Scaling of the Sheared-Flow Stabilized Z-Pinch: The Fusion Z-Pinch Experiment ``FuZE''
NASA Astrophysics Data System (ADS)
Nelson, B. A.; Shumlak, U.; Claveau, E. L.; Golingo, R. P.; Weber, T. R.; McLean, H. S.; Tummel, K. K.; Higginson, D. P.; Schmidt, A. E.; UW/LLNL Collaboration
2016-10-01
The sheared flow stabilized (SFS) Z-pinch ZaP experiment was constructed based on calculations [1] showing stabilization of kink and sausage instabilities. ZaP experimentally demonstrated production and sustainment of an SFS Z-pinch for a wide range of plasma parameters, with densities up to n =1023 m-3 and a pinch radius of a = 1 cm. [2-4] The SFS Z-pinch is resistant to the instabilities of conventional Z-pinches, yet maintains the same favorable radial scaling, making it an energy-efficient way to achieve fusion-relevant conditions. The ZaP-HD (high density) experiment has demonstrated scaling of the SFS Z-pinch to 2-3 × smaller a and 10 × higher n. [5] Supported by ZaP and ZaP-HD, the Fusion Z-pinch Experiment (FuZE) project investigates scaling plasma parameters toward fusion conditions by decreasing a 2-3 × to 1 mm, and increasing n 10 × to 1025 m-3. The approach combines improved gas injection and flexible power supplies with the successful ZaP SFS Z-pinch formation. Detailed fluid and kinetic simulations complement the experimental studies to gain scientific insight into the plasma behavior and predict scaling to higher performance. Supported by DoE FES, NNSA, and ARPA-E ALPHA.
High energy density Z-pinch plasmas using flow stabilization
Shumlak, U. Golingo, R. P. Nelson, B. A. Bowers, C. A. Doty, S. A. Forbes, E. G. Hughes, M. C. Kim, B. Knecht, S. D. Lambert, K. K. Lowrie, W. Ross, M. P. Weed, J. R.
2014-12-15
The ZaP Flow Z-Pinch research project[1] at the University of Washington investigates the effect of sheared flows on MHD instabilities. Axially flowing Z-pinch plasmas are produced that are 100 cm long with a 1 cm radius. The plasma remains quiescent for many radial Alfvén times and axial flow times. The quiescent periods are characterized by low magnetic mode activity measured at several locations along the plasma column and by stationary visible plasma emission. Plasma evolution is modeled with high-resolution simulation codes – Mach2, WARPX, NIMROD, and HiFi. Plasma flow profiles are experimentally measured with a multi-chord ion Doppler spectrometer. A sheared flow profile is observed to be coincident with the quiescent period, and is consistent with classical plasma viscosity. Equilibrium is determined by diagnostic measurements: interferometry for density; spectroscopy for ion temperature, plasma flow, and density[2]; Thomson scattering for electron temperature; Zeeman splitting for internal magnetic field measurements[3]; and fast framing photography for global structure. Wall stabilization has been investigated computationally and experimentally by removing 70% of the surrounding conducting wall to demonstrate no change in stability behavior.[4] Experimental evidence suggests that the plasma lifetime is only limited by plasma supply and current waveform. The flow Z-pinch concept provides an approach to achieve high energy density plasmas,[5] which are large, easy to diagnose, and persist for extended durations. A new experiment, ZaP-HD, has been built to investigate this approach by separating the flow Z-pinch formation from the radial compression using a triaxial-electrode configuration. This innovation allows more detailed investigations of the sheared flow stabilizing effect, and it allows compression to much higher densities than previously achieved on ZaP by reducing the linear density and increasing the pinch current. Experimental results and
High energy density Z-pinch plasmas using flow stabilization
Shumlak, U., E-mail: shumlak@uw.edu; Golingo, R. P., E-mail: shumlak@uw.edu; Nelson, B. A., E-mail: shumlak@uw.edu
2014-12-15
The ZaP Flow Z-Pinch research project[1] at the University of Washington investigates the effect of sheared flows on MHD instabilities. Axially flowing Z-pinch plasmas are produced that are 100 cm long with a 1 cm radius. The plasma remains quiescent for many radial Alfvén times and axial flow times. The quiescent periods are characterized by low magnetic mode activity measured at several locations along the plasma column and by stationary visible plasma emission. Plasma evolution is modeled with high-resolution simulation codes – Mach2, WARPX, NIMROD, and HiFi. Plasma flow profiles are experimentally measured with a multi-chord ion Doppler spectrometer. Amore » sheared flow profile is observed to be coincident with the quiescent period, and is consistent with classical plasma viscosity. Equilibrium is determined by diagnostic measurements: interferometry for density; spectroscopy for ion temperature, plasma flow, and density[2]; Thomson scattering for electron temperature; Zeeman splitting for internal magnetic field measurements[3]; and fast framing photography for global structure. Wall stabilization has been investigated computationally and experimentally by removing 70% of the surrounding conducting wall to demonstrate no change in stability behavior.[4] Experimental evidence suggests that the plasma lifetime is only limited by plasma supply and current waveform. The flow Z-pinch concept provides an approach to achieve high energy density plasmas,[5] which are large, easy to diagnose, and persist for extended durations. A new experiment, ZaP-HD, has been built to investigate this approach by separating the flow Z-pinch formation from the radial compression using a triaxial-electrode configuration. This innovation allows more detailed investigations of the sheared flow stabilizing effect, and it allows compression to much higher densities than previously achieved on ZaP by reducing the linear density and increasing the pinch current. Experimental results
Progress on Scaling the Sheared-Flow Stabilized Z-Pinch: The Fusion Z-Pinch Experiment ``FuZE''
NASA Astrophysics Data System (ADS)
Nelson, B. A.; Shumlak, U.; Claveau, E. L.; Forbes, E. G.; Golingo, R. P.; Stepanov, A. D.; Weber, T. R.; Zhang, Y.; McLean, H. S.; Higginson, D. P.; Schmidt, A. E.; Tummel, K. K.
2017-10-01
The sheared-flow-stabilized (SFS) Z-pinch ZaP experiment was constructed based on calculations showing stabilization of the kink and sausage instabilities with sufficient flow shear. ZaP experimentally demonstrated production and sustainment of an SFS Z-pinch for a wide range of plasma parameters, with densities up to n = 5 ×1022 m-3 and a pinch radius of a=1 cm. The follow-on ZaP-HD (high density) experiment demonstrated scaling of the SFS Z-pinch to 2-3x smaller radii and 10x higher densities than ZaP, with up to 1 keV temperatures. Based on the successful results of ZaP and ZaP-HD, the Fusion Z-pinch Experiment (FuZE) project is experimentally and computationally studying scaling the plasma performance toward fusion conditions, with the target of a smaller radius, a=1 mm, and higher density, n = 2 ×1024 m-3. Initial FuZE experimental results show several hundred eV ion temperatures, with pinch currents of 100-200 kA and a few mm radius. 2D kinetic calculations show stabilization of instabilities at moderate sheared flows, and 3D kinetic calculations are in progress. This work is supported by an award from US ARPA-E.
2D Kinetic Particle in Cell Simulations of a Flow-Shear Stabilized Z-Pinch
NASA Astrophysics Data System (ADS)
Tummel, Kurt; Higginson, Drew; Link, Anthony; Schmidt, Andrea; McLean, Harry; Shumlak, Uri; Nelson, Brian; Golingo, Ray; Claveau, Elliot; Forbes, Eleanor; Weber, Tobin; Zhang, Yue; Stepanov, Anton; LLNL Team; UW Team
2017-10-01
The lifetime of Z-pinch plasmas is typically limited by MHD instabilities, e.g. the m = 0 ``sausage'' and m = 1 ``kink'' modes. An attractive strategy to suppress these and related instabilities and extend the lifetime of a Z-pinch is to drive sheared axial flows in the plasma, dvz / dr ≠ 0 . This stabilization was demonstrated in a series of experiments at the UW and these long-lived Z-pinches may offer viable sources of ion beams, neutrons and radiation, or potentially, a fusion reactor. LLNL is running 2D simulations using the particle-in-cell(PIC) code, LSP, to study flow-shear Z-pinch stability and performance. The suppression of the sausage mode by axial flow-shear is seen under the present experimental conditions as well as at reactor scales, with multiple shear-flow profiles. The longevity of these sheared-flows depends on the plasma viscosity, and a preliminary viscosity and shear-flow longevity analysis is also presented. This work represents the first fully-kinetic modeling results for the flow-shear stabilized Z-pinch. This work funded by USDOE ARPA-E and performed under the auspices of Lawrence Livermore National Laboratory under Contract DE-AC52-07NA23744. LLNL-ABS-734820.
2D Kinetic Particle in Cell Simulations of a Shear-Flow Stabilized Z-Pinch
NASA Astrophysics Data System (ADS)
Tummel, Kurt; Higginson, Drew; Schmidt, Andrea; Link, Anthony; McLean, Harry; Shumlak, Uri; Nelson, Brian; Golingo, Raymond; Claveau, Elliot; Lawrence Livermore National Lab Team; University of Washington Team
2016-10-01
The Z-pinch is a relatively simple and attractive potential fusion reactor design, but attempts to develop such a reactor have consistently struggled to overcome Z-pinch instabilities. The ``sausage'' and ``kink'' modes are among the most robust and prevalent Z-pinch instabilities, but theory and simulations suggest that axial flow-shear, dvz / dr ≠ 0 , can suppress these modes. Experiments have confirmed that Z-pinch plasmas with embedded axial flow-shear display a significantly enhanced resilience to the sausage and kink modes at a demonstration current of 50kAmps. A new experiment is under way to test the concept at higher current, and efforts to model these plasmas are being expanded. The performance and stability of these devices will depend on features like the plasma viscosity, anomalous resistivity, and finite Larmor radius effects, which are most accurately characterized in kinetic models. To predict these features, kinetic simulations using the particle in cell code LSP are now in development, and initial benchmarking and 2D stability analyses of the sausage mode are presented here. These results represent the first kinetic modeling of the flow-shear stabilized Z-pinch. This work is funded by the USDOE/ARPAe Alpha Program. Prepared by LLNL under Contract DE-AC52-07NA27344.
Increasing Plasma Parameters using Sheared Flow Stabilization of a Z-Pinch
NASA Astrophysics Data System (ADS)
Shumlak, Uri
2016-10-01
Recent experiments on the ZaP Flow Z-Pinch at the University of Washington have been successful in compressing the plasma column to smaller radii, producing the predicted increases in plasma density (1018 cm-3), temperature (200 eV), and magnetic fields (4 T), while maintaining plasma stability for many Alfven times (over 40 μs) using sheared plasma flows. These results indicate the suitability of the device as a discovery science platform for astrophysical and high energy density plasma research, and keeps open a possible path to achieving burning plasma conditions in a compact fusion device. Long-lived Z-pinch plasmas have been produced with dimensions of 1 cm radius and 100 cm long that are stabilized by sheared axial flows for over 1000 Alfven radial transit times. The observed plasma stability is coincident with the presence of a sheared flow as measured by time-resolved multi-chord ion Doppler spectroscopy applied to impurity ion radiation. These measurements yield insights into the evolution of the velocity profile and show that the stabilizing behavior of flow shear agrees with theoretical calculations and 2-D MHD computational simulations. The flow shear value, extent, and duration are shown to be consistent with theoretical models of the plasma viscosity, which places a design constraint on the maximum axial length of a sheared flow stabilized Z-pinch. Measurements of the magnetic field topology indicate simultaneous azimuthal symmetry and axial uniformity along the entire 100 cm length of the Z-pinch plasma. Separate control of plasma acceleration and compression have increased the accessible plasma parameters and have generated stable plasmas with radii below 0.5 cm, as measured with a high resolution digital holographic interferometer. This work was supported by Grants from U.S. DOE, NNSA, and ARPA-E.
NASA Astrophysics Data System (ADS)
Nelson, B. A.; Shumlak, U.; Golingo, R. P.; Claveau, E. L.; McLean, H. S.; Schmidt, A. E.
2015-11-01
The ZaP experiment produces long-lived sheared-flow-stabilized Z-pinch plasmas up to 126 cm in length for several flow-through times, and up to thousands of Alfvén times. Experimental measurements of the magnetic structure along the full length of the plasma column show an axially uniform Z-pinch plasma during the observed quiescent period. Interferometry, fast-framing images, and Rogowskii coils corroborate the existence of a pinched plasma during this quiescent period of time. Detailed two-dimensional non-linear magnetohydrodynamic (MHD) calculations have been performed showing the formation and assembly of long-length, long-lived Z-pinches. Experimentally-observed plasma lifetimes and velocity-shear profiles are shown to be consistent with calculations of viscous-damping timescales based on the measured plasma parameters. A newly-funded ARPA-E ALPHA project, the Fusion Z-pinch Experiment ``FuZE'' is being constructed at the University of Washington, in collaboration with the Lawrence Livermore National Laboratory. FuZE will study scaling and stability of the successful ZaP experiment to higher pinch currents. The FuZE experimental design, goals, and plans, based on ZaP experimental results, will be presented.
A Reactor Development Scenario for the FuZE Sheared-Flow Stabilized Z-pinch
NASA Astrophysics Data System (ADS)
McLean, Harry S.; Higginson, D. P.; Schmidt, A.; Tummel, K. K.; Shumlak, U.; Nelson, B. A.; Claveau, E. L.; Forbes, E. G.; Golingo, R. P.; Stepanov, A. D.; Weber, T. R.; Zhang, Y.
2017-10-01
We present a conceptual design, scaling calculations, and development path for a pulsed fusion reactor based on a flow-stabilized Z-pinch. Experiments performed on the ZaP and ZaP-HD devices have largely demonstrated the basic physics of sheared-flow stabilization at pinch currents up to 100 kA. Initial experiments on the FuZE device, a high-power upgrade of ZaP, have achieved 20 usec of stability at pinch current 100-200 kA and pinch diameter few mm for a pinch length of 50 cm. Scaling calculations based on a quasi-steady-state power balance show that extending stable duration to 100 usec at a pinch current of 1.5 MA and pinch length of 50 cm, results in a reactor plant Q 5. Future performance milestones are proposed for pinch currents of: 300 kA, where Te and Ti are calculated to exceed 1-2 keV; 700 kA, where DT fusion power would be expected to exceed pinch input power; and 1 MA, where fusion energy per pulse exceeds input energy per pulse. This work funded by USDOE ARPA-E and performed under the auspices of Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-734770.
Time-resolved Spectroscopy of a Sheared Flow Stabilized Z-pinch Plasma
NASA Astrophysics Data System (ADS)
Forbes, Eleanor
2016-10-01
The ZaP Flow Z-pinch Project investigates the use of sheared-axial flows to stabilize an otherwise unstable plasma configuration. Diagnostics with sub-microsecond resolution are required to obtain accurate time-resolved data since the plasma pulse is approximately 100 μs. Analyzing the Doppler shift of impurity line radiation from the pinch provides a measure of the velocity profile and is a reliable method of determining the plasma sheared flow. The velocity profile is spatially resolved through the use of a 20-chord fiber bundle. The ZaP-HD experiment has used a PI-MAX intensified CCD array to record a single time-resolved spectrum per plasma pulse. Obtaining the evolution of the velocity profile using this method required spectra acquired over hundreds of pulses with identical initial parameters and varying acquisition times. The use of a Kirana 05M ultra-fast framing camera is investigated for recording time-resolved velocity profiles during a single pulse. The Kirana utilizes an ultraviolet intensifier to record 180 frames of UV light at up to 2 million frames per second. An ultraviolet optics system is designed to couple the exit port of an Acton SP-500i spectrometer to the Kirana UV intensifier and focus spectra at the camera detector plane. This work is supported by US DoE FES, NNSA, and ARPA-E ALPHA.
A Reactor Development Scenario for the FUZE Shear-flow Stabilized Z-pinch
NASA Astrophysics Data System (ADS)
McLean, H. S.; Higginson, D. P.; Schmidt, A.; Tummel, K. K.; Shumlak, U.; Nelson, B. A.; Claveau, E. L.; Golingo, R. P.; Weber, T. R.
2016-10-01
We present a conceptual design, scaling calculations, and a development path for a pulsed fusion reactor based on the shear-flow-stabilized Z-pinch device. Experiments performed on the ZaP device have demonstrated stable operation for 40 us at 150 kA total discharge current (with 100 kA in the pinch) for pinches that are 1cm in diameter and 100 cm long. Scaling calculations show that achieving stabilization for a pulse of 100 usec, for discharge current 1.5 MA, in a shortened pinch 50 cm, results in a pinch diameter of 200 um and a reactor plant Q 5 for reasonable assumptions of the various system efficiencies. We propose several key intermediate performance levels in order to justify further development. These include achieving operation at pinch currents of 300 kA, where Te and Ti are calculated to exceed 1 keV, 700 kA where fusion power exceeds pinch input power, and 1 MA where fusion energy per pulse exceeds input energy per pulse. This work funded by USDOE ARPAe ALPHA Program and performed under the auspices of Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-697801.
The ZaP Flow Z-Pinch Project - Final Technical Report
Shumlak, Uri; Nelson, Brian A.
2013-12-31
The ZaP Flow Z-Pinch Project is a project to extend the performance of the flow Z-pinch experiment at the University of Washington to investigate and isolate the relevant physics of the stabilizing effect of plasma flow. Experimental plasmas have exhibited an enhanced stability under certain operating parameters which generate a flow state (axial flows in Z-pinches and VH mode in tokamaks). Flow has also been suggested as the stabilizing mechanism in astrophysical jets.
Dynamics and Stability of Dense Z-Pinches
NASA Astrophysics Data System (ADS)
Bobrova, N. A.; Neudachin, V. V.; Razinkova, T. L.; Sasorov, P. V.
1994-03-01
This is a review of theoretical works in the field of dense Z-pinch physics performed by ITEP plasma group. The problems under discussion are. Onedimensional dense Z-pinch dynamics is investigated for a wide range of parameters. A transition between classical (compressional) and dissipative regimes of Z-pinch dynamics is followed up. Analytical expressions, determining the type of Z-pinch dynamics and temporal evolution of hot rarefied corona of the dissipative Z-pinches are obtained. Heterogeneous equilibrium states of dense radiative Z-pinches, when the corona is hot and rarefied, while pinch core is very dense and "cold", are shown to exist. The problem of instabilities of dense Z"pinch equilibrium states is investigated, taking into account relevant dissipative processes. On the basis of the results obtained, we consider the general problem of an enhanced stability of dense Z-pinch.
Analysis of Conical Wire Array Z-Pinch Stability with a Center Wire
Martinez, D.; Presura, R.; Wright, S.; Plechaty, C.; Neff, S.; Wanex, L.; Ampleford, D. J.
2009-01-21
Adding a center wire on the axis of a conical wire array produces conditions suitable for studying shear flow stabilization of the Z-pinch. The conical wire array produces and axial plasma flow while the center wire introduces a radial variation of the axial velocity. Experiments of this array configuration were preformed on the 1 MA Zebra Z-pinch generator and showed stabilization of the kink instability when a center wire was present. Comparison with equivalent cylindrical wire arrays indicates that the shear flow stabilization plays a role in the stabilization of the kink instability.
Finite-Larmor-radius effects on z-pinch stability
NASA Astrophysics Data System (ADS)
Scheffel, Jan; Faghihi, Mostafa
1989-06-01
The effect of finite Larmor radius (FLR) on the stability of m = 1 small-axial-wavelength kinks in a z-pinch with purely poloidal magnetic field is investigated. We use the incompressible FLR MHD model; a collisionless fluid model that consistently includes the relevant FLR terms due to ion gyroviscosity, Hall effect and electron diamagnetism. With FLR terms absent, the Kadomtsev criterion of ideal MHD, 2r dp/dr + m2B2/μ0 ≥ 0 predicts instability for internal modes unless the current density is singular at the centre of the pinch. The same result is obtained in the present model, with FLR terms absent. When the FLR terms are included, a normal-mode analysis of the linearized equations yields the following results. Marginally unstable (ideal) modes are stabilized by gyroviscosity. The Hall term has a damping (but not absolutely stabilizing) effect - in agreement with earlier work. On specifying a constant current and particle density equilibrium, the effect of electron diamagnetism vanishes. For a z-pinch with parameters relevant to the EXTRAP experiment, the m = 1 modes are then fully stabilized over the crosssection for wavelengths λ/a ≤ 1, where a denotes the pinch radius. As a general z-pinch result a critical line-density limit Nmax = 5 × 1018 m-1 is found, above which gyroviscous stabilization near the plasma boundary becomes insufficient. This limit corresponds to about five Larmor radii along the pinch radius. The result holds for wavelengths close to, or smaller than, the pinch radius and for realistic equilibrium profiles. This limit is far below the required limit for a reactor with contained alpha particles, which is in excess of 1020 m-1.
Optical Tomography of the ZaP Flow Z-Pinch Plasma
2005-01-01
Optical Tomography of the ZaP Flow Z- Pinch Plasma Adam Matthew Madson A thesis submitted in partial fulfillment of the requirements for the degree of...2005 2. REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE Optical Tomography of the ZaP Flow Z- Pinch Plasma 5a. CONTRACT NUMBER...Washington Abstract Optical Tomography of the ZaP Flow Z- Pinch Plasma by Adam Matthew Madson Chair of the Supervisory Committee: Associate Professor
MHD Stability of Free Boundary Toroidal Z Pinch
NASA Astrophysics Data System (ADS)
Sugisaki, Kiwamu
1990-06-01
The Magnetohydrodynamic (MHD) stability of a free boundary toroidal Z pinch plasma is investigated. Equilibrium field profiles are chosen so that μ is nearly uniform in the central region, μ and dμ/dr vanish on the boundary and Suydam’s criterion is satisfied throughout the plasma. The stability of the equilibrium is examined for the ratio b of the conducting wall radius to the plasma radius and plasma pressure. The stability of non-resonant ideal modes is determined mainly from the safty factor on the axis. Non-resonant modes are dominant for low plasma pressure, whereas resonant modes are dominant for high plasma pressure. Tearing modes are stable only for b below 1.04. The width of the magnetic islands produced from the tearing modes is evaluated. As b increases, overlap of the magnetic islands occurs over a wide area in the plasma.
Producing High-Performance, Stable, Sheared-Flow Z-Pinches in the FuZE project
NASA Astrophysics Data System (ADS)
Golingo, R. P.; Shumlak, U.,; Nelson, B. A.; Claveau, E. L.; Forbes, E. G.; Stepanov, A. D.; Weber, T. R.; Zhang, Y.; McLean, H. S.; Tummel, K. K.; Higginson, D. P.; Schmidt, A. E.; University of Washington (UW) Collaboration; Lawrence Livermore National Laboratory (LLNL) Collaboration
2017-10-01
The Fusion Z-Pinch Experiment (FuZE) has made significant strides towards generating high-performance, stable Z-pinch plasmas with goals of ne = 1018 cm-3 and T =1 keV. The Z-pinch plasmas are stabilized with a sheared axial flow that is driven by a coaxial accelerator. The new FuZE device has been constructed and reproduces the major scientific achievements the ZaP project at the University of Washington; ne = 1016 cm-3,T = 100 eV, r<1 cm, and tstable >20 μs. These parameters are measured with an array of magnetic field probes, spectroscopy, and fast framing cameras. The plasma parameters are achieved using a small fraction of the maximum energy storage and gas injection capability of the FuZE device. Higher density, ne = 5×1017 cm-3, and temperature, T = 500 eV, Z-pinch plasmas are formed by increasing the pinch current. At the higher voltages and currents, the ionization rates in the accelerator increase. By modifying the neutral gas profile in the accelerator, the plasma flow from the accelerator is maintained, driving the flow shear. Formation and sustainment of the sheared-flow Z-pinch plasma will be discussed. Experimental data demonstrating high performance plasmas in a stable Z-pinches will be shown. This work is supported by an award from US ARPA-E.
Quasi-steady accelerator operation on the ZAP flow Z-pinch
Hughes, M. C., E-mail: mchugs@uw.edu; Shumlak, U., E-mail: mchugs@uw.edu; Golingo, R. P., E-mail: mchugs@uw.edu
2014-12-15
The ZaP Flow Z-Pinch Experiment utilizes sheared flows to stabilize an otherwise unstable equilibrium. The sheared flows are maintained by streaming high velocity plasma parallel to the pinch. Previous operations of the machine show depletion of the accelerator’s neutral gas supply late in the pulse leading to pinch instability. The current distribution in the accelerator exhibits characteristic modes during this operation, which is corroborated by interferometric signals. The decrease in density precipitates a loss of plasma quiescence in the pinch, which occurs on a timescale related to the flow velocity from the plasma source. To abate the depletion, the geometrymore » of the accelerator is altered to increase the neutral gas supply. The design creates a standing deflagration front in the accelerator that persists for the pulse duration. The new operating mode is characterized by the same diagnostics as the previous mode. The lessons learned in the accelerator operations have been applied to the design of a new experiment, ZaP-HD. This work was supported by grants from the Department of Energy and the National Nuclear Security Administration.« less
Parameter scaling toward high-energy density in a quasi-steady flow Z-pinch
NASA Astrophysics Data System (ADS)
Hughes, M. C.; Shumlak, U.; Nelson, B. A.; Golingo, R. P.; Claveau, E. L.; Doty, S. A.; Forbes, E. G.; Kim, B.; Ross, M. P.
2016-10-01
Sheared axial flows are utilized by the ZaP Flow Z-Pinch Experiment to stabilize MHD instabilities. The pinches formed are 50 cm long with radii ranging from 0.3 to 1.0 cm. The plasma is generated in a coaxial acceleration region, similar to a Marshall gun, which provides a steady supply of plasma for approximately 100 us. The power to the plasma is partially decoupled between the acceleration and pinch assembly regions through the use of separate power supplies. Adiabatic scaling of the Bennett relation gives targets for future devices to reach high-energy density conditions or fusion reactors. The applicability of an adiabatic assumption is explored and work is done experimentally to clarify the plasma compression process, which may be more generally polytropic. The device is capable of a much larger parameter space than previous machine iterations, allowing flexibility in the initial conditions of the compression process to preserve stability. This work is supported by DoE FES and NNSA.
Investigating plasma viscosity with fast framing photography in the ZaP-HD Flow Z-Pinch experiment
NASA Astrophysics Data System (ADS)
Weed, Jonathan Robert
The ZaP-HD Flow Z-Pinch experiment investigates the stabilizing effect of sheared axial flows while scaling toward a high-energy-density laboratory plasma (HEDLP > 100 GPa). Stabilizing flows may persist until viscous forces dissipate a sheared flow profile. Plasma viscosity is investigated by measuring scale lengths in turbulence intentionally introduced in the plasma flow. A boron nitride turbulence-tripping probe excites small scale length turbulence in the plasma, and fast framing optical cameras are used to study time-evolved turbulent structures and viscous dissipation. A Hadland Imacon 790 fast framing camera is modified for digital image capture, but features insufficient resolution to study turbulent structures. A Shimadzu HPV-X camera captures the evolution of turbulent structures with great spatial and temporal resolution, but is unable to resolve the anticipated Kolmogorov scale in ZaP-HD as predicted by a simplified pinch model.
Flow-through Z-pinch study for radiation generation and fusion energy production
Hartman, C.W.; Eddleman, J.L.; Moir, R.; Shumlak, U.
1994-06-20
We discuss a high-density fusion reactor which utilizes a flow-through Z pinch magnetic confinement configuration. Assessment of this reactor system is motivated by simplicity and small unit size (few hundred MWe) and immunity to plasma contamination made possible at high density. The type reactor discussed here would employ a liquid Li vortex as the first wall/blanket to capture fusion neutrons with minimum induced radioactivity and to achieve high wall loading and a power density of 200 w/cm{sup 3}.
Ablation Flow Interactions in Wire Array Z-Pinches on the MAGPIE generator
NASA Astrophysics Data System (ADS)
Swadling, George; Lebedev, Sergey; Hall, Gareth; Suzuki-Vidal, Francisco; Burdiak, Guy; Niasse, Nicolas; Pickworth, Louisa; Skidmore, Jonathon; de Grouchy, Philip; Koory, Essa; Suttle, Lee; Bennett, Matthew; Yuan, Jianqiang; Harvey-Thomson, Adam; Imperial College Team; Sandia National Laboratories Collaboration
2013-10-01
We present the results of experiments investigating the interactions of ablations streams in aluminium and tungsten wire array z-pinches. These experiments were carried out on the 1.4 MA, 240 ns MAGPIE generator at Imperial College London. The primary diagnostics used for these studies were an optical Thomson scattering diagnostic and an end-on aligned, two colour, Mach-Zehnder imaging interferometer. In aluminum arrays, the interactions of the ablation flows produces a dense network of oblique shocks. Measurements of the geometry of these shocks allows us to place limits on the plasma parameters of the flows. In tungsten arrays the data shows a prolonged period of collisionless flow. No shock structures were observed, the flow densities varied smoothly between the ablation streams and the inter-wire regions. The region about the axis appears azimuthally isotropic, and Thomson scattering measurements indicate significant interpenetration of the flows in this region.
Cinematic Characterization of Convected Coherent Structures Within an Continuous Flow Z-Pinch
NASA Astrophysics Data System (ADS)
Underwood, Thomas; Rodriguez, Jesse; Loebner, Keith; Cappelli, Mark
2017-10-01
In this study, two separate diagnostics are applied to a plasma jet produced from a coaxial accelerator with characteristic velocities exceeding 105 m/s and timescales of 10 μs. In the first of these, an ultra-high frame rate CMOS camera coupled to a Z-type laser Schlieren apparatus is used to obtain flow-field refractometry data for the continuous flow Z-pinch formed within the plasma deflagration jet. The 10 MHz frame rate for 256 consecutive frames provides high temporal resolution, enabling turbulent fluctuations and plasma instabilities to be visualized over the course of a single pulse. The unique advantage of this diagnostic is its ability to simultaneously resolve both structural and temporal evolution of instabilities and density gradients within the flow. To allow for a more meaningful statistical analysis of the resulting wave motion, a multiple B-dot probe array was constructed and calibrated to operate over a broadband frequency range up to 100 MHz. The resulting probe measurements are incorporated into a wavelet analysis to uncover the dispersion relation of recorded wave motion and furthermore uncover instability growth rates. Finally these results are compared with theoretical growth rate estimates to identify underlying physics. This work is supported by the U.S. Department of Energy Stewardship Science Academic Program in addition to the National Defense Science Engineering Graduate Fellowship.
Overview of the Fusion Z-Pinch Experiment FuZE
NASA Astrophysics Data System (ADS)
Weber, T. R.; Shumlak, U.; Nelson, B. A.; Golingo, R. P.; Claveau, E. L.; McLean, H. S.; Tummel, K. K.; Higginson, D. P.; Schmidt, A. E.; UW/LLNL Team
2016-10-01
Previously, the ZaP device, at the University of Washington, demonstrated sheared flow stabilized (SFS) Z-pinch plasmas. Instabilities that have historically plagued Z-pinch plasma confinement were mitigated using sheared flows generated from a coaxial plasma gun of the Marshall type. Based on these results, a new SFS Z-pinch experiment, the Fusion Z-pinch Experiment (FuZE), has been constructed. FuZE is designed to investigate the scaling of SFS Z-pinch plasmas towards fusion conditions. The experiment will be supported by high fidelity physics modeling using kinetic and fluid simulations. Initial plans are in place for a pulsed fusion reactor following the results of FuZE. Notably, the design relies on proven commercial technologies, including a modest discharge current (1.5 MA) and voltage (40 kV), and liquid metal electrodes. Supported by DoE FES, NNSA, and ARPA-E ALPHA.
Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch
Vogman, G. V.; Shumlak, U.
2011-10-13
Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian functionmore » associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. As a result, these measurements are used to gain a better understanding of Z-pinch equilibria.« less
Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch
NASA Astrophysics Data System (ADS)
Vogman, G. V.; Shumlak, U.
2011-10-01
Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian function associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. These measurements are used to gain a better understanding of Z-pinch equilibria.
Jackson, S. L.; Shumlak, U.
2006-08-15
A holographic interferometer is used to determine the radial electron number density profile of a sheared-flow Z pinch. Chord-integrated density information is recorded during a plasma pulse using the expanded beam of a pulsed ruby laser and holographic techniques. An Interactive Data Language (IDL) computer routine that requires only minimal user interaction is used to measure the resulting fringe shift in the reconstructed interferogram. This chord-integrated density information is inverted using an Abel inversion to determine the radial electron density profile. The density profiles obtained show a radially symmetric plasma column with an electron density of 10{sup 16}-10{sup 17} cm{supmore » -3} above the background plasma density. Holographic measurements are made at different times on separate plasma pulses to track the evolution of the density profile over time. These measurements are corroborated by time-dependent measurements made using a He-Ne interferometer.« less
Overview of the FuZE Fusion Z-Pinch Experiment
NASA Astrophysics Data System (ADS)
Shumlak, U.; Nelson, B. A.; Claveau, E. L.; Forbes, E. G.; Golingo, R. P.; Stepanov, A. D.; Weber, T. R.; Zhang, Y.; McLean, H. S.; Higginson, D. P.; Schmidt, A.; Tummel, K. K.
2017-10-01
Successful results of the sheared flow stabilized (SFS) Z-pinch from ZaP and ZaP-HD have motivated the new FuZE project to scale the plasma performance to fusion conditions. The SFS Z-pinch is immune to the instabilities that plague the conventional Z-pinch yet maintains the same favorable radial scaling. The plasma density and temperature increase rapidly with decreasing plasma radius, which naturally leads to a compact configuration at fusion conditions. The SFS Z-pinch is being investigated as a novel approach to a compact fusion device in a collaborative ARPA-E ALPHA project with the University of Washington and Lawrence Livermore National Laboratory. The project includes an experimental effort coupled with high-fidelity physics modeling using kinetic and fluid simulations. Along with scaling law analysis, computational and experimental results from the FuZE device are presented. This work is supported by an award from US ARPA-E.
NASA Astrophysics Data System (ADS)
Claveau, E. L.; Shumlak, U.; Nelson, B. A.; Forbes, E. G.; Golingo, R. P.; McLean, H. S.; Stepanov, A. D.; Weber, T. R.; Zhang, Y.
2017-10-01
The FuZE project investigates scaling the sheared flow stabilized (SFS) Z-pinch to fusion conditions. FuZE will generate a 1 mm radius Z-pinch with a 300 kA plasma current. Sheared flow Z-pinches are formed by a coaxial accelerator operating in a deflagration mode. The ionization front can be controlled by the neutral gas injection. Fast-acting valves located inside the inner electrode and at 8 locations on the outer electrode provide spatial and temporal control of the gas distribution. Line-integrated plasma density inside the coaxial accelerator are obtained by an interferometry system. Magnetic field topology is measured by an array of 94 surface-mounted magnetic field probes embedded in the outer copper electrode. Coaxial accelerator current measurements obtained through the magnetic field probes and density are compared with the downstream Z-pinch properties, such as stability, temperature, and density with the goal of understanding the relation between neutral gas injection and Z-pinch plasma parameters and behavior. This work is supported by an award from US ARPA-E.
NASA Technical Reports Server (NTRS)
Miernik, Janie
2011-01-01
Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Shorter trips are better for humans in the harmful radiation environment of deep space. Nuclear propulsion and power plants can enable high Ispand payload mass fractions because they require less fuel mass. Fusion energy research has characterized the Z-Pinch dense plasma focus method. (1) Lightning is form of pinched plasma electrical discharge phenomena. (2) Wire array Z-Pinch experiments are commonly studied and nuclear power plant configurations have been proposed. (3) Used in the field of Nuclear Weapons Effects (NWE) testing in the defense industry, nuclear weapon x-rays are simulated through Z-Pinch phenomena.
Design of the Fusion Z-Pinch Experiment - FuZE
NASA Astrophysics Data System (ADS)
Shumlak, U.; McLean, H. S.; Nelson, B. A.; Golingo, R. P.; Schmidt, A.; Claveau, E. L.
2015-11-01
Based on the successful results of the sheared flow stabilized (SFS) Z-pinch from ZaP and ZaP-HD, a new experiment FuZE is designed to scale the plasma performance to fusion conditions. The SFS Z-pinch is immune to the instabilities that plague the conventional Z-pinch yet maintains the same favorable radial scaling. The plasma density and temperature increase rapidly with decreasing plasma radius, which naturally leads to a compact configuration at fusion conditions. The SFS Z-pinch is being investigated as a novel approach to a compact fusion device in a new collaborative ARPA-E ALPHA project with the University of Washington and Lawrence Livermore National Laboratory. The project includes an experimental effort coupled with high-fidelity physics modeling using kinetic and fluid simulations. Along with scaling law analysis, computational and experimental results that have informed the design and development of the FuZE apparatus are presented. This work is supported by an award from US ARPA-E.
Z-Pinch Fusion for Energy Applications
SPIELMAN,RICK B.
2000-01-01
Z pinches, the oldest fusion concept, have recently been revisited in light of significant advances in the fields of plasma physics and pulsed power engineering. The possibility exists for z-pinch fusion to play a role in commercial energy applications. We report on work to develop z-pinch fusion concepts, the result of an extensive literature search, and the output for a congressionally-mandated workshop on fusion energy held in Snowmass, Co July 11-23,1999.
Rotating plasma disks in dense Z-pinch experiments
Bennett, M. J., E-mail: m.bennett11@imperial.ac.uk, E-mail: s.lebedev@imperial.ac.uk; Lebedev, S. V., E-mail: m.bennett11@imperial.ac.uk, E-mail: s.lebedev@imperial.ac.uk; Suttle, L.
2014-12-15
We present data from the first z-pinch experiments aiming to simulate aspects of accretion disk physics in the laboratory. Using off axis ablation flows from a wire array z-pinch we demonstrate the formation of a hollow disk structure that rotates at 60 kms{sup −1} for 150 ns. By analysing the Thomson scattered spectrum we make estimates for the ion and electron temperatures as T{sub i} ∼ 60 eV and ZT{sub e} ∼ 150 to 200 eV.
NASA Astrophysics Data System (ADS)
Wessel, F. J.; Rahman, H. U.; Ney, P.; Valenzuela, J.; Beg, F.; McKee, E.; Darling, T.
2016-03-01
This paper is dedicated to Norman Rostoker, our (FJW and HUR) mentor and long-term collaborator, who will always be remembered for the incredible inspiration that he has provided us. Norman's illustrious career dealt with a broad range of fundamental-physics problems and we were fortunate to have worked with him on many important topics: intense-charged-particle beams, field-reversed configurations, and Z-pinches. Rostoker 's group at the University of CA, Irvine was well known for having implemented many refinements to the Z-pinch, that make it more stable, scalable, and efficient, including the development of: the gas-puff Z-pinch [1], which provides for the use of an expanded range of pinch-load materials; the gas-mixture Z-pinch [2], which enhances the pinch stability and increases its radiation efficiency; e-beam pre-ionization [3], which enhances the uniformity of the initial-breakdown process in a gas pinch; magnetic-flux-compression [4, 5], which allows for the amplification of an axial-magnetic field Bz; the Z-θ pinch [6], which predicts fusion in a pinch-on-fiber configuration; the Staged Z-pinch (SZP) [7], which allows for the amplification of the pinch self-magnetic field, Bθ , in addition to a Bz, and leads to a stable implosion and high-gain fusion [8, 9, 10]. This paper describes the physical basis for a magneto-inertial compression in a liner-on-target SZP [11]. Initially a high-atomic-number liner implodes under the action of the J →×B → , Lorentz Force. As the implosion becomes super Alfvénic, magnetosonic waves form, transporting current and magnetic field through the liner toward the interface of the low-atomic-number target. The target implosion remains subsonic with its surface bounded by a stable-shock front. Shock waves that pass into the target provide a source of target plasma pre-heat. At peak compression the assembly is compressed by liner inertia, with flux compression producing an intense-magnetic field near the target
The Past, Present and Future of Z-pinches
NASA Astrophysics Data System (ADS)
Haines, M. G.
1999-11-01
The Z-pinch is enjoying a renaissance as the world's most powerful soft x-ray source, and there is a growing interest in both understanding the basic physics and its application to controlled fusion, particularly through indirect drive inertial confinement. It has the advantages of being efficient and having high energy and power density. The early history will be traced from 1790, when Martinus van Marum conducted exploding wire experiments in Holland, the Australian pinching of a copper tube lightning conductor, the seminal lecture at Harwell in 1956 by Kurchatov, and the classic contributions of Bennett, Pease and Braginskii. The most notable feature of the Z-pinch is its instability. The various regimes of stability analysis will be reviewed, including resistive and viscous effects, finite ion Larmor radius and the effect of sheared axial flow. Work in the last 10 years on single fibres, especially of cryogenic deuterium, gave neutrons but, alas, they were of the same origin, namely beam-plasma interactions, as reported by Kurchatov. The renaissance has come about through the implosion first of gas puffs but now, most importantly, of arrays of fine wires. Research at Sandia National Laboratory has shown that by using more and more, finer and finer wires, the x-ray radiation emitted at stagnation increased in power and decreased in pulse width. The understanding of these results has been advanced considerably by theory, simulation and smaller-scale, well diagnosed experiments. The dominant instability during the implosion is the magneto-Rayleigh-Taylor instability. The seeding of the mode seems to be associated with the MHD m = 0 instability that develops in an uncorrelated way on each individual wire as it evolves from a molten metal cylinder surrounded by a plasma corona. The global magnetic field leads both to the inward jetting of the plasma to the axis and to the development of a correlated global mode with seed amplitude proportional to the (number of
High resolution digital holographic interferometry on the FuZE Fusion Z-Pinch Experiment
NASA Astrophysics Data System (ADS)
Weber, T. R.; Shumlak, U.; Nelson, B. A.; Claveau, E. L.; Forbes, E. G.; Golingo, R. P.; Stepanov, A. D.; Zhang, Y.; McLean, H. S.; Higginson, D. P.; Schmidt, A. E.; Tummel, K. K.; University of Washington Collaboration; Lawrence Livermore National Laboratory Collaboration
2017-10-01
The recently constructed sheared flow stabilized (SFS) Z-pinch experiment, the Fusion Z-Pinch Experiment (FuZE), is operational. The experiment is investigating scaling of SFS Z-pinch plasmas towards fusion conditions. Cylindrical plasmas are compressed to small radii (< 1 cm), and high densities (>1018 / cm3) as plasma current is increased. Diagnosing the size, density and internal structure of these small radii cylindrical plasmas require a high spatial resolution plasma density diagnostic. Motivated by this, a holographic interferometer with 10 micron spatial resolution has recently been installed on FuZE. A Nd:YAG laser is used with a digital camera to produce holograms from the plasma assembly region. Digital holograms are numerically reconstructed to obtain chord-integrated electron density of compressed plasma, with fine spatial resolution. Assuming cylindrical symmetry in the assembly region, plasma radial density profiles are reconstructed from these chord-integrated electron density data. Both chord-integrated and radial plasma density data from FuZE are presented. This work is supported by an award from US ARPA-E.
Aleksandrov, V. V.; Volkov, G. S.; Grabovski, E. V.
2016-11-15
Results from experimental studies on the implosion of arrays made of kapron fibers coated with different metals (Al, In, Sn, and Bi) are presented. It is shown that the power, total energy, and spectrum of radiation emitted by the imploding array depend on the number of metallized fibers and the mass of the metal layer deposited on them but are independent of the metal characteristics (density, atomic number, etc.). Analysis of frame X-ray images shows that the Z-pinches formed in the implosion of metallized kapron fiber arrays are more stable than those formed in wire arrays and that MHD perturbationsmore » in them develop at a slower growth rate. Due to the lower rate of plasma production from kapron fibers, the plasma formed at the periphery of the array forms a layer that plays the role of a hohlraum wall partially trapping soft X-ray emission of the Z-pinch formed in the implosion of the material of the deposited metal layer. The closure of the anode aperture doubles the energy of radiation emitted in the radial direction.« less
Z-Pinch Plasma Neutron Sources
2006-03-24
34Thermonuclear fusion by a z- theta pinch ," in Dense Z- Pinches , 2d International Conference, Laguna Beach, CA, 26-28 April 1989, edited by N. R. Pereira, J...Naval Research Laboratory Washington, DC 20375-5320 NRL/MR/6720--06-8927 Z- Pinch Plasma Neutron Sources A.L. VELIKOVICH R.W. CLARK J. DAVIs YK. CHONG...TITLE AND SUBTITLE 5a. CONTRACT NUMBER Z- Pinch Plasma Neutron Sources 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6.AUTHOR(S) 0t 5d. PROJECT NUMBER V0
Ryutov, D.D.; Derzon, M.S.; Matzen, M.K.
1998-07-01
The spectacular progress made during the last few years in reaching high energy densities in fast implosions of annular current sheaths (fast Z pinches) opens new possibilities for a broad spectrum of experiments, from x-ray generation to controlled thermonuclear fusion and astrophysics. Presently Z pinches are the most intense laboratory X ray sources (1.8 MJ in 5 ns from a volume 2 mm in diameter and 2 cm tall). Powers in excess of 200 TW have been obtained. This warrants summarizes the present knowledge of physics that governs the behavior of radiating current-carrying plasma in fast Z-pinches. This survey covers essentially all aspects of the physics of fast Z pinches: initiation, instabilities of the early stage, magnetic Rayleigh-Taylor instability in the implosion phase, formation of a transient quasi-equilibrium near the stagnation point, and rebound. Considerable attention is paid to the analysis of hydrodynamic instabilities governing the implosion symmetry. Possible ways of mitigating these instabilities are discussed. Non-magnetohydrodynamic effects (anomalous resistivity, generation of particle beams, etc.) are summarized. Various applications of fast Z pinches are briefly described. Scaling laws governing development of more powerful Z pinches are presented. The survey contains 52 figures and nearly 300 references.
RYUTOV,D.D.; DERZON,MARK S.; MATZEN,M. KEITH
1999-10-25
The spectacular progress made during the last few years in reaching high energy densities in fast implosions of annular current sheaths (fast Z pinches) opens new possibilities for a broad spectrum of experiments, from x-ray generation to controlled thermonuclear fusion and astrophysics. Presently Z pinches are the most intense laboratory X ray sources (1.8 MJ in 5 ns from a volume 2 mm in diameter and 2 cm tall). Powers in excess of 200 TW have been obtained. This warrants summarizing the present knowledge of physics that governs the behavior of radiating current-carrying plasma in fast Z pinches. This survey covers essentially all aspects of the physics of fast Z pinches: initiation, instabilities of the early stage, magnetic Rayleigh-Taylor instability in the implosion phase, formation of a transient quasi-equilibrium near the stagnation point, and rebound. Considerable attention is paid to the analysis of hydrodynamic instabilities governing the implosion symmetry. Possible ways of mitigating these instabilities are discussed. Non-magnetohydrodynamic effects (anomalous resistivity, generation of particle beams, etc.) are summarized. Various applications of fast Z pinches are briefly described. Scaling laws governing development of more powerful Z pinches are presented. The survey contains 36 figures and more than 300 references.
Development Path for Z-Pinch IFE
Olson, C.; Rochau, G.; Slutz, S.
2005-04-15
The long-range goal of the Z-Pinch IFE program is to produce an economically-attractive power plant using high-yield z-pinch-driven targets ({approx}3GJ) with low rep-rate per chamber ({approx}0.1 Hz). The present mainline choice for a Z-Pinch IFE power plant uses an LTD (Linear Transformer Driver) repetitive pulsed power driver, a Recyclable Transmission Line (RTL), a dynamic hohlraum z-pinch-driven target, and a thick-liquid wall chamber. The RTL connects the pulsed power driver directly to the z-pinch-driven target, and is made from frozen coolant or a material that is easily separable from the coolant (such as carbon steel). The RTL is destroyed by themore » fusion explosion, but the RTL materials are recycled, and a new RTL is inserted on each shot.A development path for Z-Pinch IFE has been created that complements and leverages the NNSA DP ICF program. Funding by a U.S. Congressional initiative of $4M for FY04 through NNSA DP is supporting assessment and initial research on (1) RTLs, (2) repetitive pulsed power drivers, (3) shock mitigation [because of the high yield targets], (4) planning for a proof-of-principle full RTL cycle demonstration [with a 1 MA, 1 MV, 100 ns, 0.1 Hz driver], (5) IFE target studies for multi-GJ yield targets, and (6) z-pinch IFE power plant engineering and technology development. Initial results from all areas of this research are discussed.« less
NASA Astrophysics Data System (ADS)
Wessel, Frank; Rahman, Hafiz; Ney, Paul; Darling, Tim; McKee, Erik; Covington, Aaron; Beg, Farhat; Valenzuela, Julio; Narkis, Jeff; Presura, Radu
2015-11-01
The Staged Z-pinch (SZP) is configured as a plasma shell imploding onto an uniform, plasma fill (50:50 Deuterium:Tritium); the pinch is pre-magnetized, with an axial Bz field. Gas-puff experiments, at the University of California, Irvine, 1.25 MA, 1.25 μs, and 50 kJ, demonstrated that the implosion was stable, as primary (DD) and secondary (DT) neutrons were produced at peak compression. Subsequent analysis accounts for the stability and neutron yield, indicating that the SZP implosion is magneto-inertial, shock-driven, with magneto-sonic shocks in the liner and ordinary (sonic) shocks in the target. The shock waves preheat the target, as a stable, current-carrying, shock front forms at the interface. Near-term, the SZP team will test pinch loads on the 1 MA, 130 ns, 100 kJ University of Nevada, Reno, Nevada Terawatt, Zebra Facility. This paper details the context and our specific plans for the upcoming experiments, as well as our recent simulations predicting breakeven fusion on existing devices. Funded by the US Department of Energy, ARPA-E, Control Number 1184-1527.
Spectroscopic study in Z-pinch discharge
Garamoon, A.A.; Saudy, A.H.; Shark, W.
1995-12-31
The temporal variation of the emitted line intensity has been investigated, and thus an important information about the dynamic ionization stages in the Z-pinch discharge has been studied. Also the electron temperature Te, has been deduced by using a spectroscopic technique.
High-Z Pusher Experiments on the Cobra Triple Nozzle Gas-Puff Z-Pinch
NASA Astrophysics Data System (ADS)
de Grouchy, Philip; Qi, Niansheng; Kusse, Bruce; Seyler, Charles; Atoyan, Levon; Byvank, Tom; Cahill, Adam; Greenly, John; Hoyt, Cad; Pikuz, Sergei; Shelkovenko, Tania; Hammer, David
2014-10-01
For inertial confinement fusion application and as efficient hard x-ray sources, the imploding sheath of a gas-puff z-pinch or thin liner must be accelerated to the highest possible velocity before hydrodynamic instabilities significantly disrupt the implosion symmetry. Much recent work has focused on increasing implosion stability using radially structured mass-density profiles produced by multi-nozzle gas-puff valves. The introduction of a high-Z element such as xenon into the outer gas shells in such experiments can modify radiation output during the implosion phase as well as at stagnation. In these experiments xenon is introduced into the triple-nozzle gas valve fielded on the (1 MA, 200 ns) COBRA z-pinch machine at Cornell University. The xenon is introduced only in the outer shell, only in the inner shell or in both, to investigate the radiative effects on implosion hydrodynamics and x-ray yield. Results are compared to those obtained during pure argon implosions with the same mass-density profile. Sheath thicknesses and stability are recorded using laser interferometry (532 nm) and multi-frame imaging systems. The distribution of flow velocities and of high-Z material across the pinch is investigated using a (5 GW, 527 nm) Thomson scattering probe. Work supported by DOE Grant No. DE-NA0001836.
Shlachter, J.S.
1983-01-01
The linear Z pinch is a plasma configuration which in its simplest form requires no auxiliary magnetic field; an axial current carried by the plasma produces an azimuthal confining field and provides ohmic (resistive) or implosion heating. The Lawson criterion (n tau > 10/sup 20/ m/sup -3/s) and high temperatures (T > 10 keV) must be simultaneously satisfied in any reactor scheme. Early Z-pinch experiments concentrated on the sub-atmospheric fill pressure regime, with 10/sup 19/ m/sup -3/ < n < 10/sup 23/ m/sup -3/ and a corresponding confinement time constraint of 10/sup 1/ s > tau > 10/sup -4/ s. In addition, these studies involved plasmas formed at the surface of an insulating wall; the plasmas were subsequently pinched inward by the radial j x B force. Following the implosion phase, gross MHD instabilities were invariably observed on a time scale short compared to the required confinement time.
A Gas Embedded Z-pinch Driven by SPEED2 Generator
NASA Astrophysics Data System (ADS)
Soto, Leopoldo; Pavéz, Cristian; Moreno, José; Sylvester, Gustavo; Silva, Patricio; Zambra, Marcelo; Clausse, Alejandro
2006-12-01
A gas embedded Z-pinch has been implemented using the SPEED2 generator (4.1 μF equivalent Marx generator capacity, 300 kV, 4 MA in short circuit, 187 kJ, 400 ns rise time, dI/dt˜1013 A/s). Initial conditions to produce a gas embedded z-pinch with enhanced stability by means resistive effects and by finite Larmor radius effects were obtained and electrodes were constructed in order to obtain a double column Z-pinch and a hollow discharge. Experiments were carried out in deuterium at mega amperes currents. Current derivative and voltage signals have been obtained. In addition interferograms have been obatined using a pulse Nd-YAG laser (8ns FWMH at 532nm). Preliminary results on neutron emission were also obtained.
On the possibility of neutron generation in an imploding TiD2 puff Z pinch
NASA Astrophysics Data System (ADS)
Baksht, Rina B.; Oreshkin, Vladimir I.; Rousskikh, Alexander G.
2013-08-01
Simulation of implosion of a TiD2 puff Z pinch is reported. The Z pinch is supposed to be produced by the plasma flow generated by a vacuum arc, as described by Rousskikh et al. [Phys. Plasmas 18, 092707 (2011)]. To simulate the implosion, a one-dimensional two-temperature radiative magnetohydrodynamics code was used. The simulation has shown that neutrons are generated during the implosion of a TiD2 puff Z pinch due to thermalization of the pinch plasma stagnated on axis. It has been shown that the necessary condition for neutron generation is that the ion temperature must be substantially higher than the electron temperature. For a pinch current of 1 MA, the predicted yield of "thermal" neutrons is 2.5 × 109 neutrons/shot.
Fusion Propulsion Z-Pinch Engine Concept
NASA Technical Reports Server (NTRS)
Miernik, J.; Statham, G.; Fabisinski, L.; Maples, C. D.; Adams, R.; Polsgrove, T.; Fincher, S.; Cassibry, J.; Cortez, R.; Turner, M.;
2011-01-01
Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Due to the great distances between the planets of our solar system and the harmful radiation environment of interplanetary space, high specific impulse (Isp) propulsion in vehicles with high payload mass fractions must be developed to provide practical and safe vehicles for human spaceflight missions. The Z-Pinch dense plasma focus method is a Magneto-Inertial Fusion (MIF) approach that may potentially lead to a small, low cost fusion reactor/engine assembly1. Recent advancements in experimental and theoretical understanding of this concept suggest favorable scaling of fusion power output yield 2. The magnetic field resulting from the large current compresses the plasma to fusion conditions, and this process can be pulsed over short timescales (10(exp -6 sec). This type of plasma formation is widely used in the field of Nuclear Weapons Effects testing in the defense industry, as well as in fusion energy research. A Decade Module 2 (DM2), approx.500 KJ pulsed-power is coming to the RSA Aerophysics Lab managed by UAHuntsville in January, 2012. A Z-Pinch propulsion concept was designed for a vehicle based on a previous fusion vehicle study called "Human Outer Planet Exploration" (HOPE), which used Magnetized Target Fusion (MTF) 3 propulsion. The reference mission is the transport of crew and cargo to Mars and back, with a reusable vehicle.
Investigation of plasma instabilities in the stagnated Z pinch
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Chittenden, J. P.; Mancini, R. C.; Papp, D.; Niasse, N.; Altemara, S. D.; Anderson, A. A.
2012-10-01
High-resolution laser probing diagnostics at a wavelength of 266 nm allow observation of the internal structure and instabilities in dense stagnated Z pinches, typically hidden by trailing material. The internal structure of the 1-MA Z pinch includes strong kink and sausage instabilities, loops, flares, and disruptions. Mid- and small-scale density perturbations develop in the precursor and main pinch. The three-dimensional shape and dynamics of the wire-array Z pinch are predetermined by the initial configuration of the wire array. Cylindrical, linear, and star wire-array Z pinches present different sets of instabilities seeded to the pinch at the implosion stage. Prolonged implosion of trailing mass can enhance x-ray production in wire arrays. Fast plasma motion with a velocity >100 km/s was observed in the Z pinch at stagnation with two-frame shadowgraphy. Development of instabilities in wire arrays is in agreement with three-dimensional magnetohydrodynamic simulations.
