielectrophoretic microdevice.

PubMed

Kale, Akshay; Song, Le; Lu, Xinyu; Yu, Liandong; Hu, Guoqing; Xuan, Xiangchun

2018-03-01

Insulator-based dielectrophoresis (iDEP) exploits in-channel hurdles and posts etc. to create electric field gradients for various particle manipulations. However, the presence of such insulating structures also amplifies the Joule heating in the fluid around themselves, leading to both temperature gradients and electrothermal flow. These Joule heating effects have been previously demonstrated to weaken the dielectrophoretic focusing and trapping of microscale and nanoscale particles. We find that the electrothermal flow vortices are able to entrain submicron particles for a localized enrichment near the insulating tips of a ratchet microchannel. This increase in particle concentration is reasonably predicted by a full-scale numerical simulation of the mass transport along with the coupled charge, heat and fluid transport. Our model also predicts the electric current and flow pattern in the fluid with a good agreement with the experimental observations. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Lens intracellular hydrostatic pressure is generated by the circulation of sodium and modulated by gap junction coupling

PubMed Central

Gao, Junyuan; Sun, Xiurong; Moore, Leon C.; White, Thomas W.; Brink, Peter R.

2011-01-01

We recently modeled fluid flow through gap junction channels coupling the pigmented and nonpigmented layers of the ciliary body. The model suggested the channels could transport the secretion of aqueous humor, but flow would be driven by hydrostatic pressure rather than osmosis. The pressure required to drive fluid through a single layer of gap junctions might be just a few mmHg and difficult to measure. In the lens, however, there is a circulation of Na+ that may be coupled to intracellular fluid flow. Based on this hypothesis, the fluid would cross hundreds of layers of gap junctions, and this might require a large hydrostatic gradient. Therefore, we measured hydrostatic pressure as a function of distance from the center of the lens using an intracellular microelectrode-based pressure-sensing system. In wild-type mouse lenses, intracellular pressure varied from ∼330 mmHg at the center to zero at the surface. We have several knockout/knock-in mouse models with differing levels of expression of gap junction channels coupling lens fiber cells. Intracellular hydrostatic pressure in lenses from these mouse models varied inversely with the number of channels. When the lens’ circulation of Na+ was either blocked or reduced, intracellular hydrostatic pressure in central fiber cells was either eliminated or reduced proportionally. These data are consistent with our hypotheses: fluid circulates through the lens; the intracellular leg of fluid circulation is through gap junction channels and is driven by hydrostatic pressure; and the fluid flow is generated by membrane transport of sodium. PMID:21624945

The spiral field inhibition of thermal conduction in two-fluid solar wind models

NASA Technical Reports Server (NTRS)

Nerney, S.; Barnes, A.

1978-01-01

The paper reports on two-field models which include the inhibition of thermal conduction by the spiraling interplanetary field to determine whether any of the major conclusions obtained by Nerney and Barnes (1977) needs to be modified. Comparisons with straight field line models reveal that for most base conditions, the primary effect of the inhibition of thermal conduction is the bottling-up of heat in the electrons as well as the quite different temperature profiles at a large heliocentric radius. The spiral field solutions show that coronal hole boundary conditions do not correspond to states of high-speed streams as observed at 1 AU. The two-fluid models suggest that the spiral field inhibition of thermal conduction in the equatorial plane will generate higher gas pressures in comparison with flows along the solar rotation axis (between 1 and 10 AU). In particular, massive outflows of stellar winds, such as outflow from T Tauri stars, cannot be driven by thermal conduction. The conclusions of Nerney and Barnes remain essentially unchanged.

Droplet microfluidics driven by gradients of confinement.