Instability Control in a Staged Z-pinch
WESSEL, Frank J
2011-04-22
A \\Staged Z-Pinch is a fusion-energy concept in which stored-electric energy is first converted into plasma-liner-kinetic energy, and then transferred to a coaxialtarget plasma [H. U. Rahman, F. J. Wessel, and N. Rostoker, Phys. Rev. Lett. 74, p. 714(1996)]. Proper choice of the liner and target materials, and their initial radii and mass densities, leads to dynamic stabilization, current amplification, and shock heating of the target. Simulations suggest that this configuration has merit as a alternative inertial-confinement-fusion concept, and may provide an energy release exceeding thermonuclear break-even, if tested on one of many newer pulsed power systems, for example thosemore » located at Sandia National Laboratories.« less
Plasma channel and z-pinch dynamics for heavy ion transport
NASA Astrophysics Data System (ADS)
Ponce-Marquez, David Miguel
A self stabilized, free standing, z-pinch plasma channel has been proposed to deliver the high intensity heavy ion beam from the end of a driver to the fuel target in a heavy ion inertial fusion power plant. The z-pinch relaxes emittance and energy spread requirements requiring a lower cost driver. A z-pinch transport would reduce the number of beam entry port holes to the target chamber from over a hundred to four as compared to neutralized ballistic focusing thus reducing the driver hardware exposure to neutron flux. Experiments where a double pulse discharge technique is used, z-pinch plasma channels with enhanced stability are achieved. Typical parameters are 7 kV pre-pulse discharge and 30 kV main bank discharge with 50 kA of channel current in a 7 torr background gas atmosphere. This work is an experimental study of these plasma channels examining the relevant physics necessary to understand and model such plasmas. Laser diagnostics measured the dynamical properties of neutrals and plasma. Schlieren and phase contrast techniques probe the pre-pulse gas dynamics and infrared interferometry and faraday effect polarimetry are used on the z-pinch to study its electron density and current distribution. Stability and repeatability of the z-pinch depend on the initial conditions set by the pre-pulse. Results show that the z-pinch channel is wall stabilized by an on-axis gas density depression created by the pre-pulse through hydrodynamic expansion where the ratio of the initial gas density to the final gas density is >10/1. The low on-axis density favors avalanching along the desired path for the main bank discharge. Pinch time is around 2 mus from the main bank discharge initiation with a FWHM of ≈2 cm. Results also show that typical main bank discharge plasma densities reach 1017 cm-3 peak on axis for a 30 kV, 7 torr gas nitrogen discharge. Current rise time is limited by the circuit-channel inductance with the highest contribution to the impedance due to the
Plasma channel and Z-pinch dynamics for heavy ion transport
Ponce-Marquez, David
2002-01-01
A self stabilized, free standing, z-pinch plasma channel has been proposed to deliver the high intensity heavy ion beam from the end of a driver to the fuel target in a heavy ion inertial fusion power plant. The z-pinch relaxes emittance and energy spread requirements requiring a lower cost driver. A z-pinch transport would reduce the number of beam entry port holes to the target chamber from over a hundred to four as compared to neutralized ballistic focusing thus reducing the driver hardware exposure to neutron flux. Experiments where a double pulse discharge technique is used, z-pinch plasma channels with enhanced stability are achieved. Typical parameters are 7 kV pre-pulse discharge and 30 kV main bank discharge with 50 kA of channel current in a 7 torr background gas atmosphere. This work is an experimental study of these plasma channels examining the relevant physics necessary to understand and model such plasmas. Laser diagnostics measured the dynamical properties of neutrals and plasma. Schlieren and phase contrast techniques probe the pre-pulse gas dynamics and infrared interferometry and faraday effect polarimetry are used on the z-pinch to study its electron density and current distribution. Stability and repeatability of the z-pinch depend on the initial conditions set by the pre-pulse. Results show that the z-pinch channel is wall stabilized by an on-axis gas density depression created by the pre-pulse through hydrodynamic expansion where the ratio of the initial gas density to the final gas density is > 10/1. The low on-axis density favors avalanching along the desired path for the main bank discharge. Pinch time is around 2 s from the main bank discharge initiation with a FWHM of ~ 2 cm. Results also show that typical main bank discharge plasma densities reach 10^{17} cm^{-3} peak on axis for a 30 kV, 7 torr gas nitrogen discharge. Current rise time is limited by the circuit-channel inductance with the highest contribution to the
Experimental astrophysics with high power lasers and Z pinches
Remington, B A; Drake, R P; Ryutov, D D
2004-12-10
With the advent of high energy density (HED) experimental facilities, such as high-energy lasers and fast Z-pinch, pulsed-power facilities, mm-scale quantities of matter can be placed in extreme states of density, temperature, and/or velocity. This has enabled the emergence of a new class of experimental science, HED laboratory astrophysics, wherein the properties of matter and the processes that occur under extreme astrophysical conditions can be examined in the laboratory. Areas particularly suitable to this class of experimental astrophysics include the study of opacities relevant to stellar interiors; equations of state relevant to planetary interiors; strong shock driven nonlinear hydrodynamics and radiative dynamics, relevant to supernova explosions and subsequent evolution; protostellar jets and high Mach-number flows; radiatively driven molecular clouds and nonlinear photoevaporation front dynamics; and photoionized plasmas relevant to accretion disks around compact objects, such as black holes and neutron stars.
Magnetohydrodynamic Simulation of Solid-Deuterium - Z-Pinch Experiments
NASA Astrophysics Data System (ADS)
Sheehey, Peter Trogdon
Solid-deuterium-initiated Z-pinch experiments are numerically simulated using a two-dimensional resistive magnetohydrodynamic model, which includes many important experimental details, such as "cold-start" initial conditions, thermal conduction, radiative energy loss, actual discharge current vs. time, and grids of sufficient size and resolution to allow realistic development of the plasma. The alternating -direction-implicit numerical technique used meets the substantial demands presented by such a computational task. Simulations of fiber-initiated experiments show that when the fiber becomes fully ionized (at a time depending on current ramp and fiber thickness), rapidly developing m = 0 instabilities, which originated in the coronal plasma generated from the ablating fiber, drive intense non-uniform heating and rapid expansion of the plasma column. The possibility that inclusion of additional physical effects would improve stability is explored. Finite-Larmor-radius-ordered Hall and diamagnetic pressure terms in the magnetic field evolution equation, corresponding energy equation terms, and separate ion and electron energy equations are included; these do not change the basic results. Model diagnostics, such as shadowgrams and interferograms, generated from simulation results, are in good agreement with experiment. Two alternative experimental approaches are explored: high-current magnetic implosion of hollow cylindrical deuterium shells, and "plasma -on wire" (POW) implosion of low-density plasma onto a central deuterium fiber. By minimizing instability problems, these techniques may allow attainment of higher temperatures and densities than possible with bare fiber-initiated Z -pinches. Conditions for significant D-D or D-T fusion neutron production may be realizable with these implosion -based approaches.
Diagnostic of energetic electrons in dense z-pinch plasmas
NASA Astrophysics Data System (ADS)
Shlyaptseva, A. S.; Mancini, R. C.
1997-05-01
We discuss the diagnostic of energetic electron beams in z-pinch plasmas using x-ray line polarization spectroscopy. Our previous work in this area has been related to the study of polarization of dielectronic satellite lines of Li- and Be-like Mg and Fe ions in low-density plasmas. Here we extend our work to the case of z-pinch plasmas. We calculate the polarization properties of dielectronic satellite lines of Be-like Ne, Ar and Fe ions. These results can be used to diagnose the energy and directionality of energetic electron beams. This work is motivated by the development of a new Dense Z-pinch Program at University of Nevada, Reno. (see B. S. Bauer et al. this conference). However, the results can also be applied to other z-pinch devices.
Diagnostic of energetic electrons in dense z-pinch plasmas
Shlyaptseva, A. S.; Mancini, R. C.
1997-05-05
We discuss the diagnostic of energetic electron beams in z-pinch plasmas using x-ray line polarization spectroscopy. Our previous work in this area has been related to the study of polarization of dielectronic satellite lines of Li- and Be-like Mg and Fe ions in low-density plasmas. Here we extend our work to the case of z-pinch plasmas. We calculate the polarization properties of dielectronic satellite lines of Be-like Ne, Ar and Fe ions. These results can be used to diagnose the energy and directionality of energetic electron beams. This work is motivated by the development of a new Dense Z-pinch Programmore » at University of Nevada, Reno. (see B. S. Bauer et al. this conference). However, the results can also be applied to other z-pinch devices.« less
Progress in Z-pinch inertial fusion energy.
Weed, John Woodruff
2010-03-01
The goal of z-pinch inertial fusion energy (IFE) is to extend the single-shot z-pinch inertial confinement fusion (ICF) results on Z to a repetitive-shot z-pinch power plant concept for the economical production of electricity. Z produces up to 1.8 MJ of x-rays at powers as high as 230 TW. Recent target experiments on Z have demonstrated capsule implosion convergence ratios of 14-21 with a double-pinch driven target, and DD neutron yields up to 8x10exp10 with a dynamic hohlraum target. For z-pinch IFE, a power plant concept is discussed that uses high-yield IFE targets (3 GJ) with a low rep-rate per chamber (0.1 Hz). The concept includes a repetitive driver at 0.1 Hz, a Recyclable Transmission Line (RTL) to connect the driver to the target, high-yield targets, and a thick-liquid wall chamber. Recent funding by a U.S. Congressional initiative for $4M for FY04 is supporting research on RTLs, repetitive pulsed power drivers, shock mitigation, full RTL cycle planned experiments, high-yield IFE targets, and z-pinch power plant technologies. Recent results of research in all of these areas are discussed, and a Road Map for Z-Pinch IFE is presented.
Progress on Z-pinch inertial fusion energy.
Olson, Craig Lee
2004-09-01
The goal of z-pinch inertial fusion energy (IFE) is to extend the single-shot z-pinch inertial confinement fusion (ICF) results on Z to a repetitive-shot z-pinch power plant concept for the economical production of electricity. Z produces up to 1.8 MJ of x-rays at powers as high as 230 TW. Recent target experiments on Z have demonstrated capsule implosion convergence ratios of 14-21 with a double-pinch driven target, and DD neutron yields up to 8x10exp10 with a dynamic hohlraum target. For z-pinch IFE, a power plant concept is discussed that uses high-yield IFE targets (3 GJ) with a low rep-rate permore » chamber (0.1 Hz). The concept includes a repetitive driver at 0.1 Hz, a Recyclable Transmission Line (RTL) to connect the driver to the target, high-yield targets, and a thick-liquid wall chamber. Recent funding by a U.S. Congressional initiative for $4M for FY04 is supporting research on RTLs, repetitive pulsed power drivers, shock mitigation, full RTL cycle planned experiments, high-yield IFE targets, and z-pinch power plant technologies. Recent results of research in all of these areas are discussed, and a Road Map for Z-Pinch IFE is presented.« less
Progress in Z-pinch inertial fusion energy.
Weed, John Woodruff
2010-03-01
The goal of z-pinch inertial fusion energy (IFE) is to extend the single-shot z-pinch inertial confinement fusion (ICF) results on Z to a repetitive-shot z-pinch power plant concept for the economical production of electricity. Z produces up to 1.8 MJ of x-rays at powers as high as 230 TW. Recent target experiments on Z have demonstrated capsule implosion convergence ratios of 14-21 with a double-pinch driven target, and DD neutron yields up to 8x10exp10 with a dynamic hohlraum target. For z-pinch IFE, a power plant concept is discussed that uses high-yield IFE targets (3 GJ) with a low rep-rate permore » chamber (0.1 Hz). The concept includes a repetitive driver at 0.1 Hz, a Recyclable Transmission Line (RTL) to connect the driver to the target, high-yield targets, and a thick-liquid wall chamber. Recent funding by a U.S. Congressional initiative for $4M for FY04 is supporting research on RTLs, repetitive pulsed power drivers, shock mitigation, full RTL cycle planned experiments, high-yield IFE targets, and z-pinch power plant technologies. Recent results of research in all of these areas are discussed, and a Road Map for Z-Pinch IFE is presented.« less
Z-Pinch Pulsed Plasma Propulsion Technology Development
NASA Technical Reports Server (NTRS)
Polsgrove, Tara; Adams, Robert B.; Fabisinski, Leo; Fincher, Sharon; Maples, C. Dauphne; Miernik, Janie; Percy, Tom; Statham, Geoff; Turner, Matt; Cassibry, Jason;
2010-01-01
Fusion-based propulsion can enable fast interplanetary transportation. Magneto-inertial fusion (MIF) is an approach which has been shown to potentially lead to a low cost, small reactor for fusion break even. The Z-Pinch/dense plasma focus method is an MIF concept in which a column of gas is compressed to thermonuclear conditions by an axial current (I approximates 100 MA). Recent advancements in experiments and the theoretical understanding of this concept suggest favorable scaling of fusion power output yield as I(sup 4). This document presents a conceptual design of a Z-Pinch fusion propulsion system and a vehicle for human exploration. The purpose of this study is to apply Z-Pinch fusion principles to the design of a propulsion system for an interplanetary spacecraft. This study took four steps in service of that objective; these steps are identified below. 1. Z-Pinch Modeling and Analysis: There is a wealth of literature characterizing Z-Pinch physics and existing Z-Pinch physics models. In order to be useful in engineering analysis, simplified Z-Pinch fusion thermodynamic models are required to give propulsion engineers the quantity of plasma, plasma temperature, rate of expansion, etc. The study team developed these models in this study. 2. Propulsion Modeling and Analysis: While the Z-Pinch models characterize the fusion process itself, propulsion models calculate the parameters that characterize the propulsion system (thrust, specific impulse, etc.) The study team developed a Z-Pinch propulsion model and used it to determine the best values for pulse rate, amount of propellant per pulse, and mixture ratio of the D-T and liner materials as well as the resulting thrust and specific impulse of the system. 3. Mission Analysis: Several potential missions were studied. Trajectory analysis using data from the propulsion model was used to determine the duration of the propulsion burns, the amount of propellant expended to complete each mission considered. 4
A conservative MHD scheme on unstructured Lagrangian grids for Z-pinch hydrodynamic simulations
NASA Astrophysics Data System (ADS)
Wu, Fuyuan; Ramis, Rafael; Li, Zhenghong
2018-03-01
A new algorithm to model resistive magnetohydrodynamics (MHD) in Z-pinches has been developed. Two-dimensional axisymmetric geometry with azimuthal magnetic field Bθ is considered. Discretization is carried out using unstructured meshes made up of arbitrarily connected polygons. The algorithm is fully conservative for mass, momentum, and energy. Matter energy and magnetic energy are managed separately. The diffusion of magnetic field is solved using a derivative of the Symmetric-Semi-Implicit scheme, Livne et al. (1985) [23], where unconditional stability is obtained without needing to solve large sparse systems of equations. This MHD package has been integrated into the radiation-hydrodynamics code MULTI-2D, Ramis et al. (2009) [20], that includes hydrodynamics, laser energy deposition, heat conduction, and radiation transport. This setup allows to simulate Z-pinch configurations relevant for Inertial Confinement Fusion.
On the possibility of neutron generation in an imploding TiD{sub 2} puff Z pinch
Baksht, Rina B.; Tel-Aviv University, Tel Aviv; Oreshkin, Vladimir I.
2013-08-15
Simulation of implosion of a TiD{sub 2} puff Z pinch is reported. The Z pinch is supposed to be produced by the plasma flow generated by a vacuum arc, as described by Rousskikh et al.[Phys. Plasmas 18, 092707 (2011)]. To simulate the implosion, a one-dimensional two-temperature radiative magnetohydrodynamics code was used. The simulation has shown that neutrons are generated during the implosion of a TiD{sub 2} puff Z pinch due to thermalization of the pinch plasma stagnated on axis. It has been shown that the necessary condition for neutron generation is that the ion temperature must be substantially higher thanmore » the electron temperature. For a pinch current of 1 MA, the predicted yield of 'thermal' neutrons is 2.5 × 10{sup 9} neutrons/shot.« less
On the possibility of neutron generation in an imploding TiD{sub 2} puff Z pinch
Baksht, Rina B.; Oreshkin, Vladimir I.; Rousskikh, Alexander G.
2013-08-15
Simulation of implosion of a TiD{sub 2} puff Z pinch is reported. The Z pinch is supposed to be produced by the plasma flow generated by a vacuum arc, as described by Rousskikh et al.[Phys. Plasmas 18, 092707 (2011)]. To simulate the implosion, a one-dimensional two-temperature radiative magnetohydrodynamics code was used. The simulation has shown that neutrons are generated during the implosion of a TiD{sub 2} puff Z pinch due to thermalization of the pinch plasma stagnated on axis. It has been shown that the necessary condition for neutron generation is that the ion temperature must be substantially higher than the electron temperature. For a pinch current of 1 MA, the predicted yield of 'thermal' neutrons is 2.5 × 10{sup 9} neutrons/shot.
Study of gas-puff Z-pinches on COBRA
Qi, N.; Rosenberg, E. W.; Gourdain, P. A.; Grouchy, P. W. L. de; Kusse, B. R.; Hammer, D. A.; Bell, K. S.; Shelkovenko, T. A.; Potter, W. M.; Atoyan, L.; Cahill, A. D.; Evans, M.; Greenly, J. B.; Hoyt, C. L.; Pikuz, S. A.; Schrafel, P. C.; Kroupp, E.; Fisher, A.; Maron, Y.
2014-11-15
Gas-puff Z-pinch experiments were conducted on the 1 MA, 200 ns pulse duration Cornell Beam Research Accelerator (COBRA) pulsed power generator in order to achieve an understanding of the dynamics and instability development in the imploding and stagnating plasma. The triple-nozzle gas-puff valve, pre-ionizer, and load hardware are described. Specific diagnostics for the gas-puff experiments, including a Planar Laser Induced Fluorescence system for measuring the radial neutral density profiles along with a Laser Shearing Interferometer and Laser Wavefront Analyzer for electron density measurements, are also described. The results of a series of experiments using two annular argon (Ar) and/or neon (Ne) gas shells (puff-on-puff) with or without an on- (or near-) axis wire are presented. For all of these experiments, plenum pressures were adjusted to hold the radial mass density profile as similar as possible. Initial implosion stability studies were performed using various combinations of the heavier (Ar) and lighter (Ne) gasses. Implosions with Ne in the outer shell and Ar in the inner were more stable than the opposite arrangement. Current waveforms can be adjusted on COBRA and it was found that the particular shape of the 200 ns current pulse affected on the duration and diameter of the stagnated pinched column and the x-ray yield.
Study of gas-puff Z-pinches on COBRA
NASA Astrophysics Data System (ADS)
Qi, N.; Rosenberg, E. W.; Gourdain, P. A.; de Grouchy, P. W. L.; Kusse, B. R.; Hammer, D. A.; Bell, K. S.; Shelkovenko, T. A.; Potter, W. M.; Atoyan, L.; Cahill, A. D.; Evans, M.; Greenly, J. B.; Hoyt, C. L.; Pikuz, S. A.; Schrafel, P. C.; Kroupp, E.; Fisher, A.; Maron, Y.
2014-11-01
Gas-puff Z-pinch experiments were conducted on the 1 MA, 200 ns pulse duration Cornell Beam Research Accelerator (COBRA) pulsed power generator in order to achieve an understanding of the dynamics and instability development in the imploding and stagnating plasma. The triple-nozzle gas-puff valve, pre-ionizer, and load hardware are described. Specific diagnostics for the gas-puff experiments, including a Planar Laser Induced Fluorescence system for measuring the radial neutral density profiles along with a Laser Shearing Interferometer and Laser Wavefront Analyzer for electron density measurements, are also described. The results of a series of experiments using two annular argon (Ar) and/or neon (Ne) gas shells (puff-on-puff) with or without an on- (or near-) axis wire are presented. For all of these experiments, plenum pressures were adjusted to hold the radial mass density profile as similar as possible. Initial implosion stability studies were performed using various combinations of the heavier (Ar) and lighter (Ne) gasses. Implosions with Ne in the outer shell and Ar in the inner were more stable than the opposite arrangement. Current waveforms can be adjusted on COBRA and it was found that the particular shape of the 200 ns current pulse affected on the duration and diameter of the stagnated pinched column and the x-ray yield.
Adaptive Wavelet Techniques in Z-Pinch Research
NASA Astrophysics Data System (ADS)
Afeyan, Bedros; Won, Kirk; Struve, Kenneth; Deeny, Christopher; Cuneo, Michael; Bennett, Guy; Vessey, Roger; Porter, John
2002-11-01
We examine denoising, pattern detection and information compression capabilities of special classes of wavelet families adapted to various 1D and 2D signals that arise in Z-Pinch research. In particular, we analyze X-ray bolometry data where the challenge is to extract accurate power vs time information (which requires differentiation) from noisy energy data. We will also treat X-ray images of symmetric ICF capsule implosions from double Z-Pinch hohlraum drives. Here we wish to denoise the data and identify the contributions from certain low order Legendre polynomials which indicate the degree of asymmetry found in these implosions [M. E. Cuneo et al., PRL 88, 215004-1, 2002]. A combined wavelet-Legendre, cartesian tensor product wavelet and polar coordinate decompositions will be presented together with a comparison of wavelet vs curvelet techniques. Extensions to other X-ray data from Z-Pinch implosions such as pinhole imagery or their simulation, will be given.
Axial convergent Z-pinch driven dynamic hohlraums
Slutz, S.A.; Douglas, M.R.; Nash, T.J.
1999-07-01
Axial convergence during the implosion of an initially cylindrical z pinch plasma increases the radiation temperature produced within a dynamic hohlraum. Quasi-spherical z pinch implosions have been demonstrated with thick liners initially in a spherical shape. However, wire arrays have been demonstrated to be superior to liners for generating radiation. The authors shall present numerical simulations demonstrating two methods of obtaining axial convergence with z pinch driven wire arrays. The simulations show that appropriate profiling of the mass per unit length of the wires can result in an almost spherical shaped to the wire array plasma just before stagnation. Simulations also show that proper mass profiling and shaping of material surrounding the fusion capsule can result in a nearly spherical dynamic hohlraum. Comparisons between cylindrical and axially convergent dynamic hohlraum conditions will be presented.
Study of magnetic fields and current in the Z pinch at stagnation
Ivanov, V. V.; Anderson, A. A.; Astanovitskiy, A. L.
2015-09-15
The structure of magnetic fields in wire-array Z pinches at stagnation was studied using a Faraday rotation diagnostic at the wavelength of 266 nm. The electron plasma density and the Faraday rotation angle in plasma were calculated from images of the three-channel polarimeter. The magnetic field was reconstructed with Abel transform, and the current was estimated using a simple model. Several shots with wire-array Z pinches at 0.5–1.5 MA were analyzed. The strength of the magnetic field measured in plasma of the stagnated pinch was in the range of 1–2 MG. The magnetic field and current profile in plasma near themore » neck on the pinch were reconstructed, and the size of the current-carrying plasma was estimated. It was found that current flowed in the large-size trailing plasma near the dense neck. Measurements of the magnetic field near the bulge on the pinch also showed current in trailing plasma. A distribution of current in the large-size trailing plasma can prevent the formation of multi-MG fields in the Z pinch.« less
Note: Infrared laser diagnostics for deuterium gas puff Z pinches
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; McKee, E. S.; Hammel, B. D.; Darling, T. W.; Swanson, K. J.; Covington, A. M.
2017-07-01
Deuterium gas puff Z pinches have been used for generation of strong neutron fluxes on the MA class pulse power machines. Due to the low electron density of deuterium Z-pinch plasma, regular laser diagnostics in the visible range cannot be used for observation and study of the pinch. Laser probing at the wavelength of 1064 nm was used for visualization of deuterium plasma. Infrared schlieren and interferometry diagnostics showed the deuterium gas puff plasma dynamics, instabilities, and allowed for the reconstruction of the profile of the plasma density.
{alpha} Heating in a Stagnated Z-pinch
Appelbe, Brian; Chittenden, Jeremy
2009-01-21
A computational investigation of a scheme for magneto-inertial confinement fusion in a Z-pinch is carried out. In the scheme implosion of a deuterium-tritium fuel mass is preceded by formation of a hotspot containing warm, dense plasma on axis. The presence of the hotspot increases energy yield. Compression of the hotspot by the main fuel mass initiates thermonuclear burn. There is significant heating of the plasma by thermonuclear {alpha} particles which are confined by the strong magnetic field of the Z-pinch.
Linear Transformer Drivers for Z-pinch Based Propulsion
NASA Technical Reports Server (NTRS)
Adams, Robert; Seidler, William; Giddens, Patrick; Fabisinski, Leo; Cassibry, Jason
2017-01-01
The MSFC/UAH team has been developing of a novel power management and distribution system called a Linear Transformer Driver (LTD). LTD's hold the promise of dramatically reducing the required mass to drive a z-pinch by replacing the capacitor banks which constitute half the mass of the entire system. The MSFC?UAH tea, is developing this technology in hope of integrating it with the Pulsed Fission Fusion (PuFF) propulsion concept. High-Voltage pulsed power systems used for Z-Pinch experimentation have in the past largely been based on Marx Generators. Marx generators deliver the voltage and current required for the Z-Pinch, but suffer from two significant drawbacks when applied to a flight system: they are very massive, consisting of high-voltage capacitor banks insulated in oil-filled tanks and they do not lend themselves to rapid pulsing. The overall goal of Phase 2 is to demonstrate the construction of a higher voltage stack from a number of cavities each of the design proven in Phase 1 and to characterize and understand the techniques for designing the stack. The overall goal of Phase 3 is to demonstrate the feasibility of constructing a higher energy cavity from a number of smaller LTD stacks, to characterize and understand the way in which the constituent stacks combine, and to extend this demonstration LTD to serve as the basis for a 64 kJ pulse generator for Z-Pinch experiments.
Z-pinch experiments on Saturn at 30 TW
NASA Astrophysics Data System (ADS)
Spielman, R. B.; Dukart, R. J.; Hanson, D. L.; Hammel, B. A.; Hsing, W. W.; Matzen, M. K.; Porter, J. L.
1989-12-01
We have recently completed the first gas-puff Z-pinch experiments on Saturn (32 TW, 1.4 MJ, 1.9 MV, 40-ns FWHM, and 0.11 Ω). These experiments used the most powerful driver to date for fast Z-pinch experiments. Saturn, a 36 module accelerator, uses a double post-hole vacuum convolute to deliver the total machine current to the load. The 10-nH Saturn Z-pinch diode is capable of delivering a peak current of 10.5 MA. We diagnosed the current using segmented Rogowski coils at the insulator, resistive shunts in the vacuum transmission lines, and B-dot loops and piezoelectric pressure gauges near the load. On most shots electrical losses in the vacuum convolute were minimal with nearly complete current delivery to the Z-pinch load. We have conducted experiments with deuterium, neon, argon, krypton, and xenon gas puffs. A maximum total radiation yield of 505+/-25 kJ was obtained with xenon. The peak keV x-ray yields were 100+/-5 kJ for neon L-shell radiation, 30+/-4 kJ for krypton l-shell radiation, and 39+/-4 kJ for argon K-shell radiation.
Laser pumping by intense discharges in z-pinch geometry.
Buser, R G; Ramm, D
1966-04-01
Optical properties of high-current, low-pressure, noble-gas discharges in z-pinch geometry are studied and compared with theta-pinch discharges and standard commercial light sources. Results indicate possible usefulness in systems where high peak power, high repetition rates or high uv content are demanded.
Experiments With Radiatively Cooled Supersonic Plasma Jets Generated in Conical Wire Array Z-Pinches
NASA Astrophysics Data System (ADS)
Lebedev, S. V.; Ampleford, D. J.; Bland, S. N.; Chittenden, J. P.; Ciardi, A.; Naz, N.; Haines, M. G.; Frank, A.; Blackman, E.; Gardiner, T.
2002-12-01
We present results of astrophysically relevant experiments where highly supersonic plasma jets are generated via conically convergent plasma flows in a conical wire array Z-pinch. Stagnation of plasma flow on the axis of symmetry forms a standing conical shock effectively collimating the flow in the axial direction. This scenario is essentially similar to that discussed by Canto and collaborators [1] as a purely hydrodynamic mechanism for jet formation in astrophysical systems. Experiments using different materials (Al, Fe and W) show that a hypersonic (M ~ 20), well-collimated jet is generated when the radiative cooling rate of the plasma is significant.
Mapping return currents in laser-generated Z-pinch plasmas using proton deflectometry
Manuel, M. J.-E.; Sinenian, N.; Seguin, F. H.
2012-05-14
Dynamic return currents and electromagnetic field structure in laser-generated Z-pinch plasmas have been measured using proton deflectometry. Experiments were modeled to accurately interpret deflections observed in proton radiographs. Current flow is shown to begin on axis and migrate outwards with the expanding coronal plasma. Magnetic field strengths of {approx}1 T are generated by currents that increase from {approx}2 kA to {approx}7 kA over the course of the laser pulse. Proton deflectometry has been demonstrated to be a practical alternative to other magnetic field diagnostics for these types of plasmas.
Evaluation of a Z-pinch-driven ICF Concept
NASA Astrophysics Data System (ADS)
Olson, R. E.; Chandler, G. A.; Sanford, T. W. L.; Alberts, T. E.; Derzon, M. S.; Fehl, D. L.; Gilliland, T. L.; Hebron, D. E.; Jobe, D. O.; Lash, J. S.; Leeper, R. J.; McGuire, E. J.; McGurn, J. S.; Mills, J. A.; Nash, T. J.; Ruggles, L.; Struve, K. W.; Stygar, W. A.; Torres, J. A.; Vargas, M.; Vesey, R..
1998-11-01
We are developing a technique for driving static-walled hohlraums with x-rays from a z-pinch radiation source. In this ICF concept, radiation from z-pinch stagnation provides the x-ray input on both ends of a cylindrical hohlraum containing a low density, low-Z fill; high-Z symmetry shields; and a 1-2 mm diameter cryogenic DT-filled capsule. Numerical simulations indicate that a 60 MA Z-pinch driver would be required to achieve ignition conditions. In order to gain preliminary understanding of the hohlraum concept and to test our numerical simulations, we have performed a series of hohlraum experiments with a scaled down, single-sided drive at the 20 MA level in the SNL Z-facility. In these experiments, the hohlraums (6 mm diameter and 7 mm long) have been successfully heated to radiation temperatures in the range of 80-100 eV. Experiments to date include investigations of hohlraum diagnostic hole closure, axial temperature gradients, pulse shaping, azimuthal symmetry, and radiation transport in capsule / shine shield configurations. The ignition concept, the experimental results, and the shortcomings and successes of the numerical simulations will be discussed in this presentation.
Dynamics of conical wire array Z-pinch implosions
Ampleford, D. J.; Lebedev, S. V.; Bland, S. N.
2007-10-15
A modification of the wire array Z pinch, the conical wire array, has applications to the understanding of wire array implosions and potentially to pulse shaping relevant to inertial confinement fusion. Results are presented from imploding conical wire array experiments performed on university scale 1 MA generators--the MAGPIE generator (1 MA, 240 ns) at Imperial College London [I. H. Mitchell et al., Rev. Sci Instrum. 67, 1533 (1996)] and the Nevada Terawatt Facility's Zebra generator (1 MA, 100 ns) at the University of Nevada, Reno [B. Bauer et al., in Dense Z-Pinches, edited by N. Pereira, J. Davis, and P.more » Pulsifer (AIP, New York, 1997), Vol. 409, p. 153]. This paper will discuss the implosion dynamics of conical wire arrays. Data indicate that mass ablation from the wires in this complex system can be reproduced with a rocket model with fixed ablation velocity. Modulations in the ablated plasma are present, the wavelength of which is invariant to a threefold variation in magnetic field strength. The axial variation in the array leads to a zippered precursor column formation. An initial implosion of a magnetic bubble near the cathode is followed by the implosion zippering upwards. Spectroscopic data demonstrating a variation of plasma parameters (e.g., electron temperature) along the Z-pinch axis is discussed, and experimental data are compared to magnetohydrodynamic simulations.« less
Architecture of petawatt-class z-pinch accelerators
NASA Astrophysics Data System (ADS)
Stygar, W. A.; Cuneo, M. E.; Headley, D. I.; Ives, H. C.; Leeper, R. J.; Mazarakis, M. G.; Olson, C. L.; Porter, J. L.; Wagoner, T. C.; Woodworth, J. R.
2007-03-01
We have developed an accelerator architecture that can serve as the basis of the design of petawatt-class z-pinch drivers. The architecture has been applied to the design of two z-pinch accelerators, each of which can be contained within a 104-m-diameter cylindrical tank. One accelerator is driven by slow (˜1μs) Marx generators, which are a mature technology but which necessitate significant pulse compression to achieve the short pulses (≪1μs) required to drive z pinches. The other is powered by linear transformer drivers (LTDs), which are less mature but produce much shorter pulses than conventional Marxes. Consequently, an LTD-driven accelerator promises to be (at a given pinch current and implosion time) more efficient and reliable. The Marx-driven accelerator produces a peak electrical power of 500 TW and includes the following components: (i) 300 Marx generators that comprise a total of 1.8×104 capacitors, store 98 MJ, and erect to 5 MV; (ii) 600 water-dielectric triplate intermediate-store transmission lines, which also serve as pulse-forming lines; (iii) 600 5-MV laser-triggered gas switches; (iv) three monolithic radial-transmission-line impedance transformers, with triplate geometries and exponential impedance profiles; (v) a 6-level 5.5-m-diameter 15-MV vacuum insulator stack; (vi) six magnetically insulated vacuum transmission lines (MITLs); and (vii) a triple-post-hole vacuum convolute that adds the output currents of the six MITLs, and delivers the combined current to a z-pinch load. The accelerator delivers an effective peak current of 52 MA to a 10-mm-length z pinch that implodes in 95 ns, and 57 MA to a pinch that implodes in 120 ns. The LTD-driven accelerator includes monolithic radial transformers and a MITL system similar to those described above, but does not include intermediate-store transmission lines, multimegavolt gas switches, or a laser trigger system. Instead, this accelerator is driven by 210 LTD modules that include a total of 1
Measurements of the Time Evolution of Ion Temperature Profiles on the FuZE Fusion Z-Pinch Experiment
NASA Astrophysics Data System (ADS)
Stepanov, A. D.; Shumlak, U.; Nelson, B. A.; Claveau, E. L.; Forbes, E. G.; Golingo, R. P.; Weber, T. R.; Zhang, Y.; McLean, H. S.; Higginson, D. P.; Schmidt, A.; Tummel, K. K.
2017-10-01
FuZE investigates the scaling of sheared-flow stabilized Z-pinches to fusion-relevant densities and temperatures. Long-lived (>20 μs) pinches with an embedded axial flow and stabilizing velocity shear are formed by radial compression of a flowing plasma produced in a coaxial plasma accelerator. In the near term, we plan to operate with trace amounts of deuterium to produce a small but detectable flux of D-D neutrons. This flux can be estimated if the ion temperature and density profiles are known. Density profiles are obtained from interferometry. Ion Doppler spectroscopy measures the line-integrated ion temperature along 20 chords spaced 1.2 mm apart in the plasma based on Doppler broadening of impurity lines. The time evolution of Ti profiles is measured by varying the time at which the spectrum is acquired over a series of repeatable plasma pulses. Based on experimental ion temperature and density profiles, we calculate the expected neutron flux. This estimate can be compared to the measured neutron flux to ascertain whether the neutrons are of thermonuclear origin. This work is supported by an award from US ARPA-E.
Turbulent stagnation in a Z -pinch plasma
NASA Astrophysics Data System (ADS)
Kroupp, E.; Stambulchik, E.; Starobinets, A.; Osin, D.; Fisher, V. I.; Alumot, D.; Maron, Y.; Davidovits, S.; Fisch, N. J.; Fruchtman, A.
2018-01-01
The ion kinetic energy in a stagnating plasma was previously determined by Kroupp et al. [Phys. Rev. Lett. 107, 105001 (2011), 10.1103/PhysRevLett.107.105001] from Doppler-dominated line shapes augmented by measurements of plasma properties and assuming a uniform-plasma model. Notably, the energy was found to be dominantly stored in hydrodynamic flow. Here we advance a new description of this stagnation as supersonically turbulent. Such turbulence implies a nonuniform density distribution. We demonstrate how to reanalyze the spectroscopic data consistent with the turbulent picture and show that this leads to better concordance of the overconstrained spectroscopic measurements, while also substantially lowering the inferred mean density.
Z-Pinch fusion-based nuclear propulsion
NASA Astrophysics Data System (ADS)
Miernik, J.; Statham, G.; Fabisinski, L.; Maples, C. D.; Adams, R.; Polsgrove, T.; Fincher, S.; Cassibry, J.; Cortez, R.; Turner, M.; Percy, T.
2013-02-01
Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Due to the great distances between the planets of our solar system and the harmful radiation environment of interplanetary space, high specific impulse (Isp) propulsion in vehicles with high payload mass fractions must be developed to provide practical and safe vehicles for human space flight missions. The Z-Pinch dense plasma focus method is a Magneto-Inertial Fusion (MIF) approach that may potentially lead to a small, low cost fusion reactor/engine assembly [1]. Recent advancements in experimental and theoretical understanding of this concept suggest favorable scaling of fusion power output yield [2]. The magnetic field resulting from the large current compresses the plasma to fusion conditions, and this process can be pulsed over short timescales (10-6 s). This type of plasma formation is widely used in the field of Nuclear Weapons Effects testing in the defense industry, as well as in fusion energy research. A Z-Pinch propulsion concept was designed for a vehicle based on a previous fusion vehicle study called "Human Outer Planet Exploration" (HOPE), which used Magnetized Target Fusion (MTF) [3] propulsion. The reference mission is the transport of crew and cargo to Mars and back, with a reusable vehicle. The analysis of the Z-Pinch MIF propulsion system concludes that a 40-fold increase of Isp over chemical propulsion is predicted. An Isp of 19,436 s and thrust of 3812 N s/pulse, along with nearly doubling the predicted payload mass fraction, warrants further development of enabling technologies.
History of HERMES III diode to z-pinch breakthrough and beyond :
Sanford, Thomas Williamlou.
2013-04-01
HERMES III and Z are two flagship accelerators of Sandias pulsed-power program developed to generate intense -ray fields for the study of nuclear radiation effects, and to explore high energy-density physics (including the production of intense x-ray fields for Inertia Confinement Fusion [ICF]), respectively. A diode at the exit of HERMES III converts its 20-MeV electron beam into -rays. In contrast, at the center of Z, a z-pinch is used to convert its 20-MA current into an intense burst of x-rays. Here the history of how the HERMES III diode emerged from theoretical considerations to actual hardware is discussed. Next,more » the reverse process of how the experimental discovery of wire-array stabilization in a z-pinch, led to a better theory of wirearray implosions and its application to one of the ICF concepts on Z--the DH (Dynamic Hohlraum) is reviewed. Lastly, the report concludes with how the unexpected axial radiation asymmetry measured in the DH is understood. The first discussion illustrates the evolution of physics from theory-to-observationto- refinement. The second two illustrate the reverse process of observationto- theory-to refinement. The histories are discussed through the vehicle of my research at Sandia, illustrating the unique environment Sandia provides for personal growth and development into a scientific leader.« less
History of HERMES III diode to z-pinch breakthrough and beyond :
Sanford, Thomas Williamlou.
2013-04-01
HERMES III and Z are two flagship accelerators of Sandias pulsed-power program developed to generate intense -ray fields for the study of nuclear radiation effects, and to explore high energy-density physics (including the production of intense x-ray fields for Inertia Confinement Fusion [ICF]), respectively. A diode at the exit of HERMES III converts its 20-MeV electron beam into -rays. In contrast, at the center of Z, a z-pinch is used to convert its 20-MA current into an intense burst of x-rays. Here the history of how the HERMES III diode emerged from theoretical considerations to actual hardware is discussed. Next, the reverse process of how the experimental discovery of wire-array stabilization in a z-pinch, led to a better theory of wirearray implosions and its application to one of the ICF concepts on Z--the DH (Dynamic Hohlraum) is reviewed. Lastly, the report concludes with how the unexpected axial radiation asymmetry measured in the DH is understood. The first discussion illustrates the evolution of physics from theory-to-observationto- refinement. The second two illustrate the reverse process of observationto- theory-to refinement. The histories are discussed through the vehicle of my research at Sandia, illustrating the unique environment Sandia provides for personal growth and development into a scientific leader.
Reversed current structure in a Z-pinch plasma
Lee; Kim; Kim
2000-10-30
The current profile of a Z-pinch plasma is investigated using a one-dimensional magnetohydrodynamic code. Simulation results reveal the formation of a reversed current profile, its propagation, and an ejection of plasma at boundary region, which have been observed in previous experiments. A new physical mechanism is proposed to account for such phenomena. The physical mechanism involves the propagation of a shock wave. It is found that a reversed current profile appears when a shock wave reflected at axis expands in a compressing plasma column.
Ion Beam Driven Shock Device Using Accelerated High Density Plasmoid by Phased Z-Pinch
NASA Astrophysics Data System (ADS)
Horioka, Kazuhiko; Aizawa, Tatsuhiko; Tsuchida, Minoru
1997-07-01
Different from three methods to generate high shock pressure by acceleration of high density plasma or particles (intense ion beams, plasma gun and rail gun) having their intrinsic deficiencies, new frontier is proposed to propel the shock physics and chemistry by using the high density plasma. In the present paper, new scheduled Z-pinch method is developed as a new device to generate high shock pressure. In the present method, plasma density can be compressed to the order of 10^18 to 10^19 cm-3, and high density plasma can be accelerated by zippering together with axial shock pressure, resulting in high-velocity launching of flyer. In the present paper, systematic experimental works are performed to demonstrate that high energy plasma flow can be electro-magnetically driven by the scheduled capillary Z-pinch, and to characterize the ion velocity and its current density. The estimated value of ion speed from the plasma-measurement reaches to 7 x 10^7 cm/s corresponding to 70 to 100 KeV for Ar. Copper flyer can be shot with the velocity range from 1km/s to 3km/s in the standard condition.
Time-Resolved Thomson Scattering On Gas-Puff Z-Pinch Plasmas At Pinch Time
NASA Astrophysics Data System (ADS)
Rocco, Sophia; Banasek, Jacob; Potter, William; Kusse, Bruce; Hammer, David
2017-10-01
The conditions and dynamics of neon gas puff z-pinch plasmas at pinch time are studied on COBRA, Cornell's pulsed power generator (current rise time of 240ns and approximately 0.9MA peak current). Radial tailoring of the gas puff mass-density profile using a triple-nozzle coaxial valve (two annular gas puffs and a central jet) enables production of both more stable and less stable (in regards to the magneto-Rayleigh Taylor instability) z-pinch implosions. A 526.5nm, 10J Thomson scattering diagnostic laser enables probing of the flow dynamics and plasma conditions of these implosions with both spatial and temporal resolution. The 3ns laser pulse is split in half, one of the beams delayed by up to 10ns relative to the other. This allows observation of streaked spectra for a total consecutive time of 6ns, providing sub-nanosecond resolution of the evolution of the pinch through stagnation. A gated spectrometer provides spatially-resolved spectra at the same time for comparison. Extreme ultraviolet imaging and laser schlieren imaging at multiple times enable monitoring of the implosion morphology as a function of time. Work supported by NNSA SSAP under DOE Cooperative Agreement No. DE-NA0001836 and Lawrence Livermore National Laboratory subContract No. B619181.
Performance of a Liner-on-Target Injector for Staged Z-Pinch Experiments
NASA Astrophysics Data System (ADS)
Conti, F.; Valenzuela, J. C.; Narkis, J.; Krasheninnikov, I.; Beg, F.; Wessel, F. J.; Ruskov, E.; Rahman, H. U.; McGee, E.
2016-10-01
We present the design and characterization of a compact liner-on-target injector, used in the Staged Z-pinch experiments conducted on the UNR-NTF Zebra Facility. Previous experiments and analysis indicate that high-Z gas liners produce a uniform and efficient implosion on a low-Z target plasma. The liner gas shell is produced by an annular solenoid valve and a converging-diverging nozzle designed to achieve a collimated, supersonic, Mach-5 flow. The on-axis target is produced by a coaxial plasma gun, where a high voltage pulse is applied to ionize neutral gas and accelerate the plasma by the J-> × B-> force. Measurements of the liner and target dynamics, resolved by interferometry in space and time, fast imaging, and collection of the emitted light, are presented. The results are compared to the predictions from Computational Fluid Dynamics and MHD simulations that model the injector. Optimization of the design parameters, for upcoming Staged Z-pinch experiments, will be discussed. Advanced Research Projects Agency - Energy, DE-AR0000569.
Z-Pinch Driven Isentropic Compression for Inertial Fusion
Asay, J.R.; Hall, C.A.; Holland, K.G.
1999-02-01
The achievement of high gain with inertial fusion requires the compression of hydrogen isotopes to high density and temperatures. High densities can be achieved most efficiently by isentropic compression. This requires relatively slow pressure pulses on the order of 10-20 nanoseconds; however, the pressure profile must have the appropriate time. We present 1-D numerical simulations that indicate such a pressure profile can be generated by using pulsed power driven z pinches. Although high compression is calculated, the initial temperature is too low for ignition. Ignition could be achieved by heating a small portion of this compressed fuel with a shortmore » (-10 ps) high power laser pulse as previously described. Our 1-D calculations indicate that the existing Z-accelerator could provide the driving current (-20 MA) necessary to compress fuel to roughly 1500 times solid density. At this density the required laser energy is approximately 10 kJ. Multidimensional effects such as the Rayleigh-Taylor were not addressed in this brief numerical study. These effects will undoubtedly lower fuel compression for a given chive current. Therefore it is necessary to perform z-pinch driven compression experiments. Finally, we present preliminary experimental data from the Z-accelerator indicating that current can be efficiently delivered to appropriately small loads (- 5 mm radius) and that VISAR can be used measure high pressure during isentropic compression.« less
Stimulated VUV radiation from Z-pinch necks
NASA Astrophysics Data System (ADS)
Koshelev, K. N.; Antsiferov, P. S.; Dorokhin, L. A.; Sidelnikov, Yu. V.
1997-05-01
Developing plasma foci and neck-type instabilities in Z-pinches emit beams or jets of high velocity plasma. Their highly charged ions can cause population inversion through selective charge exchange with colder ions in a target. Recent models [1] show population inversion in a disk-shaped region that moves along the discharge axis slightly slower than the plasma jet. The population inversion between n=4 and n=3 of Li-like-like ions of elements with nuclear charge Z=6-10 is high enough to see stimulated emission effects perpendicular to the discharge axis for pinches with currents of about a few hundred kA. Time-resolved and spatially resolved spectra in the vicinity of 4-3 transitions (50-52 nm) of the Li-like ion O VI were taken on the gas-puff Z-pinch installation "MP-100" [2]. Simultaneous VUV imaging of the plasma column was done using a combination of pinhole and multiframe MCP detector gated with 5 ns. The intensity ratio between 3p-4d (49.8 nm) and 3d-4f (52.0 nm) components is close to the equilibrium value 2.7 during compression, but it increases twice or three-fold when the "neck" develops. Spatially resolved measurements show that plasma regions with an anomalous ratio of these two lines are strongly correlated with the position of "neck" type instabilities.
PIC Simulations of Dense Plasma Focus Z-pinch
NASA Astrophysics Data System (ADS)
Schmidt, A.; Blackfield, D.; Tang, V.; Welch, D.; Rose, D.
2011-10-01
Dense Plasma Focus (DPF) Z-pinches are abundant sources of radiation, including neutrons, x-rays, and energetic electron and ion beams. Energetic protons and deuterons up to 10 MeV have been observed from cm-scale-length pinches, implying average acceleration gradients up to 1 GV/m. Gradients of this magnitude could potentially be exploited in the design of a compact accelerator. However, the physical mechanisms behind these immense electric fields are not well understood and thus DPF design cannot currently be optimized to maximize these gradients. At LLNL, we have assembled a DPF Z-pinch experiment and will be using a 4 MV ion probe beam to directly measure pinch-induced gradients. LSP, a fully relativistic electromagnetic Particle-In-Cell (PIC) code is used to perform time-dependent simulations of the pinch phase of the DPF and to gain insight into the origin and evolution of the large accelerating fields. LSP can be used in 2D or 3D geometries and can model the ions kinetically with fluid electrons (hybrid model) or model both species kinetically (fully kinetic model). We present results from both pressure and sheath width scans using LSP. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by the Laboratory Directed Research and Development Program (11-ERD-063) at LLNL.
Tungsten Z-Pinch Long Implosions on the Saturn Generator
DOUGLAS,MELISSA R.; DEENEY,CHRISTOPHER; SPIELMAN,RICK B.; COVERDALE,CHRISTINE A.; RODERICK,N.F.; HAINES,M.G.
1999-11-05
Recent success on the Saturn and Z accelerators at Sandia National Laboratories have demonstrated the ability to scale z-pinch parameters to increasingly larger current pulsed power facilities. Next generation machines will require even larger currents (>20 MA), placing further demands on pulsed power technology. To this end, experiments have been carried out on Saturn operating in a long pulse mode, investigating the potential of lower voltages and longer implosion times while still maintaining pinch fidelity. High wire number, 25 mm diameter tungsten arrays were imploded with implosion times ranging from 130 to 240 ns. The results were comparable to those observed in the Saturn short pulse mode, with risetimes on the order of 4.5 to 6.5 ns. Experimental data will be presented, along with two dimensional radiation magnetohydrodynamic simulations used to explain and reproduce the experiment.
Heterogeneous equilibrium states of emitting Z-pinches
NASA Astrophysics Data System (ADS)
Bobrova, N. A.; Razinkova, T. L.; Sasorov, P. V.
Physical conditions, under which the existence of highly heterogeneous equilibrium state of emitting Z-pinches is possible, are determined qualitatively. In the found range of parameters the system of equations is formulated, solutions of which describe the equilibria mentioned. For the purpose the radiation model of heavy element plasma (20 less than or equal to Z less than or equal to 80) is developed, which takes into account in the framework of local thermodynamic equilibrium the n,l - greater than n, l-1 transitions and obstruction of radiating ability in the range of low temperatures, where the transitions mentioned are not excited. In the model formulated in case of coordinated increase in the pinch and current per unit length mass the role of heat conductivity decreases but no radiation collapse of the pinch central part takes place, which leads inevitably to pinch plasma stratification into cold and hot phases.
Conceptual Design of a Z-Pinch Fusion Propulsion System
NASA Technical Reports Server (NTRS)
Adams, Robert; Polsgrove, Tara; Fincher, Sharon; Fabinski, Leo; Maples, Charlotte; Miernik, Janie; Stratham, Geoffrey; Cassibry, Jason; Cortez, Ross; Turner, Matthew;
2010-01-01
This slide presentation reviews a project that aims to develop a conceptual design for a Z-pinch thruster, that could be applied to develop advanced thruster designs which promise high thrust/high specific impulse propulsion. Overviews shows the concept of the design, which use annular nozzles with deuterium-tritium (D-T) fuel and a Lithium mixture as a cathode, Charts show the engine performance as a function of linear mass, nozzle performance (i.e., plasma segment trajectories), and mission analysis for possible Mars and Jupiter missions using this concept for propulsion. Slides show views of the concepts for the vehicle configuration, thrust coil configuration, the power management system, the structural analysis of the magnetic nozzle, the thermal management system, and the avionics suite,
Dynamics of quasi-spherical Z-pinch implosions with mass redistribution and displacement modification
Zhang Yang; Ding Ning; Sun Shunkai; Xue Chuang; Ning Cheng; Xiao Delong; Huang Jun; Li Zhenghong
2012-12-15
Implosions of (quasi-)spherical loads with mass redistribution and displacement modification are investigated numerically. Both methods can theoretically counterbalance the nonuniformity of magnetic pressure along the load surface and realize quasi-spherical Z-pinch implosions. Mass redistribution is feasible for spherical loads with large radius and weight, while the displacement modification is more suitable for light loads, such as those composed of wire arrays. Simulation results suggest that, for mass redistributed spherical loads, wall instabilities induced by polar mass flows will deform the imploding shell. For prolate spherical loads, in which the wall instability cannot develop, the kinetic energy distribution is disturbed at high latitude. These passive behaviors and their possible mitigation methods, such as reshaping the electrode, are investigated numerically in this paper.
Magnetohydrodynamic simulation of solid-deuterium-initiated Z-pinch experiments
Sheehey, Peter Trogdon
1994-02-01
Solid-deuterium-initiated Z-pinch experiments are numerically simulated using a two-dimensional resistive magnetohydrodynamic model, which includes many important experimental details, such as ``cold-start`` initial conditions, thermal conduction, radiative energy loss, actual discharge current vs. time, and grids of sufficient size and resolution to allow realistic development of the plasma. The alternating-direction-implicit numerical technique used meets the substantial demands presented by such a computational task. Simulations of fiber-initiated experiments show that when the fiber becomes fully ionized rapidly developing m=0 instabilities, which originated in the coronal plasma generated from the ablating fiber, drive intense non-uniform heating and rapid expansion of the plasma column. The possibility that inclusion of additional physical effects would improve stability is explored. Finite-Larmor-radius-ordered Hall and diamagnetic pressure terms in the magnetic field evolution equation, corresponding energy equation terms, and separate ion and electron energy equations are included; these do not change the basic results. Model diagnostics, such as shadowgrams and interferograms, generated from simulation results, are in good agreement with experiment. Two alternative experimental approaches are explored: high-current magnetic implosion of hollow cylindrical deuterium shells, and ``plasma-on-wire`` (POW) implosion of low-density plasma onto a central deuterium fiber. By minimizing instability problems, these techniques may allow attainment of higher temperatures and densities than possible with bare fiber-initiated Z-pinches. Conditions for significant D-D or D-T fusion neutron production may be realizable with these implosion-based approaches.
Staged Z-pinch Experiments on Cobra and Zebra
NASA Astrophysics Data System (ADS)
Wessel, Frank J.; Anderson, A.; Banasek, J. T.; Byvank, T.; Conti, F.; Darling, T. W.; Dutra, E.; Glebov, V.; Greenly, J.; Hammer, D. A.; Potter, W. M.; Rocco, S. V.; Ross, M. P.; Ruskov, E.; Valenzuela, J.; Beg, F.; Covington, A.; Narkis, J.; Rahman, H. U.
2017-10-01
A Staged Z-pinch (SZP), configured as a pre-magnetized, high-Z (Ar, or Kr) annular liner imploding onto a low-Z (H, or D) target, was tested on the Cornell University, Cobra Facility and the University of Nevada, Reno, Zebra Facility; each characterized similarly by a nominal 1-MA current and 100-ns risetime while possessing different diagnostic packages. XUV-fast imaging reveals that the SZP implosion dynamics is similar on both machines and that it is more stable with an axial (Bz) magnetic field, a target, or both, than without. On Zebra, where neutron production is possible, reproducible thermonuclear (DD) yields were recorded at levels in excess of 109/shot. Flux compression in the SZP is also expected to produce magnetic field intensities of the order of kilo-Tesla. Thus, the DD reaction produced tritions should also yield secondary DT neutrons. Indeed, secondaries are measured above the noise threshold at levels approaching 106/shot. Funded by the Advanced Research Projects Agency - Energy, under Grant Number DE-AR0000569.
Analytic model for the dynamic Z-pinch
Piriz, A. R., E-mail: roberto.piriz@uclm.es; Sun, Y. B.; Tahir, N. A.
2015-06-15
A model is presented for describing the cylindrical implosion of a shock wave driven by an accelerated piston. It is based in the identification of the acceleration of the shocked mass with the acceleration of the piston. The model yields the separate paths of the piston and the shock. In addition, by considering that the shocked region evolves isentropically, the approximate profiles of all the magnitudes in the shocked region are obtained. The application to the dynamic Z-pinch is presented and the results are compared with the well known snowplow and slug models which are also derived as limiting casesmore » of the present model. The snowplow model is seen to yield a trajectory in between those of the shock and the piston. Instead, the neglect of the inertial effects in the slug model is seen to produce a too fast implosion, and the pressure uniformity is shown to lead to an unphysical instantaneous piston stopping when the shock arrives to the axis.« less
Diagnostics for Z-pinch implosion experiments on PTS
Ren, X. D., E-mail: amosrxd@163.com; Huang, X. B., E-mail: amosrxd@163.com; Zhou, S. T., E-mail: amosrxd@163.com
2014-12-15
The preliminary experiments of wire array implosion were performed on PTS, a 10 MA z-pinch driver with a 70 ns rise time. A set of diagnostics have been developed and fielded on PTS to study pinch physics and implosion dynamics of wire array. Radiated power measurement for soft x-rays was performed by multichannel filtered x-ray diode array, and flat spectral responses x-ray diode detector. Total x-ray yield was measured by a calibrated, unfiltered nickel bolometer which was also used to obtain pinch power. Multiple time-gated pinhole cameras were used to produce spatial-resolved images of x-ray self-emission from plasmas. Two time-integratedmore » pinhole cameras were used respectively with 20-μm Be filter and with multilayer mirrors to record images produced by >1-keV and 277±5 eV self-emission. An optical streak camera was used to produce radial implosion trajectories, and an x-ray streak camera paired with a horizontal slit was used to record a continuous time-history of emission with one-dimensional spatial resolution. A frequency-doubled Nd:YAG laser (532 nm) was used to produce four frame laser shadowgraph images with 6 ns time interval. We will briefly describe each of these diagnostics and present some typical results from them.« less
Staged Z-pinch Experiments on the NTF Zebra Facility
NASA Astrophysics Data System (ADS)
Conti, Fabio; Anderson, A.; Darling, T. W.; Dutra, E.; Glebov, V.; Ross, M. P.; Ruskov, E.; Valenzuela, J. C.; Wessel, F. J.; Beg, F.; Covington, A.; Narkis, J.; Rahman, H. U.
2017-10-01
We report results from the latest Staged Z-pinch experiments conducted on the 1 MA, 100 ns Zebra facility at the University of Nevada, Reno. In these experiments, a high-Z annular gas liner (Ar, Kr) with initial radius of 1.2 cm implodes onto a deuterium target on axis. Measurements are presented, including data from pinch current, X-ray photodiodes and PCDs signals, visible streak imaging, XUV gated imaging, laser shadowgraphy, neutron time-of-flight and neutron yield detectors, and preliminary data analysis is discussed. The implosion velocity exceeding 300 km/s, and pinch time are consistent with MHD simulations performed with the MACH2 code. The imaging diagnostics indicates that the target column is more stable than the surrounding liner during the implosion. Primary (DD) neutrons of thermonuclear nature were produced with yields higher than 1x109 per shot, reproducibly. In addition, preliminary neutron time-of-flight results indicate that secondary (DT) neutrons can be produced above the detection threshold. Funded by the Advanced Research Projects Agency - Energy, Grant DE-AR0000569.
Current redistribution and generation of kinetic energy in the stagnated Z pinch
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Anderson, A. A.; Papp, D.; Astanovitskiy, A. L.; Talbot, B. R.; Chittenden, J. P.; Niasse, N.
2013-07-01
The structure of magnetic fields was investigated in stagnated wire-array Z pinches using a Faraday rotation diagnostic at the wavelength of 266 nm. The distribution of current in the pinch and trailing material was reconstructed. A significant part of current can switch from the main pinch to the trailing plasma preheated by x-ray radiation of the pinch. Secondary implosions of trailing plasma generate kinetic energy and provide enhanced heating and radiation of plasma at stagnation. Hot spots in wire-array Z pinches also provide enhanced radiation of the Z pinch. A collapse of a single hot spot radiates 1%-3% of x-ray energy of the Z pinch with a total contribution of hot spots of 10%-30%.
Study of the Internal Structure and Small-Scale Instabilities in the Dense Z Pinch
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Chittenden, J. P.; Altemara, S. D.; Niasse, N.; Hakel, P.; Mancini, R. C.; Papp, D.; Anderson, A. A.
2011-10-01
High-resolution laser diagnostics at the wavelength of 266 nm were applied for the investigation of Z pinches at the 1-MA generator. The internal structure of the stagnated Z pinches was observed in unprecedented detail. A dense pinch with strong instabilities was seen inside the column of the trailing plasma. Kink instability, disruptions, and micropinches were seen at the peak of the x-ray pulse and later in time. The three-dimensional structure of the stagnated Z pinch depends on the initial wire-array configuration and implosion scenario. Small-scale density perturbations were found in the precursor plasma and in the stagnated Z pinch. Development of instabilities is in agreement with three-dimensional magnetohydrodynamic simulations.
Calamy, H.; Hamann, F.; Lassalle, F.
2006-01-05
Centre d'Etudes de Gramat (France) has developed an efficient long implosion time (800 ns) Aluminum plasma radiation source (PRS). Based on the LTD technology, the SPHINX facility is developed as a 1-3MJ, 1{mu}s rise time, 4-10 MA current driver. In this paper, it was used in 1MJ, 4MA configuration to drive Aluminum nested wire arrays Z-pinches with K-shell yield up to 20 kJ and a FWHM of the x-ray pulse of about 50 ns. We present latest SPHINX experiments and some of the main physic issues of the microsecond regime. Experimental setup and results are described with the aim ofmore » giving trends that have been obtained. The main features of microsecond implosion of wire arrays can be analyzed thanks to same methods and theories as used for faster Z-pinches. The effect of load polarity was examined. The stability of the implosion , one of the critical point of microsecond wire arrays due to the load dimensions imposed by the time scale, is tackled. A simple scaling from 100 ns Z-pinch results to 800 ns ones gives good results and the use of nested arrays improves dramatically the implosion quality and the Kshell yield of the load. However, additional effects such as the impact of the return current can geometry on the implosion have to be taken into account on our loads. Axial inhomogeneity of the implosion the origin of which is not yet well understood occurs in some shots and impacts the radiation output. The shape of the radiative pulse is discussed and compared with the homogeneity of the implosion. Numerical 2D R-Z and R-{theta} simulations are used to highlight some experimental results and understand the plasma conditions during these microsecond wire arrays implosions.« less
Review of effects of dielectric coatings on electrical exploding wires and Z pinches
NASA Astrophysics Data System (ADS)
Wu, Jian; Li, Xingwen; Li, Mo; Li, Yang; Qiu, Aici
2017-10-01
As the most powerful x-ray source in the laboratories, the wire array Z pinches have been of great relevance to inertial confinement fusions, laboratory astrophysics, and other high-energy density applications. In order to produce x-ray with greater power and higher efficiency, the dynamics of wire array has been investigated extensively, and various methods have been proposed to improve the implosion quality of the wire array. This review focuses on the experimental and theoretical investigations regarding the effects of the dielectric coatings on electrical exploding wires and Z pinches. Since the early 2000, the electrical wire explosion related to the first stage of the wire array Z pinches has been studied extensively, and the results indicated that the dielectric coatings can significantly increase the joule energy deposition into a wire in the initial stage, and even the corona free explosion of tungsten wires can be achieved. Recently, there is an increasing interest in the dynamics of insulated wire array Z pinches. By applying dielectric coatings, the ablation process is suppressed, the x-ray start time is delayed, and the possibility of multi-peak radiation is decreased. This review is organized by the evolution dynamics of wire array Z pinches, and a broad introduction to relevant scientific concepts and various other applications are presented. According to the current research status, the challenges, opportunities and further developments of Z pinch loads using dielectric coatings are proposed to further promote the researches and their applications.
Comparison of 1D stagnation solutions to 3D wire-array Z pinch simulations in absence of radiation
NASA Astrophysics Data System (ADS)
Yu, Edmund; Velikovich, Alexander; Maron, Yitzhak
2013-10-01
In the idealized picture of a Z pinch, a cylindrically symmetric plasma shell implodes towards axis. In this 1D (radial) picture, the resulting stagnation is very efficient: all the kinetic energy of the shell converts to internal energy, as for instance in the Noh shock solution or the homogeneous stagnation flow. If we generalize the problem to 2D by deforming the shell from perfectly circular to oblate, the resulting stagnation will not be as efficient. As in the Hiemenz flow, in which a jet of fluid strikes a rigid flat boundary and squirts out to the sides, the more complicated flows allowed in 2D allow flow kinetic energy to redirect rather than stagnate. With this picture in mind, we might expect the stagnation of a wire-array Z pinch, which in actuality forms a highly distorted 3D imploding plasma, to dissipate its kinetic energy inefficiently due to the lack of symmetry, and be indescribable by means of the idealized 1D stagnation solutions. On the other hand, one might expect that if the imploding plasma is sufficiently messy, the non-uniformities might ``wash out,'' allowing a quasi-1D description of the averaged quantities of plasma. In this work we explore this idea, comparing predictions of 1D stagnation solutions with 3D simulation. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC0 4-94AL85000.
Theoretical z -pinch scaling relations for thermonuclear-fusion experiments
NASA Astrophysics Data System (ADS)
Stygar, W. A.; Cuneo, M. E.; Vesey, R. A.; Ives, H. C.; Mazarakis, M. G.; Chandler, G. A.; Fehl, D. L.; Leeper, R. J.; Matzen, M. K.; McDaniel, D. H.; McGurn, J. S.; McKenney, J. L.; Muron, D. J.; Olson, C. L.; Porter, J. L.; Ramirez, J. J.; Seamen, J. F.; Speas, C. S.; Spielman, R. B.; Struve, K. W.; Torres, J. A.; Waisman, E. M.; Wagoner, T. C.; Gilliland, T. L.
2005-08-01
We have developed wire-array z -pinch scaling relations for plasma-physics and inertial-confinement-fusion (ICF) experiments. The relations can be applied to the design of z -pinch accelerators for high-fusion-yield (˜0.4GJ/shot) and inertial-fusion-energy (˜3GJ/shot) research. We find that (δa/δRT)∝(m/ℓ)1/4(RΓ)-1/2 , where δa is the imploding-sheath thickness of a wire-ablation-dominated pinch, δRT is the sheath thickness of a Rayleigh-Taylor-dominated pinch, m is the total wire-array mass, ℓ is the axial length of the array, R is the initial array radius, and Γ is a dimensionless functional of the shape of the current pulse that drives the pinch implosion. When the product RΓ is held constant the sheath thickness is, at sufficiently large values of m/ℓ , determined primarily by wire ablation. For an ablation-dominated pinch, we estimate that the peak radiated x-ray power Pr∝(I/τi)3/2RℓΦΓ , where I is the peak pinch current, τi is the pinch implosion time, and Φ is a dimensionless functional of the current-pulse shape. This scaling relation is consistent with experiment when 13MA⩽I⩽20MA , 93ns⩽τi⩽169ns , 10mm⩽R⩽20mm , 10mm⩽ℓ⩽20mm , and 2.0mg/cm⩽m/ℓ⩽7.3mg/cm . Assuming an ablation-dominated pinch and that RℓΦΓ is held constant, we find that the x-ray-power efficiency ηx≡Pr/Pa of a coupled pinch-accelerator system is proportional to (τiPr7/9)-1 , where Pa is the peak accelerator power. The pinch current and accelerator power required to achieve a given value of Pr are proportional to τi , and the requisite accelerator energy Ea is proportional to τi2 . These results suggest that the performance of an ablation-dominated pinch, and the efficiency of a coupled pinch-accelerator system, can be improved substantially by decreasing the implosion time τi . For an accelerator coupled to a double-pinch-driven hohlraum that drives the implosion of an ICF fuel capsule, we find that the accelerator power and energy
Charger 1: A New Facility for Z-Pinch Research
NASA Technical Reports Server (NTRS)
Taylor, Brian; Cassibry, Jason; Cortez, Ross; Doughty, Glen; Adams, Robert; DeCicco, Anthony
2017-01-01
Charger 1 is a multipurpose pulsed power laboratory located on Redstone Arsenal, with a focus on fusion propulsion relevant experiments involving testing z-pinch diodes, pulsed magnetic nozzle and other related physics experiments. UAH and its team of pulsed power researchers are investigating ways to increase and optimize fusion production from Charger 1. Currently the team has reached high-power testing. Due to the unique safety issues related to high power operations the UAH/MSFC team has slowed repair efforts to develop safety and operations protocols. The facility is expected to be operational by the time DZP 2017 convenes. Charger 1 began life as the Decade Module 2, an experimental prototype built to prove the Decade Quad pinch configuration. The system was donated to UAH by the Defense Threat Reduction Agency (DRTA) in 2012. For the past 5 years a UAH/MSFC/Boeing team has worked to refurbish, assemble and test the system. With completion of high power testing in summer 2017 Charger 1 will become operational for experimentation. Charger 1 utilizes a Marx Bank of 72 100-kV capacitors that are charged in parallel and discharged in series. The Marx output is compressed to a pulse width of approximately 200 ns via a pulse forming network of 32 coaxial stainless steel tubes using water as a dielectric. After pulse compression a set of SF6 switches are triggered, allowing the wave front to propagate through the output line to the load. Charger 1 is capable of storing 572-kJ of energy and time compressing discharge to less than 250 ns discharge time producing a discharge of about 1 TW of discharge with 1 MV and 1 MA peak voltage and current, respectively. This capability will be used to study energy yield scaling and physics from solid density target as applied to advanced propulsion research.
Radiatively cooled supersonic plasma jets generated in wire array Z-pinches
NASA Astrophysics Data System (ADS)
Bland, Simon; Lebedev, Sergey; Chittenden, Jerry; Beg, F. N.; Ciardi, A.; Haines, M. G.
2000-10-01
We will present experiments on the generation of a highly supersonic plasma jet by a convergent plasma flow, produced by electrodynamic acceleration of plasma in a conical array of fine metallic wires (a modification of the wire array Z-pinch [1]). Stagnation of the plasma flow on the axis of symmetry forms a standing conical shock, which effectively collimates the flow in the axial direction. This scenario is essentially similar to that discussed by Cantó et al. [2] as a possible, purely hydrodynamic mechanism of jet formation in young stellar objects. Experiments using different materials (Al, Fe and W) show that a highly supersonic (M 20) and a well-collimated jet is generated when the radiative cooling rate of the plasma is significant. The interaction of this jet with a plasma target could be used for scaled [3] laboratory astrophysical experiments on hydrodynamic instabilities in decelerated plasma flow. [1] M.K. Matzen, Phys. Plasmas v.4, 1519 (1997) [2] J. Cantó, et. al. Astron. Astrophys. v.192, 287 (1994). [3] D. Ryutov et al., ApJ, v.518, 821 (1999)
Magnetized jets and shocks in radial foil Z-pinches: experiments and numerical simulations
NASA Astrophysics Data System (ADS)
Lebedev, S. V.; Suzuki-Vidal, F.; Pickworth, L. A.; Swadling, G. F.; Burdiak, G.; Skidmore, J.; Hall, G. N.; Bennett, M.; Bland, S. N.; Chittenden, J. P.; de Grouchy, P.; Derrick, J.; Hare, J.; Parker, T.; Sciortino, F.; Suttle, L.; Ciardi, A.; Rodriguez, R.; Gil, J. M.; Espinosa, G.; Hansen, E.; Frank, A.; Music, J.
2014-10-01
Different variations of the radial foil Z-pinch configuration have been investigated in the recent years on the MAGPIE generator (1.4 MA, 250 ns), particularly using over-massed aluminum foils with thicknesses of ~15 μm. This setup is characterized by a highly collimated, supersonic jet on the axis of the foil surrounded by low-density ablated plasma, both moving with the same axial velocity of ~60 km/s. Latest results show that the formation and collimation of the jet is directly related to toroidal magnetic field advected with the flow. We present new experimental results that include Thomson scattering measurements of plasma flow velocity and temperature, and a first study on the effect of foil material on jet formation. The effect of advected toroidal magnetic field in the plasma flow is clearly evidenced using a new experimental configuration that produces counter-streaming jets. The results are characterized by the formation of shocks in which the effect of magnetic field and radiative cooling are significant. The setup also allows controlling the polarity of the advected fields at the interaction point between the counter-streaming flows, and results from experiments and numerical simulations will be presented and discussed.
The anisotropic redistribution of free energy for gyrokinetic plasma turbulence in a Z-pinch
NASA Astrophysics Data System (ADS)
Navarro, Alejandro Bañón; Teaca, Bogdan; Jenko, Frank
2016-04-01
For a Z-pinch geometry, we report on the nonlinear redistribution of free energy across scales perpendicular to the magnetic guide field, for a turbulent plasma described in the framework of gyrokinetics. The analysis is performed using a local flux-surface approximation, in a regime dominated by electrostatic fluctuations driven by the entropy mode, with both ion and electron species being treated kinetically. To explore the anisotropic nature of the free energy redistribution caused by the emergence of zonal flows, we use a polar coordinate representation for the field-perpendicular directions and define an angular density for the scale flux. Positive values for the classically defined (angle integrated) scale flux, which denote a direct energy cascade, are shown to be also composed of negative angular sections, a fact that impacts our understanding of the backscatter of energy and the way in which it enters the modeling of sub-grid scales for turbulence. A definition for the flux of free energy across each perpendicular direction is introduced as well, which shows that the redistribution of energy in the presence of zonal flows is highly anisotropic.
The anisotropic redistribution of free energy for gyrokinetic plasma turbulence in a Z-pinch
Navarro, Alejandro Bañón, E-mail: banon@physics.ucla.edu; Jenko, Frank, E-mail: jenko@physics.ucla.edu; Teaca, Bogdan, E-mail: bogdan.teaca@coventry.ac.uk
2016-04-15
For a Z-pinch geometry, we report on the nonlinear redistribution of free energy across scales perpendicular to the magnetic guide field, for a turbulent plasma described in the framework of gyrokinetics. The analysis is performed using a local flux-surface approximation, in a regime dominated by electrostatic fluctuations driven by the entropy mode, with both ion and electron species being treated kinetically. To explore the anisotropic nature of the free energy redistribution caused by the emergence of zonal flows, we use a polar coordinate representation for the field-perpendicular directions and define an angular density for the scale flux. Positive values formore » the classically defined (angle integrated) scale flux, which denote a direct energy cascade, are shown to be also composed of negative angular sections, a fact that impacts our understanding of the backscatter of energy and the way in which it enters the modeling of sub-grid scales for turbulence. A definition for the flux of free energy across each perpendicular direction is introduced as well, which shows that the redistribution of energy in the presence of zonal flows is highly anisotropic.« less
Study of instabilities in wire-array Z pinches at stagnation
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Chittenden, J. P.; Mancini, R. C.; Papp, D.; Niasse, N.; Altemara, S. D.; Anderson, A. A.
2012-10-01
Stagnation of the wire array Z pinches was studied at a 1 MA generator with imaging UV and x-ray diagnostics. Cylindrical, linear, and star wire-array Z pinches present different sets of instabilities seeded to the pinch during implosion. Compact cylindrical wire arrays implode to Z-pinches with m=0 necks associated with bright spots on x-ray images. The electron temperature of bright spots measured with K-shell spectroscopy is higher by 20-40% compared to cold areas. Maximum x-ray power is generated by Z pinches with strong instabilities. Fast plasma motion with a velocity >100 km/s was observed in the Z pinch at stagnation with two-frame shadowgraphy. Plasma instabilities may present a mechanism for conversion of magnetic energy to kinetic energy. Comparison of the implosions in small-diameter cylindrical and star wire array shows that the secondary implosion of non-imploded peripheral plasma prolongs the stagnation stage and provides the enhanced x-ray production. Development of instabilities in wire arrays is in agreement with 3D MHD Gorgon simulations.
Gas puff Z-pinch implosions with external Bz field on COBRA
NASA Astrophysics Data System (ADS)
Qi, N.; de Grouchy, P.; Schrafel, P. C.; Atoyan, L.; Potter, W. M.; Cahill, A. D.; Gourdain, P.-A.; Greenly, J. B.; Hammer, D. A.; Hoyt, C. L.; Kusse, B. R.; Pikuz, S. A.; Shelkovenko, T. A.
2014-12-01
We present preliminary experimental results on mitigating Magneto-Rayleigh-Taylor (MRT) instabilities by applying an external Bz field. The experiments were conducted on the 1-MA, 200-ns COBRA generator at Cornell University. In the experiments, a triple-nozzle was used to produce z-pinch loads from concentric outer and inner annular gas puffs and a center gas puff column. A single coil was used to produce a Bz field in the pinch region. We have used two 4-frame 2-ns gated EUV cameras to obtain images of the imploding plasmas, in which the MRT instabilities were observed. The MRT instabilities can grow when the plasma accelerates toward the axis. With a triple gas puff (outer, inner and center puff), reduced acceleration or de-acceleration of the imploding plasma occurred when the outer puff plasma imploded onto the inner annular puff plasma resulting a relatively stable implosion. In the absent of the inner annular gas puff, the imploding outer annular plasma continued to accelerate toward the axis. Large turbulent flares at the edge of the implosion or pinch plasma were observed. The implosion was not stable. To stabilize the implosion without the inner gas puff, a Bz field was applied. This external Bz field was compressed by the outer imploding plasma shell. A relatively stable implosion was observed. Increasing the Bz field to 2-kG resulted in a relatively fatter pinch plasma.
Staged Z-pinch experiments on the Mega-Ampere current driver COBRA
NASA Astrophysics Data System (ADS)
Valenzuela, Julio; Banasek, Jacob; Byvank, Thomas; Conti, Fabio; Greenly, John; Hammer, David; Potter, William; Rocco, Sophia; Ross, Michael; Wessel, Frank; Narkis, Jeff; Rahman, Hafiz; Ruskov, Emil; Beg, Farhat
2017-10-01
Experiments were conducted on the Cornell's 1 MA, 100 ns current driver COBRA with the goal of better understanding the Staged Z-pinch physics and validating MHD codes. We used a gas injector composed of an annular (1.2 cm radius) high atomic number (e.g., Ar or Kr) gas-puff and an on-axis plasma gun that delivers the ionized hydrogen target. Liner implosion velocity and stability were studied using laser shadowgraphy and interferometry as well as XUV imaging. From the data, the signature of the MRT instability and zippering effect can be seen, but time integrated X-ray imaging show a stable target plasma. A key component of the experiment was the use of optical Thomson scattering (TS) diagnostics to characterize the liner and target plasmas. By fitting the experimental scattered spectra with synthetic data, electron and ion temperature as well as density can be obtained. Preliminary analysis shows significant scattered line broadening from the plasma on-axis ( 0.5 mm diameter) which can be explained by either a low temperature H plasma with Te =Ti =75eV, or by a hot plasma with Ti =3keV, Te =350eV if an Ar-H mixture is present with an Ar fraction higher than 10%. Funded by the Advanced Research Projects Agency - Energy, DE-AR0000569.
Staged Z-pinch Experiments at the 1MA Zebra pulsed-power generator: Neutron measurements
NASA Astrophysics Data System (ADS)
Ruskov, Emil; Darling, T.; Glebov, V.; Wessel, F. J.; Anderson, A.; Beg, F.; Conti, F.; Covington, A.; Dutra, E.; Narkis, J.; Rahman, H.; Ross, M.; Valenzuela, J.
2017-10-01
We report on neutron measurements from the latest Staged Z-pinch experiments at the 1MA Zebra pulsed-power generator. In these experiments a hollow shell of argon or krypton gas liner, injected between the 1 cm anode-cathode gap, compresses a deuterium plasma target of varying density. Axial magnetic field Bz <= 2 kGs, applied throughout the pinch region, stabilizes the Rayleigh-Taylor instability. The standard silver activation diagnostics and 4 plastic scintillator neutron Time of Flight (nTOF) detectors are augmented with a large area ( 1400 cm2) liquid scintillator detector to which fast gatedPhotek photomultipliers are attached. Sample data from these neutron diagnostics systems is presented. Consistently high neutron yields YDD >109 are measured, with highest yield of 2.6 ×109 . A pair of horizontally and vertically placed plastic scintillator nTOFs suggest isotropic i.e. thermonuclear origin of the neutrons produced. nTOF data from the liquid scintillator detector was cross-calibrated with the silver activation detector, and can be used for accurate calculation of the neutron yield. Funded by the Advanced Research Projects Agency - Energy, under Grant Number DE-AR0000569.
Effect of driver impedance on dense plasma focus Z-pinch neutron yield
Sears, Jason, E-mail: sears8@llnl.gov, E-mail: schmidt36@llnl.gov; Link, Anthony, E-mail: sears8@llnl.gov, E-mail: schmidt36@llnl.gov; Schmidt, Andrea, E-mail: sears8@llnl.gov, E-mail: schmidt36@llnl.gov
2014-12-15
The Z-pinch phase of a dense plasma focus (DPF) heats the plasma by rapid compression and accelerates ions across its intense electric fields, producing neutrons through both thermonuclear and beam-target fusion. Driver characteristics have empirically been shown to affect performance, as measured by neutron yield per unit of stored energy. We are exploring the effect of driver characteristics on DPF performance using particle-in-cell (PIC) simulations of a kJ scale DPF. In this work, our PIC simulations are fluid for the run-down phase and transition to fully kinetic for the pinch phase, capturing kinetic instabilities, anomalous resistivity, and beam formation duringmore » the pinch. The anode-cathode boundary is driven by a circuit model of the capacitive driver, including system inductance, the load of the railgap switches, the guard resistors, and the coaxial transmission line parameters. It is known that the driver impedance plays an important role in the neutron yield: first, it sets the peak current achieved at pinch time; and second, it affects how much current continues to flow through the pinch when the pinch inductance and resistance suddenly increase. Here we show from fully kinetic simulations how total neutron yield depends on the impedance of the driver and the distributed parameters of the transmission circuit. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for neutron source applications.« less
Measurements of high energy photons in Z-pinch experiments on primary test stand
Si, Fenni, E-mail: sifenni@163.com; Zhang, Chuanfei; Xu, Rongkun
2015-08-15
High energy photons are measured for the first time in wire-array Z-pinch experiments on the Primary Test Stand (PTS) which delivers a current up to 8 MA with a rise time of 70 ns. A special designed detecting system composed of three types of detectors is used to measure the average energy, intensity, and pulse waveform of high energy photons. Results from Pb-TLD (thermoluminescence dosimeter) detector indicate that the average energy is 480 keV (±15%). Pulse shape of high energy photons is measured by the photodiode detector consisted of scintillator coupled with a photodiode, and it is correlated with softmore » x-ray power by the same timing signal. Intensity is measured by both TLD and the photodiode detector, showing good accordance with each other, and it is 10{sup 10} cm{sup −2} (±20%) at 2 m in the horizontal direction. Measurement results show that high energy photons are mainly produced in pinch regions due to accelerated electrons. PTS itself also produces high energy photons due to power flow electrons, which is one order smaller in amplitude than those from pinch region.« less
Gas puff Z-pinches with deuterium-krypton gas mixtures
NASA Astrophysics Data System (ADS)
Darling, Timothy; McKee, Erik; Covington, Aaron; Ivanov, Vladimir; Wessel, Frank; Rahman, Hafiz
2015-11-01
We discuss experiments with single-shell, pure and mixed-gas loads on the zebra pulsed-power generator at the Nevada Terawatt Facility (NTF). These experiments are modeled using the MACH2 code and provide input and benchmarking for further models and experiments on upcoming staged Z-pinch (SZP) studies under an ARPA-E program. The 1MA-70ns rise time discharge of Zebra produces bursts of both high and low energy X-rays and neutrons if deuterium gas is present. The gas is injected from the (grounded) anode to cathode as an expanding cylindrical shell of approximately 4cm diameter. A pulsed valve and a flow-forming nozzle determine the details of the gas target geometry which is imaged as a density map using a UV excited fluorescent tracer (LIF). The gases imaged are pure Kr and D2 and binary mixtures thereof. A pure D2 pinch produces a (yet to be optimized) neutron yield in the 1e10 regime. Additional diagnostics include a 2-frame Schlieren 1064nm IR imaging diagnostic, which provides information on the implosion dynamics of the pinch. Support for this work comes from DOE/NNSA (grant # DE-NA0002075) and the ARPA-E ALPHA program.
Spectroscopic Study of Neon Z-Pinch Plasma for Sodium-Neon Photopumping Experiments
1992-01-06
plasma through the hydrogen-like state; then the plasma is allowed to cool as it is confined in a theta pinch . As the plasma recombines, cascading...ral Research Laboratory ® rigton, DC k0375-5000 AD- A244 643 NRL Memorandum Report 6930 Spectroscopic Study of Neon Z- Pinch Plasma for Sodium-Neon...Interim 4. TITLE AND SUBTITLE S. FUNDING NUMBERS Spectroscopic Study of Neon Z- Pinch Plasma for Sodium-Neon Photo- pumping Experiments 6. AUTHOR(S) PE
Recent Improvements to MACH2 and MACH3 For Fast Z-Pinch Modeling
NASA Astrophysics Data System (ADS)
Frese, Sherry D.; Frese, Michael H.
2002-12-01
Many recent changes in MACH2 have improved the code's accuracy and speed in Z-pinch simulations. New code diagnostics monitoring energy are also useful in running the code efficiently. The changes to MACH3 are less numerous, though they are more sweeping: MACH3's grid is now truly three-dimensional and composed of a multiblock structure of arbitrary hexahedral zones; its difference equations have been upgraded to that new mesh. These new capabilities are currently being applied to wire-array Z-pinch problems.
Oblique shock structures formed during the ablation phase of aluminium wire array z-pinches
Swadling, G. F.; Lebedev, S. V.; Niasse, N.
2013-02-15
A series of experiments has been conducted in order to investigate the azimuthal structures formed by the interactions of cylindrically converging plasma flows during the ablation phase of aluminium wire array Z pinch implosions. These experiments were carried out using the 1.4 MA, 240 ns MAGPIE generator at Imperial College London. The main diagnostic used in this study was a two-colour, end-on, Mach-Zehnder imaging interferometer, sensitive to the axially integrated electron density of the plasma. The data collected in these experiments reveal the strongly collisional dynamics of the aluminium ablation streams. The structure of the flows is dominated by amore » dense network of oblique shock fronts, formed by supersonic collisions between adjacent ablation streams. An estimate for the range of the flow Mach number (M = 6.2-9.2) has been made based on an analysis of the observed shock geometry. Combining this measurement with previously published Thomson Scattering measurements of the plasma flow velocity by Harvey-Thompson et al.[Physics of Plasmas 19, 056303 (2012)] allowed us to place limits on the range of the ZT{sub e} of the plasma. The detailed and quantitative nature of the dataset lends itself well as a source for model validation and code verification exercises, as the exact shock geometry is sensitive to many of the plasma parameters. Comparison of electron density data produced through numerical modelling with the Gorgon 3D MHD code demonstrates that the code is able to reproduce the collisional dynamics observed in aluminium arrays reasonably well.« less
Oblique shock structures formed during the ablation phase of aluminium wire array z-pinches
NASA Astrophysics Data System (ADS)
Swadling, G. F.; Lebedev, S. V.; Niasse, N.; Chittenden, J. P.; Hall, G. N.; Suzuki-Vidal, F.; Burdiak, G.; Harvey-Thompson, A. J.; Bland, S. N.; De Grouchy, P.; Khoory, E.; Pickworth, L.; Skidmore, J.; Suttle, L.
2013-02-01
A series of experiments has been conducted in order to investigate the azimuthal structures formed by the interactions of cylindrically converging plasma flows during the ablation phase of aluminium wire array Z pinch implosions. These experiments were carried out using the 1.4 MA, 240 ns MAGPIE generator at Imperial College London. The main diagnostic used in this study was a two-colour, end-on, Mach-Zehnder imaging interferometer, sensitive to the axially integrated electron density of the plasma. The data collected in these experiments reveal the strongly collisional dynamics of the aluminium ablation streams. The structure of the flows is dominated by a dense network of oblique shock fronts, formed by supersonic collisions between adjacent ablation streams. An estimate for the range of the flow Mach number (M = 6.2-9.2) has been made based on an analysis of the observed shock geometry. Combining this measurement with previously published Thomson Scattering measurements of the plasma flow velocity by Harvey-Thompson et al. [Physics of Plasmas 19, 056303 (2012)] allowed us to place limits on the range of the Z¯Te of the plasma. The detailed and quantitative nature of the dataset lends itself well as a source for model validation and code verification exercises, as the exact shock geometry is sensitive to many of the plasma parameters. Comparison of electron density data produced through numerical modelling with the Gorgon 3D MHD code demonstrates that the code is able to reproduce the collisional dynamics observed in aluminium arrays reasonably well.
Kalinin, Yu.; Bakshaev, Yu.; Bartov, A.
2006-01-05
A series of experiments has been carried out on the S-300 pulsed power machine (3 MA, 0.15 Ohm, 100 ns), devoted to the study of a section of magnetically insulated vacuum transporting line (MITL), by the current flow density up to 500 MA/cm{sup 2}, by the linear current flow density being up to 6 MA/cm. These parameters fairly correspond to those of the Sandia Laboratories' conceptual project of IFE reactor based on the fast Z-pinch. The goals of experiments were as follows: 1) study of the near-electrode plasma and its effect on the energy transfer; 2) testing the 2-temperature MHDmore » code NPINCH modeling the behavior of near-electrode plasmas. As a result, the conditions of plasma formation and reconnection of the MITL gap have been determined.« less
Struve, Kenneth William; Deeney, Christopher D.; Leeper, Ramon Joe; McDaniel, Dillon Heirman; Nash, Thomas J.; DeGroot, John Stacey; Sanford, Thomas W. L.
2004-08-01
A quasi-spherical z-pinch may directly compress foam or deuterium and tritium in three dimensions as opposed to a cylindrical z-pinch, which compresses an internal load in two dimensions only. Because of compression in three dimensions the quasi-spherical z-pinch is more efficient at doing pdV work on an internal fluid than a cylindrical pinch. Designs of quasi-spherical z-pinch loads for the 28 MA 100 ns driver ZR, results from zero-dimensional (0D) circuit models of quasi-spherical implosions, and results from 1D hydrodynamic simulations of quasi-spherical implosions heating internal fluids will be presented. Applications of the quasi-spherical z-pinch implosions include a high radiation temperature source for radiation driven experiments, a source of neutrons for treating radioactive waste, and a source of fusion energy for a power generator.
Energy balance in a Z pinch with suppressed Rayleigh–Taylor instability
NASA Astrophysics Data System (ADS)
Baksht, R. B.; Oreshkin, V. I.; Rousskikh, A. G.; Zhigalin, A. S.
2018-03-01
At present Z-pinch has evolved into a powerful plasma source of soft x-ray. This paper considers the energy balance in a radiating metallic gas-puff Z pinch. In this type of Z pinch, a power-law density distribution is realized, promoting suppression of Rayleigh–Taylor (RT) instabilities that occur in the pinch plasma during compression. The energy coupled into the pinch plasma, is determined as the difference between the total energy delivered to the load from the generator and the magnetic energy of the load inductance. A calibrated voltage divider and a Rogowski coil were used to determine the coupled energy and the load inductance. Time-gated optical imaging of the pinch plasma showed its stable compression up to the stagnation phase. The pinch implosion was simulated using a 1D two-temperature radiative magnetohydrodynamic code. Comparison of the experimental and simulation results has shown that the simulation adequately describes the pinch dynamics for conditions in which RT instability is suppressed. It has been found that the proportion of the Ohmic heating in the energy balance of a Z pinch with suppressed RT instability is determined by Spitzer resistance and makes no more than ten percent.
O-d energetics scaling models for Z-pinch-driven hohlraums
CUNEO,MICHAEL E.; VESEY,ROGER A.; HAMMER,J.H.
2000-06-08
Wire array Z-pinches on the Z accelerator provide the most intense laboratory source of soft x-rays in the world. The unique combination of a highly-Planckian radiation source with high x-ray production efficiency (15% wall plug), large x-ray powers and energies ( >150 TW, {ge}1 MJ in 7 ns), large characteristic hohlraum volumes (0.5 to >10 cm{sup 3}), and long pulse-lengths (5 to 20 ns) may make Z-pinches a good match to the requirements for driving high-yield scale ICF capsules with adequate radiation symmetry and margin. The Z-pinch driven hohlraum approach of Hammer and Porter [Phys.Plasmas, 6, 2129(1999)] may provide amore » conservative and robust solution to the requirements for high yield, and is currently being studied on the Z accelerator. This paper describes a multiple region, 0-d hohlraum energetic model for Z-pinch driven hohlraums in four configurations. The authors observe consistency between the models and the measured x-ray powers and hohlraum wall temperatures to within {+-}20% in flux, for the four configurations.« less
Lindemuth, Irvin R.
2009-01-21
For approximately four decades, Z-pinches and related geometries have been computationally modeled using unique Alternating Direction Implicit (ADI) numerical methods. Computational results have provided illuminating and often provocative interpretations of experimental results. A number of past and continuing applications are reviewed and discussed.
UV Laser Diagnostics of the 1-MA Z-pinch Plasmas
Altemara, S. D.; Ivanov, V. V.; Astanovitskiy, A. L.; Haboub, A.
2009-01-21
The 532 nm laser diagnostic set at the Zebra generator shows the details of the ablation and stagnation phases in cylindrical, planar, and star-like wire arrays but it cannot show the structure of the stagnated z-pinch and the implosion in small diameter loads, 1-3 mm in diameter. The absorption increment and the refraction angle of the 532 nm laser, when passing through the plasma, are too great to obtain quality images. An ultraviolet probing beam at the wavelength of 266 nm was developed to study small-diameter loads and to investigate the structure of the 1-MA z-pinch. The UV radiation has a much smaller absorption increment and refraction angles in plasmas than the 532 nm light and allows for better imaging of the z-pinch plasmas. Estimates showed that UV probing would be able to probe the high-density z-pinch plasma in experiments on the Zebra generator, and the early results of UV probing on the Zebra generator have shown promise.
High-energy electron acceleration in the gas-puff Z-pinch plasma
Takasugi, Keiichi, E-mail: takasugi@phys.cst.nihon-u.ac.jp; Miyazaki, Takanori; Nishio, Mineyuki
2014-12-15
The characteristics of hard x-ray generation were examined in the gas-puff z-pinch experiment. The experiment on reversing the voltage was conducted. In both of the positive and negative discharges, the x-ray was generated only from the anode surface, so it was considered that the electrons were accelerated by the induced electromagnetic force at the pinch time.
Recent Wire-Array Z-Pinch Experiments at Imperial College
NASA Astrophysics Data System (ADS)
Hall, Gareth; Lebedev, Sergey; Chittenden, Jeremy; Bland, Simon; Suzuki-Vidal, Francisco; Harvey-Thompson, Adam; Swadling, George; Niasse, Nicolas; Palmer, James
2008-11-01
Recent wire-array Z-pinch experiments performed on the MAGPIE generator at Imperial College are presented. Experiments have been conducted using a variety of array configurations, including radial wire arrays, cylindrical arrays, and coiled arrays. This research was sponsored by Sandia National Laboratories, Albuquerque; and the NNSA under DOE Cooperative Agreement DE-F03-02NA00057.
Investigation of the Internal Structure of the Dense Z-Pinch
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Chittenden, J. P.; Altemara, S. D.; Niasse, N.; Hakel, P.; Mancini, R. C.; Papp, D.; Anderson, A. A.; Astanovitskiy, A. L.; Nalajala, V.
2011-10-01
UV laser probing at the wavelength of 266 nm was applied for investigation of wire-array Z-pinches at the Zebra generator. A fine structure of the 1 MA stagnated pinch was observed in unprecedented details. Kink instability with loop-like structures, disruptions, and micropinches were observed in Z-pinches at the peak of the x-ray pulse and later in time. Micropinches with the diameters of 60-90 μm are located inside necks of lower-density plasma. Instability with a period of 70-200 μm was observed on the edges of Z-pinches. Micron-scale density perturbations were observed in the precursor plasma and in the current carrying areas of the dense pinch. A homogeneous Z pinch plasma column was observed in star wire arrays. Development of instabilities was compared with 3D MHD Gorgon simulations. The Gorgon modeling is in good agreement with implosion and stagnation scenarios observed in two very different cylindrical and star wire arrays. Work was supported by the DOE/NNSA under UNR grant DE-FC52-06NA27616.
Low Mass Transmission Lines for Z-Pinch Driven Inertial Fusion
SLUTZ, STEPHEN A.; OLSON, CRAIG L.; PETERSON, PER
2002-01-01
Recyclable transmission lines (RTL) are studied as a means of repetitively driving z pinches. The lowest reprocessing costs should be obtained by minimizing the mass of the RTL. Low mass transmission lines (LMTL) could also help reduce the cost of a single shot facility such as the proposed X-1 accelerator and make z-pinch driven space propulsion feasible. We present calculations to determine the minimum LMTL electrode mass to provide sufficient inertia against the magnetic pressure produced by the large currents needed to drive the z pinches. The results indicate an electrode thickness which is much smaller than the resistive skinmore » depth. We have performed experiments to determine if such thin electrodes can efficiently carry the required current. The tests were performed with various thickness of materials. The results indicate that LMTLs should efficiently carry the large z-pinch currents needed for inertial fusion. We also use our results to estimate of the performance of pulsed power driven pulsed nuclear rockets.« less
Recent advances in theoretical and numerical studies of wire array Z-pinch in the IAPCM
NASA Astrophysics Data System (ADS)
Ding, Ning; Zhang, Yang; Xiao, Delong; Wu, Jiming; Huang, Jun; Yin, Li; Sun, Shunkai; Xue, Chuang; Dai, Zihuan; Ning, Cheng; Shu, Xiaojian; Wang, Jianguo; Li, Hua
2014-12-01
Fast Z-pinch has produced the most powerful X-ray radiation source in laboratory and also shows the possibility to drive inertial confinement fusion (ICF). Recent advances in wire-array Z-pinch researches at the Institute of Applied Physics and Computational Mathematics are presented in this paper. A typical wire array Z-pinch process has three phases: wire plasma formation and ablation, implosion and the MRT instability development, stagnation and radiation. A mass injection model with azimuthal modulation coefficient is used to describe the wire initiation, and the dynamics of ablated plasmas of wire-array Z-pinches in (r, θ) geometry is numerically studied. In the implosion phase, a two-dimensional(r, z) three temperature radiation MHD code MARED has been developed to investigate the development of the Magneto-Rayleigh-Taylor(MRT) instability. We also analyze the implosion modes of nested wire-array and find that the inner wire-array is hardly affected before the impaction of the outer wire-array. While the plasma accelerated to high speed in the implosion stage stagnates on the axis, abundant x-ray radiation is produced. The energy spectrum of the radiation and the production mechanism are investigated. The computational x-ray pulse shows a reasonable agreement with the experimental result. We also suggest that using alloyed wire-arrays can increase multi-keV K-shell yield by decreasing the opacity of K-shell lines. In addition, we use a detailed circuit model to study the energy coupling between the generator and the Z-pinch implosion. Recently, we are concentrating on the problems of Z-pinch driven ICF, such as dynamic hohlraum and capsule implosions. Our numerical investigations on the interaction of wire-array Z-pinches on foam convertors show qualitative agreements with experimental results on the "Qiangguang I" facility. An integrated two-dimensional simulation of dynamic hohlraum driven capsule implosion provides us the physical insights of wire
Recent advances in theoretical and numerical studies of wire array Z-pinch in the IAPCM
Ding, Ning, E-mail: ding-ning@iapcm.ac.cn; Zhang, Yang, E-mail: ding-ning@iapcm.ac.cn; Xiao, Delong, E-mail: ding-ning@iapcm.ac.cn
2014-12-15
Fast Z-pinch has produced the most powerful X-ray radiation source in laboratory and also shows the possibility to drive inertial confinement fusion (ICF). Recent advances in wire-array Z-pinch researches at the Institute of Applied Physics and Computational Mathematics are presented in this paper. A typical wire array Z-pinch process has three phases: wire plasma formation and ablation, implosion and the MRT instability development, stagnation and radiation. A mass injection model with azimuthal modulation coefficient is used to describe the wire initiation, and the dynamics of ablated plasmas of wire-array Z-pinches in (r, θ) geometry is numerically studied. In the implosionmore » phase, a two-dimensional(r, z) three temperature radiation MHD code MARED has been developed to investigate the development of the Magneto-Rayleigh-Taylor(MRT) instability. We also analyze the implosion modes of nested wire-array and find that the inner wire-array is hardly affected before the impaction of the outer wire-array. While the plasma accelerated to high speed in the implosion stage stagnates on the axis, abundant x-ray radiation is produced. The energy spectrum of the radiation and the production mechanism are investigated. The computational x-ray pulse shows a reasonable agreement with the experimental result. We also suggest that using alloyed wire-arrays can increase multi-keV K-shell yield by decreasing the opacity of K-shell lines. In addition, we use a detailed circuit model to study the energy coupling between the generator and the Z-pinch implosion. Recently, we are concentrating on the problems of Z-pinch driven ICF, such as dynamic hohlraum and capsule implosions. Our numerical investigations on the interaction of wire-array Z-pinches on foam convertors show qualitative agreements with experimental results on the “Qiangguang I” facility. An integrated two-dimensional simulation of dynamic hohlraum driven capsule implosion provides us the physical insights of
Numerical simulations for cold layer formation in an inverse Z-pinch magnetized target fusion system
Subhash, P. V.; Madhavan, S.; Chaturvedi, S.
2009-01-15
One-dimensional magnetohydrodynamic simulations have been performed to study cold layer formation in a magnetized target fusion system with an inverse Z-pinch target plasma. Three phases of cold layer evolution has been identified. During the early compression phase, when liner velocities were not high, formation of a ''classical'' cold layer is observed, with monotonically increasing plasma densities and decreasing temperatures as the liner is approached. During the main compression phase, lasting until close to peak compression, magnetic flux leakage from the plasma to the liner is not important. The cold layer is then characterized by monotonically decreasing plasma temperature, density, and thermal conductivity. This has practical significance, since it would tend to reduce thermal losses to the liner. During the late compression and burn phases, magnetic flux leakage into the liner becomes important. This phase is characterized by a rapid increase in density and a rapid decrease in magnetic field and temperature toward the liner. This yields significantly higher values of thermal conductivity than in the bulk plasma, leading to enhanced thermal losses. During the first two phases, the entire plasma is magnetically confined. During the last phase, the cold layer changes to a wall-confined mode, while the bulk plasma continues to be magnetically confined. This is a major difference from earlier assumptions about wall confinement of such plasmas. These results show that the Kadomtsev stability parameter exceeds unity in the cold layer during the second and third phases, which may be an indication of instability. The choice of the transport model has a significant effect upon plasma evolution and the plasma lifetime. Classical transport yields plasma density levels near the liner that are significantly higher, sometimes by orders of magnitude, than those yielded by Bohm transport. During the main compression phase, Bohm diffusivity yields a lower lifetime, as
Study of the internal structure, instabilities, and magnetic fields in the dense Z-pinch
Ivanov, Vladimir V.
2016-08-17
Z-pinches are sources of hot dense plasma which generates powerful x-ray bursts and can been applied to various areas of high-energy-density physics (HEDP). The 26-MA Z machine is at the forefront of many of these applications, but important aspects of HEDP have been studied on generators at the 1 MA current level. Recent development of laser diagnostics and upgrade of the Leopard laser at Nevada Terawatt Facility (NTF) give new opportunities for the dense Z-pinch study. The goal of this project is the investigation of the internal structure of the stagnated Z pinch including sub-mm and micron-scale instabilities, plasma dynamics,more » magnetic fields, and hot spots formation and initiation. New plasma diagnostics will be developed for this project. A 3D structure and instabilities of the pinch will be compared with 3D MHD and spectroscopic modeling and theoretical analysis. The structure and dynamics of stagnated Z pinches has been studied with x-ray self-radiation diagnostics which derive a temperature map of the pinch with a spatial resolution of 70-150 µm. The regular laser diagnostics at 532 nm does not penetrate in the dense pinch due to strong absorption and refraction in trailing plasma. Recent experiments at NTF showed that shadowgraphy at the UV wavelength of 266 nm unfolds a fine structure of the stagnated Z-pinch with unprecedented detail. We propose to develop laser UV diagnostics for Z pinches with a spatial resolution <5 μm to study the small-scale plasma structures, implement two-frame shadowgraphy/interferometry, and develop methods for investigation of strong magnetic fields. New diagnostics will help to understand better basic physical processes in Z pinches. A 3D internal structure of the pinch and characteristic instabilities will be studied in wire arrays with different configurations and compared with 3D MHD simulations and analytical models. Mechanisms of “enhanced heating” of Z-pinch plasma will be studied. Fast dynamics of
Study of the internal structure, instabilities, and magnetic fields in the dense Z-pinch
Ivanov, Vladimir V.
2016-08-17
Z-pinches are sources of hot dense plasma which generates powerful x-ray bursts and can been applied to various areas of high-energy-density physics (HEDP). The 26-MA Z machine is at the forefront of many of these applications, but important aspects of HEDP have been studied on generators at the 1 MA current level. Recent development of laser diagnostics and upgrade of the Leopard laser at Nevada Terawatt Facility (NTF) give new opportunities for the dense Z-pinch study. The goal of this project is the investigation of the internal structure of the stagnated Z pinch including sub-mm and micron-scale instabilities, plasma dynamics, magnetic fields, and hot spots formation and initiation. New plasma diagnostics will be developed for this project. A 3D structure and instabilities of the pinch will be compared with 3D MHD and spectroscopic modeling and theoretical analysis. The structure and dynamics of stagnated Z pinches has been studied with x-ray self-radiation diagnostics which derive a temperature map of the pinch with a spatial resolution of 70-150 µm. The regular laser diagnostics at 532 nm does not penetrate in the dense pinch due to strong absorption and refraction in trailing plasma. Recent experiments at NTF showed that shadowgraphy at the UV wavelength of 266 nm unfolds a fine structure of the stagnated Z-pinch with unprecedented detail. We propose to develop laser UV diagnostics for Z pinches with a spatial resolution <5 μm to study the small-scale plasma structures, implement two-frame shadowgraphy/interferometry, and develop methods for investigation of strong magnetic fields. New diagnostics will help to understand better basic physical processes in Z pinches. A 3D internal structure of the pinch and characteristic instabilities will be studied in wire arrays with different configurations and compared with 3D MHD simulations and analytical models. Mechanisms of “enhanced heating” of Z-pinch plasma will be studied. Fast dynamics of stagnated
Initiation, ablation, precursor formation, and instability analysis of thin foil liner Z-pinches
NASA Astrophysics Data System (ADS)
Blesener, Isaac Curtis
This dissertation presents the results of mostly experimental work studying the early-time behavior of thin foil liners as compared to wire-array Z-pinches. It involves three studies, covering initiation, ablation and precursor formation, and instability analysis. Initiation was studied by observing the optical emission of various thickness (0.6-23.5 μm Cu) liners using a streak camera. It was found that thinner liners initiated sooner, more quickly, and more uniformly than thicker liners. This correlated well with both an increase in instantaneous dJ/dt at the time of first emission as well as the inductive voltage at the time of first emission. The threshold for uniform initiation was dJ/dt>3.5×1016Acm -2s-1. Uniform initiation is important for liners because nonuniformities could lead to enhanced instabilities and poor liner performance (compression, x-ray production, etc.). Ablation and precursor formation of wire-arrays (16x75 μm Cu) and liners (6 μm Cu) were studied using r-θ density maps and radial mass profiles created by an axial X pinch radiography diagnostic. These images show very strong differences in this stage of the Z-pinch. Wire-arrays develop complex, azimuthally varying ablation structures that lead to dense precursors. Liners, however, show significantly reduced and azimuthally uniform ablation leading to an order of magnitude less dense precursor on axis. This is likely due to the discrete versus continuous nature of wire-arrays versus liners. With wire-arrays, plasma that is created on the outside of the wires can reach the array axis by being swept through the gaps between the stationary wire cores. In contrast, liners have no “gaps” for plasma to flow through. Therefore, any plasma that is created on the outside of the liner is trapped there until the bulk of the liner moves with the implosion. Consequently, only the plasma that is created on the inside of the liner is able to contribute to precursor formation. This is an important
Characterisation of the current switch mechanism in two-stage wire array Z-pinches
Burdiak, G. C.; Lebedev, S. V.; Harvey-Thompson, A. J.
2015-11-15
In this paper, we describe the operation of a two-stage wire array z-pinch driven by the 1.4 MA, 240 ns rise-time Magpie pulsed-power device at Imperial College London. In this setup, an inverse wire array acts as a fast current switch, delivering a current pre-pulse into a cylindrical load wire array, before rapidly switching the majority of the generator current into the load after a 100–150 ns dwell time. A detailed analysis of the evolution of the load array during the pre-pulse is presented. Measurements of the load resistivity and energy deposition suggest significant bulk heating of the array mass occurs. Themore » ∼5 kA pre-pulse delivers ∼0.8 J of energy to the load, leaving it in a mixed, predominantly liquid-vapour state. The main current switch occurs as the inverse array begins to explode and plasma expands into the load region. Electrical and imaging diagnostics indicate that the main current switch may evolve in part as a plasma flow switch, driven by the expansion of a magnetic cavity and plasma bubble along the length of the load array. Analysis of implosion trajectories suggests that approximately 1 MA switches into the load in 100 ns, corresponding to a doubling of the generator dI/dt. Potential scaling of the device to higher current machines is discussed.« less
DT ignition in a Z pinch compressed by an imploding liner
NASA Astrophysics Data System (ADS)
Bilbao, L.; Bernal, L.; Linhart, J. G.; Verri, G.
2001-11-01
It has been shown that an m = 0 instability of a Z pinch carrying a current of the order of 10 MA with a rise time of less than 10 ns can generate a spark capable of igniting a fusion detonation in the adjacent DT plasma channel. A possible method for generating such currents, necessary for the implosion of an initial large radius, low temperature Z pinch, can be a radial implosion of a cylindrical fast liner. The problem has been addressed in previous publications without considering the role played by an initially impressed m = 0 perturbation, a mechanism indispensable for the generation of a spark. The liner-Z pinch dynamics can be solved at several levels of physical model completeness. The first corresponds to a zero dimensional model in which the liner has a given mass per unit length and a zero thickness, the plasma is compressed adiabatically and is isotropic, and there are no energy losses or Joule heating. The second level is one dimensional. The Z pinch plasma is described by the full set of MHD, two-fluid equations. The liner is treated first as thin and incompressible, and subsequently it is assumed that it has a finite thickness and is composed of a heavy ion plasma, having an artificial but realistic equation of state. Both plasma and liner are considered uniform in the Z direction and only DT reactions are considered. It is shown that, given sufficient energy and speed of the liner, the Z pinch can reach a volume ignition. The third level is two dimensional. Plasma and liner are treated as in the second level but either the Z pinch or the liner is perturbed by an m = 0 non-uniformity. Provided the liner energy is high enough and the initial m = 0 perturbation is correctly chosen, the final neck plasma can act as a spark for DT ignition. It is also shown that the liner energy required for generating a spark and the subsequent detonation propagation are considerably less than in the case of volume ignition.
Progress in Z-pinch research driven by the mega-ampere device SPEED2
NASA Astrophysics Data System (ADS)
Pavez, Cristian; Soto, Leopoldo; Moreno, José; Tarifeño, Ariel; Sylvester, Gustavo
2008-11-01
Several pinch configurations have being studied at the Chilean Nuclear Energy Commission using the SPEED2 generator: plasma focus, gas embedded z-pinch and wire arrays. SPEED2 is a generator based on Marx technology (4.1 μF equivalent Marx generator capacity, 300 kV, 4 MA in short circuit, 187 kJ, 400 ns rise time, dI/dt~1013 A/s). Currently the device is being operated at 70kJ stored energy producing a peak current of 2.4 MA in short circuit. In this work results related to studies in gas embedded z-pinch in deuterium and studies in wire arrays are presented.
Progress in Z-pinch research driven by the mega-ampere device SPEED2
NASA Astrophysics Data System (ADS)
Pavéz, Cristian; Soto, Leopoldo; Moreno, José; Tarifeño, Ariel; Sylvester, Gustavo
2008-04-01
Several pinch configurations have being studied at the Chilean Nuclear Energy Commission using the SPEED2 generator: plasma focus, gas embedded z-pinch and wire arrays. SPEED2 is a generator based on Marx technology (4.1 μF equivalent Marx generator capacity, 300 kV, 4 MA in short circuit, 187 kJ, 400 ns rise time, dI/dt˜1013 A/s). Currently the device is being operated at 70kJ stored energy producing a peak current of 2.4 MA in short circuit. In this work results related to studies in gas embedded z-pinch in deuterium and studies in wire arrays are presented.
Collisionless hydrodynamics of z-pinch with finite ion Larmor radius and the interchange instability
Trubnikov, B.A.; Zhdanov, S.K.
1977-01-01
The correct collisionless MHD approximation for the plasma is shown to be that of anisotropic hydrodynamics with a magnetic viscosity, with the finite ion Larmor radius being taken into account. These equations furnish a theoretical explanation for the constriction (''sausage'') wavelength observed experimentally in the plasma channel of a straight discharge (Z pinch) )S. M. Osovets, E. I. Pavlov, and V. I. Sinitsyn, Zh. Eksp. Teor. Fiz. 64, 1228 (1973) (Sov. Phys. JETP 37, 625 (1973) ).
Modelling of Capillary Z-Pinch Recombination Pumping of Hydrogen-Like Ion EUV Lasers
NASA Astrophysics Data System (ADS)
Vrba, P.; Bobrova, N. A.; Sasorov, P. V.; Vrbova, M.; Hubner, J.
We report here new results of simulations of Z-pinch recombination pumping for capillary filled by boron and compare them with previous nitrogen results. In both cases the same capillary radius and current pulse shape are taken into account. Evaluated pressure optimized gains for boron and nitrogen are 1.04 cm-1 and 0.11 cm-1, respectively. Influence of possible wall ablation is also analyzed.