PubMed

Dangla, Rémi; Kayi, S Cagri; Baroud, Charles N

2013-01-15

The miniaturization of droplet manipulation methods has led to drops being proposed as microreactors in many applications of biology and chemistry. In parallel, microfluidic methods have been applied to generate monodisperse emulsions for applications in the pharmaceuticals, cosmetics, and food industries. To date, microfluidic droplet production has been dominated by a few designs that use hydrodynamic forces, resulting from the flowing fluids, to break drops at a junction. Here we present a platform for droplet generation and manipulation that does not depend on the fluid flows. Instead, we use devices that incorporate height variations to subject the immiscible interfaces to gradients of confinement. The resulting curvature imbalance along the interface causes the detachment of monodisperse droplets, without the need for a flow of the external phase. Once detached, the drops are self-propelled due to the gradient of surface energy. We show that the size of the drops is determined by the device geometry; it is insensitive to the physical fluid properties and depends very weakly on the flow rate of the dispersed phase. This allows us to propose a geometric theoretical model that predicts the dependence of droplet size on the geometric parameters, which is in agreement with experimental measurements. The approach presented here can be applied in a wide range of standard applications, while simplifying the device operations. We demonstrate examples for single-droplet operations and high-throughput generation of emulsions, all of which are performed in simple and inexpensive devices.

Droplet microfluidics driven by gradients of confinement

PubMed Central

Dangla, Rémi; Kayi, S. Cagri; Baroud, Charles N.

2013-01-01

The miniaturization of droplet manipulation methods has led to drops being proposed as microreactors in many applications of biology and chemistry. In parallel, microfluidic methods have been applied to generate monodisperse emulsions for applications in the pharmaceuticals, cosmetics, and food industries. To date, microfluidic droplet production has been dominated by a few designs that use hydrodynamic forces, resulting from the flowing fluids, to break drops at a junction. Here we present a platform for droplet generation and manipulation that does not depend on the fluid flows. Instead, we use devices that incorporate height variations to subject the immiscible interfaces to gradients of confinement. The resulting curvature imbalance along the interface causes the detachment of monodisperse droplets, without the need for a flow of the external phase. Once detached, the drops are self-propelled due to the gradient of surface energy. We show that the size of the drops is determined by the device geometry; it is insensitive to the physical fluid properties and depends very weakly on the flow rate of the dispersed phase. This allows us to propose a geometric theoretical model that predicts the dependence of droplet size on the geometric parameters, which is in agreement with experimental measurements. The approach presented here can be applied in a wide range of standard applications, while simplifying the device operations. We demonstrate examples for single-droplet operations and high-throughput generation of emulsions, all of which are performed in simple and inexpensive devices. PMID:23284169

Negative Magnetoresistance in Viscous Flow of Two-Dimensional Electrons.

PubMed

Alekseev, P S

2016-10-14

At low temperatures, in very clean two-dimensional (2D) samples, the electron mean free path for collisions with static defects and phonons becomes greater than the sample width. Under this condition, the electron transport occurs by formation of a viscous flow of an electron fluid. We study the viscous flow of 2D electrons in a magnetic field perpendicular to the 2D layer. We calculate the viscosity coefficients as the functions of magnetic field and temperature. The off-diagonal viscosity coefficient determines the dispersion of the 2D hydrodynamic waves. The decrease of the diagonal viscosity in magnetic field leads to negative magnetoresistance which is temperature and size dependent. Our analysis demonstrates that this viscous mechanism is responsible for the giant negative magnetoresistance recently observed in the ultrahigh-mobility GaAs quantum wells. We conclude that 2D electrons in those structures in moderate magnetic fields should be treated as a viscous fluid.

Negative Magnetoresistance in Viscous Flow of Two-Dimensional Electrons

NASA Astrophysics Data System (ADS)

Alekseev, P. S.