Preliminary experimental results of tungsten wire-array Z-pinches on primary test stand
NASA Astrophysics Data System (ADS)
Huang, Xian-Bin; Zhou, Shao-Tong; Dan, Jia-Kun; Ren, Xiao-Dong; Wang, Kun-Lun; Zhang, Si-Qun; Li, Jing; Xu, Qiang; Cai, Hong-Chun; Duan, Shu-Chao; Ouyang, Kai; Chen, Guang-Hua; Ji, Ce; Wei, Bing; Feng, Shu-Ping; Wang, Meng; Xie, Wei-Ping; Deng, Jian-Jun; Zhou, Xiu-Wen; Yang, Yi
2015-07-01
The Primary Test Stand (PTS) developed at the China Academy of Engineering Physics is a 20 TW pulsed power driver, which can deliver a ˜10 MA, 70 ns rise-time (10%-90%) current to a short-circuit load and has important applications in Z-pinch driven inertial confinement fusion and high energy density physics. Preliminary results of tungsten wire-array Z-pinch experiments on PTS are presented. The load geometries investigated include 15-mm-tall cylindrical single and nested arrays with diameter ranging from 13 mm to 30 mm, consisting of 132-300 tungsten wires with 5-10 μm in diameter. Multiple diagnostics were fielded to characterize the x-ray radiation from wire-array Z pinches. The x-ray peak power (˜50 TW) and total radiated energy (˜500 kJ) were obtained from a single 20-mm-diam array with 80-ns stagnation time. The highest x-ray peak power up to 80 TW with 2.4 ns FWHM was achieved by using a nested array with 20-mm outer diameter, and the total x-ray energy from the nested array is comparable to that of single array. Implosion velocity estimated from the time-resolved image measurement exceeds 30 cm/μs. The detailed experimental results and other findings are presented and discussed.
Preliminary experimental results of tungsten wire-array Z-pinches on primary test stand
Huang, Xian-Bin; Zhou, Shao-Tong; Dan, Jia-Kun
2015-07-15
The Primary Test Stand (PTS) developed at the China Academy of Engineering Physics is a 20 TW pulsed power driver, which can deliver a ∼10 MA, 70 ns rise-time (10%–90%) current to a short-circuit load and has important applications in Z-pinch driven inertial confinement fusion and high energy density physics. Preliminary results of tungsten wire-array Z-pinch experiments on PTS are presented. The load geometries investigated include 15-mm-tall cylindrical single and nested arrays with diameter ranging from 13 mm to 30 mm, consisting of 132–300 tungsten wires with 5–10 μm in diameter. Multiple diagnostics were fielded to characterize the x-ray radiation from wire-array Z pinches.more » The x-ray peak power (∼50 TW) and total radiated energy (∼500 kJ) were obtained from a single 20-mm-diam array with 80-ns stagnation time. The highest x-ray peak power up to 80 TW with 2.4 ns FWHM was achieved by using a nested array with 20-mm outer diameter, and the total x-ray energy from the nested array is comparable to that of single array. Implosion velocity estimated from the time-resolved image measurement exceeds 30 cm/μs. The detailed experimental results and other findings are presented and discussed.« less
Comparison of Staged Z-pinch Experiments at the NTF Zebra Facility with Mach2 simulations
NASA Astrophysics Data System (ADS)
Ruskov, E.; Wessel, F. J.; Rahman, H. U.; Ney, P.; Darling, T. W.; Johnson, Z.; McGee, E.; Covington, A.; Dutra, E.; Valenzuela, J. C.; Conti, F.; Narkis, J.; Beg, F.
2016-10-01
Staged Z-pinch experiments at the University of Nevada, Reno, 1MA Z-pinch Zebra facility were conducted. A hollow shell of argon gas liner is injected between 1 cm anode-cathode gap through a supersonic nozzle of 2.0 cm diameter with a throat gap of 240 microns. A deuterium plasma fill is injected inside the argon gas shell through a plasma gun as a fusible target plasma. An axial magnetic field is also applied throughout the pinch region. Experimental measurements such as pinch current, X-ray signal, neutron yield, and streak images are compared with MACH2 radiation hydrodynamic code simulations. The argon liner density profiles, obtained from the CFD (FLUENT), are used as an input to MACH2. The comparison suggests a fairly close agreement between the experimental measurements and the simulation results. This study not only helps to benchmark the code but also suggests the importance of the Z-pinch implosion time, optimizing both liner and target plasma density to obtain the maximum energy coupling between the circuit and the load. Advanced Research Projects Agency - Energy, DE-AR0000569.
Study of micro-pinches in wire-array Z pinches
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Papp, D.; Anderson, A. A.; Talbot, B. R.; Astanovitskiy, A. L.; Nalajala, V.; Dmitriev, O.; Chittenden, J. P.; Niasse, N.; Pikuz, S. A.; Shelkovenko, T. A.
2013-11-01
Bright and hot areas with a high plasma density and temperature are observed in all kinds of Z pinches. We studied bright radiating spots produced by micro-pinches in cylindrical and planar wire-arrays at the 1 MA Zebra pulsed power generator using an x-ray streak camera synchronized with laser diagnostics, x-ray time-gated pinhole camera, and spectroscopy. Hot spots with extremely dense and relatively hot plasma arise during the collapse of the micro-pinches. These hot spots radiate a continuum spectrum with energy >2.5 keV. Typical micro-pinches in Al wire arrays generate x-ray bursts with durations of 0.4-1 ns in the soft x-ray range and 0.1-0.4 ns in the keV range. UV two-frame shadowgraphy shows spatial correlation of hot spots with the collapse and explosion of micro-pinches. Micro-pinches typically occur at the necks of the Z pinch, but can demonstrate a variety of parameters and different dynamics. An analysis of x-ray streak images shows that micro-pinches can generate >20% of the x-ray energy in some types of wire-array Z pinches.
Analysis of staged Z-pinch implosion trajectories from experiments on Zebra
NASA Astrophysics Data System (ADS)
Ross, Mike P.; Conti, F.; Darling, T. W.; Ruskov, E.; Valenzuela, J.; Wessel, F. J.; Beg, F.; Narkis, J.; Rahman, H. U.
2017-10-01
The Staged Z-pinch plasma confinement concept relies on compressing an annular liner of high-Z plasma onto a target plasma column of deuterium fuel. The interface between the liner and target is stable against the Magneto-Rayleigh-Taylor Instability, which leads to effective fuel compression and makes the concept interesting as a potential fusion reactor. The liner initiates as a neutral gas puff, while the target plasma is a partially ionized (Zeff < 10 percent column ejected from a coaxial plasma gun. The Zebra pulsed power generator (1 MA peak current, 100 ns rise time) provides the discharge that ionizes the liner and drives the Z-pinch implosion. Diverse diagnostics observe the 100-300 km/s implosions including silicon diodes, photo-conducting detectors (PCDs), laser shadowgraphy, an XUV framing camera, and a visible streak camera. The imaging diagnostics track instabilities smaller than 0.1 mm, and Z-pinch diameters below 2.5 mm are seen at peak compression. This poster correlates the data from these diagnostics to elucidate implosion behavior dependencies on liner gas, liner pressure, target pressure, and applied, axial-magnetic field. Funded by the Advanced Research Projects Agency - Energy, DE-AR0000569.
The microscopic Z-pinch process of current-carrying rarefied deuterium plasma shell
NASA Astrophysics Data System (ADS)
Ning, Cheng; Feng, Zhixing; Xue, Chuang; Li, Baiwen
2015-02-01
For insight into the microscopic mechanism of Z-pinch dynamic processes, a code of two-dimensional particle-in-cell (PIC) simulation has been developed in cylindrical coordinates. In principle, the Z-pinch of current-carrying rarefied deuterium plasma shell has been simulated by means of this code. Many results related to the microscopic processes of the Z-pinch are obtained. They include the spatio-temporal distributions of electromagnetic field, current density, forces experienced by the ions and electrons, positions and energy distributions of particles, and trailing mass and current. In radial direction, the electric and magnetic forces exerted on the electrons are comparable in magnitude, while the forces exerted on the ions are mainly the electric forces. So in the Z-pinch process, the electrons are first accelerated in Z direction and get higher velocities; then, they are driven inwards to the axis at the same time by the radial magnetic forces (i.e., Lorentz forces) of them. That causes the separations between the electrons and ions because the ion mass is much larger than the electron's, and in turn a strong electrostatic field is produced. The produced electrostatic field attracts the ions to move towards the electrons. When the electrons are driven along the radial direction to arrive at the axis, they shortly move inversely due to the static repellency among them and their tiny mass, while the ions continue to move inertially inwards, and later get into stagnation, and finally scatter outwards. Near the stagnation, the energies of the deuterium ions mostly range from 0.3 to 6 keV, while the electron energies are mostly from 5 to 35 keV. The radial components, which can contribute to the pinched plasma temperature, of the most probable energies of electron and ion at the stagnation are comparable to the Bennett equilibrium temperature (about 1 keV), and also to the highest temperatures of electron and ion obtained in one dimensional radiation
The microscopic Z-pinch process of current-carrying rarefied deuterium plasma shell
Ning, Cheng; Xue, Chuang; Li, Baiwen
2015-02-15
For insight into the microscopic mechanism of Z-pinch dynamic processes, a code of two-dimensional particle-in-cell (PIC) simulation has been developed in cylindrical coordinates. In principle, the Z-pinch of current-carrying rarefied deuterium plasma shell has been simulated by means of this code. Many results related to the microscopic processes of the Z-pinch are obtained. They include the spatio-temporal distributions of electromagnetic field, current density, forces experienced by the ions and electrons, positions and energy distributions of particles, and trailing mass and current. In radial direction, the electric and magnetic forces exerted on the electrons are comparable in magnitude, while the forcesmore » exerted on the ions are mainly the electric forces. So in the Z-pinch process, the electrons are first accelerated in Z direction and get higher velocities; then, they are driven inwards to the axis at the same time by the radial magnetic forces (i.e., Lorentz forces) of them. That causes the separations between the electrons and ions because the ion mass is much larger than the electron's, and in turn a strong electrostatic field is produced. The produced electrostatic field attracts the ions to move towards the electrons. When the electrons are driven along the radial direction to arrive at the axis, they shortly move inversely due to the static repellency among them and their tiny mass, while the ions continue to move inertially inwards, and later get into stagnation, and finally scatter outwards. Near the stagnation, the energies of the deuterium ions mostly range from 0.3 to 6 keV, while the electron energies are mostly from 5 to 35 keV. The radial components, which can contribute to the pinched plasma temperature, of the most probable energies of electron and ion at the stagnation are comparable to the Bennett equilibrium temperature (about 1 keV), and also to the highest temperatures of electron and ion obtained in one dimensional radiation
3D Resistive, Radiative MHD Modeling of Z-pinches
Jennings, C.A.; Chittenden, J.P.; Ciardi, A.; Sherlock, M.; Lebedev, S.V.; Ampleford, D.J.; Bland, S.N.; Bott, S.C.; Hall, G.; Rapley, J.
2006-01-05
We present results from GORGON, a three dimensional, parallel, radiative, resistive MHD code which we use to study the evolution of various wire array configurations. We describe the implosion of cylindrical wire arrays and the interaction of nested wire arrays on the MAGPIE generator of Imperial College. In addition to cylindrical arrays we describe results from the modeling of novel array configurations such as radial, conical and spherical wire arrays, which are of interest in laboratory astrophysics, and the understanding of basic array physics. For spherical array implosions we demonstrate a precursor flow convergence that is not entirely spherical. We show that jet formation on axis, and compression from precursor streams generates a roughly cylindrical precursor, which at late times becomes unstable. Final implosion is dominated by two magnetic cavities that expand axially to collide at the array center.This research supported by the NNSA under Department of Energy cooperative agreement DE-F03-02NA00057.
Williamson, K. M.; Kantsyrev, V. L.; Safronova, A. S.
2011-09-15
This recently developed diagnostic was designed to allow for time-gated spectroscopic study of the EUV radiation (4 nm < {lambda} < 15 nm) present during harsh wire array z-pinch implosions. The spectrometer utilizes a 25 {mu}m slit, an array of 3 spherical blazed gratings at grazing incidence, and a microchannel plate (MCP) detector placed in an off-Rowland position. Each grating is positioned such that its diffracted radiation is cast over two of the six total independently timed frames of the MCP. The off-Rowland configuration allows for a much greater spectral density on the imaging plate but only focuses at onemore » wavelength per grating. The focal wavelengths are chosen for their diagnostic significance. Testing was conducted at the Zebra pulsed-power generator (1 MA, 100 ns risetime) at University of Nevada, Reno on a series of wire array z-pinch loads. Within this harsh z-pinch environment, radiation yields routinely exceed 20 kJ in the EUV and soft x-ray. There are also strong mechanical shocks, high velocity debris, sudden vacuum changes during operation, energic ion beams, and hard x-ray radiation in excess of 50 keV. The spectra obtained from the precursor plasma of an Al double planar wire array contained lines of Al IX and AlX ions indicating a temperature near 60 eV during precursor formation. Detailed results will be presented showing the fielding specifications and the techniques used to extract important plasma parameters using this spectrometer.« less
Williamson, K. M.; Kantsyrev, V. L.; Safronova, A. S.; Wilcox, P. G.; Cline, W.; Batie, S.; LeGalloudec, B.; Nalajala, V.; Astanovitsky, A.
2011-09-15
This recently developed diagnostic was designed to allow for time-gated spectroscopic study of the EUV radiation (4 nm < {lambda} < 15 nm) present during harsh wire array z-pinch implosions. The spectrometer utilizes a 25 {mu}m slit, an array of 3 spherical blazed gratings at grazing incidence, and a microchannel plate (MCP) detector placed in an off-Rowland position. Each grating is positioned such that its diffracted radiation is cast over two of the six total independently timed frames of the MCP. The off-Rowland configuration allows for a much greater spectral density on the imaging plate but only focuses at one wavelength per grating. The focal wavelengths are chosen for their diagnostic significance. Testing was conducted at the Zebra pulsed-power generator (1 MA, 100 ns risetime) at University of Nevada, Reno on a series of wire array z-pinch loads. Within this harsh z-pinch environment, radiation yields routinely exceed 20 kJ in the EUV and soft x-ray. There are also strong mechanical shocks, high velocity debris, sudden vacuum changes during operation, energic ion beams, and hard x-ray radiation in excess of 50 keV. The spectra obtained from the precursor plasma of an Al double planar wire array contained lines of Al IX and AlX ions indicating a temperature near 60 eV during precursor formation. Detailed results will be presented showing the fielding specifications and the techniques used to extract important plasma parameters using this spectrometer.
NASA Astrophysics Data System (ADS)
Velikovich, A. L.; Giuliani, J. L.; Clark, R. W.; Mikitchuk, D.; Kroupp, E.; Maron, Y.; Fisher, A.; Schmit, P. F.
2014-10-01
Recent progress in developing the MagLIF approach to pulsed-power driven inertial confinement fusion has stimulated the interest in observation and mitigation of the magnetic Rayleigh-Taylor instability (MRTI) of liners and Z-pinches imploded in an axial magnetic field. Theoretical analysis of these issues is particularly important because direct numerical simulation of the MRTI development is challenging due to intrinsically 3D helical structure of the fastest-growing modes. We review the analytical small-amplitude theory of the MRTI perturbation development and the weakly nonlinear theory of MRTI mode interaction, emphasizing basic physics, opportunity for 3D code verification against exact analytical solutions, and stabilization criteria. The theory is compared to the experimental results obtained at Weizmann Institute with gas-puff Z pinches and on the Z facility at Sandia with solid liners imploded in an axial magnetic field. Work supported by the US DOE/NNSA, and by the US-Israel Binational Science Foundation. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
Growth rates of interchange modes in the dense z-pinch and gas blanket effects
Suydam, B.R.
1980-05-01
A class of models of the dense z-pinch in which the bulk of the plasma is neutrally stable against interchange is studied. At a radius a the plasma is abruptly terminated and surrounded by a gas blanket. Instability results from the surface current necessary to maintain pressure balance at the plasma-gas interface. A single dispersion relation applies to all models in this class and shows two effects of the gas blanket in reducing growth rate. (1) Partial support of plasma pressure by external gas pressure reduces the driving force for the instability, and (2) mass loading of the relatively dense neutral gas reduces growth rate.
The inverse skin effect in the Z-pinch and plasma focus
Usenko, P. L., E-mail: otd4@expd.vniief.ru; Gaganov, V. V.
2016-08-15
The inverse skin effect and its influence on the dynamics of high-current Z-pinch and plasma focus discharges in deuterium are analyzed. It is shown that the second compression responsible for the major fraction of the neutron yield can be interpreted as a result of the inverse skin effect resulting in the axial concentration of the longitudinal current density and the appearance of a reversed current in the outer layers of plasma pinches. Possible conditions leading to the enhancement of the inverse skin effect and accessible for experimental verification by modern diagnostics are formulated.
A study of Z-pinch in capillary filled by boron vapours
NASA Astrophysics Data System (ADS)
Vrba, P.; Vrbova, M.; Bobrova, N. A.; Sasorov, P. V.
2009-08-01
Pinching discharge in non-ablative and ablative capillaries filled by boron vapors is studied. The aim is to find out conditions for lasing at Balmer alpha transition of hydrogen-like boron ions B4+ (λ= 26.23 nm). The primary pumping process under consideration is a three-body collisional recombination, which takes place in non-stationary underheated plasma during the pinch expansion stage. The results of Z-pinch computer modeling including the plasma kinetics and gain evaluation are compared for two different quarter periods of electrical current passing through the capillary.
NASA Astrophysics Data System (ADS)
Valenzuela, J. C.; Krasheninnikov, I.; Beg, F. N.; Wessel, F.; Rahman, H.; Ney, P.; Presura, R.; McKee, E.; Darling, T.; Covington, A.
2015-11-01
Previous experimental work on staged Z-pinches demonstrated that gas liners can efficiently couple energy and implode uniformly a target-plasma. A 1.5 MA, 1 μs current driver was used to implode a magnetized, Kr liner onto a D + target, producing 1010 neutrons per shot and providing clear evidence of enhanced pinch stability. Time-of-flight data suggest that primary and secondary neutrons were produced. MHD simulations show that in Zebra, a 1.5MA and 100ns rise-time current driver, high fusion gain can be attained when the optimum liner and plasma target conditions are used. In this work we present the design and optimization of a liner-on-target nozzle to be fielded in Zebra and demonstrate high fusion gain at 1 MA current level. The nozzle is composed of an annular high atomic number gas-puff and an on-axis plasma gun that will deliver the ionized deuterium target. The nozzle optimization was carried out using the computational fluid dynamics (CFD) code fluent and the MHD code Mach2. The CFD simulation produces density and temperature profiles, as a function of the nozzle shapes and gas conditions, which are then used in Mach2 to find the optimum plasma liner implosion-pinch conditions. Funded by the US Department of Energy, ARPA-E, Control Number 1184-1527.
Measurements of the parameters of a condensed deuterated Z-pinch on the angara-5-1 facility
Aleksandrov, V. V.; Bryzgunov, V. A.; Grabovski, E. V.
2016-04-15
Results are presented from measurements of the parameters of high-temperature plasma in the Z-pinch neck formed when a current of up to 3.5 MA flows through a low-density polymer load. To enhance the effect of energy concentration, a deuterated microporous polyethylene neck with a mass density of 100 mg/cm{sup 3} and diameter of 1–1.3 mm was placed in the central part of the load. During the discharge current pulse, short-lived local hot plasma spots with typical dimensions of about 200–300 μm formed in the neck region. Their formation was accompanied by the generation of soft X-ray pulses with photon energiesmore » of E > 0.8 keV and durations of 3–4 ns. The plasma electron temperature in the vicinity of the hot spot was measured from the vacuum UV emission spectra of the iron diagnostic admixture and was found to be about 200–400 eV. The appearance of hot plasma spots was also accompanied by neutron emission with the maximum yield of 3 × 10{sup 10} neutrons/shot. The neutron energy spectra were studied by means of the time-of-flight method and were found to be anisotropic with respect to the direction of the discharge current.« less
Numerical investigation on the implosion dynamics of wire-array Z-pinches in (r, θ) geometry
NASA Astrophysics Data System (ADS)
Huang, Jun; Ding, Ning; Ning, Cheng; Sun, Shun-Kai; Zhang, Yang; Xiao, De-Long; Xue, Chuang
2012-06-01
The implosion dynamics of wire-array Z-pinches are investigated numerically in 2D (r, θ) geometry by using a resistive MHD code. It is assumed that the wires have expanded to plasmas with diameter d0, which is used as the initial condition for the consequent implosion process. In fact, the explosion process of individual wires is not included. By changing d0, the effects of the wire expansion degree on the implosion dynamics are analyzed. When d0 is larger, the current density is more concentrated at the outer side of the wires and the fraction of current flow around the wire plasmas is nearly in proportion to d0. As a result, the ablation rate of wires is increased and the implosion phase starts earlier. This conclusion agrees with the simulation works of other authors [Chittenden et al., Phys. Plasmas 11(3), 1118 (2004)]. When the array radius and initial wire plasma diameter are fixed, the increase of wire number leads to the azimuthal merge of wires during implosion. When the wires number exceed a critical value, which is related to d0, wire plasmas can merge to a continuous shell with an azimuthal perturbation in density, which depends on the initial wires number.
Larger sized planar wire arrays of complex configuration on 1.5-1.8 MA Z-pinch generator
NASA Astrophysics Data System (ADS)
Safronova, A. S.; Kantsyrev, V. L.; Weller, M. E.; Shlyaptseva, V. V.; Shrestha, I. K.; Stafford, A.; Schmidt-Petersen, M. T.; Lorance, M. Y.; Schultz, K. A.; Chuvatin, A. S.
2016-10-01
Two new approaches of (i) simultaneous study of implosion and radiative characteristics of different materials in wire array Z-pinch plasmas in one shot and (ii) investigation of larger sized wire arrays (to enhance energy coupling to plasmas and provide better diagnostic access) were developed in experiments with 1.5-1.8 MA Zebra with a Load Current Multiplier. In particular, the larger sized multi-plane Planar Wire Arrays with two outer planes placed at 9 and 15 mm from each other and then as far as at 19 mm (compared with 6 mm studied before at standard 1 MA current) and with a modified central plane with 8 to 12 empty slots were investigated. Though K-shell Al and L-shell Ni, Cu plasmas have similar electron temperatures and densities, the ablation dynamics and radiation of Al and Ni, Cu planes are somewhat different, which was investigated in detail using the full set of diagnostics and modeling. Advantages of using such wire arrays at higher currents to study plasma flow and radiation from different materials and jets are highlighted.
Ion probe beam experiments and kinetic modeling in a dense plasma focus Z-pinch
Schmidt, A., E-mail: schmidt36@llnl.gov; Ellsworth, J., E-mail: schmidt36@llnl.gov; Falabella, S., E-mail: schmidt36@llnl.gov
2014-12-15
The Z-pinch phase of a dense plasma focus (DPF) emits multiple-MeV ions in a ∼cm length. The mechanisms through which these physically simple devices generate such high energy beams in a relatively short distance are not fully understood. We are exploring the origins of these large gradients using measurements of an ion probe beam injected into a DPF during the pinch phase and the first kinetic simulations of a DPF Z-pinch. To probe the accelerating fields in our table top experiment, we inject a 4 MeV deuteron beam along the z-axis and then sample the beam energy distribution after itmore » passes through the pinch region. Using this technique, we have directly measured for the first time the acceleration of an injected ion beam. Our particle-in-cell simulations have been benchmarked on both a kJ-scale DPF and a MJ-scale DPF. They have reproduced experimentally measured neutron yields as well as ion beams and EM oscillations which fluid simulations do not exhibit. Direct comparisons between the experiment and simulations enhance our understanding of these plasmas and provide predictive design capability for accelerator and neutron source applications.« less
Primary experimental results of wire-array Z-pinches on PTS
NASA Astrophysics Data System (ADS)
Huang, X. B.; Zhou, S. T.; Ren, X. D.; Dan, J. K.; Wang, K. L.; Zhang, S. Q.; Li, J.; Xu, Q.; Cai, H. C.; Duan, S. C.; Ouyang, K.; Chen, G. H.; Ji, C.; Wang, M.; Feng, S. P.; Yang, L. B.; Xie, W. P.; Deng, J. J.
2014-12-01
The Primary Test Stand (PTS) developed at the China Academy of Engineering Physics is a multiterawatt pulsed power driver, which can deliver a ˜10 MA, 70 ns rise-time (10%-90%) current to a short circuit load and has important applications in Z-pinch driven inertial confinement fusion and high energy density physics. In this paper, primary results of tungsten wire-array Z-pinch experiments on PTS are presented. The load geometries investigated include 15-mm-tall cylindrical single and nested arrays with diameter ranging from 14.4-26.4 mm, and consisting of 132˜276 tungsten wires with 5˜10 μm in diameter. Multiple diagnostics were fielded to determine the characteristics of x-ray radiations and to obtain self-emitting images of imploding plasmas. X-ray power up to 80 TW with ˜3 ns FWMH is achieved by using nested wire arrays. The total x-ray energy exceeds 500 kJ and the peak radiation temperature is about 150 eV. Typical velocity of imploding plasmas goes around 3˜5×107 cm/s and the radial convergence ratio is between 10 and 20.
A short-pulse mode for the SPHINX LTD Z-pinch driver
NASA Astrophysics Data System (ADS)
D'Almeida, Thierry; Lassalle, Francis; Zucchini, Frederic; Loyen, Arnaud; Morell, Alain; Chuvatin, Alexander
2015-11-01
The SPHINX machine is a 6MA, 1 μs, LTD Z-pinch driver at CEA Gramat (France) and primarily used for studying radiation effects. Different power amplification concepts were examined in order to reduce the current rise time without modifying the generator discharge scheme, including the Dynamic Load Current Multiplier (DLCM) proposed by Chuvatin. A DLCM device, capable of shaping the current pulse without reducing the rise time, was developed at CEA. This device proved valuable for isentropic compression experiments in cylindrical geometry. Recently, we achieved a short pulse operation mode by inserting a vacuum closing switch between the DLCM and the load. The current rise time was reduced to ~300 ns. We explored the use of a reduced-height wire array for the Dynamic Flux Extruder in order to improve the wire array compression rate and increase the efficiency of the current transfer to the load. These developments are presented. Potential benefits of these developments for future Z pinch experiments are discussed.
Spatially resolved single crystal x-ray spectropolarimetry of wire array z-pinch plasmas
NASA Astrophysics Data System (ADS)
Wallace, M. S.; Haque, S.; Neill, P.; Pereira, N. R.; Presura, R.
2018-01-01
A recently developed single-crystal x-ray spectropolarimeter has been used to record paired sets of polarization-dependent and axially resolved x-ray spectra emitted by wire array z-pinches. In this measurement, two internal planes inside a suitable crystal diffract the x-rays into two perpendicular directions that are normal to each other, thereby separating incident x-rays into their linearly polarized components. This paper gives considerations for fielding the instrument on extended sources. Results from extended sources are difficult to interpret because generally the incident x-rays are not separated properly by the crystal. This difficulty is mitigated by using a series of collimating slits to select incident x-rays that propagate in a plane of symmetry between the polarization-splitting planes. The resulting instrument and some of the spatially resolved polarized x-ray spectra recorded for a 1-MA aluminum wire array z-pinch at the Nevada Terawatt Facility at the University of Nevada, Reno will be presented.
Comparison Between Laser Initiated Hollow Gas Embedded Z-pinches with Different Initial Radius
Veloso, Felipe; Chuaqui, Hernan; Aliaga-Rossel, Raul; Favre, Mario; Mitchell, Ian; Wyndham, Edmund
2006-12-04
An experimental study of the effect of the initial radius on the formation of hollow gas embedded z-pinches is presented. These hollow pinches are formed using a ring precursor plasma generated by focussing a 10ns, 0.2J, 1064nm, Nd:YAG laser pulse onto the cathode surface. The laser pulse is focussed into a ring shape, by using a combination of a converging lens and an axicon. Ring radius variation give place to different initial radius of hollow z-pinches. The experiments were carried out on the Gepopu generator at 110kA, 50ns rise time using flat electrodes. The anode had a central hole, allowing the laser to be focussed onto the cathode surface. Experiments were performed in hydrogen at 1/3 of atmosphere. Schlieren and interferometry are the main plasma diagnostics using the second harmonic of the same laser. Comparison between initial radius of 2 and 3mm are presented, where electron densities on the order of 1018 cm-3 were measured in both cases. Temperature estimates using Bennett relation are of 185 eV and 75 eV respectively. Pinch effect was observed for current density {approx} 5MA/cm2.
Study of Bright Spots in Wire-Array Z-Pinches
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Papp, D.; Anderson, A. A.; Talbot, B.; Astanovitskiy, A. L.; Nalajala, V.; Dmitriev, O.; Chittenden, J. P.; Niasse, N.
2013-10-01
Bright areas with a high plasma density and temperature (hot spots) were observed in all kinds of Z-pinches. Hot spots may be interpreted as results of the collapse of the plasma necks due to plasma outflowing and radiative losses of energy. We studied bright radiating spots in cylindrical and planar wire-arrays at the 1 MA Zebra generator using x-ray streak cameras synchronized with laser diagnostics, x-ray time-gated pinhole camera and spectroscopy. Hot spots in Al wire arrays generate x-ray bursts with durations of 0.4-1 ns in the soft range and 0.1-0.4 ns in the keV range. UV two-frame shadowgraphy shows spatial correlation of hot spots with micropinches. Hot spots can generate continuum radiation with energy >2.5 keV. An analysis of x-ray streak images shows that hot spots can generate >20% of the x-ray energy of the Z pinches. Work was supported by the DOE grant DE-SC0008824 and DOE/NNSA UNR grant DE-FC52-06NA27616.
Cylindrical liner Z-pinch experiments for fusion research and high-energy-density physics
NASA Astrophysics Data System (ADS)
Burdiak, G. C.; Lebedev, S. V.; Suzuki-Vidal, F.; Swadling, G. F.; Bland, S. N.; Niasse, N.; Suttle, L.; Bennet, M.; Hare, J.; Weinwurm, M.; Rodriguez, R.; Gil, J.; Espinosa, G.
2015-06-01
A gas-filled cylindrical liner z-pinch configuration has been used to drive convergent radiative shock waves into different gases at velocities of 20-50 km s-1. On application of the 1.4 MA, 240 ns rise-time current pulse produced by the Magpie generator at Imperial College London, a series of cylindrically convergent shock waves are sequentially launched into the gas-fill from the inner wall of the liner. This occurs without any bulk motion of the liner wall itself. The timing and trajectories of the shocks are used as a diagnostic tool for understanding the response of the liner z-pinch wall to a large pulsed current. This analysis provides useful data on the liner resistivity, and a means to test equation of state (EOS) and material strength models within MHD simulation codes. In addition to providing information on liner response, the convergent shocks are interesting to study in their own right. The shocks are strong enough for radiation transport to influence the shock wave structure. In particular, we see evidence for both radiative preheating of material ahead of the shockwaves and radiative cooling instabilities in the shocked gas. Some preliminary results from initial gas-filled liner experiments with an applied axial magnetic field are also discussed.
Development of a Non-LTE model for Z-pinch simulations
NASA Astrophysics Data System (ADS)
Niasse, Nicolas; Chittenden, Jeremy
2010-11-01
Predicting the energetic and spectral characteristics of Z-pinch sources is a delicate task. It requires solving the Atomic Physics equations for plasmas in a wide range of conditions. In addition, the increasing optical depth of the plasma at stagnation can have a strong influence on its own dynamics, suggesting that simultaneous solution of both the magneto-hydrodynamic and radiative response is required. This constraint places a special emphasis on code optimization. We introduce a simple atomic model that can be run inline with the three dimensional resistive Eulerian MHD code GORGON developed at Imperial College. Based on a Screened-Hydrogenic Model (SHM) with nl splitting and making use of an inexpensive modification of the SAHA equation, this code has demonstrated a good ability to mimic Non-LTE plasma conditions. Preliminary results obtained with the standalone version of the model have shown good agreement with commercial packages (PrismSpect). Comparisons of predictions produced by the inline version with data from High Energy Density Plasma Physics (HEDP) experiments at Imperial College, Sandia National Laboratory and Centre d'Études de Gramat are presented. Synthetic Z-pinch XUV images and time dependant spectra are produced.
Three-dimensional electromagnetic model of the pulsed-power Z-pinch accelerator
NASA Astrophysics Data System (ADS)
Rose, D. V.; Welch, D. R.; Madrid, E. A.; Miller, C. L.; Clark, R. E.; Stygar, W. A.; Savage, M. E.; Rochau, G. A.; Bailey, J. E.; Nash, T. J.; Sceiford, M. E.; Struve, K. W.; Corcoran, P. A.; Whitney, B. A.
2010-01-01
A three-dimensional, fully electromagnetic model of the principal pulsed-power components of the 26-MA ZR accelerator [D. H. McDaniel , in Proceedings of the 5th International Conference on Dense Z-Pinches (AIP, New York, 2002), p. 23] has been developed. This large-scale simulation model tracks the evolution of electromagnetic waves through the accelerator’s intermediate-storage capacitors, laser-triggered gas switches, pulse-forming lines, water switches, triplate transmission lines, and water convolute to the vacuum insulator stack. The insulator-stack electrodes are coupled to a transmission-line circuit model of the four-level magnetically insulated vacuum-transmission-line section and double-post-hole convolute. The vacuum-section circuit model is terminated by a one-dimensional self-consistent dynamic model of an imploding z-pinch load. The simulation results are compared with electrical measurements made throughout the ZR accelerator, and are in good agreement with the data, especially for times until peak load power. This modeling effort demonstrates that 3D electromagnetic models of large-scale, multiple-module, pulsed-power accelerators are now computationally tractable. This, in turn, presents new opportunities for simulating the operation of existing pulsed-power systems used in a variety of high-energy-density-physics and radiographic applications, as well as even higher-power next-generation accelerators before they are constructed.
Wire-number effects on high-power annular z-pinches and some characteristics at high wire number
SANFORD,THOMAS W. L.
2000-05-23
Characteristics of annular wire-array z-pinches as a function of wire number and at high wire number are reviewed. The data, taken primarily using aluminum wires on Saturn are comprehensive. The experiments have provided important insights into the features of wire-array dynamics critical for high x-ray power generation, and have initiated a renaissance in z-pinches when high numbers of wires are used. In this regime, for example, radiation environments characteristic of those encountered during the early pulses required for indirect-drive ICF ignition on the NIF have been produced in hohlraums driven by x-rays from a z-pinch, and are commented on here.
Z-Pinch Magneto-Inertial Fusion Propulsion Engine Design Concept
NASA Technical Reports Server (NTRS)
Miernik, Janie H.; Statham, Geoffrey; Adams, Robert B.; Polsgrove, Tara; Fincher, Sharon; Fabisinski, Leo; Maples, C. Dauphne; Percy, Thomas K.; Cortez, Ross J.; Cassibry, Jason
2011-01-01
Fusion-based nuclear propulsion has the potential to enable fast interplanetary transportation. Due to the great distances between the planets of our solar system and the harmful radiation environment of interplanetary space, high specific impulse (Isp) propulsion in vehicles with high payload mass fractions must be developed to provide practical and safe vehicles for human spaceflight missions. Magneto-Inertial Fusion (MIF) is an approach which has been shown to potentially lead to a low cost, small fusion reactor/engine assembly (1). The Z-Pinch dense plasma focus method is an MIF concept in which a column of gas is compressed to thermonuclear conditions by an estimated axial current of approximately 100 MA. Recent advancements in experiments and the theoretical understanding of this concept suggest favorable scaling of fusion power output yield as I(sup 4) (2). The magnetic field resulting from the large current compresses the plasma to fusion conditions, and this is repeated over short timescales (10(exp -6) sec). This plasma formation is widely used in the field of Nuclear Weapons Effects (NWE) testing in the defense industry, as well as in fusion energy research. There is a wealth of literature characterizing Z-Pinch physics and existing models (3-5). In order to be useful in engineering analysis, a simplified Z-Pinch fusion thermodynamic model was developed to determine the quantity of plasma, plasma temperature, rate of expansion, energy production, etc. to calculate the parameters that characterize a propulsion system. The amount of nuclear fuel per pulse, mixture ratio of the D-T and nozzle liner propellant, and assumptions about the efficiency of the engine, enabled the sizing of the propulsion system and resulted in an estimate of the thrust and Isp of a Z-Pinch fusion propulsion system for the concept vehicle. MIF requires a magnetic nozzle to contain and direct the nuclear pulses, as well as a robust structure and radiation shielding. The structure
NASA Astrophysics Data System (ADS)
Nash, T. J.; McDaniel, D. H.; Leeper, R. J.; Deeney, C. D.; Sanford, T. W. L.; Struve, K.; DeGroot, J. S.
2005-05-01
A quasi-spherical z-pinch may directly compress foam or deuterium and tritium in three dimensions as opposed to a cylindrical z-pinch, which compresses an internal load in two dimensions only. Because of compression in three dimensions the quasi-spherical z-pinch is more efficient at doing pdV work on an internal fluid than a cylindrical pinch. Designs of quasi-spherical z-pinch loads for the 28MA 100ns driver ZR, results from zero-dimensional (0D) circuit models of quasi-spherical implosions, and results from 1D hydrodynamic simulations of quasi-spherical implosions heating internal fluids will be presented. Applications of the quasi-spherical z-pinch implosions include a high radiation temperature source for radiation driven experiments, a source of neutrons for treating radioactive waste, and a source of fusion energy for a power generator.
Nash, T.J.; McDaniel, D.H.; Leeper, R.J.; Deeney, C.D.; Sanford, T.W.L.; Struve, K.; DeGroot, J.S.
2005-05-15
A quasi-spherical z-pinch may directly compress foam or deuterium and tritium in three dimensions as opposed to a cylindrical z-pinch, which compresses an internal load in two dimensions only. Because of compression in three dimensions the quasi-spherical z-pinch is more efficient at doing pdV work on an internal fluid than a cylindrical pinch. Designs of quasi-spherical z-pinch loads for the 28 MA 100 ns driver ZR, results from zero-dimensional (0D) circuit models of quasi-spherical implosions, and results from 1D hydrodynamic simulations of quasi-spherical implosions heating internal fluids will be presented. Applications of the quasi-spherical z-pinch implosions include a high radiation temperature source for radiation driven experiments, a source of neutrons for treating radioactive waste, and a source of fusion energy for a power generator.
Classification of the Z-Pinch Waste Stream as Low-Level Waste for Disposal
Singledecker, Steven John
2017-03-10
The purpose of this document is to describe the waste stream from Z-Pinch Residual Waste Project that due to worker safety concerns and operational efficiency is a candidate for blending Transuranic and low level waste together and can be safely packaged as low-level waste consistent with DOE Order 435.1 requirements and NRC guidance 10 CFR 61.42. This waste stream consists of the Pu-ICE post-shot containment systems, including plutonium targets, generated from the Z Machine experiments requested by LANL and conducted by SNL/NM. In the past, this TRU waste was shipped back to LANL after Sandia sends the TRU data packagemore » to LANL to certify the characterization (by CCP), transport and disposition at WIPP (CBFO) per LANL MOU-0066. The Low Level Waste is managed, characterized, shipped and disposed of at NNSS by SNL/NM per Sandia MOU # 11-S-560.« less
Design of Z-Pinch and Dense Plasma Focus Powered Vehicles
NASA Technical Reports Server (NTRS)
Polsgrove, Tara; Fincher, Sharon; Adams, Robert B.; Cassibry, Jason; Cortez, Ross; Turner, Matthew; Maples, C. Daphne; Miermik, Janie N.; Statham, Geoffrey N.; Fabisinski, Leo;
2011-01-01
Z-pinch and Dense Plasma Focus (DPF) are two promising techniques for bringing fusion power to the field of in-space propulsion. A design team comprising of engineers and scientists from UAHuntsville, NASA's George C. Marshall Space Flight Center and the University of Wisconsin developed concept vehicles for a crewed round trip mission to Mars and an interstellar precursor mission. Outlined in this paper are vehicle concepts, complete with conceptual analysis of the mission profile, operations, structural and thermal analysis and power/avionics design. Additionally engineering design of the thruster itself is included. The design efforts adds greatly to the fidelity of estimates for power density (alpha) and overall performance for these thruster concepts
Neutron Signatures of Non-Thermal Ion Distributions in Z-Pinch Driven ICF Plasmas
NASA Astrophysics Data System (ADS)
Knapp, Patrick; Jennings, Christopher; Sinars, Daniel
2012-10-01
In preparation for upcoming ICF experiments on the 26 MA Z machine (e.g., D2 gas puff, MagLIF [1]), we are studying the neutron energy spectra produced by magnetically-driven loads beyond the archetypal single temperature, uniform plasma. Z-pinch sources frequently exhibit evidence of unusual neutron spectra [2], which can be attributed to three-dimensional turbulent motion, high-energy beams, and other phenomena leading to non-Maxwellian ion distributions. Understanding the nature of our plasma neutron sources is critical for understanding how they scale with increasing current. We will show Monte Carlo and analytic calculations for plausible scenarios and discuss the corresponding signatures for the existing set of time-of-flight diagnostics on Z.[4pt] [1] S. A. Slutz et al. Phys. Plasmas 17, 056303 (2010)[0pt] [2] V.V. Vikhrev and V.D. Korolev, Plasma Dynamics, Vol. 33, No. 5 (2007)
Rep-rated Z-Pinch Power Plant Concept - Direct Energy Conversion and Shrapnel Generation*
NASA Astrophysics Data System (ADS)
de Groot, John S.; Gronbech-Jensen, Niels; Miller, Greg; Olsen, Craig L.; Rochau, Gary E.; Derzon, Mark S.; Slutz, Steven A.; Spielman, Rick B.; Peterson, Per F.; Rochau, Gregory A.; Pederson, Robert R.
2000-10-01
We are developing direct energy conversion schemes and shrapnel generation models to be used to optimize a high yield z-pinch IFE power plant concept. The concept uses high yield ( 10 GJ) at low rep-rate ( 0.1 Hz), with a Recyclable Transmission Line (RTL) to provide the necessary standoff between the fusion target and the power plant chamber. The RTL would be cast out of a conventional power plant coolant material (such as Li or Flibe) that can be used to absorb the fusion energy, breed tritium, and mitigate the shock to the first wall. Current results of initial work on this concept will be discussed. *Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy Under Contract DE-AC04-94AL85000.
X-ray spectrograph for quick turnaround measurement of z-pinch plasma parameters
NASA Astrophysics Data System (ADS)
Failor, Bruce H.; Song, Yuanxu; Yadlowsky, Edward J.; Hazelton, Robert C.; Moschella, John J.
1999-01-01
Our objective is to diagnose primarily Ar z-pinch plasmas with 1019
Use of vacuum arc plasma guns for a metal puff Z-pinch system
Rousskikh, A. G.; Zhigalin, A. S.; Oreshkin, V. I.
2011-09-15
The performance of a metal puff Z-pinch system has been studied experimentally. In this type of system, the initial cylindrical shell 4 cm in diameter was produced by ten plasma guns. Each gun initiates a vacuum arc operating between magnesium electrodes. The net current of the guns was 80 kA. The arc-produced plasma shell was compressed by using a 450-kA, 450-ns driver, and as a result, a plasma column 0.3 cm in diameter was formed. The electron temperature of the plasma reached 400 eV at an average ion concentration of 1.85 {center_dot} 10{sup 18} cm{sup -3}. The power of themore » Mg K-line radiation emitted by the plasma for 15-30 ns was 300 MW/cm.« less
Classification of the Z-Pinch Waste Stream as Low-Level Waste for Disposal
Singledecker, Steven John
2017-03-10
The purpose of this document is to describe the waste stream from Z-Pinch Residual Waste Project that due to worker safety concerns and operational efficiency is a candidate for blending Transuranic and low level waste together and can be safely packaged as low-level waste consistent with DOE Order 435.1 requirements and NRC guidance 10 CFR 61.42. This waste stream consists of the Pu-ICE post-shot containment systems, including plutonium targets, generated from the Z Machine experiments requested by LANL and conducted by SNL/NM. In the past, this TRU waste was shipped back to LANL after Sandia sends the TRU data package to LANL to certify the characterization (by CCP), transport and disposition at WIPP (CBFO) per LANL MOU-0066. The Low Level Waste is managed, characterized, shipped and disposed of at NNSS by SNL/NM per Sandia MOU # 11-S-560.
MAIZE: a 1 MA LTD-Driven Z-Pinch at The University of Michigan
Gilgenbach, R. M.; Gomez, M. R.; Zier, J. C.; Tang, W. W.; French, D. M.; Lau, Y. Y.; Mazarakis, M. G.; Cuneo, M. E.; Johnston, M. D.; Oliver, B. V.; Mehlhorn, T. A.; Kim, A. A.; Sinebryukhov, V. A.
2009-01-21
Researchers at The University of Michigan have constructed and tested a 1-MA Linear Transformer Driver (LTD), the first of its type to reach the USA. The Michigan Accelerator for Inductive Z-pinch Experiments, (MAIZE), is based on the LTD developed at the Institute of High Current Electronics in collaboration with Sandia National Labs and UM. This LTD utilizes 80 capacitors and 40 spark gap switches, arranged in 40 'bricks,' to deliver a 1 MA, 100 kV pulse with 100 ns risetime into a matched resistive load. Preliminary resistive-load test results are presented for the LTD facility.Planned experimental research programs at UM include: a) Studies of Magneto-Raleigh-Taylor instability of planar foils, and b) Vacuum convolute studies including cathode and anode plasma.
3D MHD Simulations of Radial Wire Array Z-pinches
Niasse, N.; Chittenden, J. P.; Bland, S. N.; Suzuki-Vidal, F. A.; Hall, G. N.; Lebedev, S. V.; Calamy, H.; Zucchini, F.; Lassalle, F.; Bedoch, J. P.
2009-01-21
Recent experiments carried out on the MAGPIE (1 MA, 250 ns), OEDIPE (730 kA, 1.5 {mu}s) and SPHINX (4 MA, 700 ns)[1] facilities have shown the relatively high level of scalability of the Radial Wire Array Z-pinches. These configurations where the wires stretch radially outwards from a central cathode offer numerous advantages over standard cylindrical arrays. In particular, imploding in a very stable and compact way, they seem suitable for coupling to small scale hohlraums. Making use of the 3D resistive magneto-hydrodynamic code GORGON[2] developed at Imperial College, the dynamic of the radial wire arrays is investigated. Influence of the cathode hotspots and wires angle on the x-ray emissions is also discussed. Comparison with experiments is offered to validate the numerical studies.
Development of the Axial Instability in Low Wire Number Wire Array Z-Pinches
Knapp, P. F.; Bell, K. S.; Blesener, I. C.; Chalenski, D. A.; Douglass, J. D.; Greenly, J. B.; Martin, M. R.; McBride, R. D.; Pikuz, S. A.; Shelkovenko, T. A.; Hammer, D. A.; Kusse, B. R.; Hall, G. N.
2009-01-21
We are investigating the development of the axial instability, a modulation of the size of the coronal plasma that develops around each wire in wire-array Z-pinches. The modulation is a result of nonuniform ablation of material from the relatively cold wire core. It has long been known that the wavelength of this modulation is constant late in time and, since it is unique to different materials, it has come to be known as the fundamental mode. In these experiments we imaged individual wires with laser shadowgraphy early in time primarily in low wire number, large wire diameter aluminum arrays for ease of viewing. We Observe the development of this modulation from the time of initiation of coronal plasma, obtaining its dominant wavelength and amplitude growth as a function of time. We also studied the instability on coiled wires, which modify the wire ablation mechanism and completely suppress the fundamental mode[Hall2008]. time is discussed.
Magneto-Hydrodynamic Modeling in the Design and Interpretation of Wire Array Z-pinches
Chittenden, J. P.; Niasse, N. P.; Jennings, C. A.
2009-01-21
Magneto-hydrodynamic simulations provide a powerful tool for improving our understanding of the complex physical processes underlying the behavior of wire array Z-pinches. We show how, by using large scale parallel 3D simulations of the array as a whole, it is possible to encompass all of the important features of the wire ablation, implosion and stagnation phases and to observe how these phenomena control the X-ray pulse that is achieved. Comparison of code results with experimental data from the 'Z' and MAGPIE pulsed power generators is shown to provide a detailed benchmark test for the models. The simulation results are also used to highlight key areas for future research.
Radiative properties of argon gas puff z-pinch implosions on COBRA
NASA Astrophysics Data System (ADS)
Ouart, N. D.; de Grouchy, P. W. L.; Qi, N.; Giuliani, J. L.; Dasgupta, A.; Shelkovenko, T. A.; Pikuz, S. A.; Hammer, D. A.; Kusse, B. R.; Apruzese, J. P.; Clark, R. W.
2016-10-01
Spatially resolved and time-integrated x-ray spectroscopy, combined with modeling of the spectra with detailed radiation kinetics and transport, is a powerful method to study the conditions in a hot moving plasma. K-shell argon spectra were measured from gas puff implosions with different center jet masses on the 1 MA COBRA generator at Cornell University. The outer to inner plenum pressures (1 and 3 psia, respectively) were the same for all shots producing an outer to inner mass ratio of 1:1. This paper uses non-local thermodynamic equilibrium kinetic modeling to infer the ion density, electron temperature, K-shell radiating mass, and K-shell powers from stagnating argon gas puff z-pinch implosion. We find that the implosions with a center jet produced bright spot regions of plasma with higher temperature and density than those without a jet.
End-On Laser Interferometry of Wire Array Z-Pinch Implosions on the MAGPIE Generator
NASA Astrophysics Data System (ADS)
Swadling, George; Lebedev, Sergey; Chittenden, Jeremy; Hall, Gareth; Suzuki-Vidal, Francisco; Harvey-Thompson, Adam; Niasse, Nicolas; Burdiak, Guy; Khoory, Essa; Pickworth, Louisa; de Grouchi, Philip; Suttle, Lee; Magpie Project Team
2011-10-01
New end-on measurements have taken of the areal electron density distribution of wire array z-pinches during the ablation phase. These measurements have been used to investigate the differences in dynamics between aluminium and tungsten arrays. The experiments were carried out on the 1.4 MA peak current, 240ns rise-time MAGPIE generator at Imperial College, London. The measurements were taken using a two colour Mach-Zender style imaging interferometer. Probing is provided by the 2nd and 3rd harmonics (532nm and 355nm) of a pulsed Nd:YAG laser with a pulse duration of 500ps. Analysis of the results is presented and comparisons made to both the rocket model and simulations produced using the GORGON MHD code.
3D MHD Simulations of Radial Wire Array Z-pinches
NASA Astrophysics Data System (ADS)
Niasse, N.; Chittenden, J. P.; Bland, S. N.; Suzuki-Vidal, F. A.; Hall, G. N.; Lebedev, S. V.; Calamy, H.; Zucchini, F.; Lassalle, F.; Bedoch, J. P.
2009-01-01
Recent experiments carried out on the MAGPIE (1 MA, 250 ns), OEDIPE (730 kA, 1.5 μs) and SPHINX (4 MA, 700 ns)[1] facilities have shown the relatively high level of scalability of the Radial Wire Array Z-pinches. These configurations where the wires stretch radially outwards from a central cathode offer numerous advantages over standard cylindrical arrays. In particular, imploding in a very stable and compact way, they seem suitable for coupling to small scale hohlraums. Making use of the 3D resistive magneto-hydrodynamic code GORGON[2] developed at Imperial College, the dynamic of the radial wire arrays is investigated. Influence of the cathode hotspots and wires angle on the x-ray emissions is also discussed. Comparison with experiments is offered to validate the numerical studies.
Development of laser based diagnostics for wire array z-pinch experiments on the MAGPIE generator
NASA Astrophysics Data System (ADS)
Swadling, George; Lebedev, S. V.; Bland, S. N.; Hall, G. N.; Suzuki-Vidal, F.; Niasse, N.; Burdiak, G.; Khoory, E.; Pickworth, L.; Hutchison, C.
2009-11-01
End on Interferometric imaging is a useful technique for diagnosing the electron density distribution in the interior of wire array z-pinches during their ablation phase. These measurements are limited as there is often no known density reference point in the image. By using a time resolved, CW line integrated interferometry system, we can measure the electron density for a single point on the image. This allows us to calculate the density distribution across the remainder of the image. Two new quadrature interferometry systems are discussed, the first free space and the second fiber based. Also discussed is a new fiber based multipoint Heterodyne Velocimetry (HET-V) system, for the time resolved measurement of large velocities and accelerations, and a new faraday rotation current probe system, to measure rapidly rising currents in new switched mode wire arrays.
Magneto-Hydrodynamic Modeling in the Design and Interpretation of Wire Array Z-pinches
NASA Astrophysics Data System (ADS)
Chittenden, J. P.; Niasse, N. P.; Jennings, C. A.
2009-01-01
Magneto-hydrodynamic simulations provide a powerful tool for improving our understanding of the complex physical processes underlying the behavior of wire array Z-pinches. We show how, by using large scale parallel 3D simulations of the array as a whole, it is possible to encompass all of the important features of the wire ablation, implosion and stagnation phases and to observe how these phenomena control the X-ray pulse that is achieved. Comparison of code results with experimental data from the 'Z' and MAGPIE pulsed power generators is shown to provide a detailed benchmark test for the models. The simulation results are also used to highlight key areas for future research.
Development of absorption spectroscopy for wire-array Z-pinches
NASA Astrophysics Data System (ADS)
Anderson, A.; Ivanov, V. V.; Hakel, P.; Mancini, R. C.; Wiewior, P.; Durmaz, T.; Astanovitskiy, A. L.; Chalyy, O.; Altemara, S. D.; Papp, D.; McKee, E.; Chittenden, J. P.; Niasse, N.; Shevelko, A. P.
2010-11-01
The 50 TW Leopard laser was coupled with the 1 MA Zebra generator for the x-ray backlighting of wire arrays. The Leopard laser is based on the chirped pulse amplification and can operate in subpicosecond or subnanosecond regimes. Several materials were tested in both regimes and samarium was selected for subnanosecond backlighting in the range of 7-9 å. One ray of Al wire-arrays was investigated at the ablation and implosion stages. Two focusing conical spectrometers with mica crystals recorded reference and main spectra on x-ray film. Collimators protected spectrometers against the x-ray burst from the main Z-pinch. Comparison of spectra of backlighting radiation with reference spectra indicates absorption lines in the range of 8.2-8.4 å. The electron temperature of wire-array plasma was estimated from simulations with atomic kinetics models.
The effects of insulating coatings and current prepulse on tungsten planar wire array Z-pinches
Li, M., E-mail: limo@nint.ac.cn; Li, Y.; State Key Laboratory of Intense Pulsed Radiation Simulation and Effect, Northwest Institute of Nuclear Technology, Xi'an 710024
2015-12-15
This paper presents experimental results on the effects of insulating coatings and current prepulse on tungsten planar wire array Z-pinches on ∼100 ns main current facility. Optical framing images indicated that without a current prepulse the wire ablation process was asymmetrical and the implosion was zippered. The x-ray peak power was ∼320 GW. By using insulating coatings on the wire surface the asymmetry remained, and the processes of ablation and implosion were delayed by ∼30 ns. The x-ray burst was narrow and decreased to ∼200 GW. When current prepulses were used on both standard and insulated wire arrays, implosion symmetry was improved and themore » x-ray burst was improved (to ∼520 GW peak power). In addition, there was a strong emitting precursor column for insulated loads with the current prepulse.« less
The role of Z-pinch fusion transmutation of waste in the nuclear fuel cycle.
Smith, James Dean; Drennen, Thomas E.; Rochau, Gary Eugene; Martin, William Joseph; Kamery, William; Phruksarojanakun, Phiphat; Grady, Ryan; Cipiti, Benjamin B.; Wilson, Paul Philip Hood; Mehlhorn, Thomas Alan; Guild-Bingham, Avery; Tsvetkov, Pavel Valeryevich
2007-10-01
The resurgence of interest in reprocessing in the United States with the Global Nuclear Energy Partnership has led to a renewed look at technologies for transmuting nuclear waste. Sandia National Laboratories has been investigating the use of a Z-Pinch fusion driver to burn actinide waste in a sub-critical reactor. The baseline design has been modified to solve some of the engineering issues that were identified in the first year of work, including neutron damage and fuel heating. An on-line control feature was added to the reactor to maintain a constant neutron multiplication with time. The transmutation modeling effort has been optimized to produce more accurate results. In addition, more attention was focused on the integration of this burner option within the fuel cycle including an investigation of overall costs. This report presents the updated reactor design, which is able to burn 1320 kg of actinides per year while producing 3,000 MWth.
Non-thermal x-ray emission from wire array z-pinches
Ampleford, David; Hansen, Stephanie B.; Jennings, Christopher Ashley; Webb, Timothy Jay; Harper-Slaboszewicz, V.; Loisel, Guillaume Pascal; Flanagan, Timothy McGuire; Bell, Kate Suzanne; Jones, Brent M.; McPherson, Leroy A.; Rochau, Gregory A.; Chittenden, Jeremy P.; Sherlock, Mark; Appelbe, Brian; Giuliani, John; Ouart, Nicholas; Seely, John
2015-12-01
We report on experiments demonstrating the transition from thermally-dominated K-shell line emission to non-thermal, hot-electron-driven inner-shell emission for z pinch plasmas on the Z machine. While x-ray yields from thermal K-shell emission decrease rapidly with increasing atomic number Z, we find that non-thermal emission persists with favorable Z scaling, dominating over thermal emission for Z=42 and higher (hn ≥ 17keV). Initial experiments with Mo (Z=42) and Ag (Z=47) have produced kJ-level emission in the 17-keV and 22-keV Kα lines respectively. We will discuss the electron beam properties that could excite these non - thermal lines. We also report on experiments that have attempted to control non - thermal K - shell line emission by modifying the wire array or load hardware setup.
Investigation of the interaction pulse in nested wire array z-pinches
NASA Astrophysics Data System (ADS)
Ampleford, D. J.; Jennings, C. A.; Cuneo, M. E.; Deeney, C.; Bland, S. N.; Lebedev, S. V.; Bott, S. C.; Hall, G. N.; Suzuki, F.; Chittenden, J. P.
2006-10-01
Radiation pulse shaping is vital for z-pinch driven ICF concepts. One method to achieve such pulse shaping is to use the foot pulse generated by the interaction between two nested wire arrays. We present data from experiments investigating this interaction pulse on the MAGPIE generator (1MA, 240ns) at Imperial College London. On MAGPIE, the current through the inner array is suppressed by enhancing its inductance, leading to a similar current fraction to that observed on the Z-generator. In these experiments time gated imaging of photon energies >30eV indicates that radiation is emitted as leading bubbles of the imploding outer array reach and pass the inner array. Experiments using novel configurations to eliminate possible heating mechanisms will also be discussed, and data will be compared to simulations from the Gorgon 3D MHD code.
Implosion dynamics of condensed Z-pinch at the Angara-5-1 facility
NASA Astrophysics Data System (ADS)
Aleksandrov, V. V.; Grabovski, E. V.; Gritsuk, A. N.; Volobuev, I. V.; Kazakov, E. D.; Kalinin, Yu. G.; Korolev, V. D.; Laukhin, Ya. I.; Medovshchikov, S. F.; Mitrofanov, K. N.; Oleinik, G. M.; Pimenov, V. G.; Smirnova, E. A.; Ustroev, G. I.; Frolov, I. N.
2017-08-01
The implosion dynamics of a condensed Z-pinch at load currents of up to 3.5 MA and a current rise time of 100 ns was studied experimentally at the Angara-5-1 facility. To increase the energy density, 1- to 3-mm-diameter cylinders made of a deuterated polyethylene-agar-agar mixture or microporous deuterated polyethylene with a mass density of 0.03-0.5 g/cm3 were installed in the central region of the loads. The plasma spatiotemporal characteristics were studied using the diagnostic complex of the Angara-5-1 facility, including electron-optical streak and frame imaging, time-integrated X-ray imaging, soft X-ray (SXR) measurements, and vacuum UV spectroscopy. Most information on the plasma dynamics was obtained using a ten-frame X-ray camera ( E > 100 eV) with an exposure of 4 ns. SXR pulses were recorded using photoemissive vacuum X-ray detectors. The energy characteristics of neutron emission were measured using the time-offlight method with the help of scintillation detectors arranged along and across the pinch axis. The neutron yield was measured by activation detectors. The experimental results indicate that the plasma dynamics depends weakly on the load density. As a rule, two stages of plasma implosion were observed. The formation of hot plasma spots in the initial stage of plasma expansion from the pinch axis was accompanied by short pulses of SXR and neutron emission. The neutron yield reached (0.4-3) × 1010 neutrons/shot and was almost independent of the load density due to specific features of Z-pinch dynamics.
Giuliani, J. L.; Thornhill, J. W.; Dasgupta, A.
2014-03-15
The difference between the ion thermal and effective temperatures is investigated through simulations of the Ne gas puff z-pinch reported by Kroupp et al. [Phys. Rev. Lett. 107, 105001 (2011)]. Calculations are performed using a 2D, radiation-magnetohydrodynamic code with Tabular Collisional-Radiative Equilibrium, namely Mach2-TCRE [Thornhill et al., Phys. Plasmas 8, 3480 (2001)]. The extensive data set of imaging and K-shell spectroscopy from the experiments provides a challenging validation test for z-pinch simulations. Synthetic visible images of the implosion phase match the observed large scale structure if the breakdown occurs at the density corresponding to the Paschen minimum. At the beginningmore » of stagnation (−4 ns), computed plasma conditions change rapidly showing a rising electron density and a peak in the ion thermal temperature of ∼1.8 keV. This is larger than the ion thermal temperature (<400 eV) inferred from the experiment. By the time of peak K-shell power (0 ns), the calculated electron density is similar to the data and the electron and ion thermal temperatures are equilibrated, as is observed. Effective ion temperatures are obtained from calculated emission line widths accounting for thermal broadening and Doppler velocity shifts. The observed, large effective ion temperatures (∼4 keV) early in the stagnation of this Ne pinch can be explained solely as a combination of compressional ion heating and steep radial velocity gradients near the axis. Approximations in the modeling are discussed in regard to the higher ion thermal temperature and lower electron density early in the stagnation compared to the experimental results.« less
Neutron Production from Z-pinch Plasmas at the 1 MA Zebra Generator
NASA Astrophysics Data System (ADS)
McKee, Erik Scott
Neutrons produced deuterium Z-pinch plasmas are widely acknowledged to be a consequence of highly accelerated deuterons undergoing nuclear fusion with relatively stationary deuterons. The acceleration is thought to occur in intense fields created in the MHD instabilities that punctuate the plasma column. Interestingly, the energies of the accelerated ions exceed the applied voltage across the electrode gap. We use the 1 MA Zebra pulsed-power generator at the Nevada Terawatt Facility (NTF) to explore this poorly understood fast neutron production mechanism by creating deuterium Z-pinches in three distinct types of target loads. The loads are a cylindrical shell of deuterium gas, the far less explored deuterided palladium wire arrays, and a deuterium-carbon ablated laser plume target, which is unique to the NTF. The pinch dynamics vary considerably in these three targets and provide the opportunity to explore the ion acceleration mechanism. We infer the characteristics of the accelerating fields from a wide range of diagnostic data including the neutron yield, energy spectrum and angular distribution, and the properties of the matching electron beams that are accelerated in the same field, and the energetic X-rays they produce on stopping. The plasma and the instabilities were recorded on several high-speed imaging diagnostics along with time-integrated soft (<10 keV) X-ray pinhole images. The three load types produced total neutron yields in the 108-1010 n/pulse range. The synchronization we observe between the ion and electron beams and the development of instabilities leads us to conrm the acceleration hypothesis. We also present the characteristics of the fields and ion beams in these varied pinches.
Subhash, P. V.; Madhavan, S.; Chaturvedi, S.
2006-07-15
This article reports, for the first time, two-dimensional magnetohydrodynamic liner-on-plasma simulations for the compression phase of a magnetized target fusion (MTF) system with an inverse Z-pinch target. These simulations evolve the complete liner-plasma system along with the driving pulsed-power source. First, it has been demonstrated that closely coupled liner-on-plasma simulations produce results that are significantly different from loosely coupled simulations that have been reported in the literature. Second, it has been found that an initially stable plasma, satisfying the Kadomtsev criteria, and with a small initial pressure perturbation in the axial direction, remains stable all through the compression phase, even though there are large changes in the pressure and magnetic field levels. Third, a plasma that violates the Kadomtsev criteria, even by a small amount, turns out to be unstable, as predicted by theory. In practical terms, this means that it is preferable to stay well away from the stability limit, even at the cost of some reduction of initial plasma pressure. Fourth, even during the burn phase, when there is a large and rapid increase in plasma pressure due to fusion energy deposition, an initially stable plasma generally tends to remain stable, and even improves its stability margin. This observation shows that the inverse Z pinch is fairly benign as a MTF target, as an initially stable plasma remains stable during both the compression and burn phases. Fifth, certain unusual features are observed in the temperature profile--these depend upon the time scale for implosion. This has implications for plasma-surface interactions at the liner and central conductor.
NASA Astrophysics Data System (ADS)
Subhash, P. V.; Madhavan, S.; Chaturvedi, S.
2006-07-01
This article reports, for the first time, two-dimensional magnetohydrodynamic liner-on-plasma simulations for the compression phase of a magnetized target fusion (MTF) system with an inverse Z-pinch target. These simulations evolve the complete liner-plasma system along with the driving pulsed-power source. First, it has been demonstrated that closely coupled liner-on-plasma simulations produce results that are significantly different from loosely coupled simulations that have been reported in the literature. Second, it has been found that an initially stable plasma, satisfying the Kadomtsev criteria, and with a small initial pressure perturbation in the axial direction, remains stable all through the compression phase, even though there are large changes in the pressure and magnetic field levels. Third, a plasma that violates the Kadomtsev criteria, even by a small amount, turns out to be unstable, as predicted by theory. In practical terms, this means that it is preferable to stay well away from the stability limit, even at the cost of some reduction of initial plasma pressure. Fourth, even during the burn phase, when there is a large and rapid increase in plasma pressure due to fusion energy deposition, an initially stable plasma generally tends to remain stable, and even improves its stability margin. This observation shows that the inverse Z pinch is fairly benign as a MTF target, as an initially stable plasma remains stable during both the compression and burn phases. Fifth, certain unusual features are observed in the temperature profile—these depend upon the time scale for implosion. This has implications for plasma-surface interactions at the liner and central conductor.
NASA Astrophysics Data System (ADS)
Peterson, Kyle John
2003-10-01
Magnetic flux compression is a well established technique for the generation of ultrahigh magnetic fields, large currents, and large energy densities. It has been suggested as a means for power density amplification on Z-pinch generators such as Decade Quad, at Arnold Engineering Development Center, and it may be especially suitable as a means for producing higher powers of K-shell radiation from high atomic number loads such as titanium. Although many one-dimensional models of flux compression on Z-pinch generators exist, an improvement in understanding is needed about the physics and implosion dynamics on a two-dimensional level. To this end, a two-dimensional resistive magnetohydrodynamic code was used to study a particular flux compression concept for use on Decade Quad. In the concept under study, compression occurs for self generated opposing azimuthal magnetic fields. In order to provide appropriate boundary conditions for the simulations, a non-linear circuit model was developed to enable calculation of the dynamically changing inductive and resistive impedances of the two coupled current paths such that they are consistent with the developing plasma. Good flux compression is observed despite magnetic flux losses. Two dimensional calculations are shown to match reasonably well with one-dimensional results. However, results also indicate Rayleigh-Taylor instabilities significantly affect implosion dynamics through the creation of isolated magnetic flux pockets, formation of circular currents, and the redistribution of current flow. It is also found that the Aluminum plasma armature shorts out on the stator, and thereby causes a nonideal current distribution in the titanium plasma. Consequently, the titanium plasma does not receive sufficient energy transfer for efficient K-shell radiative emission.
NASA Astrophysics Data System (ADS)
Lemke, R. W.; Bailey, J. E.; Chandler, G. A.; Nash, T. J.; Slutz, S. A.; Mehlhorn, T. A.
2005-01-01
Z-pinch plasmas are susceptible to the magnetic Rayleigh-Taylor (MRT) instability. The Z-pinch dynamic hohlraum (ZPDH), as implemented on the Z machine at Sandia National Laboratories, is composed of an annular tungsten plasma that implodes onto a coaxial foam convertor. The collision between tungsten Z pinch and convertor launches a strong shock in the foam. Shock heating generates radiation that is trapped by the tungsten Z pinch. The radiation can be used to implode a fuel-filled, inertial confinement fusion capsule. Hence, it is important to understand the influence that the MRT instability has on shock generation. This paper presents results of an investigation to determine the affect that the MRT instability has on characteristics of the radiating shock in a ZPDH. Experiments on Z were conducted in which a 1.5cm tall, nested array (two arrays with initial diameters of 2.0 and 4.0cm), tungsten wire plasma implodes onto a 5mg/cc, CH2 foam convertor to create a ˜135eV dynamic hohlraum. X-ray pinhole cameras viewing along the ZPDH axis recorded time and space resolved images of emission produced by the radiating shock. These measurements showed that the shock remained circular to within ±30-60μm as it propagated towards the axis, and that it was highly uniform along its height. The measured emission intensities are compared with synthetic x-ray images obtained by postprocessing two-dimensional, radiation magnetohydrodynamic simulations in which the amplitude of MRT perturbations is varied. These simulations accurately reproduce the measured shock trajectory and spatial profiles of the dynamic hohlraum interior emission as a function of time, even for large MRT amplitudes. Furthermore, the radiating shock remains relatively uniform in the axial direction regardless of the MRT amplitude because nonuniformities are tamped by the interaction of the tungsten Z-pinch plasma with the foam. These results suggest that inertial confinement fusion implosions driven by a
Conversion of electromagnetic energy in Z-pinch process of single planar wire arrays at 1.5 MA
NASA Astrophysics Data System (ADS)
Liangping, Wang; Mo, Li; Juanjuan, Han; Jian, Wu; Ning, Guo; Aici, Qiu
2014-06-01
The electromagnetic energy conversion in the Z-pinch process of single planar wire arrays was studied on Qiangguang generator (1.5 MA, 100 ns). Electrical diagnostics were established to monitor the voltage of the cathode-anode gap and the load current for calculating the electromagnetic energy. Lumped-element circuit model of wire arrays was employed to analyze the electromagnetic energy conversion. Inductance as well as resistance of a wire array during the Z-pinch process was also investigated. Experimental data indicate that the electromagnetic energy is mainly converted to magnetic energy and kinetic energy and ohmic heating energy can be neglected before the final stagnation. The kinetic energy can be responsible for the x-ray radiation before the peak power. After the stagnation, the electromagnetic energy coupled by the load continues increasing and the resistance of the load achieves its maximum of 0.6-1.0 Ω in about 10-20 ns.
Transition from Beam-Target to Thermonuclear Fusion in High-Current Deuterium Z-Pinch Simulations.
Offermann, Dustin T; Welch, Dale R; Rose, Dave V; Thoma, Carsten; Clark, Robert E; Mostrom, Chris B; Schmidt, Andrea E W; Link, Anthony J
2016-05-13
Fusion yields from dense, Z-pinch plasmas are known to scale with the drive current, which is favorable for many potential applications. Decades of experimental studies, however, show an unexplained drop in yield for currents above a few mega-ampere (MA). In this work, simulations of DD Z-Pinch plasmas have been performed in 1D and 2D for a constant pinch time and initial radius using the code Lsp, and observations of a shift in scaling are presented. The results show that yields below 3 MA are enhanced relative to pure thermonuclear scaling by beamlike particles accelerated in the Rayleigh-Taylor induced electric fields, while yields above 3 MA are reduced because of energy lost by the instability and the inability of the beamlike ions to enter the pinch region.
Transition from Beam-Target to Thermonuclear Fusion in High-Current Deuterium Z-Pinch Simulations
NASA Astrophysics Data System (ADS)
Offermann, Dustin; Welch, Dale; Rose, Dave; Thoma, Carsten; Clark, Robert; Mostrom, Chris; Schmidt, Andrea; Link, Anthony
2016-10-01
Fusion yields from dense, Z-pinch plasmas are known to scale with the drive current, which is favorable for many potential applications. Decades of experimental studies, however, show an unexplained drop in yield for currents above a few mega-ampere (MA). In this work, simulations of DD Z-Pinch plasmas have been performed in 1D and 2D for a constant pinch time and initial radius using the code L
Staged Z-pinch Experiments on the University of Nevada, Reno, NTF Zebra Facility
NASA Astrophysics Data System (ADS)
Wessel, Frank J.; Ruskov, E.; Rahman, H. U.; Ney, P.; Darling, T. W.; Johnson, Z.; McGee, E.; Covington, A.; Dutra, E.; Valenzuela, J. C.; Conti, F.; Narkis, J.; Beg, F.
2016-10-01
A Staged Z-pinch load is tested on the University of Nevada, Reno, Zebra Facility, located at the Nevada Terawatt Facility. The annular liner was argon (1-cm radius × 0.5-cm thickness), the target was a deuterium fill (either gas, or plasma), and the axial-magnetic field was either, Bz = 0, 100 G. This paper presents experimental data and analyses, including neutron-total yield and time-of-flight measurements. The results are benchmarked against the predictions from a 2D-MHD simulations. Results from this first (Spring 2016) series of experiments indicate that the initial-operating points selected for the mass injectors were sub-optimal. Design revisions are underway and changes in the injector timing will be implemented the Fall 2016 campaign. Companion papers in this session, and in poster papers, provide the basis for the SZP, designs and performance for the injectors, and details on the Zebra Facility. Advanced Research Projects Agency - Energy, DE-AR0000569.
Computational investigation of the limits to Pease-Braginskii collapse of a Z-pinch
Nielsen, P.D.
1981-06-01
This dissertation investigates the one-dimensional limits to such a radiation enhanced collapse through the use of a Lagrangian simulation code, LASNEX. The code includes the effects of a wide range of phenomena - opacity, ionization, experimentally determined equations of state, magnetic effects on transport coefficients, and external electrical circuits. Special attention was given to the magnetic field subroutines. They were revised to include ion acoustic and lower hybrid drift induced resistivity and to increase accuracy and efficiency. The magnetic pressure term was differenced in a manner that eliminates any influence of zone size, allowing large, low density zones outside the plasma column. In these large zones, magnetic flux and energy were determined by direct integration instead of summation to increase overall conservation. With these changes, the computational timesteps were determined by phenomena in the plasma instead of the Alfven velocity in the low density region. These modifications improved the accuracy of the code on Z-pinch problems by a factor of 10-100 depending on the minimum pinch radius reached.
New compact hohlraum configuration research at the 1.7 MA Z-pinch generator
Kantsyrev, V. L., E-mail: victor@unr.edu; Shrestha, I. K.; Esaulov, A. A.
2014-12-15
A new compact Z-pinch x-ray hohlraum design with parallel-driven x-ray sources was experimentally demonstrated in a full configuration with a central target and tailored shine shields (to provide a symmetric temperature distribution on the target) at the 1.7 MA Zebra generator. This presentation reports on the joint success of two independent lines of research. One of these was the development of new sources – planar wire arrays (PWAs). PWAs turned out to be a prolific radiator. Another success was the drastic improvement in energy efficiency of pulsed-power systems, such as the Load Current Multiplier (LCM). The Zebra/LCM generator almost doubledmore » the plasma load current to 1.7 MA. The two above-mentioned innovative approaches were used in combination to produce a new compact hohlraum design for ICF, as jointly proposed by SNL and UNR. Good agreement between simulated and measured radiation temperature of the central target is shown. Experimental comparison of PWAs with planar foil liners (PFL) - another viable alternative to wire array loads at multi-MA generators show promising data. Results of research at the University of Nevada Reno allowed for the study of hohlraum coupling physics at University-scale generators. The advantages of new hohlraum design applications for multi-MA facilities with W or Au double PWAs or PFL x-ray sources are discussed.« less
The role of Z-pinches and related configurations in magnetized target fusion
Lindemuth, I.R.
1997-07-10
The use of a magnetic field within a fusion target is now known as Magnetized Target Fusion in the US and as MAGO (Magnitnoye Obzhatiye, or magnetic compression) in Russia. In contrast to direct, hydrodynamic compression of initially ambient-temperature fuel (e.g., ICF), MTF involves two steps: (a) formation of a warm, magnetized, wall-confined plasma of intermediate density within a fusion target prior to implosion; (b) subsequent quasi-adiabatic compression and heating of the plasma by imploding the confining wall, or pusher. In many ways, MTF can be considered a marriage between the more mature MFE and ICF approaches, and this marriagemore » potentially eliminates some of the hurdles encountered in the other approaches. When compared to ICF, MTF requires lower implosion velocity, lower initial density, significantly lower radial convergence, and larger targets, all of which lead to substantially reduced driver intensity, power, and symmetry requirements. When compared to MFE, MTF does not require a vacuum separating the plasma from the wall, and, in fact, complete magnetic confinement, even if possible, may not be desirable. The higher density of MTF and much shorter confinement times should make magnetized plasma formation a much less difficult step than in MFE. The substantially lower driver requirements and implosion velocity of MTF make z-pinch magnetically driven liners, magnetically imploded by existing modern pulsed power electrical current sources, a leading candidate for the target pusher of an MTF system.« less
High density Z pinch as a small low-energy fusion device
NASA Astrophysics Data System (ADS)
Hammel, J. E.; Scudder, D. W.; Shlachter, J. S.
A Z pinch in the density range 0.5 x 10 to the 20th power to 10 to the 21st power cu cm was investigated. The pinch was created in one to four atmospheres of hydrogen on the axis of a cylindrical chamber through the combination of laser beam preionization and high electric field breakdown between electrodes separated by 5 cm. The low divergence laser beam focused by a 2 m focal length lens entered the chamber through a .64 cm hole in the ground electrode and was dumped in a cavity in the high voltage electrode. The pinch electrodes were driven by a 1.6 ohm, 600 kV water transmission line switched to the load through a multipoint water breakdown switch. The line was charged by a 12 kJ, 600 kV Marx generator. The 30 nsec neodymium laser pulse was fired 50 to 100 nsec prior to the arrival of the high voltage pulse. The 500 kV pulse gave an initial current rise rate of 4 x 10 to the 12th power and a peak current of 300 kA in 200 nsec.
Nonthermal effects on the diagnostics of a collapsing gas shell Z-pinch
NASA Astrophysics Data System (ADS)
Jones, L. A.; Kania, D. R.
The collapsing gas shell Z pinch is powered by a 72 kJ - 600 kV Marx bank. This Marx bank consists of 12, 6 stage modules which are used to pulse charge a 1 (UC OMEGA) -90 nsec long water line in approx. 500 nsec. The plasma produced by this device is well diagnosed, but rather than present the results of all the diagnostics, only those relevant to nonthermal effects are discussed. A spectrum taken with a 1 m vacuum ultraviolet spectrograph is shown. A section of the spectrum was microdensitometered to show Ar X-XIII. This same instrument was used to image the spectrum both axially and radially. The same portion of the spectrum discussed above is shown along with a time integrated, filtered (1 to 6 keV) X-ray pinhole picture. These pictures show that the collapsed plasma is axially inhomogeneous, i.e., He-like argon, represented by the X-ray pinhole picture, forms in hot spots along the axis and lower ionization stages fill in the regions between the hot spots. A spectrum taken with a curved crystal instrument is presented. This spectrum shows the argon XVII, He-like resonance and intercombination lines, along with satellite structures from argon X to XVI. Another part of the spectrum contains weak H-like lines.
Z-Pinch Wire-Electrode Contact Resistance Studies Using Weighted and Soft Metal Gasket Contacts*
NASA Astrophysics Data System (ADS)
Gomez, M. R.; Zier, J. C.; Thurtell, A. F.; French, D. M.; Gilgenbach, R. M.; Tang, W.; Lau, Y. Y.
2008-11-01
The contact made between z-pinch wires and electrodes has a significant effect on both the energy deposited in the wires and the uniformity of the expansion profile of the wires. We have shown that using soft metal gaskets can improve wire-electrode contact significantly over typical weighted contacts. Images of wire expansion profile and wire plasma emission will be presented for single and double wire shots on a 16 kA, 100 kV 4-stage Marx bank with 150 ns risetime. Bench resistance measurements for aluminum, stainless steel, and tungsten wires with diameters ranging from 7.5 um to 30 um will be presented. These measurements utilized both soft metal gasket contacts (gaskets include: indium, silver, aluminum, tin, and lead) and double-ended wire weight contacts (weights ranged from 0.4 g to 1.9 g). *This research was supported by U. S. DoE through Sandia National Laboratories award document numbers 240985, 768225, 790791 and 805234 to the University of Michigan. MRG supported by NNSA Fellowship and JCZ supported by NPSC Fellowship sponsored by Sandia National Labs.
Construction and Initial Tests of MAIZE: 1 MA LTD-Driven Z-Pinch *
NASA Astrophysics Data System (ADS)
Gilgenbach, R. M.; Gomez, M. R.; Zier, J. C.; Tang, W.; French, D. M.; Lau, Y. Y.; Mazarakis, M. G.; Cuneo, M. E.; Johnston, M. D.; Oliver, B. V.; Mehlhorn, T. A.; Kim, A. A.; Sinebryukhov, V. A.
2008-11-01
We report construction and initial testing of a 1-MA Linear Transformer Driver (LTD), The Michigan Accelerator for Inductive Z-pinch Experiments, (MAIZE). This machine, the first of its type to reach the USA, is based on the joint HCEI, Sandia Laboratories, and UM development effort. The compact LTD uses 80 capacitors and 40 spark gap switches, in 40 ``bricks'', to deliver 1 MA, 100 kV pulses with 70 ns risetime into a matched resistive load. Test results will be presented for a single brick and the full LTD. Design and construction will be presented of a low-inductance MITL. Experimental research programs under design and construction at UM include: a) Studies of Magneto-Raleigh-Taylor Instability of planar foils, and b) Vacuum convolute studies including cathode and anode plasma. Theory and simulation results will be presented for these planned experiments. Initial experimental designs and moderate-current feasibility experiments will be discussed. *Research supported by U. S. DoE through Sandia National Laboratories award document numbers 240985, 768225, 790791 and 805234 to the UM. MRG supported by NNSA Fellowship and JCZ supported by NPSC Fellowship / Sandia National Labs.
WITHDRAWN - Dynamics of Precursor Coronal Plasmas and Wire Ablation in Wire Array Z-Pinches
NASA Astrophysics Data System (ADS)
Oliver, B. V.; Yu, E. P.; Sasorov, P.
2005-10-01
The radial acceleration of low density (relative to the wire core) coronal plasmas, towards the axis of wire-array Z pinches, is observed in a variety of experiments on various pulsed-power accelerators [S. V. Lebedev, et al., Phys. Rev. Lett. 85, 98 (2000); V.V. Aleksandrov, et al., Fizika Plazmy 27, 99 (2001); M.E. Cuneo, et al., Bull. Am. Phys. Soc. 43, 234 (2001)]. The dynamics of these coronal plasmas play an important role in the distribution of both current and mass prior to the run in phase of the full array. An extension of previously reported 1-D theory of coronal plasma dynamics to include two dimensional effects and the role of the core state in the plasma production/ablation process is presented. The plasma production rate can be determined either by electron thermal and or radiation conduction from the coronal plasma to the wire core. In either case electron thermal conduction is necessary. For very high current parameter regimes (e.g. > 20 MA), details of the core state need to be considered in the analysis. Two dimensional considerations suggest a weak scaling of ablation rate with the ratio of wire core diameter to inter-wire gap and suggest that strong two-dimensional effects reduce the production rate. It is concluded that to accurately model wire ablation, the material properties of both the ablated plasma and the wire core need to be determined.
Z-Pinch-Driven Hemispherical Capsule Implosions for Fast Ignitor Fuel Assembly
NASA Astrophysics Data System (ADS)
Hanson, D. L.; Vesey, R. A.; Sinars, D. B.; Cuneo, M. E.; Adams, R. G.; Slutz, S. A.; Porter, J. L.; Johnston, R. R.; Wenger, D. F.; Schroen, D. G.; Russell, C.
2004-11-01
Rad-hydro simulations indicate that partial-sphere fusion capsules can be compressed to peak densities of interest for fast ignition experiments with the symmetry control available in a single-ended indirect drive vacuum hohlraum configuration. We are presently investigating this approach to fast ignitor fuel assembly using pulsed-power driver technology. Current from the Sandia Z accelerator implodes a single wire-array z-pinch in the primary hohlraum, efficiently generating thermal x rays to drive the ablative compression of a hemispherical capsule moving on a high density glide surface in the secondary hohlraum. We report on recent work in two areas: (1) x-ray backlighter imaging of 3.0-mm-diam., 110-um-thick GDP hemispherical capsule implosions, complicated at high convergence by gold plasma expansion from the glide surface; and (2) development of a hemispherical liquid cryogenic fusion capsule in which a liquid cryogenic fuel layer is condensed in situ from a low pressure external gas supply and confined between concentric plastic shells mounted on the glide surface. Progress in measurement of shell distortion using high resolution 6.151 keV monochromatic crystal imaging will be discussed. Technology issues for liquid cryogenic fuel capsule development and progress toward demonstration of a working capsule will be presented. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.
Radial and Azimuthal Velocity Profiles in Gas-Puff Z-Pinches
NASA Astrophysics Data System (ADS)
Rocco, Sophia; Engelbrecht, Joseph; Banasek, Jacob; de Grouchy, Philip; Qi, Niansheng; Hammer, David
2016-10-01
The dynamics of neon, argon, and krypton (either singly or in combination) gas puff z-pinch plasmas are studied on Cornell's 1MA, 100-200ns rise-time COBRA pulsed power generator. The triple-nozzle gas puff valve, consisting of two annular gas puffs and a central jet, allows radial tailoring of the gas puff mass-density profile and the use of 1, 2 or 3 different gases at different pressures. Interferometry supplies information on sheath thickness and electron density, variously filtered PCDs and silicon diodes measure hard and soft x-ray production, and multi frame visible and extreme UV imaging systems allow tracking of the morphology of the plasma. A 527nm, 10J Thomson scattering diagnostic system is used to determine radial and azimuthal velocities. Implosion velocities of 170km/s (Kr) and 300km/s (Ne/Ar) are observed. We are investigating the correlations between instability growth, plasma density profile, velocity partitioning as a function of radius, and radiation production. Research supported by the NNSA Stewardship Sciences Academic Programs under DOE Cooperative Agreement No. DE-NA0001836.
Temperature Evolution of a 1 MA Triple-Nozzle Gas-Puff Z-Pinch
NASA Astrophysics Data System (ADS)
de Grouchy, Philip; Banasek, Jacob; Engelbrecht, Joey; Qi, Niansheng; Atoyan, Levon; Byvank, Tom; Cahill, Adam; Moore, Hannah; Potter, William; Ransohoff, Lauren; Hammer, David; Kusse, Bruce; Laboratory of Plasma Studies Team
2015-11-01
Mitigation of the Rayleigh-Taylor instability (RTI) plays a critical role in optimizing x-ray output at high-energy ~ 13 keV using the triple-nozzle Krypton gas-puff at Sandia National Laboratory. RTI mitigation by gas-puff density profiling using a triple-nozzle gas-puff valve has recently been recently demonstrated on the COBRA 1MA z-pinch at Cornell University. In support of this work we investigate the role of shell cooling in the growth of RTI during gas-puff implosions. Temperature measurements within the imploding plasma shell are recorded using a 527 nm, 10 GW Thomson scattering diagnostic for Neon, Argon and Krypton puffs. The mass-density profile is held constant at 22 microgram per centimeter for all three puffs and the temperature evolution of the imploding material is recorded. In the case of Argon puffs we find that the shell ion and electron effective temperatures remain in equilibrium at around 1keV for the majority of the implosion phase. In contrast scattered spectra from Krypton are dominated by of order 10 keV effective ion temperatures. Supported by the NNSA Stewardship Sciences Academic Programs.
New compact hohlraum configuration research at the 1.7 MA Z-pinch generator
NASA Astrophysics Data System (ADS)
Kantsyrev, V. L.; Chuvatin, A. S.; Rudakov, L. I.; Velikovich, A. L.; Shrestha, I. K.; Esaulov, A. A.; Safronova, A. S.; Shlyaptseva, V. V.; Osborne, G. C.; Astanovitsky, A. L.; Weller, M. E.; Stafford, A.; Schultz, K. A.; Cooper, M. C.; Cuneo, M. E.; Jones, B.; Vesey, R. A.
2014-12-01
A new compact Z-pinch x-ray hohlraum design with parallel-driven x-ray sources was experimentally demonstrated in a full configuration with a central target and tailored shine shields (to provide a symmetric temperature distribution on the target) at the 1.7 MA Zebra generator. This presentation reports on the joint success of two independent lines of research. One of these was the development of new sources - planar wire arrays (PWAs). PWAs turned out to be a prolific radiator. Another success was the drastic improvement in energy efficiency of pulsed-power systems, such as the Load Current Multiplier (LCM). The Zebra/LCM generator almost doubled the plasma load current to 1.7 MA. The two above-mentioned innovative approaches were used in combination to produce a new compact hohlraum design for ICF, as jointly proposed by SNL and UNR. Good agreement between simulated and measured radiation temperature of the central target is shown. Experimental comparison of PWAs with planar foil liners (PFL) - another viable alternative to wire array loads at multi-MA generators show promising data. Results of research at the University of Nevada Reno allowed for the study of hohlraum coupling physics at University-scale generators. The advantages of new hohlraum design applications for multi-MA facilities with W or Au double PWAs or PFL x-ray sources are discussed.
Large scale parallel computing simulations of wire array Z-pinches
NASA Astrophysics Data System (ADS)
Chittenden, Jeremy; Niasse, Nicolas; Ciardi, Andrea
2008-11-01
Until recently simulations of wire array Z-pinches have been undertaken in a piece-wise fashion, modelling either only part of the array volume, or modelling different aspects of the array behaviour separately. Recent simulations of a single wire in the array suggest that the short wavelength modulations of the ablating plasma observed in experiments are the result of a modified m=0 like instability. In order to simulate the growth of magneto-Rayleigh-Taylor instabilities during the implosion phase, a separate calculation is usually performed in which estimates for the structure of the modulated ablation are used to provide the initial seed perturbation for the implosion. Improvements to the parallel computing architecture of the Gorgon 3D resistive MHD code, however, mean that is now possible to run with large enough computational grids to encompass the entire volume of the array whilst retaining sufficient resolution to model the spontaneous development of the modulated ablation structure from microscopic noise. Thus we can model the evolution of the wire array from the point of initial plasma formation, right through the implosion, without imposing any predetermined perturbation or structure. A detailed comparison of synthetic diagnostic images with data from MAGPIE experiments is used to test this method. Preliminary data from similar simulations of Z experiments are also presented.
Staged Z-pinch Simulations for the UNR, Nevada Terawatt Zebra Facility
NASA Astrophysics Data System (ADS)
Ney, Paul; Rahman, Hafiz; Wessel, Frank; Narkis, Jeff; Valenzuela, Julio; Beg, Farhat; Presura, Radu; Darling, Tim; McKee, Erik; Covington, Aaron
2015-11-01
We simulate a Staged Z-pinch imploded on the 1 MA, 130 ns, 100 kJ, Nevada Terawatt Zebra Facility. The load is a magnetized, cylindrical, double gas-puff, plasma liner imploding onto a plasma target. Simulations use the 2-1/2 D, radiation-MHD code, MACH2. Three different liner gases are evaluated: Ar, Kr, and Xe and the target is either: DD, or DT, with a liner-plasma radius of: 1.0 cm and 2.0 cm, and a 5.0-mm thickness. Initial conditions are optimized to produce the highest neutron yield. Shocks propagate at different speeds in the liner and target, leading to a shock front at the interface. Magnetosonic shock waves pre-heat the target plasma and provide a stable implosion. The shock front provides a secondary conduction channel which builds up during implosion. The axial magnetic field controls the MRT instability and traps α-particles, leading to ignition. Magnetic flux is compressed, and at peak parameters the magnetic field and current density exceed, by an order of magnitude, values outside the pinch, providing a magneto-inertial confinement. A smaller radius provides 102 -103 × higher neutron yield. Funded by the US Department of Energy, ARPA-E, Control Number 1184-1527.
Investigation of magnetic flux transport and shock formation in a staged Z-pinch
NASA Astrophysics Data System (ADS)
Narkis, J.; Rahman, H. U.; Wessel, F. J.; Beg, F. N.
2017-10-01
Target preheating is an integral component of magnetized inertial fusion in reducing convergence ratio. In the staged Z-pinch concept, it is achieved via one or more shocks. Previous work [Narkis et al., Phys. Plasmas 23, 122706 (2016)] found that shock formation in the target occurred earlier in higher-Z liners due to faster flux transport to the target/liner interface. However, a corresponding increase in magnitude of magnetic pressure was not observed, and target implosion velocity (and therefore shock strength) remained unchanged. To investigate other means of increasing the magnitude of transported flux, a Korteweg-de Vries-Burgers equation from the 1-D single-fluid, resistive magnetohydrodynamic equations is obtained. Solutions to the nondispersive (i.e., Burgers) equation depend on nondimensional coefficients, whose dependence on liner density, temperature, etc., suggests an increase in target implosion velocity, and therefore shock strength, can be obtained by tailoring the mass of a single-liner gas puff to a double-liner configuration. In the selected test cases of 1-D simulated implosions of krypton on deuterium, the peak Mach number increased from ˜ 5 to ˜ 8 . While a notable increase was seen, Mach numbers exceeding 10 (implosion velocities exceeding ˜25 cm/μs) are necessary for adequate shock preheating.
Kinetic Modeling of Ion Beams in Dense Plasma Focus Z-Pinches
NASA Astrophysics Data System (ADS)
Link, A.; Bennett, N.; Falabella, S.; Higginson, D. P.; Olsen, R.; Podpaly, Y. A.; Povilus, A.; Shaw, B.; Sipes, N.; Welch, D. R.; Schmidt, A.
2016-10-01
Dense plasma focus (DPF) Z-pinches are compact devices capable of producing MeV ion beams, x-rays, and (for D or DT gas fill) neutrons. We report on predictions of ion beam generation using the particle-in-cell code LSP. These simulations include full-scale electrodes, an external pulse power circuit and model through the run-down phase as a fluid, transitioning to a fully kinetic simulation during the run-in phase and through the pinch. Simulations of a deuterium filled DPF predict a substantial number of ions accelerated to energies greater than 50 keV escape the dense plasma in the pinch region and could be used to enhance total neutron yield by employing a solid target. Results of the simulations will be presented and compared to experimental observations. LLNL-ABS-697617 This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (LLNL) under Contract DE-AC52-07NA27344 and with support from the Computing Grand Challenge program at LLNL.
Gas Puff Z-Pinches at 1-MA and 200-ns on COBRA
NASA Astrophysics Data System (ADS)
Hammer, David; Qi, Niansheng; Rosenberg, Elliott; Atoyan, Levon; Potter, William; Blesener, Kate; Cahill, Adam; Gourdain, Pierre-Alexandre; Greenly, John; Hoyt, Cad; Kusse, Bruce; Pikuz, Sergei; Schrafel, Peter; Shelkovenko, Tatiana
2013-10-01
We report 6-cm diameter, double-shell gas puff Z-pinch experiments at 1 MA on the COBRA pulsed power generator, in which the implosion dynamics in puff-on-puff load configurations with and without a wire on the pinch axis were studied. Diagnostics used included: Planar Laser Induced Fluorescence Analyzer for measuring initial density profiles of the gas puff; a Laser Shearing Interferometer and a Laser Wavefront Analyzer for density profiles in the implosion and pinch phases; fiber-coupled, gated visible-light spectrometers for radially resolved imploding plasma spectra; gated XUV cameras for implosion dynamics; filtered pinhole x-ray cameras for imaging x-ray emission; and a double-crystal x-ray spectrometer for axially resolved pinch plasma densities and temperatures. From these, we derived the implosion velocity, ion charge states and then the imploding plasma temperatures, obtained the time evolution of the imploding plasma sheath structure and Magnetic Rayleigh-Taylor instability, and observed the most stable implosion with light-ions (Ne) imploding on heavy-ions (Ar), unstable implosions with heavy-ions (Ar) imploding on light-ions (Ne), and tighter, denser and less hot pinch plasma with a wire on axis. Details of the results will be presented. Supported by NNSA under DOE Coop. Agreement DE- NA0001836.
Development And Characterization Of A Liner-On-Target Injector For Staged Z-Pinch Experiments
NASA Astrophysics Data System (ADS)
Valenzuela, J. C.; Conti, F.; Krasheninnikov, I.; Narkis, J.; Beg, F.; Wessel, F. J.; Rahman, H. U.
2016-10-01
We present the design and optimization of a liner-on-target injector for Staged Z-pinch experiments. The injector is composed of an annular high atomic number (e.g. Ar, Kr) gas-puff and an on-axis plasma gun that delivers the ionized deuterium target. The liner nozzle injector has been carefully studied using Computational Fluid Dynamics (CFD) simulations to produce a highly collimated 1 cm radius gas profile that satisfies the theoretical requirement for best performance on the 1 MA Zebra current driver. The CFD simulations produce density profiles as a function of the nozzle shape and gas. These profiles are initialized in the MHD MACH2 code to find the optimal liner density for a stable, uniform implosion. We use a simple Snowplow model to study the plasma sheath acceleration in a coaxial plasma gun to help us properly design the target injector. We have performed line-integrated density measurements using a CW He-Ne laser to characterize the liner gas and the plasma gun density as a function of time. The measurements are compared with models and calculations and benchmarked accordingly. Advanced Research Projects Agency - Energy, DE-AR0000569.
Analyses in Support of Z-Pinch IFE and Actinide Transmutation - LLNL Progress Report for FY-06
Meier, W R; Moir, R W; Abbott, R
2006-09-19
This report documents results of LLNL's work in support of two studies being conducted by Sandia National Laboratories (SNL): the development of the Z-pinch driven inertial fusion energy (Z-IFE), and the use of Z-pinch driven inertial fusion as a neutron source to destroy actinides from fission reactor spent fuel. LLNL's efforts in FY06 included: (1) Development of a systems code for Z-IFE and use of the code to examine the operating parameter space in terms of design variables such as the Z-pinch driver energy, the chamber pulse repetition rate, the number of chambers making up the power plant, and themore » total net electric power of the plant. This is covered in Section 3 with full documentation of the model in Appendix A. (2) Continued development of innovative concepts for the design and operation of the recyclable transmission line (RTL) and chamber for Z-IFE. The work, which builds on our FY04 and FY05 contributions, emphasizes design features that are likely to lead to a more attractive power plant including: liquid jets to protect all structures from direct exposure to neutrons, rapid insertion of the RTL to maximize the potential chamber rep-rate, and use of cast flibe for the RTL to reduce recycling and remanufacturing costs and power needs. See Section 4 and Appendix B. (3) Description of potential figures of merit (FOMs) for actinide transmutation technologies and a discussion of how these FOMs apply and can be used in the ongoing evaluation of the Z-pinch actinide burner, referred to as the In-Zinerator. See Section 5. (4) A critique of, and suggested improvements to, the In-Zinerator chamber design in response to the SNL design team's request for feedback on its preliminary design. This is covered in Section 6.« less
Energy Transformation in Z-Pinch and Plasma Focus Discharges with Wire and Wire-in-Liner Loads
NASA Astrophysics Data System (ADS)
Kubeš, Pavel; Kravárik, Jozef; Klír, Daniel; Scholz, Marek; Paduch, Marian; Tomaszewski, Krzysztof; Karpinski, Leslaw; Bakshaev, Yury L.; Blinov, Peter I.; Chernenko, Andrey S.; Dan'ko, Sergey A.; Korolev, Valery D.; Shashkov, Andrey Y.; Tumanov, Victor I.
2002-12-01
The results of the study of the Z-pinch and plasma-focus plasmas at presence of the axial C, Al, or Cu wires of sufficient high diameter are discused in this paper. The wire was positioned on the top of the inner electrode of the PF 1000 plasma focus (1.8 MA, IPPLM Warsaw), or at the axis with or without the tungsten or alumine wire array load at the S-300 facility (3 MA, RRC Kurchatov Institute, Moscow), and at the axis of the small Z-pinch Z-150 (50 kA, CTU Prague). The plasma corona around the wire was generated both by the current going through the wires and by the implosion of the wire array or of the current sheath. The experiments showed interesting results often observed in some shots of Z-pinch type discharges - existence of helical structures, two relatively long and stable pinch phases, oscillation of pinch diameter, and back return of the plasma exploding from the pinch. All these observed phenomena can be evolved by spontaneous self-generation and transformation of the axial magnetic field in the pinch during the plasma implosion and explosion. A configuration of axial and azimuthal magnetic field confines the plasma and later transforms or dissipates during a few tens or hundreds ns. A fast transformation of internal magnetic fields can induce a sufficiently high electric field for generation of keV particles and radiation. Study and usage of Z-pinch discharges is connected with solving of two principal problems, limitation of instability development and a way of generation of high energy particles and radiation. The first problem is partially solved by the faster increase of the current, by better cylindrical symmetry of the load and plasma, by higher density of the plasma or by the presence of a stronger magnetized plasma.
Spectroscopic Studies of the Soft X-Ray Radiation from Gas-Puff Z-Pinches on Cobra
NASA Astrophysics Data System (ADS)
Shelkovenko, T. A.; Pikuz, S. A.; de Grouchy, P. W. L.; Qi, N.; Atoyan, L.; Kusse, B. R.; Hammer, D. A.
2015-11-01
Gas-puff Z-pinch experiments have been conducted on the 0.8-1.2 MA, 100-240 ns pulse duration COBRA pulsed power generator. Triple nozzle gas-puff loads consisting of Ne, Ar and Kr gases in different combination and pressures with pre-ionization were used in the most recent experiments. Photo-conducting diodes (PCDs) and pinhole cameras with different filters were used to study the X-ray timing, intensity and spatial distribution in different energy bands. Spectrographs with spatial and temporal resolution were used to study the soft x-ray radiation from the gas-puff Z-pinches. One spectrograph with two spherically bent mica crystals was used to study radiation with 200 micron spatial resolution and high spectral resolution. An x-ray streak camera with one spherically bent quartz crystal was used to study the x-ray radiation with up to 10 ps temporal resolution. The x-ray spectra were used to estimate spatial and temporal distributions of plasma parameters and determine the intensity of the line and continuum radiation from the Z-pinches plasma. Work supported by the National Nuclear Security Administration Stewardship Sciences Academic Programs under Department of Energy Cooperative Agreement No. DE-NA0001836.
NASA Astrophysics Data System (ADS)
Nobile, Arthur; Balkey, Matthew; Bartos, Jacob; Batha, Steven; Brooks, Paul; Cameron, Bernard; Cobble, James; Cooley, Jason; Day, Robert; Edwards, John; Elliott, Joyce; Elliott, Norman; Fincke, James; Gomez, Veronica; Hatch, Douglas; Keiter, Paul; Kyrala, George; Lanier, Nicholas; Manzanares, Ruben; Papin, Pallas; Perea, Ron; Pierce, Timothy; Randolph, Blaine; Sandoval, David; Sebring, Robert; Rivera, Gerald; Schmidt, Derek; Snow, Ron; Steckle, Warren; Tierney, Thomas; Valdez, Adelaida; Watt, Robert
2004-11-01
Several new targets have recently been developed and fielded to investigate physical phenomena occurring in the high energy density regime. Phenomena studied included interacting hydrodynamic jets, hydrodynamic instabilities in convergent geometry, radiation flow, shock propagation in ignition-relevant materials, and issues associated with double shell targets for achieving ignition on NIF. Targets to study interacting hydrodynamic jets have been fabricated for a NIF campaign. Challenges associated with these targets included producing thin (150 μm) Al disks with 100 and 160 μm precisely placed high quality holes, and fabrication of a thin wall (40 μm) 800 μm diameter cylindrical shock tube filled with low density (90 mg/cm3) carbonized resorcinol formaldehyde foam. Cylindrical targets to investigate hydrodynamic instabilities in convergent geometry as a function of initial surface perturbations have been fabricated. Many experimental campaigns with these targets have been conducted at OMEGA. These targets have been fabricated with a wide range of surface perturbations on an imploding Al marker layer using precision machining methods. The key challenge with these targets was fabrication of a high quality Al marker layer, and placement of specified surface features on the marker layer. Targets to investigate radiation flow and shock propagation in silicon aerogel were developed and fielded at the Sandia Z Pinch facility. The challenging feature associated with these targets was a high quality silicon aerogel disk that is attached to a gold washer containing a hole. Experiments on OMEGA have recently been conducted for the purpose of developing data on radiation absorption and shock propagation through ignition relevant materials. Specifically, we have fabricated targets for these experiments to investigate radiation absorption and shock propagation in Be-Cu alloys. The challenges associated with these targets were fabrication and characterization of very thin Be
Insights and Applications of 2-D Simulations to Z-Pinch Experiments
NASA Astrophysics Data System (ADS)
Peterson, Darrell L.
1998-11-01
A two-dimensional (2-D) Eulerian radiation-magnetohydrodynamic code has been used to successfully simulate z-pinch experiments fielded on several facilities with a wide variety of drive conditions, timescales and loads.(Peterson, et al, Phys. Plasmas) 3, 368 (1996); Matuska, et al, Phys. Plasmas 3, 1415 (1996); and Peterson, et al, Phys. Plasmas to be published Sept. 1998 The 2-D simulations of these experiments reproduce important quantities of interest including the radiation pulse energy, power and pulsewidth. To obtain this agreement a variable parameter, the level of random density perturbations imposed early in the implosion, is adjusted which then seeds the development of magnetically driven Rayleigh-Taylor instabilities. The instabilities greatly affect the dynamics of the implosion and the resulting production of radiation. Analysis of such simulations allows insights into the physical processes by which these calculations reproduce the experimental results. As an example, simulations of Sandia ``Z'' accelerator experiments have shown a short-wavelength growth phase, saturation after breaking through the plasma shell, followed by longer wavelength development. This effect seems to be responsible in the simulations for the survival of the imploding plasma shell as a coherent entity, and the resultant high quality of the radiation pulse. At the same time, the thickened shell allows for an extended time period of energy deposition by the Lorentz force into the plasma which then accounts for the high energy yields. As another example, the insights gained from the simulations have allowed for investigation of possible physical processes which produce high powers in ``nested array'' implosions and high temperatures within ``dynamic hohlraum'' loads. Building on these insights, the 2-D code has been used in designing new experiments to optimize the desired physical conditions and in interpreting the experimental results obtained. These examples and others will be
Ampleford, D. J.; Jennings, C. A.; Cuneo, M. E.
2010-05-15
Astrophysical observations have demonstrated many examples of bow shocks, for example, the head of protostellar jets or supernova remnants passing through the interstellar medium or between discrete clumps in jets. For such systems where supersonic and super-Alfvenic flows and radiative cooling are all important, carefully scaled laboratory experiments can add insight into the physical processes involved. The early stage of a wire array z-pinch implosion consists of the steady ablation of material from fine metallic wires. Ablated material is accelerated toward the array axis by the JxB force. This flow is highly supersonic (M>5) and becomes super-Alfvenic (M{sub A}>2). Radiativemore » cooling is significant in this flow and can be controlled by varying the material in the ablated plasma. The introduction of wires as obstructions in this steady flow leads to the formation of bow shocks, which can be used as a laboratory testbed for astrophysical bow shocks. The magnetic field associated with this obstruction wire can be controlled by varying the current through it. Differences in the shock for different cooling rates and different magnetic fields associated with the obstruction will be discussed, along with comparisons of dimensionless parameters in the experiments to astrophysical systems.« less
Design of a 5-MA 100-ns linear-transformer-driver accelerator for wire array Z-pinch experiments
NASA Astrophysics Data System (ADS)
Zhou, Lin; Li, Zhenghong; Wang, Zhen; Liang, Chuan; Li, Mingjia; Qi, Jianmin; Chu, Yanyun
2016-03-01
The linear-transformer-driver (LTD) is a recently developed pulsed-power technology that shows great promise for a number of applications. These include a Z -pinch-driven fission-fusion-hybrid reactor that is being developed by the Chinese Academy of Engineering Physics. In support of the reactor development effort, we are planning to build an LTD-based accelerator that is optimized for driving wire-array Z -pinch loads. The accelerator comprises six modules in parallel, each of which has eight series 0.8-MA LTD cavities in a voltage-adder configuration. Vacuum transmission lines are used from the interior of the adder to the central vacuum chamber where the load is placed. Thus the traditional stack-flashover problem is eliminated. The machine is 3.2 m tall and 12 m in outer diameter including supports. A prototype cavity was built and tested for more than 6000 shots intermittently at a repetition rate of 0.1 Hz. A novel trigger, in which only one input trigger pulse is needed by utilizing an internal trigger brick, was developed and successfully verified in these shots. A full circuit modeling was conducted for the accelerator. The simulation result shows that a current pulse rising to 5.2 MA in 91 ns (10%-90%) can be delivered to the wire-array load, which is 1.5 cm in height, 1.2 cm in initial radius, and 1 mg in mass. The maximum implosion velocity of the load is 32 cm /μ s when compressed to 0.1 of the initial radius. The maximum kinetic energy is 78 kJ, which is 11.7% of the electric energy stored in the capacitors. This accelerator is supposed to enable a radiation energy efficiency of 20%-30%, providing a high efficient facility for research on the fast Z pinch and technologies for repetition-rate-operated accelerators.
Deuterium z-pinch as a powerful source of multi-MeV ions and neutrons for advanced applications
Klir, D.; Kubes, P.; Rezac, K.
2016-03-15
A novel configuration of a deuterium z-pinch has been used to generate a nanosecond pulse of fast ions and neutrons. At a 3 MA current, the peak neutron yield of (3.6 ± 0.5) × 10{sup 12} was emitted within 20 ns implying the production rate of 10{sup 20} neutrons/s. High neutron yields resulted from the magnetization of MeV deuterons inside plasmas. Whereas deuterons were trapped in the radial direction, a lot of fast ions escaped the z-pinch along the z-axis. A large number of >25 MeV ions were emitted into a 250 mrad cone. The cut-off energy of broad energy spectra of hydrogen ions approached 40 MeV.more » The total number of >1 MeV and >25 MeV deuterons were 10{sup 16} and 10{sup 13}, respectively. Utilizing these ions offers a real possibility of various applications, including the increase of neutron yields or the production of short-lived isotopes in samples placed in ion paths. On the basis of our experiments with various samples, we concluded that a single shot would have been sufficient to obtain GBq positron activity of {sup 13}N isotopes via the {sup 12}C(d,n){sup 13}N reaction. Furthermore, the first z-pinch generated neutron radiograph produced by ≈20 ns pulses is presented in this paper.« less
Enhanced keV peak power and yield using twisted pair 'cables' in a z-pinch
Hoyt, C. L.; Knapp, P. F.; Pikuz, S. A.
2012-06-11
Individual wires in a z-pinch were replaced with twisted pair 'cables' of similar linear mass on the COBRA pulsed power generator, resulting in peak power and yield increases in radiation above 1 keV. A cable is defined here as two or more fine wires twisted together to form a continuous strand with a wavelength ({lambda}{sub t}) dependent on the twists per unit length. The magnitude of {lambda}{sub t} appears to play a strong role in these increases, with the largest gains found for a {lambda}{sub t} of Almost-Equal-To 0.75 mm.
Investigating radial wire array Z pinches as a compact x-ray source on the Saturn generator
Ampleford, David J.; Bland, S. N.; Jennings, Christopher A.
2015-08-27
Radial wire array z pinches, where wires are positioned radially outward from a central cathode to a concentric anode, can act as a compact bright x-ray source that could potentially be used to drive a hohlraum. Experiments were performed on the 7-MA Saturn generator using radial wire arrays. These experiments studied a number of potential risks in scaling radial wire arrays up from the 1-MA level, where they have been shown to be a promising compact X-ray source. Data indicates that at 7 MA, radial wire arrays can radiate ~9 TW with 10-ns full-width at half-maximum from a compact pinch.
Conversion of electromagnetic energy in Z-pinch process of single planar wire arrays at 1.5 MA
Liangping, Wang; Mo, Li; Juanjuan, Han; Ning, Guo; Jian, Wu; Aici, Qiu
2014-06-15
The electromagnetic energy conversion in the Z-pinch process of single planar wire arrays was studied on Qiangguang generator (1.5 MA, 100 ns). Electrical diagnostics were established to monitor the voltage of the cathode-anode gap and the load current for calculating the electromagnetic energy. Lumped-element circuit model of wire arrays was employed to analyze the electromagnetic energy conversion. Inductance as well as resistance of a wire array during the Z-pinch process was also investigated. Experimental data indicate that the electromagnetic energy is mainly converted to magnetic energy and kinetic energy and ohmic heating energy can be neglected before the final stagnation. The kinetic energy can be responsible for the x-ray radiation before the peak power. After the stagnation, the electromagnetic energy coupled by the load continues increasing and the resistance of the load achieves its maximum of 0.6–1.0 Ω in about 10–20 ns.
A non-LTE kinetic model for quick analysis of K-shell spectra from Z-pinch plasmas
Li, J. Huang, X. B. Cai, H. C. Yang, L. B. Xie, W. P. Duan, S. C.