2016-10-01

At low temperatures, in very clean two-dimensional (2D) samples, the electron mean free path for collisions with static defects and phonons becomes greater than the sample width. Under this condition, the electron transport occurs by formation of a viscous flow of an electron fluid. We study the viscous flow of 2D electrons in a magnetic field perpendicular to the 2D layer. We calculate the viscosity coefficients as the functions of magnetic field and temperature. The off-diagonal viscosity coefficient determines the dispersion of the 2D hydrodynamic waves. The decrease of the diagonal viscosity in magnetic field leads to negative magnetoresistance which is temperature and size dependent. Our analysis demonstrates that this viscous mechanism is responsible for the giant negative magnetoresistance recently observed in the ultrahigh-mobility GaAs quantum wells. We conclude that 2D electrons in those structures in moderate magnetic fields should be treated as a viscous fluid.

Parametric modulation of thermomagnetic convection in magnetic fluids.

PubMed

Engler, H; Odenbach, S

2008-05-21

Previous theoretical investigations on thermal flow in a horizontal fluid layer have shown that the critical temperature difference, where heat transfer changes from diffusion to convective flow, depends on the frequency of a time-modulated driving force. The driving force of thermal convection is the buoyancy force resulting from the interaction of gravity and the density gradient provided by a temperature difference in the vertical direction of a horizontal fluid layer. An experimental investigation of such phenomena fails because of technical problems arising if buoyancy is to be changed by altering the temperature difference or gravitational acceleration. The possibility of influencing convective flow in a horizontal magnetic fluid layer by magnetic forces might provide us with a means to solve the problem of a time-modulated magnetic driving force. An experimental setup to investigate the dependence of the critical temperature difference on the frequency of the driving force has been designed and implemented. First results show that the time modulation of the driving force has significant influence on the strength of the convective flow. In particular a pronounced minimum in the strength of convection has been found for a particular frequency.

Was That Assumption Necessary? Reconsidering Boundary Conditions for Analytical Solutions to Estimate Streambed Fluxes

NASA Astrophysics Data System (ADS)

Luce, Charles H.; Tonina, Daniele; Applebee, Ralph; DeWeese, Timothy

2017-11-01

Two common refrains about using the one-dimensional advection diffusion equation to estimate fluid fluxes and thermal conductivity from temperature time series in streambeds are that the solution assumes that (1) the surface boundary condition is a sine wave or nearly so, and (2) there is no gradient in mean temperature with depth. Although the mathematical posing of the problem in the original solution to the problem might lead one to believe these constraints exist, the perception that they are a source of error is a fallacy. Here we develop a mathematical proof demonstrating the equivalence of the solution as developed based on an arbitrary (Fourier integral) surface temperature forcing when evaluated at a single given frequency versus that derived considering a single frequency from the beginning. The implication is that any single frequency can be used in the frequency-domain solutions to estimate thermal diffusivity and 1-D fluid flux in streambeds, even if the forcing has multiple frequencies. This means that diurnal variations with asymmetric shapes or gradients in the mean temperature with depth are not actually assumptions, and deviations from them should not cause errors in estimates. Given this clarification, we further explore the potential for using information at multiple frequencies to augment the information derived from time series of temperature.

Thermodynamic Analysis of a Rankine Cycle Powered Vapor Compression Ice Maker Using Solar Energy

PubMed Central

Hu, Bing; Bu, Xianbiao; Ma, Weibin

2014-01-01

To develop the organic Rankine-vapor compression ice maker driven by solar energy, a thermodynamic model was developed and the effects of generation temperature, condensation temperature, and working fluid types on the system performance were analyzed. The results show that the cooling power per square meter collector and ice production per square meter collector per day depend largely on generation temperature and condensation temperature and they increase firstly and then decrease with increasing generation temperature. For every working fluid there is an optimal generation temperature at which organic Rankine efficiency achieves the maximum value. The cooling power per square meter collector and ice production per square meter collector per day are, respectively, 126.44 W m−2 and 7.61 kg m−2 day−1 at the generation temperature of 140°C for working fluid of R245fa, which demonstrates the feasibility of organic Rankine cycle powered vapor compression ice maker. PMID:25202735

Partnership for Edge Physics Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kritz, Arnold H.; Rafiq, Tariq

A major goal of our participation in the Edge Physics Simulation project has been to contribute to the understanding of the self-organization of tokamak turbulence fluctuations resulting in the formation of a staircase structure in the ion temperature. A second important goal is to demonstrate how small scale turbulence in plasmas self-organizes with dynamically driven quasi-stationary flow shear. These goals have been accomplished through the analyses of the statistical properties of XGC1 flux driven Gyrokinetic electrostatic ion temperature gradient (ITG) turbulence simulation data in which neutrals are included. The ITG turbulence data, and in particular fluctuation data, were obtained frommore » a massively parallel flux-driven gyrokinetic full-f particle-in-cell simulation of a DIII-D like equilibrium. Below some the findings are summarized. It was observed that the emergence of staircase structure is related to the variations in the normalized temperature gradient length (R/LT) and the poloidal flow shear. Average turbulence intensity is found to be large in the vicinity of minima in R/LTi, where ITG growth is expected to be lower. The distributions of the occurrences of potential fluctuation are found to be Gaussian away from the staircase-step locations, but they are found to be non-Gaussian in the vicinity of staircase-step locations. The results of analytically derived expressions for the distribution of the occurrences of turbulence intensity and intensity flux were compared with the corresponding quantities computed using XGC1 simulation data and good agreement is found. The derived expressions predicts inward and outward propagation of turbulence intensity flux in an intermittent fashion. The outward propagation of turbulence intensity flux occurs at staircase-step locations and is related to the change in poloidal flow velocity shear and to the change in the ion temperature gradient. The standard deviation, skewness and kurtosis for turbulence quantities were computed and found to be large in the vicinity of the staircase-step structures. Large values of skewness and kurtosis can be explained by a temporary opening and closing of the structure which allows turbulence intensity events to propagate. The staircase patterns may reduce the ion heat transport and a manipulation of these patterns may be used to optimize heat transport in tokamaks. An additional objective of the research in support of the Edge Physics Simulation initiative has been to improve the understanding of scrape-off layer thermal transport. In planning experiments and designing future tokamaks, it is important to understand the physical effects that contribute to divertor heat-load fluxes. The research accomplished will contribute to developing new models for the scrape-off layer region. The XGC0 code was used to compute the heat fluxes and the heat-load width in the outer divertor plates of C-Mod and DIII-D tokamaks. It was observed that the width of the XGC0 neoclassical heat-load was approximately inversely proportional to the total plasma current. Anomalous transport in the H-mode pedestal region of five Alcator C-Mod discharges, representing a collisionality scan, was analyzed. The understanding of anomalous transport in the pedestal region is important for the development of a comprehensive model for the H-mode pedestal slope. It was found that the electron thermal anomalous diffusivities at the pedestal top increase with the electron collisionality. This dependence can point to the DRIBM as the modes that drive the anomalous transport in the plasma edge of highly collisional discharges. The effects of plasma shaping on the H-mode pedestal structure was also investigated. The differences in the predicted H-mode pedestal width and height for the DIII-D discharges with different elongation and triangularities were discussed. For the discharges with higher elongation, it was found that the gradients of the plasma profiles in the H-mode pedestal reach semi-steady states. In these simulations, the pedestal slowly continued to evolve to higher pedestal pressures and bootstrap currents until the peeling ballooning stability conditions were satisfied. The discharges with lower elongation do not reach the semi-steady state, and ELM crashes were triggered at earlier times. The plasma elongation was found to have a stronger stabilizing effect than the plasma triangularity. For the discharges with lower elongation and lower triangularity, the ELM frequency was large, and the H-mode pedestal evolves rapidly. It was found that the temperature of neutrals in the scrape-off-layer region can affect the dynamics of the H-mode pedestal buildup. However, the final pedestal profiles were nearly independent of the neutral temperature. The elongation and triangularity affected the pedestal widths of plasma density and electron temperature profiles differently. This study illustrated a new mechanism for controlling the pedestal bootstrap current and the pedestal stability.« less