2014-12-15
Analyzing and modeling K-shell spectra emitted by low-to moderate-atomic number plasma is a useful and effective way to retrieve temperature density of z-pinch plasmas. In this paper, a non-LTE population kinetic model for quick analysis of K-shell spectra was proposed. The model contains ionization stages from bare nucleus to neutral atoms and includes all the important atomic processes. In the present form of the model, the plasma is assumed to be both optically thin and homogeneous with constant temperature and density, and only steady-state situation is considered. According to the detailed calculations for aluminum plasmas, contours of ratios of certain K-shell lines in electron temperature and density plane as well as typical synthesized spectra were presented and discussed. The usefulness of the model is demonstrated by analyzing the spectrum from a neon gas-puff Z-pinch experiment performed on a 1 MA pulsed-power accelerator.
A non-LTE kinetic model for quick analysis of K-shell spectra from Z-pinch plasmas
Li, J., E-mail: s.duan@163.com; Huang, X. B., E-mail: s.duan@163.com; Cai, H. C., E-mail: s.duan@163.com
2014-12-15
Analyzing and modeling K-shell spectra emitted by low-to moderate-atomic number plasma is a useful and effective way to retrieve temperature density of z-pinch plasmas. In this paper, a non-LTE population kinetic model for quick analysis of K-shell spectra was proposed. The model contains ionization stages from bare nucleus to neutral atoms and includes all the important atomic processes. In the present form of the model, the plasma is assumed to be both optically thin and homogeneous with constant temperature and density, and only steady-state situation is considered. According to the detailed calculations for aluminum plasmas, contours of ratios of certainmore » K-shell lines in electron temperature and density plane as well as typical synthesized spectra were presented and discussed. The usefulness of the model is demonstrated by analyzing the spectrum from a neon gas-puff Z-pinch experiment performed on a 1 MA pulsed-power accelerator.« less
Single crystal X-ray spectropolarimeter for HED plasmas and its use on wire array z-pinches
NASA Astrophysics Data System (ADS)
Wallace, Matt; Haque, Showera; Neill, Paul; Kastengren, Alan; Pereira, Nino; Presura, Radu
2016-10-01
When energetic electrons in a plasma have a preferred direction the resulting X-rays can be polarized. This makes plasma X-ray polarization spectroscopy, spectropolarimetry, useful for revealing information about the anisotropy of the electron velocity distribution, and X-ray spectropolarimetry has indeed been used for this in both space and laboratory plasmas. For pulsed plasmas the spectrum's polarization is typically measured by obtaining each component of polarization separately, with two crystals both at a 45 degree Bragg angle or one on successive shots. However, obtaining the two orthogonal polarizations can be done using one crystal. Crystals with hexagonal symmetry present pairs of internal planes that diffract incident X-rays in two directions that are perpendicular to each other and the incident ray. The polarization splitting properties of quartz crystals were confirmed with linearly polarized X-rays from the APS. An X-cut crystal with (10-10) planes in polarization splitting orientation is now being used on wire array z-pinches at UNR. The design of a single crystal X-ray polarimeter, and what data obtained so far indicate about the anisotropy of wire array z-pinch plasmas will be presented. Work supported by U.S. DOE, NNSA Grant DE-NA0001834 and coop. agreement DE-FC52-06NA27616. Use of APS supported by U.S. DOE, OBES, Contract No. DE-AC02-06CH11357.
Sharpe, Robin Arthur; Kingsep, Alexander S.; Smith, David Lewis
2007-01-01
Z-Pinch Inertial Fusion Energy (Z-IFE) complements and extends the single-shot z-pinch fusion program on Z to a repetitive, high-yield, power plant scenario that can be used for the production of electricity, transmutation of nuclear waste, and hydrogen production, all with no CO{sub 2} production and no long-lived radioactive nuclear waste. The Z-IFE concept uses a Linear Transformer Driver (LTD) accelerator, and a Recyclable Transmission Line (RTL) to connect the LTD driver to a high-yield fusion target inside a thick-liquid-wall power plant chamber. Results of RTL and LTD research are reported here, that include: (1) The key physics issues for RTLsmore » involve the power flow at the high linear current densities that occur near the target (up to 5 MA/cm). These issues include surface heating, melting, ablation, plasma formation, electron flow, magnetic insulation, conductivity changes, magnetic field diffusion changes, possible ion flow, and RTL mass motion. These issues are studied theoretically, computationally (with the ALEGRA and LSP codes), and will work at 5 MA/cm or higher, with anode-cathode gaps as small as 2 mm. (2) An RTL misalignment sensitivity study has been performed using a 3D circuit model. Results show very small load current variations for significant RTL misalignments. (3) The key structural issues for RTLs involve optimizing the RTL strength (varying shape, ribs, etc.) while minimizing the RTL mass. Optimization studies show RTL mass reductions by factors of three or more. (4) Fabrication and pressure testing of Z-PoP (Proof-of-Principle) size RTLs are successfully reported here. (5) Modeling of the effect of initial RTL imperfections on the buckling pressure has been performed. Results show that the curved RTL offers a much greater buckling pressure as well as less sensitivity to imperfections than three other RTL designs. (6) Repetitive operation of a 0.5 MA, 100 kV, 100 ns, LTD cavity with gas purging between shots and automated
Sharpe, Robin Arthur; Kingsep, Alexander S. (Kurchatov Institute, Moscow, Russia); Smith, David Lewis; Olson, Craig Lee; Ottinger, Paul F. (Naval Research Laboratory, Washington, DC); Schumer, Joseph Wade (Naval Research Laboratory, Washington, DC); Welch, Dale Robert (Voss Scientific, Albuquerque, NM); Kim, Alexander (High Currents Institute, Tomsk, Russia); Kulcinski, Gerald L. (University of Wisconsin, Madison, WI); Kammer, Daniel C. (University of Wisconsin, Madison, WI); Rose, David Vincent (Voss Scientific, Albuquerque, NM); Nedoseev, Sergei L. (Kurchatov Institute, Moscow, Russia); Pointon, Timothy David; Smirnov, Valentin P.; Turgeon, Matthew C.; Kalinin, Yuri G. (Kurchatov Institute, Moscow, Russia); Bruner, Nichelle "Nicki" (Voss Scientific, Albuquerque, NM); Barkey, Mark E. (University of Alabama, Tuscaloosa, AL); Guthrie, Michael (University of Wisconsin, Madison, WI); Thoma, Carsten (Voss Scientific, Albuquerque, NM); Genoni, Tom C. (Voss Scientific, Albuquerque, NM); Langston, William L.; Fowler, William E.; Mazarakis, Michael Gerrassimos
2007-01-01
Z-Pinch Inertial Fusion Energy (Z-IFE) complements and extends the single-shot z-pinch fusion program on Z to a repetitive, high-yield, power plant scenario that can be used for the production of electricity, transmutation of nuclear waste, and hydrogen production, all with no CO{sub 2} production and no long-lived radioactive nuclear waste. The Z-IFE concept uses a Linear Transformer Driver (LTD) accelerator, and a Recyclable Transmission Line (RTL) to connect the LTD driver to a high-yield fusion target inside a thick-liquid-wall power plant chamber. Results of RTL and LTD research are reported here, that include: (1) The key physics issues for RTLs involve the power flow at the high linear current densities that occur near the target (up to 5 MA/cm). These issues include surface heating, melting, ablation, plasma formation, electron flow, magnetic insulation, conductivity changes, magnetic field diffusion changes, possible ion flow, and RTL mass motion. These issues are studied theoretically, computationally (with the ALEGRA and LSP codes), and will work at 5 MA/cm or higher, with anode-cathode gaps as small as 2 mm. (2) An RTL misalignment sensitivity study has been performed using a 3D circuit model. Results show very small load current variations for significant RTL misalignments. (3) The key structural issues for RTLs involve optimizing the RTL strength (varying shape, ribs, etc.) while minimizing the RTL mass. Optimization studies show RTL mass reductions by factors of three or more. (4) Fabrication and pressure testing of Z-PoP (Proof-of-Principle) size RTLs are successfully reported here. (5) Modeling of the effect of initial RTL imperfections on the buckling pressure has been performed. Results show that the curved RTL offers a much greater buckling pressure as well as less sensitivity to imperfections than three other RTL designs. (6) Repetitive operation of a 0.5 MA, 100 kV, 100 ns, LTD cavity with gas purging between shots and automated operation is
Fusion neutron detector for time-of-flight measurements in z-pinch and plasma focus experiments
NASA Astrophysics Data System (ADS)
Klir, D.; Kravarik, J.; Kubes, P.; Rezac, K.; Litseva, E.; Tomaszewski, K.; Karpinski, L.; Paduch, M.; Scholz, M.
2011-03-01
We have developed and tested sensitive neutron detectors for neutron time-of-flight measurements in z-pinch and plasma focus experiments with neutron emission times in tens of nanoseconds and with neutron yields between 106 and 1012 per one shot. The neutron detectors are composed of a BC-408 fast plastic scintillator and Hamamatsu H1949-51 photomultiplier tube (PMT). During the calibration procedure, a PMT delay was determined for various operating voltages. The temporal resolution of the neutron detector was measured for the most commonly used PMT voltage of 1.4 kV. At the PF-1000 plasma focus, a novel method of the acquisition of a pulse height distribution has been used. This pulse height analysis enabled to determine the single neutron sensitivity for various neutron energies and to calibrate the neutron detector for absolute neutron yields at about 2.45 MeV.
Kantsyrev, V. L.; Safronova, A. S.; Esaulov, A. A.; Williamson, K. M.; Shrestha, I.; Ouart, N. D.; Yilmaz, M. F.; Wilcox, P. G.; Osborne, G. C.; Weller, M. E.; Shlyaptseva, V. V.; Chuvatin, A. S.; Rudakov, L. I.; Greenly, J. B.; McBride, R. D.; Knapp, P. F.; Blessener, I. C.; Bell, K. S.; Chalenski, D. A.; Hammer, D. A.
2009-01-21
The presented research focuses on investigation of Z-pinch plasma formation, implosion, and radiation characteristics as a function of the load configuration. The single planar and multi-planar wire arrays as well as compact cylindrical wire arrays were studied on the 1.3 MA UNR Zebra and 1 MA Cornell COBRA generators. The largest yields and powers were found for W and Mo double planar and compact wire arrays. A possibility of radiation pulse shaping was demonstrated. Two types of bright spots were observed in plasmas. A comparison of Mo double planar and compact wire array data indicates the possibility that the same heating mechanism operates during the final implosion and stagnation stages.
NASA Astrophysics Data System (ADS)
Klir, D.; Shishlov, A. V.; Kokshenev, V. A.; Kubes, P.; Labetsky, A. Yu; Rezac, K.; Cherdizov, R. K.; Cikhardt, J.; Cikhardtova, B.; Dudkin, G. N.; Fursov, F. I.; Garapatsky, A. A.; Kovalchuk, B. M.; Kravarik, J.; Kurmaev, N. E.; Orcikova, H.; Padalko, V. N.; Ratakhin, N. A.; Sila, O.; Turek, K.; Varlachev, V. A.
2015-04-01
Z-pinch experiments with deuterium gas puffs have been carried out on the GIT-12 generator at 3 MA currents. Recently, a novel configuration of a deuterium gas-puff z-pinch was used to accelerate deuterons and to generate fast neutrons. In order to form a homogeneous, uniformly conducting layer at a large initial radius, an inner deuterium gas puff was surrounded by an outer hollow cylindrical plasma shell. The plasma shell consisting of hydrogen and carbon ions was formed at the diameter of 350 mm by 48 plasma guns. A linear mass of the plasma shell was about 5 µg cm-1 whereas a total linear mass of deuterium gas in single or double shell gas puffs was about 100 µg cm-1. The implosion lasted 700 ns and seemed to be stable up to a 5 mm radius. During stagnation, m = 0 instabilities became more pronounced. When a disruption of necks occurred, the plasma impedance reached 0.4 Ω and high energy (>2 MeV) bremsstrahlung radiation together with high energy deuterons were produced. Maximum neutron energies of 33 MeV were observed by axial time-of-flight detectors. The observed neutron spectra could be explained by a suprathermal distribution of deuterons with a high energy tail f≤ft({{E}\\text{d}}\\right)\\propto E\\text{d}-(1.8+/- 0.2) . Neutron yields reached 3.6 × 1012 at a 2.7 MA current. A high neutron production efficiency of 6 × 107 neutrons per one joule of plasma energy resulted from the generation of high energy deuterons and from their magnetization inside plasmas.
Experimental study of star-like and small-diameter wire-array z-pinches on the 1-MA Zebra generator
NASA Astrophysics Data System (ADS)
Ivanov, V. V.; Sotnikov, V. I.; Kindel, J. M.; Shevelko, A. P.; Hakel, P.; Mancini, R. C.; Astanovitskiy, A. L.; Haboub, A.; Altemara, S. D.; Kazakov, E. D.; Le Galloudec, B.; Nalajala, V.
2009-01-01
Star-like wire arrays and small-diameter (1-3 mm in diameter) cylindrical loads were tested in the 1-MA Zebra generator. Mitigation of plasma inhomogeneity was observed in the implosions of star-like loads, which consisted of multiple nested, cylindrical arrays aligned azimuthally such that the wires appear as linear array "rays" extending from the axis of symmetry. The implosion in these loads is directed along the "rays" of the star and cascades from wire to wire to the center to form moving plasma columns with smooth leading edges. Despite the low azimuthal symmetry, a star-like wire array produces a stable x-ray pulse with a high peak power and a short duration of 8-12-ns. This can be linked to the stabilization of instabilities due to the multiple nesting. X-ray generation and implosion dynamics in wire arrays 1-16 mm in diameter were investigated to find a transition between the regime with prevailing kinetic energy and "non-kinetic" plasma heating. Loads 3-8 mm in diameter generate the highest x-ray power at the Zebra generator. The fall of x-ray power in 1-2-mm loads can be linked to the lack of kinetic energy. Laser probing diagnostics show the formation of "necks" on the pinch during the bubble-like implosion. The energy balance provides the evidence of the enhanced plasma heating in z-pinches. Features of the implosions in small-diameter wire-arrays can help to identify the mechanisms of energy dissipation.
Two and Three-dimensional Modelling of the Different Phases of Wire Array Z-pinch Evolution
NASA Astrophysics Data System (ADS)
Chittenden, Jeremy P.
2000-10-01
The spectacular recent improvements in the performance of imploding Z-pinches formed from metallic wire arrays have yielded the world's most powerful laboratory X-ray source, with applications to inertial confinement fusion research and other high energy density applications. Achieving high yield fusion in a hohlraum driven by a wire array Z-pinch will require further substantial increases in X-ray power. Designing optimal loads for such future experiments requires an in-depth knowledge of what factors limit the X-ray power. The two main limiting factors in present generation experiments are the slow rate of wire ablation, which leads to injection of mass into the interior of the array prior to implosion and the development of the Rayleigh-Taylor instability. Computational modelling of these phenomena can be extremely complex due to the intrinsically three-dimensional nature of the problem. Whilst 3D resistive MHD codes are now becoming available, simulations of the entire experiment with adequate spatial resolution remains unfeasible. An alternative approach is to model different phases of the evolution using different specialised 2D and 3D models and attempt to link them together to form a composite model of the whole experiment. This has the added advantage that this series of simpler problems can be more readily compared to experiments for the all important code verification. 2D and 3D ``cold-start" or ``wire initiation" calculations are presented showing how the passage of current begins the plasma formation process but also excites the m=0 instability in each wire. 2D simulations in the r-theta plane then show how the mass injected between the wires determines the radial profile for the implosion. This model is also used to explore how nested arrays (where a second array is placed concentrically within the first) can be used to increase X-ray power. The results of these two models can then be used to construct the radial and axial structure of the plasma for
One- and two-dimensional modeling of argon K-shell emission from gas-puff Z-pinch plasmas
NASA Astrophysics Data System (ADS)
Thornhill, J. W.; Chong, Y. K.; Apruzese, J. P.; Davis, J.; Clark, R. W.; Giuliani, J. L.; Terry, R. E.; Velikovich, A. L.; Commisso, R. J.; Whitney, K. G.; Frese, M. H.; Frese, S. D.; Levine, J. S.; Qi, N.; Sze, H.; Failor, B. H.; Banister, J. W.; Coleman, P. L.; Coverdale, C. A.; Jones, B.; Deeney, C.
2007-06-01
In this paper, a theoretical model is described and demonstrated that serves as a useful tool for understanding K-shell radiating Z-pinch plasma behavior. Such understanding requires a self-consistent solution to the complete nonlocal thermodynamic equilibrium kinetics and radiation transport in order to realistically model opacity effects and the high-temperature state of the plasma. For this purpose, we have incorporated into the MACH2 two-dimensional magnetohydrodynamic (MHD) code [R. E. Peterkin et al., J. Comput. Phys. 140, 148 (1998)] an equation of state, called the tabular collisional radiative equilibrium (TCRE) model [J. W. Thornhill et al., Phys. Plasmas 8, 3480 (2001)], that provides reasonable approximations to the plasma's opacity state. MACH2 with TCRE is applied toward analyzing the multidimensional implosion behavior that occurred in Decade Quad (DQ) [D. Price et al., Proceedings of the 12th IEEE Pulsed Power Conference, Monterey, CA, edited by C. Stallings and H. Kirbie (IEEE, New York, 1999), p. 489] argon gas puff experiments that employed a 12cm diameter nozzle with and without a central gas jet on axis. Typical peak drive currents and implosion times in these experiments were ˜6MA and ˜230ns. By using Planar Laser Induced Fluorescence measured initial density profiles as input to the calculations, the effect these profiles have on the ability of the pinch to efficiently produce K-shell emission can be analyzed with this combined radiation-MHD model. The calculated results are in agreement with the experimental result that the DQ central-jet configuration is superior to the no-central-jet experiment in terms of producing more K-shell emission. These theoretical results support the contention that the improved operation of the central-jet nozzle is due to the better suppression of instabilities and the higher-density K-shell radiating conditions that the central-jet configuration promotes. When we applied the model toward projecting argon K
NASA Astrophysics Data System (ADS)
Tarifeño, Ariel; Pavez, Cristian; Cárdenas, Miguel; Soto, Leopoldo
2008-10-01
Zero-dimensional simulations are used to gain an insight into the optimal setup for which the best energy transfer efficiency between the generator and the load system, and high currents at the moment of pinch are expected in wire array experiments using the SPEED2 generator. The generator is characterized by 4.1 μF equivalent Marx generator capacity, 300 kV maximum charge voltage, 187 kJ and 4 MA maximum current in short circuit at maximum charge voltage, 400 ns first quarter of period and dI/dt~1013 A s-1. The model used in the simulations describes the dynamics of the current sheet coupled to the dynamics of the electric circuit. In order to have a better understanding of the generator behaviour when magnetic flux compression experiments using wire arrays are driven in SPEED2, the presence of an external axial magnetic field has also been considered. Based on the simulations results, a load design criteria for wire arrays experiments in SPEED2 is presented . The procedure to find a load design criterion presented here, is quite general and could be applied to experiments such as wire arrays or gas puff Z-pinches when these are driven by using low impedance capacitive generators.
Design of a 100 J Dense Plasma Focus Z-pinch Device as a Portable Neutron Source
NASA Astrophysics Data System (ADS)
Jiang, Sheng; Higginson, Drew; Link, Anthony; Liu, Jason; Schmidt, Andrea
2015-11-01
The dense plasma focus (DPF) Z-pinch devices are capable of accelerating ions to high energies through MV/mm-scale electric fields. When deuterium is used as the filling gas, neutrons are generated through beam-target fusion when fast D beams collide with the bulk plasma. The neutron yield on a DPF scales favorably with current, and could be used as portable sources for active interrogation. Past DPF experiments have been optimized empirically. Here we use the particle-in-cell (PIC) code LSP to optimize a portable DPF for high neutron yield prior to building it. In this work, we are designing a DPF device with about 100 J of energy which can generate 106 - 107 neutrons. The simulations are run in the fluid mode for the rundown phase and are switched to kinetic to capture the anomalous resistivity and beam acceleration process during the pinch. A scan of driver parameters, anode geometries and gas pressures are studied to maximize the neutron yield. The optimized design is currently under construction. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and supported by the Laboratory Directed Research and Development Program (15-ERD-034) at LLNL.
NASA Astrophysics Data System (ADS)
Rousculp, C. L.; Reass, W. A.; Oro, D. M.; Griego, J. R.; Turchi, P. J.; Reinovsky, R. E.; Saunders, A.; Mariam, F. G.; Morris, C.
2014-10-01
The first pulse-power driven, dynamic, liner-on-target experiment was successfully conducted at the Los Alamos proton radiography (pRad) facility. 100% data return was achieved on this experiment including a 21-image pRad movie. The experiment was driven with the PHELIX pulsed-power machine that utilizes a high-efficiency (k ~ 0.93) transformer to couple a small capacitor bank (U ~ 300 kJ) to a low inductance condensed-matter experimental load in a Z-pinch configuration. The current pulse (Ipeak = 3.7 MA, δt ~10 μs) was measured via a fiber optic Faraday rotation diagnostic. The experimental load consisted of a cylindrical Al liner (6 cm diam, 3 cm tall, 0.8 mm thick) and a cylindrical Al target (3 cm diam, 3 cm tall, 0.1 mm thick) that was coated with a thin (0.1 mm) uniform layer of tungsten powder (1 micron diam). It is observed that the shock-launched powder layer fully detaches from the target into a spatially correlated, radially converging (vr ~ 800 m/s) ring. The powder distribution is highly modulated in azimuth indicating particle interactions are significant. Results are compared to MHD simulations. Work supported by United States-DOE under Contract DE-AC52-06NA25396.
Simulations for a Staged Z-pinch and MagLIF at 26 MA, 130 ns, and 22 MJ
NASA Astrophysics Data System (ADS)
Rahman, Hafiz; Wessel, Frank; Ney, Paul; Narkis, Jeff; Valenzuela, Julio; Beg, Farhat; Presura, Radu
2015-11-01
Simulations for a Staged Z-pinch (SZP), using a 6-mm diameter, 100- μm thick Silver plasma shell, imploding onto a uniform (target) plasma fill of Deuterium, are compared to MagLIF, configured similarly, except with a 500 μm Beryllium solid liner. Both pinches are pre-magnetized with: Bz = 0, 3, 7, and 10 T and the driver parameters are: τ1 / 4 = 130 ns, Ipeak = 26 MA, Estored = 22 MJ; the simulation code is MACH2, a 2-1/2 D, radiation-MHD code. Solid-liner simulations reproduce well, experimental results. Plasma-liner simulations exhibit magnetosonic shocks in the liner and ordinary sonic shocks in the target, preheating the plasma. A conduction-channel, shock-front at the interface remains stable throughout compression, even as the liner's outer surface becomes RT unstable. At peak compression the target decelerates and interface instability appears, triggering ignition and a fusion yield of, Y > 200 MJ; that is, 10 × greater than Estored . The yield from the solid liner implosion is 4 orders-of-magnitude less, even though it is more stable than the SZP. Funded by the US Department of Energy, ARPA-E, Control Number 1184-1527.
Tangri, V.; Harvey-Thompson, Adam James; Giuliani, J. L.; ...
2016-10-19
Radiation-magnetohydrodynamic simulations using the non-LTE Mach2-TCRE code in (r,z) geometry are performed for two pairs of recent Ar gas-puff Z-pinch experiments on the refurbished Z generator with an 8 cm diameter nozzle. One pair of shots had an outer-to-inner shell mass ratio of 1:1.6 and a second pair had a ratio of 1:1.
Sheng, Liang; Peng, Bodong; Yuan, Yuan
2016-01-15
The experimental results of the insulated-standard hybrid wire array Z pinches carried out on “QiangGuang-I” facility at Northwest Institute of Nuclear Technology were presented and discussed. The surface insulating can impose a significant influence on the dynamics and radiation characteristics of the hybrid wire array Z pinches, especially on the early stage (t/t{sub imp} < 0.6). The expansion of insulated wires at the ablation stage is suppressed, while the streams stripped from the insulated wires move faster than that from the standard wires. The foot radiation of X-ray is enhanced by increment of the number of insulated wires, 19.6 GW, 33.6 GW, and 68.6 GWmore » for shots 14037S, 14028H, and 14039I, respectively. The surface insulation also introduces nonhomogeneity along the single wire—the streams move much faster near the electrodes. The colliding boundary of the hybrid wire array Z pinches is bias to the insulated side approximately 0.6 mm.« less
Jones, B; Coverdale, C A; Nielsen, D S; Jones, M C; Deeney, C; Serrano, J D; Nielsen-Weber, L B; Meyer, C J; Apruzese, J P; Clark, R W; Coleman, P L
2008-10-01
A multicolor, time-gated, soft x-ray pinhole imaging instrument is fielded as part of the core diagnostic set on the 25 MA Z machine [M. E. Savage et al., in Proceedings of the Pulsed Power Plasma Sciences Conference (IEEE, New York, 2007), p. 979] for studying intense wire array and gas puff Z-pinch soft x-ray sources. Pinhole images are reflected from a planar multilayer mirror, passing 277 eV photons with <10 eV bandwidth. An adjacent pinhole camera uses filtration alone to view 1-10 keV photons simultaneously. Overlaying these data provides composite images that contain both spectral as well as spatial information, allowing for the study of radiation production in dense Z-pinch plasmas. Cu wire arrays at 20 MA on Z show the implosion of a colder cloud of material onto a hot dense core where K-shell photons are excited. A 528 eV imaging configuration has been developed on the 8 MA Saturn generator [R. B. Spielman et al., and A. I. P. Conf, Proc. 195, 3 (1989)] for imaging a bright Li-like Ar L-shell line. Ar gas puff Z pinches show an intense K-shell emission from a zippering stagnation front with L-shell emission dominating as the plasma cools.
Sheng, Liang; Peng, Bodong; Yuan, Yuan; Zhang, Mei; Zhao, Chen; Zhao, Jizhen; Wang, Liangping; Li, Yang Li, Mo
2016-01-15
The experimental results of the insulated-standard hybrid wire array Z pinches carried out on “QiangGuang-I” facility at Northwest Institute of Nuclear Technology were presented and discussed. The surface insulating can impose a significant influence on the dynamics and radiation characteristics of the hybrid wire array Z pinches, especially on the early stage (t/t{sub imp} < 0.6). The expansion of insulated wires at the ablation stage is suppressed, while the streams stripped from the insulated wires move faster than that from the standard wires. The foot radiation of X-ray is enhanced by increment of the number of insulated wires, 19.6 GW, 33.6 GW, and 68.6 GW for shots 14037S, 14028H, and 14039I, respectively. The surface insulation also introduces nonhomogeneity along the single wire—the streams move much faster near the electrodes. The colliding boundary of the hybrid wire array Z pinches is bias to the insulated side approximately 0.6 mm.
NASA Astrophysics Data System (ADS)
Sheng, Liang; Peng, Bodong; Li, Yang; Yuan, Yuan; Li, Mo; Zhang, Mei; Zhao, Chen; Zhao, Jizhen; Wang, Liangping
2016-01-01
The experimental results of the insulated-standard hybrid wire array Z pinches carried out on "QiangGuang-I" facility at Northwest Institute of Nuclear Technology were presented and discussed. The surface insulating can impose a significant influence on the dynamics and radiation characteristics of the hybrid wire array Z pinches, especially on the early stage (t/timp < 0.6). The expansion of insulated wires at the ablation stage is suppressed, while the streams stripped from the insulated wires move faster than that from the standard wires. The foot radiation of X-ray is enhanced by increment of the number of insulated wires, 19.6 GW, 33.6 GW, and 68.6 GW for shots 14037S, 14028H, and 14039I, respectively. The surface insulation also introduces nonhomogeneity along the single wire—the streams move much faster near the electrodes. The colliding boundary of the hybrid wire array Z pinches is bias to the insulated side approximately 0.6 mm.
Larger sized wire arrays on 1.5 MA Z-pinch generator
Safronova, A. S., E-mail: alla@unr.edu; Kantsyrev, V. L., E-mail: alla@unr.edu; Weller, M. E., E-mail: alla@unr.edu
2014-12-15
Experiments on the UNR Zebra generator with Load Current Multiplier (LCM) allow for implosions of larger sized wire array loads than at standard current of 1 MA. Advantages of larger sized planar wire array implosions include enhanced energy coupling to plasmas, better diagnostic access to observable plasma regions, and more complex geometries of the wire loads. The experiments with larger sized wire arrays were performed on 1.5 MA Zebra with LCM (the anode-cathode gap was 1 cm, which is half the gap used in the standard mode). In particular, larger sized multi-planar wire arrays had two outer wire planes frommore » mid-atomic-number wires to create a global magnetic field (gmf) and plasma flow between them. A modified central plane with a few Al wires at the edges was put in the middle between outer planes to influence gmf and to create Al plasma flow in the perpendicular direction (to the outer arrays plasma flow). Such modified plane has different number of empty slots: it was increased from 6 up to 10, hence increasing the gap inside the middle plane from 4.9 to 7.7 mm, respectively. Such load configuration allows for more independent study of the flows of L-shell mid-atomic-number plasma (between the outer planes) and K-shell Al plasma (which first fills the gap between the edge wires along the middle plane) and their radiation in space and time. We demonstrate that such configuration produces higher linear radiation yield and electron temperatures as well as advantages of better diagnostics access to observable plasma regions and how the load geometry (size of the gap in the middle plane) influences K-shell Al radiation. In particular, K-shell Al radiation was delayed compared to L-shell mid-atomic-number radiation when the gap in the middle plane was large enough (when the number of empty slots was increased up to ten)« less
X-ray emission from z pinches at 107 A: Current scaling, gap closure, and shot-to-shot fluctuations
NASA Astrophysics Data System (ADS)
Stygar, W. A.; Ives, H. C.; Fehl, D. L.; Cuneo, M. E.; Mazarakis, M. G.; Bailey, J. E.; Bennett, G. R.; Bliss, D. E.; Chandler, G. A.; Leeper, R. J.; Matzen, M. K.; McDaniel, D. H.; McGurn, J. S.; McKenney, J. L.; Mix, L. P.; Muron, D. J.; Porter, J. L.; Ramirez, J. J.; Ruggles, L. E.; Seamen, J. F.; Simpson, W. W.; Speas, C. S.; Spielman, R. B.; Struve, K. W.; Torres, J. A.; Vesey, R. A.; Wagoner, T. C.; Gilliland, T. L.; Horry, M. L.; Jobe, D. O.; Lazier, S. E.; Mills, J. A.; Mulville, T. D.; Pyle, J. H.; Romero, T. M.; Seamen, J. J.; Smelser, R. M.
2004-04-01
We have measured the x-ray power and energy radiated by a tungsten-wire-array z pinch as a function of the peak pinch current and the width of the anode-cathode gap at the base of the pinch. The measurements were performed at 13- and 19-MA currents and 1-, 2-, 3-, and 4-mm gaps. The wire material, number of wires, wire-array diameter, wire-array length, wire-array-electrode design, normalized-pinch-current time history, implosion time, and diagnostic package were held constant for the experiments. To keep the implosion time constant, the mass of the array was increased as I2 (i.e., the diameter of each wire was increased as I), where I is the peak pinch current. At 19 MA, the mass of the 300-wire 20-mm-diam 10-mm-length array was 5.9 mg. For the configuration studied, we find that to eliminate the effects of gap closure on the radiated energy, the width of the gap must be increased approximately as I. For shots unaffected by gap closure, we find that the peak radiated x-ray power Pr∝I1.24±0.18, the total radiated x-ray energy Er∝I1.73±0.18, the x-ray-power rise time τr∝I0.39±0.34, and the x-ray-power pulse width τw∝I0.45±0.17. Calculations performed with a time-dependent model of an optically thick pinch at stagnation demonstrate that the internal energy and radiative opacity of the pinch are not responsible for the observed subquadratic power scaling. Heuristic wire-ablation arguments suggest that quadratic power scaling will be achieved if the implosion time τi is scaled as I-1/3. The measured 1σ shot-to-shot fluctuations in Pr, Er, τr, τw, and τi are approximately 12%, 9%, 26%, 9%, and 2%, respectively, assuming that the fluctuations are independent of I. These variations are for one-half of the pinch. If the half observed radiates in a manner that is statistically independent of the other half, the variations are a factor of 21/2 less for the entire pinch. We calculate the effect that shot-to-shot fluctuations of a single pinch would have on
Characterization of Axially-Directed X-Rays Generated from a Target within a Z-Pinch
NASA Astrophysics Data System (ADS)
Sanford, T. W. L.; Chandler, G. A.; Cuneo, M. E.; Fehl, D. L.; Hebron, D. E.; Leeper, R. J.; Lemke, R. W.; Mock, R. C.; Olson, R. E.; Nash, T. J.; Porter, J. L.; Ruggles, L. E.; Ruiz, C. L.; Simpson, W. W.; Peterson, D. L.; Chrien, R. E.; Idzorek, G. C.; Watt, R. G.
2000-10-01
X-ray powers on the order of 10 TW over an area of 4.5 mm2 are produced in the axial direction from the compression of a low-density foam target centered within a z-pinch on the Z generator. The x-rays from this source are used for high-energy-density physics experiments, including the heating of hohlraums for ICF studies [1]. In this paper, detailed characteristics of this radiation source measured using an upgraded axial-radiation-diagnostic suite [2] together with other on- and off-axis diagnostics are summarized and discussed in terms of Eulerian and Lagrangian radiation-magnetohydrodynamic code simulations. The source, characterized here, employs a nested array of 10-mm-long tungsten wires, at radii of 20 and 10 mm, having a total masses of 2 and 1 mg, and wire numbers of 240 and 120, respectively. The target is a 14 mg/cc CH2 foam cylinder of 5-mm diameter. The codes take into account the development of the Rayleigh-Taylor instability in the r-z plane, and provide integrated calculations of the implosion together with the x-ray generation. [1] T. W. L. Sanford, R. E. Olson, R. L. Bowers, et al, Phys. Rev. Lett 83, 5511 (1999). [2] T. J. Nash, M. S. Derzon, G. A. Chandler, et al, Rev. Sci. Instrum. 70, 464 (1999). Sandia is a multiprogram laboratory operated by the Sandia Corporation, a Lockheed Martin Company, for the U.S. Department of Energy under Contract No. DE-AC04-94AL85000.
Xiao, Delong; Ding, Ning; Sun, Shunkai
2014-04-15
The interaction of a light tungsten wire-array Z-pinch with an embedded heavy foam converter, whose mass ratio is typically less than 0.16, is numerically analyzed and experimentally investigated on the 1.3 MA “QiangGuang I” facility. Computational results show that this implosion process can be divided into three stages: acceleration of the tungsten wire-array plasma, collision, and stagnation. The tungsten plasma is accelerated to a high speed by the J × B force and interacts weakly with the foam plasma in the first stage. Strong energy conversions take place in the second collision stage. When the high speed tungsten plasma impacts on themore » foam converter, the plasma is thermalized and a radial radiation peak is produced. Meanwhile, a shock wave is generated due to the collision. After the shock rebounds from the axis and meets the W/Foam boundary, the plasma stagnates and the second radial radiation peak appears. The collision and stagnation processes were observed and the two-peak radial radiation pulse was produced in experiments. Increasing the wire-array radius from 4 mm to 6 mm, the kinetic energy of the tungsten plasma is increased, causing a stronger thermalization and generating a higher first radiation peak. Experimental results also showed a higher ratio of the first peak to the second peak in the case of larger wire-array radius. If we add a thin CH film cover onto the surface of the embedded foam converter, the first radiation peak will be hardly changed, because the acceleration of the tungsten plasma is not evidently affected by the film cover. However, the second radiation peak decreases remarkably due to the large load mass and the corresponding weak compression.« less
Osborne, Glenn C.; Esaulov, Andrey A.; Apruzese, John P.; Shrestha, I.; Kantsyrev, Victor Leonidovich; Shlyaptseva, V.; Coverdale, Christine Anne; Rudakov, Leonid I.; Williamson, K. M.; Deeney, Christopher; Ouart, Nicholas D.; Weller, M. E.; Safronova, Alla S.
2010-07-01
The planar wire array research on Zebra at UNR that started in 2005 continues experiments with new types of planar loads with results for consideration and comprehensive analysis [see, for example, Kantsyrev et al, HEDP 5, 115 (2009)]. The detailed studies of radiative properties of such loads are important and spectroscopy and imaging constitute a very valuable and informative diagnostic tool. The set of theoretical codes is implemented which provides non-LTE kinetics, wire ablation dynamic, and MHD modeling. This talk is based on the results of new recent experiments with planar wire arrays on Zebra at UNR. We start with results on radiative properties of a uniform single planar wire array (SPWA) from alloyed Al wires and move to combined triple planar wire arrays (TPWA) made from two materials, Cu and Al. Such combined TPWA includes three planar wire rows that are parallel to each other and made of either Cu or Al alloyed wires. Three different configurations (Al/Cu/Al, Cu/Al/Cu, and Cu/Cu/Al) are considered and compared with each other, and with the results from SPWA of the same materials. X-ray time-gated and time integrated pinhole images and spectra are analyzed together with bolometer, PCD, and XRD measurements, and optical images. Emphasis is made on the radiative properties and temporal and spatial evolution of plasma parameters of such two-component plasmas. The opacity effects are considered and the important question of what causes K-shell Al lines to be optically thin in combined TPWAs is addressed. In conclusion, the new findings from studying multi-planar wire array implosions are summarized and their input to Z-pinch radiation physics is discussed.
Theory of formation of helical structures in a perfectly conducting, premagnetized Z-pinch liner
NASA Astrophysics Data System (ADS)
Yu, Edmund; Velikovich, Alexander; Peterson, Kyle
2014-10-01
The magnetized liner inertial fusion (MagLIF) concept uses an azimuthal magnetic field to collapse a thick metallic liner containing preheated fusion fuel. A critical component of the concept is an axial magnetic field, permeating both the fuel and surrounding liner, which reduces the compression necessary to achieve fusion conditions. Recent experiments demonstrate that a liner premagnetized with a 10 T axial field develops helical structures with a pitch significantly larger than an estimate of Bz /Bθ would suggest. The cause of the helical perturbations is still not understood. In this work, we present an analytic, linear theory in which we model the liner as a perfectly conducting metal, and study how bumps and divots on its surface redirect current flow, resulting in perturbations to B as well as j × B . We show that in the presence of axial and azimuthal magnetic field, the theory predicts divots will grow and deform at an angle determined by the magnetic field. We compare theoretical results with three dimensional, resistive MHD simulations. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the National Nuclear Security Administration under DE-AC04-94AL85000.
Low impedance z-pinch drivers without post-hole convolute current adders.
Savage, Mark Edward; Seidel, David Bruce; Mendel, Clifford Will, Jr.
2009-09-01
Present-day pulsed-power systems operating in the terawatt regime typically use post-hole convolute current adders to operate at sufficiently low impedance. These adders necessarily involve magnetic nulls that connect the positive and negative electrodes. The resultant loss of magnetic insulation results in electron losses in the vicinity of the nulls that can severely limit the efficiency of the delivery of the system's energy to a load. In this report, we describe an alternate transformer-based approach to obtaining low impedance. The transformer consists of coils whose windings are in parallel rather than in series, and does not suffer from the presence of magnetic nulls. By varying the pitch of the coils windings, the current multiplication ratio can be varied, leading to a more versatile driver. The coupling efficiency of the transformer, its behavior in the presence of electron flow, and its mechanical strength are issues that need to be addressed to evaluate the potential of transformer-based current multiplication as a viable alternative to conventional current adder technology.
Modifying Wire Array Z-pinch Ablation Structure and Implosion Dynamics Using Coiled Arrays
NASA Astrophysics Data System (ADS)
Hall, Gareth N.; Bland, Simon N.; Lebedev, Sergey V.; Chittenden, Jeremy P.; Palmer, James B. A.; Suzuki-Vidal, Francisco A.; Swadling, George F.; Niasse, Nicolas; Knapp, P. F.; Blesener, I. C.; McBride, R. D.; Chalenski, D. A.; Bell, K. S.; Greenly, J. B.; Blanchard, T.; Wilhelm, H.; Hammer, D. A.; Kusse, B. R.; Bott, Simon C.
2009-01-01
Coiled arrays, a cylindrical array in which each wire is formed into a helix, suppress the modulation of ablation at the fundamental wavelength. Outside the vicinity of the wire cores, ablation flow from coiled arrays is modulated at the coil wavelength and has a 2-stream structure in the r,θ plane. Within the vicinity of the helical wires, ablation is concentrated at positions with the greatest azimuthal displacement and plasma is axially transported from these positions such that the streams become aligned with sections of the coil furthest from the array axis. The GORGON MHD code accurately reproduces this observed ablation structure, which can be understood in terms of J×B forces that result from the interaction of the global magnetic field with a helical current path as well as additional current paths suggested by the simulations. With this ability to control where ablation streamers occur, large wavelength coils were constructed such that the breaks that form in the wires had sufficient axial separation to prevent perturbations in the implosion sheath from merging. This produces a new mode of implosion in which the global instability can be controlled and perturbations correlated between all wires in an array. For large wavelength 8-wire coiled arrays, this produced a dramatic increase in x-ray power, equalling that of a 32-wire straight array. These experiments were carried out on the MAGPIE generator (1 MA, 240 ns) at Imperial College, and the COBRA generator (1 MA, 100 ns) at Cornell University.
Wang, Kun-lun; Ren, Xiao-dong; Huang, Xian-bin, E-mail: caephxb2003@aliyun.com
2015-11-15
Fast z-pinch is a very efficient way of converting electromagnetic energy to radiation. With an 8-10 MA current on primary test stand facility, about 1 MJ electromagnetic energy is delivered to vacuum chamber, which heats z-pinch plasma to radiate soft x-ray. To develop a pulsed high power x-ray source, we studied the applicability of diagnosing x-ray power from tungsten wire array z-pinch with a flat spectral response x-ray diode (FSR-XRD). The detector was originally developed to diagnose radiation of a hohlraum in SG-III prototype laser facility. It utilized a gold cathode XRD and a specially configured compound gold filter tomore » yield a nearly flat spectral response in photon energy range of 0.1-4 keV. In practice, it was critical to avoid surface contamination of gold cathode. It is illustrated that an exposure of an XRD to multiple shots caused a significant change of response. Thus, in diagnosing x-ray power and energy, we used each XRD in only one shot after calibration. In a shot serial, output of FSR-XRD was compared with output of a nickel bolometer. In these shots, the outputs agreed with each other within their uncertainties which were about 12% for FSR-XRD and about 15% for bolometer. Moreover, the ratios between the FSR-XRD and the bolometer among different shots were explored. In 8 shots, the standard deviation of the ratio was 6%. It is comparable to XRD response change of 7%.« less
BOWERS,RICHARD; CHANDLER,GORDON A.; HEBRON,DAVID E.
1999-11-01
Hohlraums of full ignition scale (6-mm diameter by 7-mm length) have been heated by x-rays from a z-pinch magnet on Z to a variety of temperatures and pulse shapes which can be used to simulate the early phases of the National Ignition Facility (NIF) temperature drive. The pulse shape is varied by changing the on-axis target of the z pinch in a static-wall-hohlraum geometry. A 2-{micro}m-thick walled Cu cylindrical target of 8-mm diameter filled with 10 mg/cm{sup 3} CH, for example, produces foot-pulse conditions of {approx}85 eV for a duration of {approx}10 ns, while a solid cylindrical target of 5-mmmore » diameter and 14-mg/cm{sup 3} CH generates first-step-pulse conditions of {approx}122 eV for a duration of a few ns. Alternatively, reducing the hohlraum size (to 4-mm diameter by 4-mm length) with the latter target has increased the peak temperature to {approx}150 eV, which is characteristic of a second-step-pulse temperature. In general, the temperature T of these x-ray driven hohlraums is in agreement with the Planckian relation T{approx}(P/A){sup 1/4}. P is the measured x-ray input power and A is the surface area of the hohlraum. Fully-integrated 2-D radiation-hydrodynamic simulations of the z pinch and subsequent hohlraum heating show plasma densities within the useful volume of the hohlraums to be on the order of air or less.« less
NASA Astrophysics Data System (ADS)
Sakai, Y.; Takahashi, S.; Watanabe, M.; Kim, G.-H.; Hotta, E.
2010-04-01
By using a water transmission line, current wave shaping was demonstrated for a fast capillary Z-pinch discharge recombination soft x-ray laser study. The pulsed power system consists of a water capacitor, a gap switch, a transmission line, and a capillary plasma load. A voltage wave initiated at the water capacitor propagates toward the capillary load through the transmission line. Control of the pulse delay that occurred in the transmission line provides the superposition of the forward and the backward voltage waves effectively in order to perform current wave shaping with higher current amplitude and rapid current decay.
Huang, B.; Tomizuka, T.; Xie, B.
2013-11-15
The development and use of a single-fluid two-temperature approximated 2-D Magneto-Hydrodynamics code is reported. Z-pinch dynamics and the evolution of Magneto-Rayleigh-Taylor (MRT) instabilities in a gas jet type Extreme Ultraviolet (EUV) source are investigated with this code. The implosion and stagnation processes of the Z-pinch dynamics and the influence of initial perturbations (single mode, multi- mode, and random seeds) on MRT instability are discussed in detail. In the case of single mode seeds, the simulation shows that the growth rates for mm-scale wavelengths up to 4 mm are between 0.05 and 0.065 ns{sup −1}. For multi-mode seeds, the mode couplingmore » effect leads to a series of other harmonics, and complicates MRT instability evolution. For perturbation by random seeds, the modes evolve to longer wavelengths and finally converge to a mm-scale wavelength approximately 1 mm. MRT instabilities can also alter the pinch stagnation state and lead to temperature and density fluctuations along the Z axis, which eventually affects the homogeneity of the EUV radiation output. Finally, the simulation results are related to experimental results to discuss the mitigations of MRT instability.« less
NASA Astrophysics Data System (ADS)
Nawaz, M. F.; Jancarek, Alexandr; Nevrkla, Michal; Duda, Martin Jakub; Pina, Ladislav
2017-05-01
The development and demonstration of a soft X-ray (SXR) microscope, based on a Z-pinching capillary discharge source has been realized. The Z-pinching plasma acts as a source of SXR radiation. A ceramic capacitor bank is pulsed charged up to 80 kV, and discharged through a pre- ionized nitrogen filled ceramic capillary. The discharge current has an amplitude of 25 kA. Working within the water-window spectral region (λ = 2.88 nm), corresponding to the 1s2-1s2p quantum transition of helium-like nitrogen (N5+), the microscope has a potential in exploiting the natural contrast existing between the K-absorption edges of carbon and oxygen as the main constituents of biological materials, and hence imaging them with high spatial resolution. The SXR microscope uses the grazing incidence ellipsoidal condenser mirror for the illumination, and the Fresnel zone plate optics for the imaging of samples onto a BI-CCD camera. The half- pitch spatial resolution of 100 nm [1] was achieved, as demonstrated by the knife-edge test. In order to enhance the photon-flux at the sample plane, a new scheme for focusing the radiation, from multiple capillary sources has been investigated. Details about the source, and the construction of the microscope are presented and discussed.
NASA Astrophysics Data System (ADS)
Niasse, Nicolas; Chittenden, Jeremy
2012-10-01
The last few years have seen considerable advances in the application of high performance computing techniques to 3D simulations of wire array Z-pinches. Whilst the intense soft X-ray radiation output is the principle application of wire arrays, the ability to encompass spectrally detailed models of this emission within such 3D calculations was thought to be computationally prohibitive. We have developed a non-LTE atomic and radiation physics model with detailed configuration accounting and n-l splitting which is sufficiently streamlined to run in-line with large scale 3D simulations. In order to handle the volume of data generated by the spectral treatment of the billions of numerical cells, a novel data structure derived from a self-balancing binary search tree was developed, enabling the use of non-LTE DCA calculations within large scale 3D simulations for the first time. A brief description of the model is provided and the application of the simulations to understanding the X-ray generation processes within wire array Z-pinches on the Z generator at Sandia National Laboratory is reported. The contribution of the ion temperature and the motion of the unstable plasma at stagnation to the Doppler widths of the lines is described in detail.
NASA Astrophysics Data System (ADS)
Dutra, Eric; Presura, Radu; Angermeier, William; Mancini, Roberto; Covington, Aaron
2017-10-01
In plasma pinch experiments, measurements of current distributions and losses across the anode-cathode (A-K) gap are needed to ensure uniform and repeatable implosions. Traditional B-dots measure current a considerable distance away from the plasma source and provide little detailed information on the current distribution across the plasma sheath near the pinch. In the experiments presented here, visible spectroscopic techniques were used to measure magnetically induced Zeeman splitting. Ionic plasma species were chosen such that the Zeeman splitting of different fine structure doublets split non-uniformly with increasing magnetic field strength in the plasma. This differential splitting enables measurements of non-directional B-field strengths in the plasma across a wide range of conditions. More specifically, the optical emission of Al III, C IV, and O VI doublets, 2P3/2 to 2S1/2 and 2P1/2 to 2S1/2 transitions were measured and used to determine the Zeeman broadening. We have applied this technique to diagnose time- and space-resolved B-field strengths in laser ablation Z-pinch experiments (LAZE). Experiments were conducted at the Nevada Terawatt Facility (NTF) using the TW-class Leopard laser and the 1 MA Zebra Z-pinch. The currents inferred from Zeeman spectroscopy measurements were compared to those determined from the B-dot diagnostics. DOE/NV/25946 ''3272.
NASA Astrophysics Data System (ADS)
Sanford, T. W. L.; Bailey, J. E.; Chandler, G. A.; Cuneo, M. E.; Fehl, D. L.; Hebron, D. E.; Leeper, R. J.; Lemke, R. W.; Mock, R. C.; Olson, R. E.; Nash, T. J.; Porter, J. L.; Ruggles, L. E.; Ruiz, C. L.; Simpson, W. W.; Struve, K. W.; Stygar, W. A.; Bowers, R. L.; Chrien, R. E.; Idzorek, G. C.; Matuska, W.; Peterson, D. L.; Watt, R. G.
2001-01-01
X-ray powers on the order of 10 TW over an area of 4.5 mm2 are produced in the axial direction from the compression of a low-density foam target centered within a z-pinch on the Z generator.1 The x rays from this source are used for high-energy-density physics experiments, including the heating of hohlraums for inertial confinements fusion studies.2 In this article, detailed characteristics of this radiation source measured using an upgraded axial-radiation-diagnostic suite3 together with other on- and off-axis diagnostics are summarized and discussed in terms of Eulerian and Lagrangian radiation-magnetohydrodynamic code simulations. The source, characterized here, employs a nested array of 10-mm-long tungsten wires, at radii of 20 and 10 mm, having a total masses of 2 and 1 mg, and wire numbers of 240 and 120, respectively. The target is a 14 mg/cc CH2 foam cylinder of 5 mm diameter. The codes take into account the development of the Rayleigh-Taylor instability in the r-z plane, and provide integrated calculations of the implosion together with the x-ray generation. The radiation exiting the imploding target through the 4.5 mm2 aperture is measured primarily by the axial diagnostic suite that now includes diagnostics at an angle of ˜30° to the z axis. The near on-axis diagnostics include: (1) a seven-element filtered silicon-diode array,4 (2) a five-element filtered x-ray diffraction (XRD) array,5 (3) a six-element filtered PCD array,6 (4) a three-element bolometer,7 (5) time-resolved and time-integrating crystal spectrometers, and (6) two fast-framing x-ray pinhole cameras having 11 frames each. The filtered silicon diodes, XRDs, and PCDs are sensitive to 1-200, 140-2300, and 1000-4000 eV x rays, respectively. They (1) establish the magnitude of the prepluse generated during the run in of the imploding wire arrays, (2) measure the Planckian nature of the dominant thermal, and (3) nonthermal component of the emission. The bolometers and XRDs mounted on the near
NASA Astrophysics Data System (ADS)
Cherdizov, R. K.; Fursov, F. I.; Kokshenev, V. A.; Kurmaev, N. E.; Labetsky, A. Yu; Ratakhin, N. A.; Shishlov, A. V.; Cikhardt, J.; Cikhardtova, B.; Klir, D.; Kravarik, J.; Kubes, P.; Rezac, K.; Dudkin, G. N.; Garapatsky, A. A.; Padalko, V. N.; Varlachev, V. A.
2017-05-01
The Z-pinch experiments with deuterium gas-puff surrounded by an outer plasma shell were carried out on the GIT-12 generator (Tomsk, Russia) at currents of 2 MA. The plasma shell consisting of hydrogen and carbon ions was formed by 48 plasma guns. The deuterium gas-puff was created by a fast electromagnetic valve. This configuration provides an efficient mode of the neutron production in DD reaction, and the neutron yield reaches a value above 1012 neutrons per shot. Neutron diagnostics included scintillation TOF detectors for determination of the neutron energy spectrum, bubble detectors BD-PND, a silver activation detector, and several activation samples for determination of the neutron yield analysed by a Sodium Iodide (NaI) and a high-purity Germanium (HPGe) detectors. Using this neutron diagnostic complex, we measured the total neutron yield and amount of high-energy neutrons.
Boldarev, A. S.; Bolkhovitinov, E. A.; Vichev, I. Yu.
2015-02-15
Methods and results of studies of the radiation spectra of high-current Z-pinches with different elemental compositions are presented. To examine a wide spectral range (E{sub hν} = 30–3000 eV), two diagnostics tools were used—a transmission grating and a reflecting mica crystal. The radiation characteristics of the pinch are determined by its elemental composition. For currents of 2–3 MA and low-Z elements (aluminum), the hard end of the radiation spectrum is represented by spectral lines with clearly pronounced K lines, while for high-Z elements (tungsten), the spectrum lies in the softer photon energy range and is quasi-continuous. Two methods of spectrummore » processing were used to determine the plasma parameters. The parameters of aluminum plasma were traditionally determined from the intensity ratios of the K lines taking into account the plasma transparency for these lines. The spectra of tungsten plasma were compared with the results of computer simulations of pinch compression with allowance for both magnetohydrodynamic and plasma radiation processes. The applicability of these methods of spectral analysis is discussed.« less
NASA Astrophysics Data System (ADS)
Kantsyrev, V. L.; Safronova, A. S.; Shrestha, I. K.; Shlyaptseva, V. V.; Butcher, C. J.; Stafford, A.; Schultz, K. A.; Campbell, P. C.; Miller, S.; Yager-Elorriaga, D. A.; Jordan, N. M.; McBride, R. D.; Gilgenbach, R. M.
2017-10-01
The results of first experiments with Al double planar foil liners (DPFL) at the University of Michigan's low impedance Linear Transformer Driver (LTD) MAIZE generator are presented. The DPFL is a promising alternative load to wire arrays on future 40-60 MA generators. Last decade, there was a significant progress in efficient, repetitive Z-pinch generators such as the LTD for prospective ICF research. Though we have recently presented the results on the Planar Wires Arrays (PWAs) on MAIZE, there is no data collected yet for DPFLs on LTD machines. Diagnostics include x-ray Si-diodes, a Faraday cup, x-ray pinhole cameras and spectrometers, and an ultra-fast 12-frame self-emission imaging system. Implosion and x-ray radiative characteristics of Al DPFLs (two planes 1.8 µm thick and 3.5 mm wide placed at 3 mm) are analyzed in detail and compared with data from Al double PWAs and results on Al DPFLs obtained early at high impedance generator. Experimental data demonstrate successful implosion of DPFL on LTD and therefore set the direction of the new work with thin foils. Research is supported by NNSA under DOE Grant DE-NA0003047.
NASA Astrophysics Data System (ADS)
Boldarev, A. S.; Bolkhovitinov, E. A.; Vichev, I. Yu.; Volkov, G. S.; Gasilov, V. A.; Grabovskii, E. V.; Gritsuk, A. N.; Dan'ko, S. A.; Zaitsev, V. I.; Novikov, V. G.; Oleinik, G. M.; Ol'khovskaya, O. G.; Rupasov, A. A.; Fedulov, M. V.; Shikanov, A. S.
2015-02-01
Methods and results of studies of the radiation spectra of high-current Z-pinches with different elemental compositions are presented. To examine a wide spectral range ( E hν = 30-3000 eV), two diagnostics tools were used—a transmission grating and a reflecting mica crystal. The radiation characteristics of the pinch are determined by its elemental composition. For currents of 2-3 MA and low- Z elements (aluminum), the hard end of the radiation spectrum is represented by spectral lines with clearly pronounced K lines, while for high- Z elements (tungsten), the spectrum lies in the softer photon energy range and is quasi-continuous. Two methods of spectrum processing were used to determine the plasma parameters. The parameters of aluminum plasma were traditionally determined from the intensity ratios of the K lines taking into account the plasma transparency for these lines. The spectra of tungsten plasma were compared with the results of computer simulations of pinch compression with allowance for both magnetohydrodynamic and plasma radiation processes. The applicability of these methods of spectral analysis is discussed.