Characterization of Sodium Thermal Hydraulics with Optical Fiber Temperature Sensors

NASA Astrophysics Data System (ADS)

Weathered, Matthew Thomas

The thermal hydraulic properties of liquid sodium make it an attractive coolant for use in Generation IV reactors. The liquid metal's high thermal conductivity and low Prandtl number increases efficiency in heat transfer at fuel rods and heat exchangers, but can also cause features such as high magnitude temperature oscillations and gradients in the coolant. Currently, there exists a knowledge gap in the mechanisms which may create these features and their effect on mechanical structures in a sodium fast reactor. Two of these mechanisms include thermal striping and thermal stratification. Thermal striping is the oscillating temperature field created by the turbulent mixing of non-isothermal flows. Usually this occurs at the reactor core outlet or in piping junctions and can cause thermal fatigue in mechanical structures. Meanwhile, thermal stratification results from large volumes of non-isothermal sodium in a pool type reactor, usually caused by a loss of coolant flow accident. This stratification creates buoyancy driven flow transients and high temperature gradients which can also lead to thermal fatigue in reactor structures. In order to study these phenomena in sodium, a novel method for the deployment of optical fiber temperature sensors was developed. This method promotes rapid thermal response time and high spatial temperature resolution in the fluid. The thermal striping and stratification behavior in sodium may be experimentally analyzed with these sensors with greater fidelity than ever before. Thermal striping behavior at a junction of non-isothermal sodium was fully characterized with optical fibers. An experimental vessel was hydrodynamically scaled to model thermal stratification in a prototypical sodium reactor pool. Novel auxiliary applications of the optical fiber temperature sensors were developed throughout the course of this work. One such application includes local convection coefficient determination in a vessel with the corollary application of level sensing. Other applications were cross correlation velocimetry to determine bulk sodium flow rate and the characterization of coherent vortical structures in sodium with temperature frequency data. The data harvested, instrumentation developed and techniques refined in this work will help in the design of more robust reactors as well as validate computational models for licensing sodium fast reactors.

Trains of electron micro-bunches in plasma wake-field acceleration

NASA Astrophysics Data System (ADS)

Lécz, Zsolt; Andreev, Alexander; Konoplev, Ivan; Seryi, Andrei; Smith, Jonathan

2018-07-01

Plasma-based charged particle accelerators have been intensively investigated in the past three decades due to their capability to open up new horizons in accelerator science and particle physics yielding electric field accelerating gradient more than three orders of magnitudes higher than in conventional devices. At the current stage the most advanced and reliable mechanism for accelerating electrons is based on the propagation of an intense laser pulse or a relativistic electron beam in a low density gaseous target. In this paper we concentrate on the electron beam-driven plasma wake-field acceleration and demonstrate using 3D PiC simulations that a train of electron micro-bunches with ∼10 fs period can be generated behind the driving beam propagating in a density down-ramp. We will discuss the conditions and properties of the micro-bunches generated aiming at understanding and study of multi-bunch mechanism of injection. It is show that the periodicity and duration of micro-bunches can be controlled by adjusting the plasma density gradient and driving beam charge.

Microbial community stratification controlled by the subseafloor fluid flow and geothermal gradient at the Iheya North hydrothermal field in the Mid-Okinawa Trough (Integrated Ocean Drilling Program Expedition 331).

PubMed

Yanagawa, Katsunori; Breuker, Anja; Schippers, Axel; Nishizawa, Manabu; Ijiri, Akira; Hirai, Miho; Takaki, Yoshihiro; Sunamura, Michinari; Urabe, Tetsuro; Nunoura, Takuro; Takai, Ken

2014-10-01

The impacts of lithologic structure and geothermal gradient on subseafloor microbial communities were investigated at a marginal site of the Iheya North hydrothermal field in the Mid-Okinawa Trough. Subsurface marine sediments composed of hemipelagic muds and volcaniclastic deposits were recovered through a depth of 151 m below the seafloor at site C0017 during Integrated Ocean Drilling Program Expedition 331. Microbial communities inferred from 16S rRNA gene clone sequencing in low-temperature hemipelagic sediments were mainly composed of members of the Chloroflexi and deep-sea archaeal group. In contrast, 16S rRNA gene sequences of marine group I Thaumarchaeota dominated the microbial phylotype communities in the coarse-grained pumiceous gravels interbedded between the hemipelagic sediments. Based on the physical properties of sediments such as temperature and permeability, the porewater chemistry, and the microbial phylotype compositions, the shift in the physical properties of the sediments is suggested to induce a potential subseafloor recharging flow of oxygenated seawater in the permeable zone, leading to the generation of variable chemical environments and microbial communities in the subseafloor habitats. In addition, the deepest section of sediments under high-temperature conditions (∼90°C) harbored the sequences of an uncultivated archaeal lineage of hot water crenarchaeotic group IV that may be associated with the high-temperature hydrothermal fluid flow. These results indicate that the subseafloor microbial community compositions and functions at the marginal site of the hydrothermal field are highly affected by the complex fluid flow structure, such as recharging seawater and underlying hydrothermal fluids, coupled with the lithologic transition of sediments. Copyright © 2014, American Society for Microbiology. All Rights Reserved.

Microbial Community Stratification Controlled by the Subseafloor Fluid Flow and Geothermal Gradient at the Iheya North Hydrothermal Field in the Mid-Okinawa Trough (Integrated Ocean Drilling Program Expedition 331)

PubMed Central

Breuker, Anja; Schippers, Axel; Nishizawa, Manabu; Ijiri, Akira; Hirai, Miho; Takaki, Yoshihiro; Sunamura, Michinari; Urabe, Tetsuro; Nunoura, Takuro; Takai, Ken

2014-01-01

The impacts of lithologic structure and geothermal gradient on subseafloor microbial communities were investigated at a marginal site of the Iheya North hydrothermal field in the Mid-Okinawa Trough. Subsurface marine sediments composed of hemipelagic muds and volcaniclastic deposits were recovered through a depth of 151 m below the seafloor at site C0017 during Integrated Ocean Drilling Program Expedition 331. Microbial communities inferred from 16S rRNA gene clone sequencing in low-temperature hemipelagic sediments were mainly composed of members of the Chloroflexi and deep-sea archaeal group. In contrast, 16S rRNA gene sequences of marine group I Thaumarchaeota dominated the microbial phylotype communities in the coarse-grained pumiceous gravels interbedded between the hemipelagic sediments. Based on the physical properties of sediments such as temperature and permeability, the porewater chemistry, and the microbial phylotype compositions, the shift in the physical properties of the sediments is suggested to induce a potential subseafloor recharging flow of oxygenated seawater in the permeable zone, leading to the generation of variable chemical environments and microbial communities in the subseafloor habitats. In addition, the deepest section of sediments under high-temperature conditions (∼90°C) harbored the sequences of an uncultivated archaeal lineage of hot water crenarchaeotic group IV that may be associated with the high-temperature hydrothermal fluid flow. These results indicate that the subseafloor microbial community compositions and functions at the marginal site of the hydrothermal field are highly affected by the complex fluid flow structure, such as recharging seawater and underlying hydrothermal fluids, coupled with the lithologic transition of sediments. PMID:25063666

Two-dimensional Nonlinear Simulations of Temperature-anisotropy Instabilities with a Proton-alpha Drift

NASA Astrophysics Data System (ADS)

Markovskii, S. A.; Chandran, Benjamin D. G.; Vasquez, Bernard J.