Boldarev, A. S.; Bolkhovitinov, E. A.; Vichev, I. Yu.; Volkov, G. S.; Gasilov, V. A.; Grabovskii, E. V.; Gritsuk, A. N.; Dan’ko, S. A.; Zaitsev, V. I.; Novikov, V. G.; Oleinik, G. M.; Ol’khovskaya, O. G.; Rupasov, A. A.; Fedulov, M. V.; Shikanov, A. S.
2015-02-15
Methods and results of studies of the radiation spectra of high-current Z-pinches with different elemental compositions are presented. To examine a wide spectral range (E{sub hν} = 30–3000 eV), two diagnostics tools were used—a transmission grating and a reflecting mica crystal. The radiation characteristics of the pinch are determined by its elemental composition. For currents of 2–3 MA and low-Z elements (aluminum), the hard end of the radiation spectrum is represented by spectral lines with clearly pronounced K lines, while for high-Z elements (tungsten), the spectrum lies in the softer photon energy range and is quasi-continuous. Two methods of spectrum processing were used to determine the plasma parameters. The parameters of aluminum plasma were traditionally determined from the intensity ratios of the K lines taking into account the plasma transparency for these lines. The spectra of tungsten plasma were compared with the results of computer simulations of pinch compression with allowance for both magnetohydrodynamic and plasma radiation processes. The applicability of these methods of spectral analysis is discussed.
Awe, T. J.; Yu, E. P.; Yates, K. C.; ...
2017-02-21
Ultrafast optical microscopy of metal z-pinch rods pulsed with megaampere current is contributing new data and critical insight into what provides the fundamental seed for the magneto-Rayleigh-Taylor (MRT) instability. A two-frame near infrared/visible intensified-charge-coupled device gated imager with 2-ns temporal resolution and 3-μm spatial resolution captured emissions from the nonuniformly Joule heated surfaces of ultrasmooth aluminum (Al) rods. Nonuniform surface emissions are consistently first observed from discrete, 10-μm scale, subelectronvolt spots. Aluminum 6061 alloy, with micrometer-scale nonmetallic resistive inclusions, forms several times more spots than 99.999% pure Al 5N; 5-10 ns later, azimuthally stretched elliptical spots and distinct strata (40-100more » μm wide by 10 μm tall) are observed on Al 6061, but not on Al 5N. In such overheat strata, aligned parallel to the magnetic field, we find that they are highly effective seeds for MRT instability growth. Our data give credence to the hypothesis that early nonuniform Joule heating, such as the electrothermal instability, may provide the dominant seed for MRT.« less
NASA Astrophysics Data System (ADS)
Qi, Niansheng; de Grouchy, Philip; Hoyt, Cad; Shelkovenko, Tania; Pikuz, Sergei; Atoyan, Levon; Potter, William; Cahill, Adam; Greenly, John; Kusse, Bruce; Hammer, David
2014-10-01
We present the x-ray spectra obtained during Ar/Ne gas puff z-pinch experiments on the 1MA, 200ns COBRA pulsed power generator at Cornell University. A triple-nozzle gas-puff, which produces two annular (``outer'' and ``inner'') gas puffs and a high density center jet, is used to tailor the radial mass density distribution. Argon and/or neon plasmas are imploded. Filtered x-ray photo-conducting detectors are used for timing the neon and argon K-shell emission and a filtered x-ray pinhole camera images the K-shell x-ray source size. A spectrometer with three spherical mica crystals is used to capture the K-shell x-ray emission. Our objective is to diagnose the Ar and Ne pinch plasma densities (1019-1020 cm-3) and temperatures (0.5-2 keV) with 0.1 mm axial and/or radial spatial resolution from the K-shell X-ray spectra. The He-like resonance to intercombination line ratio will be used to estimate the electron density and the He-like resonance to Li-like satellite line ratio will be used to estimate the electron temperature. We will also add Cl as a dopant in either the center Ar gas jet or inner annular puff for K-shell x-ray spectrum studies. Work supported by DOE Grant No. DE-NA0001836.
Awe, T. J.; Yu, E. P.; Yates, K. C.; Yelton, W. G.; Bauer, B. S.; Hutchinson, T. M.; Fuelling, S.; Mckenzie, B. B.
2017-02-21
Ultrafast optical microscopy of metal z-pinch rods pulsed with megaampere current is contributing new data and critical insight into what provides the fundamental seed for the magneto-Rayleigh-Taylor (MRT) instability. A two-frame near infrared/visible intensified-charge-coupled device gated imager with 2-ns temporal resolution and 3-μm spatial resolution captured emissions from the nonuniformly Joule heated surfaces of ultrasmooth aluminum (Al) rods. Nonuniform surface emissions are consistently first observed from discrete, 10-μm scale, subelectronvolt spots. Aluminum 6061 alloy, with micrometer-scale nonmetallic resistive inclusions, forms several times more spots than 99.999% pure Al 5N; 5-10 ns later, azimuthally stretched elliptical spots and distinct strata (40-100 μm wide by 10 μm tall) are observed on Al 6061, but not on Al 5N. In such overheat strata, aligned parallel to the magnetic field, we find that they are highly effective seeds for MRT instability growth. Our data give credence to the hypothesis that early nonuniform Joule heating, such as the electrothermal instability, may provide the dominant seed for MRT.
NASA Astrophysics Data System (ADS)
Chong, Y. K.; Thornhill Giuliani, J. W., Jr.; Apruzese, J. P.; Terry, R. E.; Davis, J.
2001-10-01
The recent development of the computationally efficient tabulated collisional radiative equilibrium (TCRE) radiation transport model(J.W. Thornhill, J.P. Apruzese, J. Davis, R.W. Clark, A.L. Velikovich, J.L. Giuliani, Jr., Y.K. Chong, K.G. Whitney, C. Deeney, C.A. Coverdale and F.L. Cochran, Phys. Plasmas 7, 3480 (2001).) has made possible full multidimensional radiation MHD simulations of hot dense Z-pinch plasmas with a realistic description of the non-LTE ionization dynamics and radiation transport physics. In this study, we focus on the implementation of the TCRE radiation transport model in the Mach2 2D radiation MHD code. An application of the model is made through a full dynamical simulation of an argon gas puff pinch driven by a circuit model of the Z generator. An analysis of the simulation, in particular, the K- and L-shell radiation yields, as well as the spectral and spatial characteristics of the radiation will be presented. In addition, a comparison of this multidimensional transport method will be made with the existing radiative diffusion model.
Mitrofanov, K. N., E-mail: mitrofan@triniti.ru; Grabovski, E. V.; Gritsuk, A. N.
2013-01-15
Results are presented from experimental studies of the structure of the compressed plasma of a Z-pinch produced during the implosion of a foam-wire load at the current of up to 3 MA. The foam-wire load consisted of two nested cylindrical cascades, one of which was a solid or hollow cylinder made of low-density agar-agar foam, while the other was a wire array. The wall thickness of a hollow foam cylinder was 100-200 {mu}m. The images of the pinch and its spectrum obtained with the help of multiframe X-ray cameras and a grazing incidence spectrograph with a spatial resolution were analyzed.more » Data on the spatial structure of the emitting regions and the soft X-ray (SXR) spectrum of the Z-pinch in the final stage of compression of a foam-wire load were obtained. The implosion modes characterized by the formation of hot regions during implosion of such loads were revealed. The characteristic scale lengths of the hot regions were determined. It is shown that the energy distribution of SXR photons in the energy range from 80 eV to 1 keV forms the spatial structure of Z-pinch images recorded during the implosion of foam-wire loads. It is revealed that the spectral density of SXR emission in the photon energy range of 300-600 eV from hot Z-pinch regions exceeds the spectral density of radiation from the neighboring Z-pinch regions by more than one order of magnitude. Groups of lines related to the absorption and emission of radiation by atoms and multicharged ions of carbon and oxygen in the outer foam cascade of a foam-wire load were recorded for the first time by analyzing the spatial distribution of the SXR spectra of multicharged ions of the Z-pinch. The groups of absorption lines of ions (C III, O III, O IV, and O VI) corresponding to absorption of SXR photons in the Z-pinch of a tungsten wire array, which served as the inner cascade of a foam-wire load, were identified. The plasma electron temperature measured from the charge composition of carbon and oxygen
Instability control in a Staged Z-pinch, using an axial-magnetic field and target plasma
NASA Astrophysics Data System (ADS)
Rahman, Hafiz U.; Beg, F.; Conti, F.; Covington, A.; Darling, T.; Dutra, E.; Narkis, J.; Ney, P.; Ross, M.; Ruskov, E.; Valenzuela, J.; Wessel, F.
2017-10-01
Experiments on Zebra at UNR, and COBRA at Cornell, show evidence of a uniform pinch by the inclusion of low-Z target plasma (H, or D) inside a hollow gas shell of high-Z (Ar, or Kr) liner plasma. Adding an axial magnetic field of 1 - 2 kG improves the pinch stability. Numerical simulation is conducted using the 2-1/2 D radiation-MHD code MACH2. During implosion, magnetosonic-type shock waves propagate radially inward at different speeds in the liner and target plasmas, producing a shock front at the liner - target interface and a conduction channel ahead of the liner that preheats the target. This secondary conduction channel remains stable throughout the compression, even as the outer surface of the liner becomes Rayleigh-Taylor (RT) unstable. An axial magnetic field reduces the growth of the RT instability and enhances the secondary conduction channel. And in some cases reverses the effects of the RT instability, resulting in a uniform pinch. Simulations reveal that Bz field ``piles-up'' at the liner-target interface, instead of compressing uniformly over the entire volume. This scenario confines the target plasma in a magnetic well resulting in a high- β, stable plasma. Funded by the Advanced Research Projects Agency - Energy, under Grant Number DE-AR0000569.
Stability of compressible Taylor-Couette flow
NASA Technical Reports Server (NTRS)
Kao, Kai-Hsiung; Chow, Chuen-Yen
1991-01-01
Compressible stability equations are solved using the spectral collocation method in an attempt to study the effects of temperature difference and compressibility on the stability of Taylor-Couette flow. It is found that the Chebyshev collocation spectral method yields highly accurate results using fewer grid points for solving stability problems. Comparisons are made between the result obtained by assuming small Mach number with a uniform temperature distribution and that based on fully incompressible analysis.
Stabilization of flow past a rounded cylinder
NASA Astrophysics Data System (ADS)
Samtaney, Ravi; Zhang, Wei
2016-11-01
We perform global linear stability analysis on low-Re flow past a rounded cylinder. The cylinder corners are rounded with a radius R, normalized as R+ = R / D where D is the cylinder diameter, and its effect on the flow stability characteristics is investigated. We compute the critical Reynolds number (Recr) for the onset of first instability, and quantify the perturbation growth rate for the super-critical flows. It is found that the flow can be stabilized by partially rounding the cylinder. Compared with the square and circular cylinders, the partially rounded cylinder has a higher Recr , attaining a maximum at around R+ = 0 . 30 , and the perturbation growth rate of the super-critical flows is reduced for Re <= 100 . We perform sensitivity analysis to explore the source of the stabilization. The growth rate sensitivity to base flow modification has two different spatial structures: the growth rate is sensitive to the wake backflow in a large region for square-like cylinders (R+ -> 0 . 00), while only the near-wake backflow is crucial for circular-like cylinders (R+ -> 0 . 50). The stability analysis results are also verified with those of the direct simulations and very good agreement is achieved. Supported by the KAUST Office of Competitive Research Funds under Award No. URF/1/1394-01. The supercomputer Shaheen at KAUST was utilized for the simulations.
Flame stabilizer for stagnation flow reactor
Hahn, David W.; Edwards, Christopher F.
1999-01-01
A method of stabilizing a strained flame in a stagnation flow reactor. By causing a highly strained flame to be divided into a large number of equal size segments it is possible to stablize a highly strained flame that is on the verge of extinction, thereby providing for higher film growth rates. The flame stabilizer is an annular ring mounted coaxially and coplanar with the substrate upon which the film is growing and having a number of vertical pillars mounted on the top surface, thereby increasing the number of azimuthal nodes into which the flame is divided and preserving an axisymmetric structure necessary for stability.
Stability of flow focusing: The minimum attainable flow rate
NASA Astrophysics Data System (ADS)
Montanero, J. M.; Rebollo, N.; Acero, A.; Ferrera, C.; Herrada, M. A.; Ganan-Calvo, A. M.
2011-11-01
We analyze both theoretically and experimentally the stability of the steady jetting regime reached when liquid jets are focused by coaxial gas streams. In the low-viscosity case, viscous dissipation in the feeding capillary and liquid meniscus seem to be the origin of the instability. For high-viscosity liquids, the breakdown of the jetting regime takes place when the pressure drop cannot overcome the resistance force offered by surface tension. The characteristic flow rates for which the tapering menisci become unstable do not depend on the pressure drop applied to the system to produce the micro-jet. They increase (decrease) with viscosity for very low (high) viscosity liquids. Experiments confirmed the validity of the above conclusions. For each applied pressure drop, there is a minimum liquid flow rate below which the liquid meniscus drips. The minimum flow rates become practically independent of the applied pressure drop for sufficiently large values of this quantity. There exists an optimum value of the capillary-to-orifice distance for which the minimum flow rate attains a limiting value, which constitutes the lowest flow rate attainable with a given configuration in the steady jetting regime. A two-dimensional stability map with a high degree of validity is plotted on the plane defined by the Reynolds and capillary numbers based on the limiting flow rate.
Stability of Thin Liquid Sheet Flows
NASA Technical Reports Server (NTRS)
McConley, Marc W.; Chubb, Donald L.; McMaster, Matthew S.; Afjeh, Abdollah A.
1997-01-01
A two-dimensional, linear stability analysis of a thin nonplanar liquid sheet flow in vacuum is carried out. A sheet flow created by a narrow slit of W and tau attains a nonplanar cross section as a consequence of cylinders forming on the sheet edge under the influence of surface tension forces. The region where these edge cylinders join the sheet is one of high curvature, and this is found to be the location where instability is most likely to occur. The sheet flow is found to be unstable, but with low growth rates for symmetric wave disturbances and high growth rates for antisymmetric disturbances. By combining the symmetric and antisymmetric disturbance modes, a wide range of stability characteristics is obtained. The product of unstable growth rate and flow time is proportional to the width-to-thickness ratio of the sift generating the sheet Three-dimensional effects can alter these results, particularly when the sheet length-to-width ratio is not much greater than unity.
On stability and turbulence of fluid flows
NASA Technical Reports Server (NTRS)
Heisenberg, Werner
1951-01-01
This investigation is divided into two parts, the treatment of the stability problem of fluid flows on the one hand, and that of the turbulent motion on the other. The first part summarizes all previous investigations under a unified point of view, that is, sets up as generally as possible the conditions under which a profile possesses unstable or stable characteristics, and indicates the methods for solution of the stability equation for any arbitrary velocity profile and for calculation of the critical Reynolds number for unstable profiles. In the second part, under certain greatly idealizing assumptions, differential equations for the turbulent motions are derived and from them qualitative information about several properties of the turbulent velocity distribution is obtained.
Patterns and stability of a whirlpool flow
NASA Astrophysics Data System (ADS)
Carrión, Luis; Herrada, Miguel A.; Shtern, Vladimir N.; María López-Herrera, José
2017-04-01
This numerical study reveals stable multi-eddy patterns of a steady axisymmetric air-water flow driven by the rotating bottom disk in a vertical sealed cylindrical container. As rotation strength Re increases, eddies emerge, coalesce, separate, and disappear in both air and water. The topological scenario varies with water volume fraction H w according to the results obtained for H w = 0.3, 0.5, and 0.8. Interesting features are: (a) zipper-like chains of air and water eddies forming as the interface bends and (b) bubble-ring air eddies existing in the Re ranges specified in the paper. The stability analysis, performed with the help of a novel efficient technique for two-fluid flows, shows that these multi-eddy motions are stable. The shear-layer instability develops as the interface approaches either the top or bottom of the container and some eddies vanish. The physical reasoning behind the eddy formation and the flow instability is provided. The results are of fundamental interest and can have applications in bioreactors.
Stability analysis for laminar flow control, part 1
NASA Technical Reports Server (NTRS)
Benney, D. J.; Orszag, S. A.
1977-01-01
The basic equations for the stability analysis of flow over three dimensional swept wings are developed and numerical methods for their solution are surveyed. The equations for nonlinear stability analysis of three dimensional disturbances in compressible, three dimensional, nonparallel flows are given. Efficient and accurate numerical methods for the solution of the equations of stability theory were surveyed and analyzed.
Special Course on Stability and Transition of Laminar Flow
1984-06-01
layers developing on a very slightly heated wall . Two accelerating flows were studied. The following expression provides accurate repre- sentations...the stability theory itself. Reynolds [1] suggested in 1883 for laminar -turbulent transition in pipe flow "that the condition might be one of...rue Ancelle, 92200 Neuilly sur Seine, France 6. Title SPECIAL COURSE ON STABILITY AND TRANSITION OF LAMINAR FLOW 7. Presented at ^ AGARD Special
Elementary stratified flows with stability at low Richardson number
Barros, Ricardo; Choi, Wooyoung
2014-12-15
We revisit the stability analysis for three classical configurations of multiple fluid layers proposed by Goldstein [“On the stability of superposed streams of fluids of different densities,” Proc. R. Soc. A. 132, 524 (1931)], Taylor [“Effect of variation in density on the stability of superposed streams of fluid,” Proc. R. Soc. A 132, 499 (1931)], and Holmboe [“On the behaviour of symmetric waves in stratified shear layers,” Geophys. Publ. 24, 67 (1962)] as simple prototypes to understand stability characteristics of stratified shear flows with sharp density transitions. When such flows are confined in a finite domain, it is shown thatmore » a large shear across the layers that is often considered a source of instability plays a stabilizing role. Presented are simple analytical criteria for stability of these low Richardson number flows.« less
Emergent stability in a large, free-flowing watershed.
Moore, Jonathan W; Beakes, Michael P; Nesbitt, Holly K; Yeakel, Justin D; Patterson, David A; Thompson, Lisa A; Phillis, Corey C; Braun, Douglas C; Favaro, Corinna; Scott, David; Carr-Harris, Charmaine; Atlas, William I
2015-02-01
While it is widely recognized that financial stock portfolios can be stabilized through diverse investments, it is also possible that certain habitats can function as natural portfolios that stabilize ecosystem processes. Here we propose and examine the hypothesis that free-flowing river networks act as such portfolios and confer stability through their integration of upstream geological, hydrological, and biological diversity. We compiled a spatially (142 sites) and temporally (1980-present) extensive data set on fisheries, water flows, and temperatures, from sites within one of the largest watersheds in the world that remains without dams on its mainstem, the Fraser River, British Columbia, Canada. We found that larger catchments had more stable fisheries catches, water flows, and water temperatures than smaller catchments. These data provide evidence that free-flowing river networks function as hierarchically nested portfolios with stability as an emergent property. Thus, free-flowing river networks can represent a natural system for buffering variation and extreme events.
Linear stability of compressible Taylor-Couette flow
NASA Technical Reports Server (NTRS)
Kao, Kai-Hsiung; Chow, Chuen-Yen
1992-01-01
A temporal stability analysis of compressible Taylor-Couette flow is presented. The viscous flow studied in this paper is contained between two concentric cylinders of infinite length, which are rotating with different angular velocities and are kept at different surface temperatures. The effects of differential rotation and temperature difference on the stability of Taylor-Couette flow are contrasted for a range of Mach numbers ranging from incompressible to Mach 3.0. The relative motion of the cylinders dramatically affects the characteristics of the Couette flow at the onset of instability. The flow is stabilized or destabilized depending upon the temperature ratio and speeds of the two cylinders. Independent of Mach number and temperature ratio, increasing Reynolds number generally promotes a destabilizing effect, indicating the inviscid nature of the Taylor-Couette flow.
Stability of compressible Taylor-Couette flow
NASA Technical Reports Server (NTRS)
Kao, K.; Chow, C.
1992-01-01
The objectives of this paper are to: (1) develop both analytical and numerical tools that can be used to predict the onset of instability and subsequently to simulate the transition process by which the originally laminar flow evolves into a turbulent flow; and (2) conduct the preliminary investigations with the purpose of understanding the mechanisms of the vortical structures of the compressible flow between tow concentric cylinders.
Magnetohydrodynamic stability of stochastically driven accretion flows.
Nath, Sujit Kumar; Mukhopadhyay, Banibrata; Chattopadhyay, Amit K
2013-07-01
We investigate the evolution of magnetohydrodynamic (or hydromagnetic as coined by Chandrasekhar) perturbations in the presence of stochastic noise in rotating shear flows. The particular emphasis is the flows whose angular velocity decreases but specific angular momentum increases with increasing radial coordinate. Such flows, however, are Rayleigh stable but must be turbulent in order to explain astrophysical observed data and, hence, reveal a mismatch between the linear theory and observations and experiments. The mismatch seems to have been resolved, at least in certain regimes, in the presence of a weak magnetic field, revealing magnetorotational instability. The present work explores the effects of stochastic noise on such magnetohydrodynamic flows, in order to resolve the above mismatch generically for the hot flows. We essentially concentrate on a small section of such a flow which is nothing but a plane shear flow supplemented by the Coriolis effect, mimicking a small section of an astrophysical accretion disk around a compact object. It is found that such stochastically driven flows exhibit large temporal and spatial autocorrelations and cross-correlations of perturbation and, hence, large energy dissipations of perturbation, which generate instability. Interestingly, autocorrelations and cross-correlations appear independent of background angular velocity profiles, which are Rayleigh stable, indicating their universality. This work initiates our attempt to understand the evolution of three-dimensional hydromagnetic perturbations in rotating shear flows in the presence of stochastic noise.
Tearing mode stability in a toroidally flowing plasma
NASA Astrophysics Data System (ADS)
Sen, A.; Chandra, D.; Kaw, P.
2013-05-01
The effect of a sheared toroidal equilibrium flow on the tearing mode stability index, Δ‧, is studied. A flow modified external kink equation for a single helicity mode is derived in a toroidal geometry. The corrections to Δ‧ arising from flow contributions are estimated on the basis of a boundary layer calculation. Toroidal shear flow is seen to have a destabilizing influence on the tearing mode in a manner similar to pure axial flows in a cylindrical geometry. However, the increase in Δ‧ as a function of increasing flow is seen to be smaller than the cylindrical case due to beneficial magnetic curvature effects. Shear flow associated stabilization, as observed in many recent experiments, might be arising from other physical effects such as toroidal mode couplings which are neglected in the present model.
Stability of stagnation via an expanding accretion shock wave
NASA Astrophysics Data System (ADS)
Velikovich, A. L.; Murakami, M.; Taylor, B. D.; Giuliani, J. L.; Zalesak, S. T.; Iwamoto, Y.
2016-05-01
Stagnation of a cold plasma streaming to the center or axis of symmetry via an expanding accretion shock wave is ubiquitous in inertial confinement fusion (ICF) and high-energy-density plasma physics, the examples ranging from plasma flows in x-ray-generating Z pinches [Maron et al., Phys. Rev. Lett. 111, 035001 (2013)] to the experiments in support of the recently suggested concept of impact ignition in ICF [Azechi et al., Phys. Rev. Lett. 102, 235002 (2009); Murakami et al., Nucl. Fusion 54, 054007 (2014)]. Some experimental evidence indicates that stagnation via an expanding shock wave is stable, but its stability has never been studied theoretically. We present such analysis for the stagnation that does not involve a rarefaction wave behind the expanding shock front and is described by the classic ideal-gas Noh solution in spherical and cylindrical geometry. In either case, the stagnated flow has been demonstrated to be stable, initial perturbations exhibiting a power-law, oscillatory or monotonic, decay with time for all the eigenmodes. This conclusion has been supported by our simulations done both on a Cartesian grid and on a curvilinear grid in spherical coordinates. Dispersion equation determining the eigenvalues of the problem and explicit formulas for the eigenfunction profiles corresponding to these eigenvalues are presented, making it possible to use the theory for hydrocode verification in two and three dimensions.
On the linear stability of compressible plane Couette flow
NASA Technical Reports Server (NTRS)
Duck, Peter W.; Erlebacher, Gordon; Hussaini, M. Yousuff
1991-01-01
The linear stability of compressible plane Couette flow is investigated. The correct and proper basic velocity and temperature distributions are perturbed by a small amplitude normal mode disturbance. The full small amplitude disturbance equations are solved numerically at finite Reynolds numbers, and the inviscid limit of these equations is then investigated in some detail. It is found that instability can occur, although the stability characteristics of the flow are quite different from unbounded flows. The effects of viscosity are also calculated, asymptotically, and shown to have a stabilizing role in all the cases investigated. Exceptional regimes to the problem occur when the wavespeed of the disturbances approaches the velocity of either of the walls, and these regimes are also analyzed in some detail. Finally, the effect of imposing radiation-type boundary conditions on the upper (moving) wall (in place of impermeability) is investigated, and shown to yield results common to both bounded and unbounded flows.
Studies on dispersive stabilization of porous media flows
Daripa, Prabir, E-mail: prabir.daripa@math.tamu.edu; Gin, Craig
2016-08-15
Motivated by a need to improve the performance of chemical enhanced oil recovery (EOR) processes, we investigate dispersive effects on the linear stability of three-layer porous media flow models of EOR for two different types of interfaces: permeable and impermeable interfaces. Results presented are relevant for the design of smarter interfaces in the available parameter space of capillary number, Peclet number, longitudinal and transverse dispersion, and the viscous profile of the middle layer. The stabilization capacity of each of these two interfaces is explored numerically and conditions for complete dispersive stabilization are identified for each of these two types ofmore » interfaces. Key results obtained are (i) three-layer porous media flows with permeable interfaces can be almost completely stabilized by diffusion if the optimal viscous profile is chosen, (ii) flows with impermeable interfaces can also be almost completely stabilized for short time, but become more unstable at later times because diffusion flattens out the basic viscous profile, (iii) diffusion stabilizes short waves more than long waves which leads to a “turning point” Peclet number at which short and long waves have the same growth rate, and (iv) mechanical dispersion further stabilizes flows with permeable interfaces but in some cases has a destabilizing effect for flows with impermeable interfaces, which is a surprising result. These results are then used to give a comparison of the two types of interfaces. It is found that for most values of the flow parameters, permeable interfaces suppress flow instability more than impermeable interfaces.« less
Extension to nonlinear stability theory of the circular Couette flow
NASA Astrophysics Data System (ADS)
Yau, Pun Wong; Wang, Shixiao; Rusak, Zvi
2016-11-01
A nonlinear stability analysis of the viscous circular Couette flow to axisymmetric perturbations under axial periodic boundary conditions is developed. The analysis is based on investigating the properties of a reduced Arnol'd energy-Casimir function Ard of Wang (2009). We show that all the inviscid flow effects as well as all the viscous-dependent terms related to the flow boundaries vanish. The evolution of ΔArd depends solely on the viscous effects of the perturbation's dynamics inside the flow domain. The requirement for the temporal decay of ΔArd leads to novel sufficient conditions for the nonlinear stability of the circular Couette flow in response to axisymmetric perturbations. Comparisons with historical studies show that our results shed light on the experimental measurements of Wendt (1933) and significantly extend the classical nonlinear stability results of Serrin (1959) and Joseph & Hung (1971). When the flow is nonlinearly stable and evolves axisymmetrically for all time, then it always decays asymptotically in time to the circular Couette flow determined uniquely by the setup of the rotating cylinders. This study provides new physical insights into a classical flow problem that was studied for decades.
Stability of aluminium reduction cells with mean flow
NASA Astrophysics Data System (ADS)
Kurenkov, A.; Thess, A.; Zikanov, O.; Segatz, M.; Droste, Ch.; Vogelsang, D.
2004-06-01
We report results of the linear stability analysis undertaken to investigate the effect of the mean flow of liquid metal on the stability of aluminum reduction cells. A simplified model of the cell is considered that consists of thin layers of aluminum and cryolite superimposed in an infinite horizontal channel with electrically non-conducting walls. A vertical uniform magnetic field and an electric current are applied in the opposite directions. In the basic steady state, a uniform flow of aluminum is assumed, while cryolite is at rest. The onset of the instability is caused by the action of two different mechanisms. The first is the Kelvin-Helmholtz instability of the mean flow. The second, essentially the MHD mechanism, is a consequence of destabilizing electromagnetic (Lorentz) forces produced by nonuniformities of the electric current due to interface deflections. We use the shallow water approximation and solve the problem for the cases of pure Kelvin-Helmholtz (zero magnetic field) and pure MHD (zero mean flow) instabilities and for the general case. We compute the stability chart and derive the parameters that determine the stability threshold. It is found that, while both playing a destabilizing role, the instability mechanisms do not affect each other. In particular, a uniform mean flow changes the direction of propagation of interfacial waves but leaves the MHD stability threshold unaltered. Figs 4, Refs 12.
Estimating Z-Pinch computing resources.
Brunner, Thomas A.
2007-04-01
The Z facility at Sandia National Laboratories produces high energy density environments. Computer simulations of the experiments provide key insights and help make the most efficient use of the facility. This document estimates the computer resources needed in order to support the experimental program. The resource estimate is what we would like to have in about five years and assumes that we will have a robust, scalable simulation capability as well as enough physicists to run the simulations.
flowVS: channel-specific variance stabilization in flow cytometry.
Azad, Ariful; Rajwa, Bartek; Pothen, Alex
2016-07-28
Comparing phenotypes of heterogeneous cell populations from multiple biological conditions is at the heart of scientific discovery based on flow cytometry (FC). When the biological signal is measured by the average expression of a biomarker, standard statistical methods require that variance be approximately stabilized in populations to be compared. Since the mean and variance of a cell population are often correlated in fluorescence-based FC measurements, a preprocessing step is needed to stabilize the within-population variances. We present a variance-stabilization algorithm, called flowVS, that removes the mean-variance correlations from cell populations identified in each fluorescence channel. flowVS transforms each channel from all samples of a data set by the inverse hyperbolic sine (asinh) transformation. For each channel, the parameters of the transformation are optimally selected by Bartlett's likelihood-ratio test so that the populations attain homogeneous variances. The optimum parameters are then used to transform the corresponding channels in every sample. flowVS is therefore an explicit variance-stabilization method that stabilizes within-population variances in each channel by evaluating the homoskedasticity of clusters with a likelihood-ratio test. With two publicly available datasets, we show that flowVS removes the mean-variance dependence from raw FC data and makes the within-population variance relatively homogeneous. We demonstrate that alternative transformation techniques such as flowTrans, flowScape, logicle, and FCSTrans might not stabilize variance. Besides flow cytometry, flowVS can also be applied to stabilize variance in microarray data. With a publicly available data set we demonstrate that flowVS performs as well as the VSN software, a state-of-the-art approach developed for microarrays. The homogeneity of variance in cell populations across FC samples is desirable when extracting features uniformly and comparing cell populations with
Global stability of plane Couette flow beyond the energy stability limit
NASA Astrophysics Data System (ADS)
Fuentes, Federico; Goluskin, David
2017-11-01
This talk will present computations verifying that the laminar state of plane Couette flow is nonlinearly stable to all perturbations. The Reynolds numbers up to which this globally stability is verified are larger than those at which stability can be proven by the energy method, which is the typical method for demonstrating nonlinear stability of a fluid flow. This improvement is achieved by constructing Lyapunov functions that are more general than the energy. These functions are not restricted to being quadratic, and they are allowed to depend explicitly on the spectrum of the velocity field in the eigenbasis of the energy stability operator. The optimal choice of such a Lyapunov function is a convex optimization problem, and it can be constructed with computer assistance by solving a semidefinite program. This general method will be described in a companion talk by David Goluskin; the present talk focuses on its application to plane Couette flow.
Stabilization of flow past a cylinder with rounded corners
NASA Astrophysics Data System (ADS)
Zhang, Wei; Samtaney, Ravi
2015-11-01
We present results of global linear stability analysis for flow past a cylinder in the low Reynolds number regime Re = 50 - 110 . The four corners of the square cylinder are rounded with a radius of curvature R+ = R / D in which R is the rounding radius and D is the cylinder diameter. Analysis is carried out for R+ = 0 . 00 (square cylinder with sharp corners) to R+ = 0 . 50 (circular cylinder) to investigate its effect on the stability characteristics of the flow. The results reveal that the flow may be stabilized by the rounding of the corners for Re <= 100 , up to the minimum point beyond which further rounding has a destabilizing effect on the flow. The stabilization is less effective as the Reynolds number increases and for Re = 110 the square (resp. circular) cylinder has the least (resp. most) unstable growth rate. As R+ increases, the peak of the perturbation kinetic energy growth shifts closer to the cylinder and rapidly damps in the downstream region. The perturbation kinetic energy budget is examined and with the largest contribution due to the transfer of energy from the shear of the base flow. Supported by the KAUST Office of Competitive Research Funds under Award No. URF/1/1394-01.The IBM Blue Gene/P Shaheen at KAUST was utilized for the simulations.
The linear stability of Hunt-Rayleigh-Bénard flow
NASA Astrophysics Data System (ADS)
Qi, Tian-Yu; Liu, Chan; Ni, Ming-Jiu; Yang, Juan-Cheng
2017-06-01
The stability of a pressure driven flow in a duct heated from below and subjected to a vertical magnetic field (Hunt-Rayleigh-Bénard flow) is studied. We use the Chebyshev collocation approach to solve the eigenvalue problem for the small-amplitude perturbations. It is demonstrated that the magnetic field can stabilize the flow, while the temperature field can disturb the flow. There exists a threshold for the Hartmann number below which the growth rate changes with the Prandtl number non-monotonously (first increases and then decreases) with a critical Prandtl number for the maximum growth rate. By comparing the R e - α neutral curves at different Rayleigh numbers, we find that the critical Reynolds number decreases with the increase in the Rayleigh number, which has an obvious influence on the long-wave instability and a little influence on the short-wave instability. The dominant mode of the long-wave instability changes from the boundary layer instability to the inflectional instability with the increase in the growth rate, which forms a new flow map. We also compare the R a - α curves and find that the critical Rayleigh number decreases with the increase in the Reynolds number. The obtained results gain an insight into the flow stability affected by the temperature field and the magnetic field.
Stability investigations of airfoil flow by global analysis
NASA Technical Reports Server (NTRS)
Morzynski, Marek; Thiele, Frank
1992-01-01
As the result of global, non-parallel flow stability analysis the single value of the disturbance growth-rate and respective frequency is obtained. This complex value characterizes the stability of the whole flow configuration and is not referred to any particular flow pattern. The global analysis assures that all the flow elements (wake, boundary and shear layer) are taken into account. The physical phenomena connected with the wake instability are properly reproduced by the global analysis. This enhances the investigations of instability of any 2-D flows, including ones in which the boundary layer instability effects are known to be of dominating importance. Assuming fully 2-D disturbance form, the global linear stability problem is formulated. The system of partial differential equations is solved for the eigenvalues and eigenvectors. The equations, written in the pure stream function formulation, are discretized via FDM using a curvilinear coordinate system. The complex eigenvalues and corresponding eigenvectors are evaluated by an iterative method. The investigations performed for various Reynolds numbers emphasize that the wake instability develops into the Karman vortex street. This phenomenon is shown to be connected with the first mode obtained from the non-parallel flow stability analysis. The higher modes are reflecting different physical phenomena as for example Tollmien-Schlichting waves, originating in the boundary layer and having the tendency to emerge as instabilities for the growing Reynolds number. The investigations are carried out for a circular cylinder, oblong ellipsis and airfoil. It is shown that the onset of the wake instability, the waves in the boundary layer, the shear layer instability are different solutions of the same eigenvalue problem, formulated using the non-parallel theory. The analysis offers large potential possibilities as the generalization of methods used till now for the stability analysis.
Numerical studies of transverse curvature effects on transonic flow stability
NASA Technical Reports Server (NTRS)
Macaraeg, M. G.; Daudpota, Q. I.
1992-01-01
A numerical study of transverse curvature effects on compressible flow temporal stability for transonic to low supersonic Mach numbers is presented for axisymmetric modes. The mean flows studied include a similar boundary-layer profile and a nonsimilar axisymmetric boundary-layer solution. The effect of neglecting curvature in the mean flow produces only small quantitative changes in the disturbance growth rate. For transonic Mach numbers (1-1.4) and aerodynamically relevant Reynolds numbers (5000-10,000 based on displacement thickness), the maximum growth rate is found to increase with curvature - the maximum occurring at a nondimensional radius (based on displacement thickness) between 30 and 100.
CodingFlow: Enable Video Coding for Video Stabilization.
Liu, Shuaicheng; Li, Mingyu; Zhu, Shuyuan; Zeng, Bing
2017-07-01
Video coding focuses on reducing the data size of videos. Video stabilization targets at removing shaky camera motions. In this paper, we enable video coding for video stabilization by constructing the camera motions based on the motion vectors employed in the video coding. The existing stabilization methods rely heavily on image features for the recovery of camera motions. However, feature tracking is time-consuming and prone to errors. On the other hand, nearly all captured videos have been compressed before any further processing and such a compression has produced a rich set of block-based motion vectors that can be utilized for estimating the camera motion. More specifically, video stabilization requires camera motions between two adjacent frames. However, motion vectors extracted from video coding may refer to non-adjacent frames. We first show that these non-adjacent motions can be transformed into adjacent motions such that each coding block within a frame contains a motion vector referring to its adjacent previous frame. Then, we regularize these motion vectors to yield a spatially-smoothed motion field at each frame, named as CodingFlow, which is optimized for a spatially-variant motion compensation. Based on CodingFlow, we finally design a grid-based 2D method to accomplish the video stabilization. Our method is evaluated in terms of efficiency and stabilization quality, both quantitatively and qualitatively, which shows that our method can achieve high-quality results compared with the state-of-the-art methods (feature-based).
Study of the stability of compressible Couette flow
NASA Astrophysics Data System (ADS)
Girard, Jeffrey John
1988-07-01
A two-dimensional disturbance of plane Couette flow was studied. All reviewed analyses of the basic problem have led to the conclusion that the flow is unconditionally stable. All of the literature assumed the fluid was incompressible. The assumption that a fluid is incompressible neglects solutions to the problem. The motivation of the analysis presented herein is a hypothesis that some of the acoustic disturbances in the fluid, usually neglected, may interact with the mean vorticity to produce more sound. This hypothesis was discussed by Vaidya (1988). The fluid considered herein has been a viscous, heat-conducting, ideal gas. For the cases investigated in this study, most solutions exhibited stability. However, solutions at somewhat unrealistically high Mach numbers exhibited an unstable nature. For even low Mach number flows, the sound solution was the least stable solution. It is thought that the interaction between the sound perturbation and the mean flow has fed energy to the disturbance from the mean flow. Enough energy was transferred to balance some of the viscous dissipation. At low Mach numbers not enough energy was transferred to tip the flow to instability. The established theory has been challenged. All previous analyses of the basic infinitesimal perturbation problem have suggested unconditional stability. Some unstable regimes are shown.
The stabilizing effect of compressibility in turbulent shear flow
NASA Technical Reports Server (NTRS)
Sarkar, S.
1994-01-01
Direct numerical simulation of turbulent homogeneous shear flow is performed in order to clarify compressibility effects on the turbulence growth in the flow. The two Mach numbers relevant to homogeneous shear flow are the turbulent Mach number M(t) and the gradient Mach number M(g). Two series of simulations are performed where the initial values of M(g) and M(t) are increased separately. The growth rate of turbulent kinetic energy is observed to decrease in both series of simulations. This 'stabilizing' effect of compressibility on the turbulent energy growth rate is observed to be substantially larger in the DNS series where the initial value of M(g) is changed. A systematic companion of the different DNS cues shows that the compressibility effect of reduced turbulent energy growth rate is primarily due to the reduced level of turbulence production and not due to explicit dilatational effects. The reduced turbulence production is not a mean density effect since the mean density remains constant in compressible homogeneous shear flow. The stabilizing effect of compressibility on the turbulence growth is observed to increase with the gradient Mach number M(g) in the homogeneous shear flow DNS. Estimates of M(g) for the mixing and the boundary layer are obtained. These estimates show that the parameter M(g) becomes much larger in the high-speed mixing layer relative to the high-speed boundary layer even though the mean flow Mach numbers are the same in the two flows. Therefore, the inhibition of turbulent energy production and consequent 'stabilizing' effect of compressibility on the turbulence (over and above that due to the mean density variation) is expected to be larger in the mixing layer relative to the boundary layer in agreement with experimental observations.
Stability of a rivulet in a co-flowing microchannel
NASA Astrophysics Data System (ADS)
Herrada, Miguel A.; Mohamed, Ahmed S.; Montanero, Jose M.; Ganan-Calvo, Alfonso
2014-11-01
We here analyze the stability of a gas (liquid) rivulet on a hydrophobic (hydrophilic) strip along one of the inner sides of a quadrangular microfluidic channel where a liquid (gas) co-flows. The results essentially differ from those of co-flowing cylindrical capillary jets because the contact-line-anchorage conditions affect the rivulet's instability nature. The temporal stability analysis shows that the rivulet becomes unstable not only for (unperturbed) contact angles larger than 90° (as can be expected) but also for values smaller than that angle. The maximum growth factor exhibits a non-monotonic dependence with respect to the Reynolds number (i.e., the viscosities). In fact, there are intervals of that parameter where the fluid system becomes unstable, while all the perturbations are damped outside that interval. The gaseous rivulet does not stabilize as the Reynolds number decreases, which means that it can be unstable even in the Stokes limit and for contact angles less than 90°. In addition, the stability of a flowing liquid rivulet is not determined by its contact angle exclusively (as occurs in the static case), but by the Reynolds number as well. Liquid rivulets with contact angles less than 90? can be unstable for sufficiently high Reynolds numbers. Partial support from the Ministry of Science and Education, Junta de Extremadura, and Junta de Andalucía (Spain) through Grants Nos. DPI2010-21103, GR10047, and P08-TEP-04128, respectively, is gratefully acknowledged.
The stability of a flexible cantilever in viscous channel flow
NASA Astrophysics Data System (ADS)
Cisonni, Julien; Lucey, Anthony D.; Elliott, Novak S. J.; Heil, Matthias
2017-05-01
Most studies of the flow-induced flutter instability of a flexible cantilever have assumed inviscid flow because of the high flow speeds and the large scale of the structures encountered in the wide range of applications of this fluid-structure interaction (FSI) system. However, for instance, in the fields of energy harvesting and biomechanics, low flow speeds and small- and micro-scale systems can give relatively low Reynolds numbers so that fluid viscosity needs to be explicitly accounted for to provide reliable predictions of channel-immersed-cantilever stability. In this study, we employ a numerical model coupling the Navier-Stokes equations and a one-dimensional elastic beam model. We conduct a parametric investigation to determine the conditions leading to flutter instability of a slender flexible cantilever immersed in two-dimensional viscous channel flow for Reynolds numbers lower than 1000. The large set of numerical simulations carried out allows predictions of the influence of decreasing Reynolds numbers and of the cantilever confinement on the single-mode neutral stability of the FSI system and on the pre- and post-critical cantilever motion. This model's predictions are also compared to those of a FSI model containing a two-dimensional solid model in order to assess, primarily, the effect of the cantilever slenderness in the simulations. Results show that an increasing contribution of viscosity to the hydrodynamic forces significantly alters the instability boundaries. In general, a decrease in Reynolds number is predicted to produce a stabilisation of the FSI system, which is more pronounced for high fluid-to-solid mass ratios. For particular fluid-to-solid mass ratios, viscous effects can lower the critical velocity and lead to a change in the first unstable structural mode. However, at constant Reynolds number, the effects of viscosity on the system stability are diminished by the confinement of the cantilever, which strengthens the importance of
LInear stability analysis of granular Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Alam, Meheboob
2017-11-01
The linear stability analysis of the circular Couette flow of granular materials is carried out in the rapid shear regime. The kinetic-theory based continuum models, with a separate balance equation for granular/fluctuation energy, is employed, and the underlying rheological model is likely to be valid for a range of density from the dilute to dense regime. The steady base state equations for the case of rotating inner cylinder and stationary outer cylinder are solved numerically; it is found that the inelastic dissipation can make the flow radially inhomogeneous even in the narrow-gap limit. The linear stability equations are solved using spectral collocation method. The onset of Taylor-like vortices and the effects of inelastic dissipation and compressibility on them are analysed.
Bi-stability in turbulent, rotating spherical Couette flow
NASA Astrophysics Data System (ADS)
Zimmerman, Daniel S.; Triana, Santiago Andrés; Lathrop, D. P.
2011-06-01
Flow between concentric spheres of radius ratio η =ri/ro=0.35 is studied in a 3 m diameter experiment. We have measured the torques required to maintain constant boundary speeds as well as localized wall shear stress, velocity, and pressure. At low Ekman number E =2.1×10-7 and modest Rossby number 0.07
Linear stability of the flow in a toroidal pipe
NASA Astrophysics Data System (ADS)
Schlatter, Philipp; Canton, Jacopo; Oerlue, Ramis
2014-11-01
While hydrodynamic stability and transition to turbulence in straight pipes has been studied extensively, the mechanisms leading to instability in curved pipes are less documented. Here, the first (linear) instability of the flow inside a toroidal pipe is investigated as an initial step in the study of the related laminar-turbulent transition process. In the toroidally bent pipe, the flow is governed by two parameters: the Reynolds number and the curvature of the torus, given as the ratio between the radii of the pipe and of the torus, and is maintained in motion by fixed axial flux. We use classical modal stability analysis, which includes computing nonlinear steady states for each parameter pair, and then studying the stability by solving an eigenproblem of the linearised Navier-Stokes operator. Results show that the flow is indeed modally unstable for all the studied curvatures in the range 0.01-1, with the Reynolds number about 3000. The frequency, wavenumber and mode shapes are strongly dependent on the curvature: The corresponding critical modes are mainly located in the region of the Dean vortices, and represent in general travelling waves. Also time-dependent nonlinear simulations highlight the importance of the linear modes in the transition process in the bent pipe.
Stability of the Kolmogorov flow and its modifications
NASA Astrophysics Data System (ADS)
Revina, S. V.
2017-06-01
Recurrence formulas are obtained for the kth term of the long wavelength asymptotics in the stability problem for general two-dimensional viscous incompressible shear flows. It is shown that the eigenvalues of the linear eigenvalue problem are odd functions of the wave number, while the critical values of viscosity are even functions. If the velocity averaged over the long period is nonzero, then the loss of stability is oscillatory. If the averaged velocity is zero, then the loss of stability can be monotone or oscillatory. If the deviation of the velocity from its period-average value is an odd function of spatial variable about some x 0, then the expansion coefficients of the velocity perturbations are even functions about x 0 for even powers of the wave number and odd functions about for x 0 odd powers of the wave number, while the expansion coefficients of the pressure perturbations have an opposite property. In this case, the eigenvalues can be found precisely. As a result, the monotone loss of stability in the Kolmogorov flow can be substantiated by a method other than those available in the literature.
flowVS: channel-specific variance stabilization in flow cytometry
Azad, Ariful; Rajwa, Bartek; Pothen, Alex
2016-07-28
Comparing phenotypes of heterogeneous cell populations from multiple biological conditions is at the heart of scientific discovery based on flow cytometry (FC). When the biological signal is measured by the average expression of a biomarker, standard statistical methods require that variance be approximately stabilized in populations to be compared. Since the mean and variance of a cell population are often correlated in fluorescence-based FC measurements, a preprocessing step is needed to stabilize the within-population variances.
The inviscid stability of supersonic flow past a sharp cone
NASA Technical Reports Server (NTRS)
Duck, Peter W.; Shaw, Stephen J.
1990-01-01
The laminar boundary layer which forms on a sharp cone in a supersonic freestream, where lateral curvature plays a key role in the physics of the problem is considered. This flow is then analyzed from the point of view of linear, temporal, inviscid stability. The basic, non-axisymmetric disturbance equations are derived for general flows of this class, and a so called triply generalized inflexion condition is found for the existence of subsonic neutral modes of instability. This condition is analogous to the well-known generalized inflexion condition found in planar flows, although in the present case the condition depends on both axial and aximuthal wavenumbers. Extensive numerical results are presented for the stability problem at a freestream Mach number of 3.8, for a range of streamwise locations. These results reveal that a new mode of instability may occur, peculiar to flows of this type involving curvature. Additionally, asymptotic analyses valid close to the tip of the cone, far downstream of the cone are presented, and these give a partial (asymptotic) description of this additional mode of instability.
Flow and Stability of Evaporating Rivulets on Surfaces with Topography
NASA Astrophysics Data System (ADS)
Gambaryan-Roisman, Tatiana
2005-11-01
Surfaces with topography promote rivulet flow patterns, which are characterized by a high cumulative length of contact lines. This property is very advantageous for evaporators and cooling devices, since the local evaporation rate in the vicinity of contact lines (micro region evaporation) is extremely high. The liquid flow in rivulets is subject to different kinds of instabilities, including the kinematic instability and the capillary instability. The instabilities may lead to the development of wavy flow patterns and to film rupture. The effect of the micro region evaporation on the rivulet stability has never been investigated. We develop a model describing the hydrodynamics and heat and mass transfer in flowing rivulets on surfaces with topography under the action of gravity, surface tension, thermocapillarity and the phase change. The contact line behaviour is modelled using the disjoining potential. The perfectly wetting case is described using the usual h-3 potential. The partially wetting case is modelled using the integrated Lennard-Jones potential. The developed model is used for investigating the effects of the surface topography, gravity, thermocapillarity and the micro region evaporation on the rivulet stability.
Local interstellar gasdynamical stability in spiral arm flow
NASA Technical Reports Server (NTRS)
Balbus, S. A.
1986-01-01
The stability of two-dimensional interstellar gas flow passing through a spiral potential has been investigated. The background flow is assumed to move in a tightly wound potential, which may be regarded as external or self-generated. The unperturbed flow, which may be time dependent, is self-gravitating and satisfies the Roberts equations of motion. A polytropic, single-fluid assumption has been used. Magnetic effects are not considered. The motivation behind this work is to try to understand how much of the diversity of spiral arm morphology can be understood by large scale gas dynamical processes alone. To this end, it is suggested that spurring and feathering, and forming molecular cloud complexes may be closely related in the sense of having dynamically similar origins.
Equilibrium and Stability of the Brillouin Flow in Inverted Magnetron
NASA Astrophysics Data System (ADS)
Simon, David; Lau, Yue Ying; Franzi, Matt; Greening, Geoff; Gilgenbach, Ronald; Marhdahl, Peter; Hoff, Brad; Luginsland, John
2012-10-01
One embodiment of the novel recirculating planar magnetron, RPM [1] utilizes an inverted configuration for fast startup. While the negative mass behavior on the thin electron layer model [2] is well-known for the inverted magnetron, the corresponding behavior for the equilibrium Brillouin flow [3] is an open question. Simulations using the particle-in-cell codes ICEPIC and/or MAGIC will be performed and compared to the solution to the eigenvalue problem that governs the stability of Brillouin flow, leading to a fundamental study of the flow's negative, positive, and infinite mass properties. Research supported by AFOSR (grant#: FA9550-10-1-0104), AFRL, and L-3 Communications Electron Devices. [4pt] [1] R. M. Gilgenbach, et.al., IEEE Trans. Plasma Sci. 39, 980 (2011); Also patent pending.[0pt] [2] D. M. French, et al., Appl. Phys. Lett. 97, 111501 (2010).[0pt] [3] D. Simon, et al., Phys. Plasmas 19, 043103 (2012).
Study of the Stability of Compressible Couette Flow.
NASA Astrophysics Data System (ADS)
Girard, Jeffrey John
This study is concerned with a two-dimensional disturbance of plane Couette flow. All reviewed analyses of the basic problem have led to the conclusion that the flow is unconditionally stable. All of the literature assumed the fluid was incompressible. The assumption that a fluid is incompressible neglects solutions to the problem. The motivation of the analysis presented herein is a hypothesis that some of the acoustic disturbances in the fluid, usually neglected, may interact with the mean vorticity to produce more sound. This hypothesis was discussed by Vaidya (1988). The fluid considered herein has been a viscous, heat-conducting, ideal gas. For the cases investigated in this study, most solutions exhibited stability. There were found, however, solutions at somewhat unrealistically high Mach numbers which exhibited unstable nature. Further, it was found that for even low Mach number flows, the sound solution was the least stable solution. It is thought that the interaction between the sound perturbation and the mean flow has fed energy to the disturbance from the mean flow. Enough energy was transferred to balance some of the viscous dissipation. At low Mach numbers, for the investigated cases, not enough energy was transferred to tip the flow to instability. The established theory has been challenged. All previous analysis of the basic infinitesimal perturbation problem has suggested unconditional stability. This work has shown some unstable regimes. This keeps the hope alive that analysis may one day explain the experimental evidence (which is at much lower Mach numbers). The future work should concentrate on the sound solution for this problem. It has been shown to be the least stable, though it is usually neglected. An attempt should be made to investigate the possibility of reducing the lowest Mach number for instability. Suggestions for this have been provided in Chapter 4.
Hydrogen peroxide stabilization in one-dimensional flow columns
NASA Astrophysics Data System (ADS)
Schmidt, Jeremy T.; Ahmad, Mushtaque; Teel, Amy L.; Watts, Richard J.
2011-09-01
Rapid hydrogen peroxide decomposition is the primary limitation of catalyzed H 2O 2 propagations in situ chemical oxidation (CHP ISCO) remediation of the subsurface. Two stabilizers of hydrogen peroxide, citrate and phytate, were investigated for their effectiveness in one-dimensional columns of iron oxide-coated and manganese oxide-coated sand. Hydrogen peroxide (5%) with and without 25 mM citrate or phytate was applied to the columns and samples were collected at 8 ports spaced 13 cm apart. Citrate was not an effective stabilizer for hydrogen peroxide in iron-coated sand; however, phytate was highly effective, increasing hydrogen peroxide residuals two orders of magnitude over unstabilized hydrogen peroxide. Both citrate and phytate were effective stabilizers for manganese-coated sand, increasing hydrogen peroxide residuals by four-fold over unstabilized hydrogen peroxide. Phytate and citrate did not degrade and were not retarded in the sand columns; furthermore, the addition of the stabilizers increased column flow rates relative to unstabilized columns. These results demonstrate that citrate and phytate are effective stabilizers of hydrogen peroxide under the dynamic conditions of one-dimensional columns, and suggest that citrate and phytate can be added to hydrogen peroxide before injection to the subsurface as an effective means for increasing the radius of influence of CHP ISCO.
A general method to determine the stability of compressible flows
NASA Technical Reports Server (NTRS)
Guenther, R. A.; Chang, I. D.
1982-01-01
Several problems were studied using two completely different approaches. The initial method was to use the standard linearized perturbation theory by finding the value of the individual small disturbance quantities based on the equations of motion. These were serially eliminated from the equations of motion to derive a single equation that governs the stability of fluid dynamic system. These equations could not be reduced unless the steady state variable depends only on one coordinate. The stability equation based on one dependent variable was found and was examined to determine the stability of a compressible swirling jet. The second method applied a Lagrangian approach to the problem. Since the equations developed were based on different assumptions, the condition of stability was compared only for the Rayleigh problem of a swirling flow, both examples reduce to the Rayleigh criterion. This technique allows including the viscous shear terms which is not possible in the first method. The same problem was then examined to see what effect shear has on stability.
Hydrogen peroxide stabilization in one-dimensional flow columns.
Schmidt, Jeremy T; Ahmad, Mushtaque; Teel, Amy L; Watts, Richard J
2011-09-25
Rapid hydrogen peroxide decomposition is the primary limitation of catalyzed H(2)O(2) propagations in situ chemical oxidation (CHP ISCO) remediation of the subsurface. Two stabilizers of hydrogen peroxide, citrate and phytate, were investigated for their effectiveness in one-dimensional columns of iron oxide-coated and manganese oxide-coated sand. Hydrogen peroxide (5%) with and without 25 mM citrate or phytate was applied to the columns and samples were collected at 8 ports spaced 13 cm apart. Citrate was not an effective stabilizer for hydrogen peroxide in iron-coated sand; however, phytate was highly effective, increasing hydrogen peroxide residuals two orders of magnitude over unstabilized hydrogen peroxide. Both citrate and phytate were effective stabilizers for manganese-coated sand, increasing hydrogen peroxide residuals by four-fold over unstabilized hydrogen peroxide. Phytate and citrate did not degrade and were not retarded in the sand columns; furthermore, the addition of the stabilizers increased column flow rates relative to unstabilized columns. These results demonstrate that citrate and phytate are effective stabilizers of hydrogen peroxide under the dynamic conditions of one-dimensional columns, and suggest that citrate and phytate can be added to hydrogen peroxide before injection to the subsurface as an effective means for increasing the radius of influence of CHP ISCO. Copyright © 2011. Published by Elsevier B.V.