2018-04-01

We present two-dimensional hybrid simulations of proton-cyclotron and mirror instabilities in a proton-alpha plasma with particle-in-cell ions and a neutralizing electron fluid. The instabilities are driven by the protons with temperature perpendicular to the background magnetic field larger than the parallel temperature. The alpha particles with initially isotropic temperature have a nonzero drift speed with respect to the protons. The minor ions are known to influence the relative effect of the proton-cyclotron and mirror instabilities. In this paper, we show that the mirror mode can dominate the power spectrum at the nonlinear stage even if its linear growth rate is significantly lower than that of the proton-cyclotron mode. The proton-cyclotron instability combined with the alpha-proton drift is a possible cause of the nonzero magnetic helicity observed in the solar wind for fluctuations propagating nearly parallel to the magnetic field. Our simulations generally confirm this concept but reveal a complex helicity spectrum that is not anticipated from the linear theory of the instability.

Electron Profile Stiffness and Critical Gradient Length Studies in the Alcator C-Mod Tokamak

NASA Astrophysics Data System (ADS)

Houshmandyar, Saeid; Hatch, David R.; Liao, Kenneth T.; Zhao, Bingzhe; Phillips, Perry E.; Rowan, William L.; Cao, Norman; Ernst, Darin R.; Rice, John E.

2017-10-01

Electron temperature profile stiffness was investigated at Alcator C-Mod L-mode discharges. Electrons were heated by ion cyclotron range of frequencies (ICRF) through minority heating. The intent of the heating mechanism was to vary the heat flux and simultaneously, gradually change the local gradient. The electron temperature gradient scale length (LTe- 1 = | ∇Te |/Te) was accurately measured through a novel technique, using the high-resolution radiometer ECE diagnostic. The TRANSP power balance analysis (Q/QGB) and the measured scale length (a/LTe) result in critical scale length measurements at all major radius locations. These measurements suggest that the profiles are already at the critical values. Furthermore, the dependence of the stiffness on plasma rotation and magnetic shear will be discussed. In order to understand the underlying mechanism of turbulence for these discharges, simulations using the gyrokinetic code, GENE, were carried out. For linear runs at electron scales, it was found that the largest growth rates are very sensitive to a/LTe variation, which suggests the presence of ETG modes, while the sensitivity studies in the ion scales indicate ITG/TEM modes. Supported by USDoE awards DE-FG03-96ER54373 and DE-FC02-99ER54512.

Unsteady laminar flow with convective heat transfer through a rotating curved square duct with small curvature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mondal, Rabindra Nath, E-mail: rnmondal71@yahoo.com; Shaha, Poly Rani; Roy, Titob

Unsteady laminar flow with convective heat transfer through a curved square duct rotating at a constant angular velocity about the center of curvature is investigated numerically by using a spectral method, and covering a wide range of the Taylor number −300≤Tr≤1000 for the Dean number Dn = 1000. A temperature difference is applied across the vertical sidewalls for the Grashof number Gr = 100, where the outer wall is heated and the inner wall cooled, the top and bottom walls being adiabatic. Flow characteristics are investigated with the effects of rotational parameter, Tr, and the pressure-driven parameter, Dn, for themore » constant curvature 0.001. Time evolution calculations as well as their phase spaces show that the unsteady flow undergoes through various flow instabilities in the scenario ‘multi-periodic → chaotic → steady-state → periodic → multi-periodic → chaotic’, if Tr is increased in the positive direction. For negative rotation, however, time evolution calculations show that the flow undergoes in the scenario ‘multi-periodic → periodic → steady-state’, if Tr is increased in the negative direction. Typical contours of secondary flow patterns and temperature profiles are obtained at several values of Tr, and it is found that the unsteady flow consists of two- to six-vortex solutions if the duct rotation is involved. External heating is shown to generate a significant temperature gradient at the outer wall of the duct. This study also shows that there is a strong interaction between the heating-induced buoyancy force and the centrifugal-Coriolis instability in the curved channel that stimulates fluid mixing and consequently enhances heat transfer in the fluid.« less