Stability of particle motions in a narrow channel flow.
Sugihara-Seki, M; Skalak, R
1989-01-01
Single rows or two rows of identical circular cylinders spaced regularly in a narrow channel flow have been shown to be capable of steady flow provided the cylinders are located at equal lateral positions and with equal spacings in the flow direction. The stability of such steady flows of circular cylinders is studied for periodic perturbations of the particle positions, assuming that every other cylinder is equally perturbed in lateral position and spacing along the channel. This results in two rows which are not symmetrically placed. The suspending fluid is assumed to be an incompressible Newtonian fluid. It is assumed that no external forces or moments act on the cylinders and the effects of inertia forces on the motion of the fluid and the cylinders are negligible. The velocity field of the suspending fluid and the instantaneous velocities of the cylinders are computed by the finite element method. The translational velocities of the cylinders are obtained for a large number of particle positions, from which the trajectories of their relative motion are determined for various initial positions near the regular single-file and two-file arrangements. It is shown that when the initial arrangements of the cylinders are slightly perturbed from the regular (alternating) two-file flows, the trajectories of their relative motions become small closed loops around the regular two-file arrangements. In contrast, such small closed trajectories are not obtained when they start from the arrangements near the regular single-file flows or regular (symmetric) double-file flows, suggesting that these flows are unstable under the conditions examined.
Oxygen Mass Flow Rate Generated for Monitoring Hydrogen Peroxide Stability
NASA Technical Reports Server (NTRS)
Ross, H. Richard
2002-01-01
Recent interest in propellants with non-toxic reaction products has led to a resurgence of interest in hydrogen peroxide for various propellant applications. Because peroxide is sensitive to contaminants, material interactions, stability and storage issues, monitoring decomposition rates is important. Stennis Space Center (SSC) uses thermocouples to monitor bulk fluid temperature (heat evolution) to determine reaction rates. Unfortunately, large temperature rises are required to offset the heat lost into the surrounding fluid. Also, tank penetration to accomodate a thermocouple can entail modification of a tank or line and act as a source of contamination. The paper evaluates a method for monitoring oxygen evolution as a means to determine peroxide stability. Oxygen generation is not only directly related to peroxide decomposition, but occurs immediately. Measuring peroxide temperature to monitor peroxide stability has significant limitations. The bulk decomposition of 1% / week in a large volume tank can produce in excess of 30 cc / min. This oxygen flow rate corresponds to an equivalent temperature rise of approximately 14 millidegrees C, which is difficult to measure reliably. Thus, if heat transfer were included, there would be no temperature rise. Temperature changes from the surrounding environment and heat lost to the peroxide will also mask potential problems. The use of oxygen flow measurements provides an ultra sensitive technique for monitoring reaction events and will provide an earlier indication of an abnormal decomposition when compared to measuring temperature rise.
Electromagnetically Sustained Liquid Metal Flow for Feedback Stabilization Studies
NASA Astrophysics Data System (ADS)
Mirhoseini, Seyyed Mohammad; Volpe, Francesco
2015-11-01
Liquid metal walls in fusion reactors, whether nearly static or rapidly flowing, will be subject to instabilities that will make them locally bulge, thus entering in contact with the plasma, or deplete, hence exposing the underlying solid substrate. To prevent this, research has begun at Columbia University to create liquid metal flows and demonstrate their stabilization by electromagnetic forces, adjusted in feedback with thickness measurements. Here we present initial results regarding the sustainment of a flow of Galinstan (a gallium, indium, tin alloy) by a special pump consisting of a ferromagnetic rotor, with permanent magnets mounted on it. The magnetic field is partly ``frozen'' in the liquid metal surrounding the rotor. Therefore, as the field rotates, the liquid metal rotates as well, although with a slip factor. This solution was preferred to conventional pumps, which would enter in electrical contact with the metal flow. The pump, 3D-printed at Columbia, allows to adjust the flow-velocity from few mm/s to several cm/s.
Flow-stabilized levitation in a magnetic stirrer.
NASA Astrophysics Data System (ADS)
Baldwin, Kyle; Fairhurst, David; de Fouchier, Jean-Baptiste; Atkinson, Patrick; Darwent, Thomas; Hill, Richard; Swift, Michael
Magnetic stirrers are a useful tool for preparing solutions as the mixing vessel can be completely sealed, with no physical contact between the drive magnet and stir-bar. However, colloquially, stir-bars are known as ``fleas'' due to the onset of jumping at high speeds, which halts mixing. Here, we investigate the transition from spinning to jumping and discover an intriguing additional state, where the flea is levitated several centimeters while moving in a superposition of rotation and oscillation. This is of interest as Earnshaw's theorem states that there is no arrangement of static permanent magnets that be levitated stably. Current mag-lev technology side-steps this via secondary effects (e . g . diamagnetic repulsion or superconductive flux-line pinning), none of which can account for the flea's stability. We map the equations of motion onto a driven damped-pendulum system, universally characterize the onset of jumping, and successfully predict the oscillating flea's behavior. We further find that the stability is maintained by the flea's oscillation, which, at intermediate Reynolds numbers (Re 10), pumps fluid out from the ends of the flea, creating a streaming flow that centers it. If, however, Re is too low/too high, the respective flows are reciprocal/reversed, which both destabilize the levitation. This levitation technique demonstrates increasing Re can reverse the streaming flows relevant to propulsion, and could be cheaply implemented to study a variety of fluid and biological systems. We acknowledge support from NTU and the Erasmus student programme.
Viscous linear stability analysis of rectangular duct and cavity flows
NASA Astrophysics Data System (ADS)
Theofilis, V.; Duck, P. W.; Owen, J.
2004-04-01
The viscous linear stability of four classes of incompressible flows inside rectangular containers is studied numerically. In the first class the instability of flow through a rectangular duct, driven by a constant pressure gradient along the axis of the duct (essentially a two-dimensional counterpart to plane Poiseuille flow PPF), is addressed. The other classes of flow examined are generated by tangential motion of one wall, in one case in the axial direction of the duct, in another perpendicular to this direction, corresponding respectively to the two-dimensional counterpart to plane Couette flow (PCF) and the classic lid-driven cavity (LDC) flow, and in the fourth case a combination of both the previous tangential wall motions. The partial-derivative eigenvalue problem which in each case governs the temporal development of global three-dimensional small-amplitude disturbances is solved numerically. The results of Tatsumi & Yoshimura (1990) for pressure-gradient-driven flow in a rectangular duct have been confirmed; the relationship between the eigenvalue spectrum of PPF and that of the rectangular duct has been investigated. Despite extensive numerical experimentation no unstable modes have been found in the wall-bounded Couette flow, this configuration found here to be more stable than its one-dimensional limit. In the square LDC flow results obtained are in line with the predictions of Ding & Kawahara (1998b), Theofilis (2000) and Albensoeder et al. (2001b) as far as one travelling unstable mode is concerned. However, in line with the predictions of the latter two works and contrary to all previously published results it is found that this mode is the third in significance from an instability analysis point of view. In a parameter range unexplored by Ding & Kawahara (1998b) and all prior investigations two additional eigenmodes exist, which are both more unstable than the mode that these authors discovered. The first of the new modes is stationary (and would
Ecological Stability Properties of Microbial Communities Assessed by Flow Cytometry.
Liu, Zishu; Cichocki, Nicolas; Bonk, Fabian; Günther, Susanne; Schattenberg, Florian; Harms, Hauke; Centler, Florian; Müller, Susann
2018-01-01
Natural microbial communities affect human life in countless ways, ranging from global biogeochemical cycles to the treatment of wastewater and health via the human microbiome. In order to probe, monitor, and eventually control these communities, fast detection and evaluation methods are required. In order to facilitate rapid community analysis and monitor a community's dynamic behavior with high resolution, we here apply community flow cytometry, which provides single-cell-based high-dimensional data characterizing communities with high acuity over time. To interpret time series data, we draw inspiration from macroecology, in which a rich set of concepts has been developed for describing population dynamics. We focus on the stability paradigm as a promising candidate to interpret such data in an intuitive and actionable way and present a rapid workflow to monitor stability properties of complex microbial ecosystems. Based on single-cell data, we compute the stability properties resistance, resilience, displacement speed, and elasticity. For resilience, we also introduce a method which can be implemented for continuous online community monitoring. The proposed workflow was tested in a long-term continuous reactor experiment employing both an artificial and a complex microbial community, which were exposed to identical short-term disturbances. The computed stability properties uncovered the superior stability of the complex community and demonstrated the global applicability of the protocol to any microbiome. The workflow is able to support high temporal sample densities below bacterial generation times. This may provide new opportunities to unravel unknown ecological paradigms of natural microbial communities, with applications to environmental, biotechnological, and health-related microbiomes. IMPORTANCE Microbial communities drive many processes which affect human well-being directly, as in the human microbiome, or indirectly, as in natural environments or in
A stability criterion for heterogeneous density-driven flows
NASA Astrophysics Data System (ADS)
Musuuza, J.; Radu, F. A.
2009-04-01
Variable density flows can occur due to temperature differences in deep aquifers and due to salinity differences at normal and nuclear waste repositories; and in coastal aquifers. Therefore, their relevance cuts across many practical applications like exploitation of geothermal energy resources, oil recovery from aquifers and leachate migration at waste disposal sites. A typical feature of density dependent flow problems is that they can become unstable (physically or numerically). Variable density flow problems are difficult to solve due to the non-linearities and coupling between fluid flow and solute transport processes. A big challenge to-date is to derive a general criterion that states whether flow is physically stable or unstable; and the optimum computational grid resolution required to solve a problem without creating numerical (artificial) instabilities. We extend the ideas introduced in [1] to develop an explicit criterion based on homogenization theory techniques. At present, the criterion only includes the effects of density, viscosity medium heterogeneity and flow velocity. The validity of the criterion is carefully tested in numerical simulations for the problem defined in [2], with the solution stability guaranteed by the appropriate choice of dispersivities, mesh diameter and time step. The numerical simulations are performed with the software toolbox UG and the investigations then proceed by varying the 4 above-named parameters. REFERENCES [1]Held, R., S. Attinger, and W. Kinzelbach (2005), Homogenization and effective parameters for the Henry problem in heterogeneous formations, Water Resour. Res., 41, W11420, doi:10.1029/2004WR003674. [2]Schincariol R. A., F. W. Schwarz, and C. A. Mendoza (1997), On the generation of instabilities in variable density flow, Water Resour. Res., 30(4), 913-927.
Symmetry and stability in Taylor-Couette flow
NASA Technical Reports Server (NTRS)
Golubitsky, M.; Stewart, I.
1986-01-01
The flow of a fluid between concentric rotating cylinders (the Taylor problem) is studied by exploiting the symmetries of the system. The Navier-Stokes equations, linearized about Couette flow, possess two zero and four purely imaginary eigenvalues at a suitable value of the speed of rotation of the outer cylinder. There is thus a reduced bifurcation equation on a six-dimensonal space which can be shown to commute with an action of the symmetry group 0(2) x S0(2). The group structure is used to analyze this bifurcation equation in the simplest (nondegenerate) case, and to compute the stabilities of solutions. In particular, when the outer cylinder is counterrotated, transitions which seem to agree with recent experiments of Andereck, Liu, and Swinney (1984) are obtained. It is also possible to obtain the 'main sequence' in this model. This sequence is normally observed in experiments when the outer cylinder is held fixed.
Stability theory applications to laminar-flow control
NASA Technical Reports Server (NTRS)
Malik, Mujeeb R.
1987-01-01
In order to design Laminar Flow Control (LFC) configurations, reliable methods are needed for boundary-layer transition predictions. Among the available methods, there are correlations based upon R sub e, shape factors, Goertler number and crossflow Reynolds number. The most advanced transition prediction method is based upon linear stability theory in the form of the e sup N method which has proven to be successful in predicting transition in two- and three-dimensional boundary layers. When transition occurs in a low disturbance environment, the e sup N method provides a viable design tool for transition prediction and LFC in both 2-D and 3-D subsonic/supersonic flows. This is true for transition dominated by either TS, crossflow, or Goertler instability. If Goertler/TS or crossflow/TS interaction is present, the e sup N will fail to predict transition. However, there is no evidence of such interaction at low amplitudes of Goertler and crossflow vortices.
Predicting the stability of a compressible periodic parallel jet flow
NASA Technical Reports Server (NTRS)
Miles, Jeffrey H.
1996-01-01
It is known that mixing enhancement in compressible free shear layer flows with high convective Mach numbers is difficult. One design strategy to get around this is to use multiple nozzles. Extrapolating this design concept in a one dimensional manner, one arrives at an array of parallel rectangular nozzles where the smaller dimension is omega and the longer dimension, b, is taken to be infinite. In this paper, the feasibility of predicting the stability of this type of compressible periodic parallel jet flow is discussed. The problem is treated using Floquet-Bloch theory. Numerical solutions to this eigenvalue problem are presented. For the case presented, the interjet spacing, s, was selected so that s/omega =2.23. Typical plots of the eigenvalue and stability curves are presented. Results obtained for a range of convective Mach numbers from 3 to 5 show growth rates omega(sub i)=kc(sub i)/2 range from 0.25 to 0.29. These results indicate that coherent two-dimensional structures can occur without difficulty in multiple parallel periodic jet nozzles and that shear layer mixing should occur with this type of nozzle design.
Stability of Inviscid Flow over Airfoils Admitting Multiple Numerical Solutions
NASA Astrophysics Data System (ADS)
Liu, Ya; Xiong, Juntao; Liu, Feng; Luo, Shijun
2012-11-01
Multiple numerical solutions at the same flight condition are found of inviscid transonic flow over certain airfoils (Jameson et al., AIAA 2011-3509) within some Mach number range. Both symmetric and asymmetric solutions exist for a symmetric airfoil at zero angle of attack. Global linear stability analysis of the multiple solutions is conducted. Linear perturbation equations of the Euler equations around a steady-state solution are formed and discretized numerically. An eigenvalue problem is then constructed using the modal analysis approach. Only a small portion of the eigen spectrum is needed and thus can be found efficiently by using Arnoldi's algorithm. The least stable or unstable mode corresponds to the eigenvalue with the largest real part. Analysis of the NACA 0012 airfoil indicates stability of symmetric solutions of the Euler equations at conditions where buffet is found from unsteady Navier-Stokes equations. Euler solutions of the same airfoil but modified to include the displacement thickness of the boundary layer computed from the Navier-Stokes equations, however, exhibit instability based on the present linear stability analysis. Graduate Student.
Linear Stability Analysis of Free Surface Liquid Metal Flow
NASA Astrophysics Data System (ADS)
Giannakis, D.; Rosner, R.; Fischer, P.; Ji, H.; Burin, M.; McMurtry, K.
2006-10-01
We study the linear stability of the flow of a liquid metal on a planar surface in the presence of an external magnetic field. The objective is to account for the behavior encountered in a free surface MHD experiment at Princeton, but the model has a range of astrophysical and industrial applications (see companion poster). This class of free surface flow exhibits two mechanisms of linear instability. In the so-called `soft' instability, a downstream propagating surface wave of large wavelength becomes mildly unstable. The second, `hard', instability is of the critical layer type and takes place at shorter wavelengths. Solving the eigenvalue problem posed by the coupled Orr-Sommerfeld and induction equations via a spectral method, we find that in the regime of relevance to the Princeton experiment (Reynolds number, magnetic Reynolds number and Hartmann number up to 10 ^ 5 , 10 ^ - 1 , and 10 ^ 3 , respectively) MHD effects suppress both types of instability. The soft instability is efficiently suppressed via resistive dissipation if the background magnetic field is normal to the basic flow. In contrast, the hard instability is strongly suppressed irrespective of the details of the background magnetic field configuration, even at moderate Hartmann numbers.
Richardson's criterion for the stability of stratified shear flow
NASA Astrophysics Data System (ADS)
Miles, John
1986-10-01
Chandrasekhar's derivation, from energy considerations, of the sufficient condition R>1/4 for stability of a stratified shear flow, in which R is the local Richardson number, is amended to obtain R>1, in agreement with the earlier arguments of Richardson, Taylor, and Prandtl(L. F. Richardson, Proc. R. Soc. London Ser. A 97, 354 (1920); G. I. Taylor, Rapp. P. V. Reun. Cons. Permanent Int. d'Exploration Mer 76, 35 (1931); Sci. Pap. 2, 240; L. Prandtl, Vorträge aus dem Gebiete der Aerodynamik und verwandten Gebieten (Springer, Berlin, 1930), pp. 1-7; L. Prandtl, Führer durch die Strömungslehre (Vieweg, Braunschweig, 1942), p. 337; Essentials of Fluid Dynamics [English translation of 1949 edition of Führer durch die Strömungslehre (Hafner, New York, 1952), pp. 381 and 382]).
Natural laminar flow and airplane stability and control
NASA Technical Reports Server (NTRS)
Vandam, Cornelis P.
1986-01-01
Location and mode of transition from laminar to turbulent boundary layer flow have a dominant effect on the aerodynamic characteristics of an airfoil section. The influences of these parameters on the sectional lift and drag characteristics of three airfoils are examined. Both analytical and experimental results demonstrate that when the boundary layer transitions near the leading edge as a result of surface roughness, extensive trailing-edge separation of the turbulent boundary layer may occur. If the airfoil has a relatively sharp leading-edge, leading-edge stall due to laminar separation can occur after the leading-edge suction peak is formed. These two-dimensional results are used to examine the effects of boundary layer transition behavior on airplane longitudinal and lateral-directional stability and control.
The inviscid stability of supersonic flow past a sharp cone
NASA Technical Reports Server (NTRS)
Duck, Peter W.; Shaw, Stephen J.
1990-01-01
The effects of lateral curvature on the development of supersonic laminar inviscid boundary-layer flow on a sharp cone with adiabatic wall conditions are investigated analytically, with a focus on the linear temporal inviscid stability properties. The derivation of the governing equations and of a 'triply generalized' inflexion condition is outlined, and numerical results for freestream Mach number 3.8 are presented in extensive graphs and characterized in detail. A third instability mode related to the viscous mode observed by Duck and Hall (1990) using triple-deck theory is detected and shown to be more unstable and to have larger growth rates than the second mode in some cases. It is found that the 'sonic' neutral mode is affected by the lateral curvature and becomes a supersonic neutral mode.
Active Flow Control and Global Stability Analysis of Separated Flow Over a NACA 0012 Airfoil
NASA Astrophysics Data System (ADS)
Munday, Phillip M.
definition of the coefficient of momentum, which successfully characterizes suppression of separation and lift enhancement. The effect of angular momentum is incorporated into the modified coefficient of momentum by introducing a characteristic swirling jet velocity based on the non-dimensional swirl number. With the modified coefficient of momentum, this single value is able to categorize controlled flows into separated, transitional, and attached flows. With inadequate control input (separated flow regime), lift decreased compared to the baseline flow. Increasing the modified coefficient of momentum, flow transitions from separated to attached and accordingly results in improved aerodynamic forces. Modifying the spanwise spacing, it is shown that the minimum modified coefficient of momentum input required to begin transitioning the flow is dependent on actuator spacing. The growth (or decay) of perturbations can facilitate or inhibit the influence of flow control inputs. Biglobal stability analysis is considered to further analyze the behavior of control inputs on separated flow over a symmetric airfoil. Assuming a spanwise periodic waveform for the perturbations, the eigenvalues and eigenvectors about a base flow are solved to understand the influence of spanwise variation on the development of the flow. Two algorithms are developed and validated to solve for the eigenvalues of the flow: an algebraic eigenvalue solver (matrix based) and a time-stepping algorithm. The matrix based approach is formulated without ever storing the matrices, creating a computationally memory efficient algorithm. Increasing the Reynolds number to Re = 23,000 over a NACA 0012 airfoil, the time-stepper method is implemented due to rising computational cost of the matrix-based method. Stability analysis about the time-averaged flow is performed for spanwise wavenumbers of beta = 1/c, 10pi/ c and 20pi/c, which the latter two wavenumbers are representative of the spanwise spacing between the
Stability analysis of traffic flow with extended CACC control models
NASA Astrophysics Data System (ADS)
Ya-Zhou, Zheng; Rong-Jun, Cheng; Siu-Ming, Lo; Hong-Xia, Ge
2016-06-01
To further investigate car-following behaviors in the cooperative adaptive cruise control (CACC) strategy, a comprehensive control system which can handle three traffic conditions to guarantee driving efficiency and safety is designed by using three CACC models. In this control system, some vital comprehensive information, such as multiple preceding cars’ speed differences and headway, variable safety distance (VSD) and time-delay effect on the traffic current and the jamming transition have been investigated via analytical or numerical methods. Local and string stability criterion for the velocity control (VC) model and gap control (GC) model are derived via linear stability theory. Numerical simulations are conducted to study the performance of the simulated traffic flow. The simulation results show that the VC model and GC model can improve driving efficiency and suppress traffic congestion. Project supported by the National Natural Science Foundation of China (Grant Nos. 71571107 and 11302110). The Scientific Research Fund of Zhejiang Province, China (Grant Nos. LY15A020007, LY15E080013, and LY16G010003). The Natural Science Foundation of Ningbo City (Grant Nos. 2014A610030 and 2015A610299), the Fund from the Government of the Hong Kong Administrative Region, China (Grant No. CityU11209614), and the K C Wong Magna Fund in Ningbo University, China.
Effectiveness of flow stabilization in small-scale wastewater treatment facilities.
Nakajima, J; Tanaka, R
2005-01-01
Household type Johkasous which have a flow stabilization function were surveyed on their performance. The water level, flow velocity and SS were measured after the maximum flow entering the anaerobic filter chamber with or without flow stabilization operation. In operation without the flow stabilization, the flow peak directly reached the biofiltration chamber and the flow rate kept at 1 cm/sec during 3-4 min in the connection baffle between the two anaerobic chambers. This suggested the possibility of sludge transfer from the first anaerobic chamber. Moreover the increase of SS in the second anaerobic chamber indicated sludge transfer from the second anaerobic chamber to the biofiltration chamber. In contrast, in operation with flow stabilization the relaxation of the water flow in the second anaerobic chamber and the biofilm chamber was verified. By the increase of the water level in the first anaerobic chamber, the flow stabilization performance was satisfactorily obtained. A model describing the change of the water level was developed and the calculated values and the measured value agreed well. The model will be useful in the design of the flow stabilization function.
NASA Technical Reports Server (NTRS)
Lutze, F. H.
1980-01-01
The technique of using a curved and rolling flow wind tunnel to extract pure rotary stability derivatives is presented. Descriptions of the curved flow and the rolling flow test sections of the Virginia Tech Stability Wind Tunnel are given including methods for obtaining the proper velocity profiles and correcting the data acquired. Results of testing current fighter configurations in this facility are presented with particular attention given to comparing pure rotary derivatives with combined rotary and unsteady derivatives obtained by standard oscillation tests. Also the effect of curved and rolling flow on lateral static stability derivatives is examined.
Stability Analysis of High-Speed Boundary-Layer Flow with Gas Injection
2014-06-01
boundary-layer flow with gas injection 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Alexander V. Fedorov ...distribution unlimited Stability analysis of high-speed boundary-layer flow with gas injection Alexander V. Fedorov * and Vitaly G. Soudakov...Laminar Flow, AGARD Report Number 709, 1984. 2. Fedorov , A., “Transition and Stability of High-Speed Boundary Layers,” Annu. Rev. Fluid Mech., Vol
Stability of Poiseuille flow in a fluid overlying an anisotropic and inhomogeneous porous layer
NASA Astrophysics Data System (ADS)
Deepu, P.; Anand, Prateek; Basu, Saptarshi
2015-08-01
We present the linear stability analysis of horizontal Poiseuille flow in a fluid overlying a porous medium with anisotropic and inhomogeneous permeability. The generalized Darcy model is used to describe the flow in the porous medium with the Beavers-Joseph condition at the interface of the two layers and the eigenvalue problem is solved numerically. The effect of major system parameters on the stability characteristics is addressed in detail. It is shown that the anisotropic and inhomogeneous modulation of the permeability of the underlying porous layer provides an effective means for passive control of the flow stability.
Nonlinear stability analysis of Darcy's flow with viscous heating.
Celli, Michele; Alves, Leonardo S de B; Barletta, Antonio
2016-05-01
The nonlinear stability of a rectangular porous channel saturated by a fluid is here investigated. The aspect ratio of the channel is assumed to be variable. The channel walls are considered impermeable and adiabatic except for the horizontal top which is assumed to be isothermal. The viscous dissipation is acting inside the channel as internal heat generator. A basic throughflow is imposed, and the nonlinear convective stability is investigated by means of the generalized integral transform technique. The neutral stability curve is compared with the one obtained by the linear stability analysis already present in the literature. The growth rate analysis of different unstable modes is performed. The Nusselt number is investigated for several supercritical configurations in order to better understand how the system behaves when conditions far away from neutral stability are considered. The patterns of the neutrally stable convective cells are also reported. Nonlinear simulations support the results obtained by means of the linear stability analysis, confirming that viscous dissipation alone is indeed capable of inducing mixed convection. Low Gebhart or high Péclet numbers lead to a transient overheating of the originally motionless fluid before it settles in its convective steady state.
The effects of flow separation on shuttle dynamics and aeroelastic stability
NASA Technical Reports Server (NTRS)
Reding, J. P.; Ericsson, L. E.
1977-01-01
The effects of flow separation on the dynamic and aeroelastic stability of various shuttle configurations have been investigated. Flow separation is shown to affect the aeroelastic stability of the 747/Orbiter yaw modes, the orbiter dynamic stability and possibly the aeroelastic stability of the wing torsional mode, and to dominate both the dynamic and aeroelastic stability of the launch configuration. Limit cycle oscillations of certain launch configuration modes are the result of sudden flow separation. The limit cycle oscillations threaten the structural integrity in two ways: (1) by outright overstressing of the structure due to large modal deflection, (2) by fatigue due to the continued flexing of the structure. Fatigue is a more significant consideration for the reusable (100 flights) shuttle than it has been for previous space boosters.
On a modification of GLS stabilized FEM for solving incompressible viscous flows
NASA Astrophysics Data System (ADS)
Burda, P.; Novotný, J.; Ístek, J.
2006-07-01
We deal with 2D flows of incompressible viscous fluids with high Reynolds numbers. Galerkin Least Squares technique of stabilization of the finite element method is studied and its modification is described. We present a number of numerical results obtained by the developed method, showing its contribution to solving flows with high Reynolds numbers. Several recommendations and remarks are included. We are interested in positive as well as negative aspects of stabilization, which cannot be divorced.
Boundary-Layer Stability Analysis of the Mean Flows Obtained Using Unstructured Grids
NASA Technical Reports Server (NTRS)
Liao, Wei; Malik, Mujeeb R.; Lee-Rausch, Elizabeth M.; Li, Fei; Nielsen, Eric J.; Buning, Pieter G.; Chang, Chau-Lyan; Choudhari, Meelan M.
2012-01-01
Boundary-layer stability analyses of mean flows extracted from unstructured-grid Navier- Stokes solutions have been performed. A procedure has been developed to extract mean flow profiles from the FUN3D unstructured-grid solutions. Extensive code-to-code validations have been performed by comparing the extracted mean ows as well as the corresponding stability characteristics to the predictions based on structured-grid solutions. Comparisons are made on a range of problems from a simple at plate to a full aircraft configuration-a modified Gulfstream-III with a natural laminar flow glove. The future aim of the project is to extend the adjoint-based design capability in FUN3D to include natural laminar flow and laminar flow control by integrating it with boundary-layer stability analysis codes, such as LASTRAC.
The Stability of Particulate Ladden Laminar Boundary-Layer Flows
NASA Technical Reports Server (NTRS)
Acrivos, Andreas
1996-01-01
During the course of this investigation, the following two topics were studied theoretically: (1) forced convection and sedimentation past a flat plate, and (2) the effect of rain on airfoil performance. The prototype of the first topic is that of air flowing past the wing section of an aircraft under heavy rain and high windshear. The long-range objective of this project was to identify the various factors determining the dynamics of the flow and then to develop a theoretical framework for modeling such systems. The second topic focused on the idea that the presence of the gas-liquid interface (being the air flow around the airfoil and the thin liquid film created by the rain) accelerates flow separation and thus induces performance losses.
Acoustic Streaming in Microgravity: Flow Stability and Heat Transfer Enhancement
NASA Technical Reports Server (NTRS)
Trinh, E. H.
1999-01-01
Experimental results are presented for drops and bubbles levitated in a liquid host, with particular attention given to the effect of shape oscillations and capillary waves on the local flow fields. Some preliminary results are also presented on the use of streaming flows for the control of evaporation rate and rotation of electrostatically levitated droplets in 1 g. The results demonstrate the potential for the technological application of acoustic methods to active control of forced convection in microgravity.
Investigation of the Stability of Melt Flow in Gating Systems
NASA Astrophysics Data System (ADS)
Tiedje, Niels Skat; Larsen, Per
2011-02-01
Melt flow in four different gating systems designed for the production of brake disks was analyzed experimentally and by numerical modeling. In the experiments, molds were fitted with glass fronts and melt flow was recorded on video. The video recordings were compared with the modeling of melt flow in the gating systems. Particular emphasis was on analyzing local pressure and formation of pressure waves in the gating system. It was possible to compare melt flow patterns in experiments directly with modeled flow patterns. Generally, there was good agreement between flow patterns and filling times. However, the description of free liquid surfaces proved to be incorrect in the numerical model. The modeled pressure fields served to explain how specific parts of the gating systems cause instability and are a good tool to describe the quality of a gating system. The results show clearly that sharp changes in the geometry of the gating system causes pressure waves to form that eventually lead to defective castings. It is clear that sharp corners and dead ends in gating systems should be avoided, and that more streamlined, organic, or naturally pressurized designs based on fluid dynamic principles will are necessary to design gating systems for the production of high-quality castings.
Linear stability of general magnetically insulated electron flow
Swegle, J.A.; Mendel, C.W. Jr.; Seidel, D.B.
1984-01-01
We have formulated a linear stability theory for magnetically insulated systems by linearizing the general 3-D, time-dependent theory of Mendel, Seidel, and Slutz. In the physically interesting case of electron trajectories which are nearly laminar, with only small transverse motion, we have found that several suggestive simplifications occur in the eigenvalue equations.
The Hydrodynamic Stability of a Fluid-Particle Flow: Instabilities in Gas-Fluidized Beds
ERIC Educational Resources Information Center
Liu, Xue; Howley, Maureen A.; Johri, Jayati; Glasser, Benjamin J.
2008-01-01
A simplified model of an industrially relevant fluid-particle flow system is analyzed using linear stability theory. Instabilities of the uniform state of a fluidized bed are investigated in response to small flow perturbations. Students are expected to perform each step of the computational analysis, and physical insight into key mechanistic…
The Influence of Plant Root Systems on Subsurface Flow: Implications for Slope Stability
Although research has explained how plant roots mechanically stabilize soils, in this article we explore how root systems create networks of preferential flow and thus influence water pressures in soils to trigger landslides. Root systems may alter subsurface flow: Hydrological m...
Stability of Long's vortex at large flow force
NASA Technical Reports Server (NTRS)
Foster, M. R.; Smith, F. T.
1989-01-01
Long's self-similar vortex is known to have two solutions for each supercritical value of the flow force. Each of those solutions is shown to have a double structure if the flow force is large. The inertial instabilities of one of those large-flow-force limit solutions are investigated, showing that they are related to the instabilities of the Bickley jet in one regime. However, the swirl in the vortex becomes important for long waves, very strongly modifying the sinuous and varicose, Bickley modes. The asymptotic results obtained agree well with the numerical solutions for the sinuous mode, but not for the varicose mode, the difficulty in the latter case being apparently due to mode jumping.
Long arc stabilities with various arc gas flow rates
NASA Astrophysics Data System (ADS)
Maruyama, K.; Takeda, K.; Sugimoto, M.; Noguchi, Y.
2014-11-01
A new arc torch for use in magnetically driven arc device was developed with a commercially available TIG welding arc torch. The torch has a water-cooling system to the torch nozzle and has a nozzle nut to supply a swirling-free plasma gas flow. Its endurance against arc thermal load is examined. Features of its generated arc are investigated.
Calculations of the stability of some axisymmetric flows proposed as a model of vortex breakdown
NASA Technical Reports Server (NTRS)
Mhuiris, N. M. G.
1986-01-01
The term vortex breakdown refers to the abrupt and drastic changes of structure that can sometimes occur in swirling flows. It was conjectured that the bubble type of breakdown can be viewed as an axisymmetric wave traveling upstream in a primarily columnar vortex flow. In this scenario the wave's upstream progress is impeded only when it reaches a critical amplitude and it loses stability to some nonaxisymmetric disturbance. The stability of some axisymmetric wavy flows to three dimensional disturbances, viewing the amplitude of the wave as a bifurcation parameter is examined. The stability of a set of related columnar vortex flows, constructed by taking the two dimensional flow at a single axial location and extending it throughout the domain without variation, is investigated. The method used will be to expand the perturbation velocity in a series of divergence free vectors which ensures that the continuity equation for the incompressible fluid is satisfied exactly by the computed velocity field. Projections of the stability equation onto the space of inviscid vector fields eliminated the pressure term from the equation and reduces the differential eigen problem to a generalized matrix eigen problem. Results are presented both for the one dimensional, columnar vortex flows and also for the wavy bubble flow.
Analysis of a Stabilized CNLF Method with Fast Slow Wave Splittings for Flow Problems
Jiang, Nan; Tran, Hoang A.
2015-04-01
In this work, we study Crank-Nicolson leap-frog (CNLF) methods with fast-slow wave splittings for Navier-Stokes equations (NSE) with a rotation/Coriolis force term, which is a simplification of geophysical flows. We propose a new stabilized CNLF method where the added stabilization completely removes the method's CFL time step condition. A comprehensive stability and error analysis is given. We also prove that for Oseen equations with the rotation term, the unstable mode (for which u(n+1) + u(n-1) equivalent to 0) of CNLF is asymptotically stable. Numerical results are provided to verify the stability and the convergence of the methods.
Albatsh, Fadi M.; Ahmad, Shameem; Mekhilef, Saad; Mokhlis, Hazlie; Hassan, M. A.
2015-01-01
This study examines a new approach to selecting the locations of unified power flow controllers (UPFCs) in power system networks based on a dynamic analysis of voltage stability. Power system voltage stability indices (VSIs) including the line stability index (LQP), the voltage collapse proximity indicator (VCPI), and the line stability index (Lmn) are employed to identify the most suitable locations in the system for UPFCs. In this study, the locations of the UPFCs are identified by dynamically varying the loads across all of the load buses to represent actual power system conditions. Simulations were conducted in a power system computer-aided design (PSCAD) software using the IEEE 14-bus and 39- bus benchmark power system models. The simulation results demonstrate the effectiveness of the proposed method. When the UPFCs are placed in the locations obtained with the new approach, the voltage stability improves. A comparison of the steady-state VSIs resulting from the UPFCs placed in the locations obtained with the new approach and with particle swarm optimization (PSO) and differential evolution (DE), which are static methods, is presented. In all cases, the UPFC locations given by the proposed approach result in better voltage stability than those obtained with the other approaches. PMID:25874560
NASA Astrophysics Data System (ADS)
Müller, T.; Hoffmann, T.
2012-04-01
Debris flows play a crucial role in the coupling of hillslope-sediment sources and channels in mountain environments. In most landscape evolution models (LEMs), the sediment transport by debris flows is (if at all) often represented by simple empirical rules. This generally results from the mismatch of the coarse resolution of the LEMs and the small scale impacts of debris flow processes. To extend the accuracy and predictive power of LEMs, either a higher resolution of LEMs in combination with process-based debris flow models or a better parametrisation of subpixel scale debris flow processes is necessary. Furthermore, the simulation of sediment transport by debris flows is complicated by their episodic nature and unknown factors controlling the frequency and magnitude of events. Here, we present first results using a slope stability model (SINMAP) and an event-based debris flow routing model (SCIDDICA-S4c) to simulate the effects of debris flows in LEMs. The model was implemented in the XULU modelling platform developed by the Department of Computer Science at the University of Bonn. The combination of the slope stability model and the event-based routing and mass balance model enables us to simulate the triggering and routing of debris flow material through the iteration of single events over several thousand years. Although a detailed calibration and validation remains to be done, the resulting debris flow-affected areas in a test elevation model correspond well with data gained from a geomorphological mapping of the corresponding area, justifying our approach. The increased computation speed allows to run high resolution LEM in convenient short time at relatively low cost. This should encourage the development of more detailed LEMs, in which process-based models should be incorporated.
Linear stability analysis of magnetohydrodynamic duct flows with perfectly conducting walls
Liu, Lishuai; Ye, Xuemin
2017-01-01
The stability of magnetohydrodynamic flow in a duct with perfectly conducting walls is investigated in the presence of a homogeneous and constant static magnetic field. The temporal growth and spatial distribution of perturbations are obtained by solving iteratively the direct and adjoint governing equations with respect of perturbations, based on nonmodal stability theory. The effect of the applied magnetic field, as well as the aspect ratio of the duct on the stability of the magnetohydrodynamic duct flow is taken into account. The computational results show that, weak jets appear near the sidewalls at a moderate magnetic field and the velocity of the jet increases with the increase of the intensity of the magnetic field. The duct flow is stable at either weak or strong magnetic field, but becomes unstable at moderate intensity magnetic field, and the stability is invariance with the aspect ratio of the duct. The instability of magnetohydrodynamic duct flow is related with the exponential growth of perturbations evolving on the fully developed jets. Transient growth of perturbations is also observed in the computation and the optimal perturbation is found to be in the form of streamwise vortices and localized within the sidewall layers. By contrast, the Hartmann layer perpendicular to the magnetic field is irrelevant to the stability issue of the magnetohydrodynamic duct flow. PMID:29077734
Linear stability analysis of magnetohydrodynamic duct flows with perfectly conducting walls.
Dong, Shuai; Liu, Lishuai; Ye, Xuemin
2017-01-01
The stability of magnetohydrodynamic flow in a duct with perfectly conducting walls is investigated in the presence of a homogeneous and constant static magnetic field. The temporal growth and spatial distribution of perturbations are obtained by solving iteratively the direct and adjoint governing equations with respect of perturbations, based on nonmodal stability theory. The effect of the applied magnetic field, as well as the aspect ratio of the duct on the stability of the magnetohydrodynamic duct flow is taken into account. The computational results show that, weak jets appear near the sidewalls at a moderate magnetic field and the velocity of the jet increases with the increase of the intensity of the magnetic field. The duct flow is stable at either weak or strong magnetic field, but becomes unstable at moderate intensity magnetic field, and the stability is invariance with the aspect ratio of the duct. The instability of magnetohydrodynamic duct flow is related with the exponential growth of perturbations evolving on the fully developed jets. Transient growth of perturbations is also observed in the computation and the optimal perturbation is found to be in the form of streamwise vortices and localized within the sidewall layers. By contrast, the Hartmann layer perpendicular to the magnetic field is irrelevant to the stability issue of the magnetohydrodynamic duct flow.
NASA Astrophysics Data System (ADS)
Haga, Taiki
2018-02-01
We investigate the stability and critical velocity of a weakly interacting Bose gas flowing in a random potential. By applying the Bogoliubov theory to a disordered Bose system with a steady flow, the condensate density and the superfluid density are determined as functions of the disorder strength, flow velocity, and temperature. The critical velocity, at which the steady flow becomes unstable, is calculated from the spectrum of hydrodynamic excitation. We also show that in two dimensions the critical velocity strongly depends on the system size.
Crossflow Stability and Transition Experiments in Swept-Wing Flow
NASA Technical Reports Server (NTRS)
Dagenhart, J. Ray; Saric, William S.
1999-01-01
An experimental examination of crossflow instability and transition on a 45deg swept wing was conducted in the Arizona State University Unsteady Wind Tunnel. The stationary-vortex pattern and transition location are visualized by using both sublimating chemical and liquid-crystal coatings. Extensive hot-wire measurements were obtained at several measurement stations across a single vortex track. The mean and travelling wave disturbances were measured simultaneously. Stationary crossflow disturbance profiles were determined by subtracting either a reference or a span-averaged velocity profile from the mean velocity data. Mean, stationary crossflow, and traveling wave velocity data were presented as local boundary layer profiles and contour plots across a single stationary crossflow vortex track. Disturbance mode profiles and growth rates were determined. The experimental data are compared with predictions from linear stability theory.
Stability of Contact Lines in Fluids: 2D Stokes Flow
NASA Astrophysics Data System (ADS)
Guo, Yan; Tice, Ian
2018-02-01
In an effort to study the stability of contact lines in fluids, we consider the dynamics of an incompressible viscous Stokes fluid evolving in a two-dimensional open-top vessel under the influence of gravity. This is a free boundary problem: the interface between the fluid in the vessel and the air above (modeled by a trivial fluid) is free to move and experiences capillary forces. The three-phase interface where the fluid, air, and solid vessel wall meet is known as a contact point, and the angle formed between the free interface and the vessel is called the contact angle. We consider a model of this problem that allows for fully dynamic contact points and angles. We develop a scheme of a priori estimates for the model, which then allow us to show that for initial data sufficiently close to equilibrium, the model admits global solutions that decay to equilibrium exponentially quickly.
Flow and stability of a viscoelastic liquid curtain
NASA Astrophysics Data System (ADS)
Gaillard, Antoine; Lebon, Luc; Roche, Matthieu; Gay, Cyprien; Lerouge, Sandra; Limat, Laurent
2017-11-01
We experimentally investigate the flow of a sheet of viscoelastic liquid falling freely from a thin slit under gravity. We observe new phenomena that are not described by the Newtonian curtain theory derived by Brown and Taylor. For low-viscosity elastic fluids, the mean falling velocity does not reduce to a free fall, even far downstream from the slit: we observe a shift towards sub-gravity accelerations. This corresponds to a dramatic increase of the length of the transient regime where gravity is balanced by internal stress instead of inertia. The flow in the curtain is stable for dilute and semi-dilute aqueous solutions of polyethylene oxide (PEO), a flexible polymer, but it becomes time dependent and horizontally modulated for aqueous solutions of partially hydrolyzed polyacrylamide (HPAM), a semi-rigid polyelectrolyte. In the latter case, the curtain becomes varicose. This extrusion instability results from the existence of large vortices at the entrance of the slit, where the liquid undergoes a strong planar contraction, which creates over-fed and under-fed regions. Finally, we show that the varicose curtain is prone to hole opening in its thinner parts and may cease to exist.
NASA Astrophysics Data System (ADS)
Wang, Chao; Ji, Ming; Zhang, Ying; Jiang, Wentao; Lu, Xiaoyan; Wang, Jiaoying; Yang, Heng
2016-01-01
The electronic image stabilization technology based on improved optical-flow motion vector estimation technique can effectively improve the non normal shift, such as jitter, rotation and so on. Firstly, the ORB features are extracted from the image, a set of regions are built on these features; Secondly, the optical-flow vector is computed in the feature regions, in order to reduce the computational complexity, the multi resolution strategy of Pyramid is used to calculate the motion vector of the frame; Finally, qualitative and quantitative analysis of the effect of the algorithm is carried out. The results show that the proposed algorithm has better stability compared with image stabilization based on the traditional optical-flow motion vector estimation method.
TF34 engine compression system computer study. [simulation of flow stability
NASA Technical Reports Server (NTRS)
Hosny, W. M.; Steenken, W. G.
1979-01-01
The stability of the fan and the compressor components was examined individually using linearized and time dependent, one dimensional stability analysis techniques. The stability of the fan core integrated compression system was investigated using a two dimensional compression system model. The analytical equations on which this model was based satisfied the mass, axial momentum, radial momentum, and energy conservation equations for flow through a finite control volume. The results gave an accurate simulation of the flow through the compression system. The speed lines of the components were reproduced; the points of instability were accurately predicted; the locations where the instability was initiated in the fan and the core were indicated; and the variation of the bypass ratio during flow throttling was calculated. The validity of the analytical techniques was then established by comparing these results with test data and with results obtained from the steady state cycle deck.
ATC Enhancement Considering Transient Stability by Optimal Power Flow Control Using UPFC
NASA Astrophysics Data System (ADS)
Masuta, Taisuke; Motoki, Hiroaki; Yokoyama, Akihiko
With recent development of power electronics technology, power system stability enhancement and optimal power flow control by using Flexible AC Transmission System (FACTS) devices have so far been studied. The FACTS devices to relieve multiple constraints can also make it possible to enhance Available Transfer Capability (ATC) without construction of new transmission lines. In this paper, a new method for improving transient stability by Unified Power Flow Controller (UPFC) is proposed. Then the proposed method is applied to an OPF control method by using UPFC for relieving multiple constraints. The new OPF method is used for enhancement of ATC taking into account Transient stability constraints as well as overload and steady-state stability constraints. The OPF problem is formulated to minimize total capacity of inverters of UPFC. Effectiveness of the proposed method is shown by numerical examples for IEEJ East-10-machine test system.
Core-annular miscible two-fluid flow in a slippery pipe: A stability analysis
NASA Astrophysics Data System (ADS)
Chattopadhyay, Geetanjali; Usha, Ranganathan; Sahu, Kirti Chandra
2017-09-01
This study is motivated by the preliminary direct numerical simulations in double-diffusive (DD) core-annular flows with slip at the wall which displayed elliptical shaped instability patterns as in a rigid pipe case; however, slip at the pipe wall delays the onset of instability for a range of parameters and increases the phase speed. This increased our curiosity to have a thorough understanding of the linear stability characteristics of the miscible DD two-fluid flow in a pipe with slip at the pipe wall. The present study, therefore, addresses the linear stability of viscosity-stratified core-annular Poiseuille flow of miscible fluids with matched density in a slippery pipe in the presence of two scalars diffusing at different rates. The physical mechanisms responsible for the occurrence of instabilities in the DD system are explained through an energy budget analysis. The differences and similarities between core-annular flow in a slippery pipe and in a plane channel with velocity slip at the walls are explored. The stability characteristics are significantly affected by the presence of slip. The diffusivity effect is non-monotonic in a DD system. A striking feature of instability is that only a band of wavenumbers is destabilized in the presence of moderate to large inertial effects. Both the longwave and shortwave are stabilized at small Reynolds numbers. Slip exhibits a dual role of stabilizing or destabilizing the flow. The preliminary direct numerical simulations confirm the predictions of the linear stability analysis. The present study reveals that it may be possible to control the instabilities in core-annular pressure driven pipe flows by imposing a velocity slip at the walls.
Two-phase flow stability structure in a natural circulation system
Zhou, Zhiwei
1995-09-01
The present study reports a numerical analysis of two-phase flow stability structures in a natural circulation system with two parallel, heated channels. The numerical model is derived, based on the Galerkin moving nodal method. This analysis is related to some design options applicable to integral heating reactors with a slightly-boiling operation mode, and is also of general interest to similar facilities. The options include: (1) Symmetric heating and throttling; (2) Asymmetric heating and symmetric throttling; (3) Asymmetric heating and throttling. The oscillation modes for these variants are discussed. Comparisons with the data from the INET two-phase flow stability experiment have qualitatively validated the present analysis.
Discharge stabilization studies of CO laser gas mixtures in quasi-steady supersonic flow
NASA Technical Reports Server (NTRS)
Srinivasan, G.; Smith, J. A.
1976-01-01
Experiments were conducted to study the applicability of a double discharge stabilization scheme in conditions appropriate for high energy CO lasers in supersonic flows. A Ludwieg tube impulse flow facility and a ballasted capacitor bank provided essentially steady flow and discharge conditions (d.c.) for times longer than ten electrode length-flow transit times. Steady, arc-free, volume discharges were produced in a Mach 3 test cavity using an auxiliary discharge to stabilize the main discharge in N2 and He/CO mixture. A signigicant result is the lack of observed plasma E/N changes in response to auxiliary discharge current changes. Also, where glow discharges were obtained, the energy loading achieved was very much less than the threshold level required for laser operation.
Thermonuclear dynamo inside ultracentrifuge with supersonic plasma flow stabilization
Winterberg, F.
2016-01-15
Einstein's general theory of relativity implies the existence of virtual negative masses in the rotational reference frame of an ultracentrifuge with the negative mass density of the same order of magnitude as the positive mass density of a neutron star. In an ultracentrifuge, the repulsive gravitational field of this negative mass can simulate the attractive positive mass of a mini-neutron star, and for this reason can radially confine a dense thermonuclear plasma placed inside the centrifuge, very much as the positive mass of a star confines its plasma by its own attractive gravitational field. If the centrifuge is placed inmore » an externally magnetic field to act as the seed field of a magnetohydrodynamic generator, the configuration resembles a magnetar driven by the release of energy through nuclear fusion, accelerating the plasma to supersonic velocities, with the magnetic field produced by the thermomagnetic Nernst effect insulating the hot plasma from the cold wall of the centrifuge. Because of the supersonic flow and the high plasma density the configuration is stable.« less
Thermonuclear dynamo inside ultracentrifuge with supersonic plasma flow stabilization
Winterberg, F.
2016-01-15
Einstein's general theory of relativity implies the existence of virtual negative masses in the rotational reference frame of an ultracentrifuge with the negative mass density of the same order of magnitude as the positive mass density of a neutron star. In an ultracentrifuge, the repulsive gravitational field of this negative mass can simulate the attractive positive mass of a mini-neutron star, and for this reason can radially confine a dense thermonuclear plasma placed inside the centrifuge, very much as the positive mass of a star confines its plasma by its own attractive gravitational field. If the centrifuge is placed in an externally magnetic field to act as the seed field of a magnetohydrodynamic generator, the configuration resembles a magnetar driven by the release of energy through nuclear fusion, accelerating the plasma to supersonic velocities, with the magnetic field produced by the thermomagnetic Nernst effect insulating the hot plasma from the cold wall of the centrifuge. Because of the supersonic flow and the high plasma density the configuration is stable.
Stability Analysis of High-Speed Boundary-Layer Flow with Gas Injection (Briefing Charts)
2014-06-01
boundary-layer flow with gas injection 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER Alexander V. Fedorov ...Release; Distribution Unlimited Stability analysis of high-speed boundary-layer flow with gas injection Alexander Fedorov and Vitaly Soudakov Moscow...Dispersion relation from WKB analysis*,**: *Guschin, V.R., & Fedorov , A.V., Fluid Dynamics, Vol. 24, No.1, 1989 **Guschin, V.R., & Fedorov , A.V., NASA
NASA Astrophysics Data System (ADS)
Chatterjee, Ajay; Fabris, Drazen
2017-10-01
This paper considers the linear stability of confined planar impinging jet flow of a non-Newtonian inelastic fluid. The rheology is shear rate dependent with asymptotic Newtonian behavior in the zero shear limit, and the analysis examines both shear thinning and shear thickening behavior. The planar configuration is such that the width of the inlet nozzle is smaller than the distance from the jet exit to the impinging surface, giving an aspect ratio e = 8 for which two-dimensional time dependent flow is readily manifest. For values of the power-law index n in the range 0.4 ≤n ≤1.1 , the bi-global linear stability of the laminar flow is analyzed for Newtonian Reynolds numbers Re ≲200 . The calculations show that for certain values of n, including the Newtonian value n = 1, the steady flow exhibits multiplicity leading to hysteresis in the primary separation vortex reattachment point and a consequent jump in stability behavior. Even in the absence of hysteresis, relatively small changes in viscosity significantly affect stability characteristics. For Newtonian and mildly shear thinning or shear thickening fluids, an unstable flow shows a decaying perturbation growth rate as Re is increased, and for certain values of n, the flow may be restabilized at a larger Re before eventually becoming unstable again. This decay in the growth rate of the critical antisymmetric mode may be correlated as a function of the reattachment point RP of the primary separation vortex in the underlying steady flow. Representative results are analyzed in detail and discussed in the context of some experimental observations of time-dependent Newtonian impinging flow. The stability results are used to construct the neutral stability curve (n, Re) that displays multiplicity and contains several cusp points associated with flow restabilization and hysteresis. Integration of the full nonlinear equation reveals the structure of the time periodic flow field for both Newtonian and non
Marietti, Y; Debierre, J M; Bock, T M; Kassner, K
2001-06-01
An asymptotic interface equation for directional solidification near the absolute stability limit is extended by a nonlocal term describing a shear flow parallel to the interface. In the long-wave limit considered, the flow acts destabilizing on a planar interface. Moreover, linear stability analysis suggests that the morphology diagram is modified by the flow near onset of the Mullins-Sekerka instability. Via numerical analysis, the bifurcation structure of the system is shown to change. Besides the known hexagonal cells, structures consisting of stripes arise. Due to its symmetry-breaking properties, the flow term induces a lateral drift of the whole pattern, once the instability has become active. The drift velocity is measured numerically and described analytically in the framework of a linear analysis. At large flow strength, the linear description breaks down, which is accompanied by a transition to flow-dominated morphologies which is described in the following paper. Small and intermediate flows lead to increased order in the lattice structure of the pattern, facilitating the elimination of defects. Locally oscillating structures appear closer to the instability threshold with flow than without.
Influence of energetics on the stability of viscoelastic Taylor-Couette flow
NASA Astrophysics Data System (ADS)
Al-Mubaiyedh, U. A.; Sureshkumar, R.; Khomami, B.
1999-11-01
Previously reported isothermal linear stability analyses of viscoelastic Taylor-Couette flow have predicted transitions to nonaxisymmetric and time-dependent secondary flows for elasticity numbers E≡De/Re>0.01. In contrast, recent experiments by Baumert and Muller using constant viscosity Boger fluids have shown that the primary flow transition leads to axisymmetric and stationary Taylor-type toroidal vortices. Moreover, experimentally observed onset Deborah number is an order of magnitude lower than that predicted by isothermal linear stability analyses. In this work, we explore the influence of energetics on the stability characteristics of the viscoelastic Taylor-Couette flow. Our analysis is based on a thermodynamically consistent reformulation of the Oldroyd-B constitutive model that takes into account the influence of thermal history on polymeric stress, and an energy equation that takes into account viscous dissipation effects. Our calculations reveal that for experimentally realizable values of Peclet and Brinkman numbers, the most dangerous eigenvalue is real, corresponding to a stationary and axisymmetric mode of instability. Moreover, the critical Deborah number associated with this eigenvalue is an order of magnitude lower than those associated with the nonisothermal extensions of the most dangerous eigenvalues of the isothermal flow. Eigenfunction analysis shows stratification of perturbation hoop stress across the gap width drives a radial secondary flow. The convection of base state temperature gradients by this radial velocity perturbation leads to this new mode of instability. The influence of geometric and kinematic parameters on this instability is also investigated.
NASA Technical Reports Server (NTRS)
Al-Maaitah, Ayman A.; Nayfeh, Ali H.; Ragab, Saad A.
1989-01-01
The effect of suction on the stability of compressible flows over backward-facing steps is investigated. Mach numbers up to 0.8 are considered. The results show that continuous suction stabilizes the flow outside the separation bubble, but it destabilizes the flow inside it. Nevertheless, the overall N factor decreases as the suction level increases due to the considerable reduction of the separation bubble. For the same suction flow rate, properly distributed suction strips stabilize the flow more than continuous suction. The size of the separation bubble, and hence its effect on the instability can be considerably reduced by placing strips with high suction velocities in the separation region.
A numerical study of aortic flow stability and comparison with in vivo flow measurements.
Kousera, C A; Wood, N B; Seed, W A; Torii, R; O'Regan, D; Xu, X Y
2013-01-01
The development of an engineering transitional turbulence model and its subsequent evaluation and validation for some diseased cardiovascular flows have been suggestive of its likely utility in normal aortas. The existence of experimental data from human aortas, acquired in the early 1970s with catheter-mounted hot film velocimeters, provided the opportunity to compare the performance of the model on such flows. A generic human aorta, derived from magnetic resonance anatomical and velocity images of a young volunteer, was used as the basis for varying both Reynolds number (Re) and Womersley parameter (α) to match four experimental data points from human ascending aortas, comprising two with disturbed flow and two with apparently undisturbed flow. Trials were made with three different levels of inflow turbulence intensity (Tu) to find if a single level could represent the four different cases with 4000 < Re < 10,000 and 17 < α < 26. A necessary boundary condition includes the inflow "turbulence" level, and convincing results were obtained for all four cases with inflow Tu = 1.0%, providing additional confidence in the application of the transitional model in flows in larger arteries. The Reynolds-averaged Navier-Stokes (RANS)-based shear stress transport (SST) transitional model is capable of capturing the correct flow state in the human aorta when low inflow turbulence intensity (1.0%) is specified.
Plasma Density Effects on Toroidal Flow Stabilization of Edge Localized Modes
NASA Astrophysics Data System (ADS)
Cheng, Shikui; Zhu, Ping; Banerjee, Debabrata
2016-10-01
Recent EAST experiments have demonstrated mitigation and suppression of edge localized modes (ELMs) with toroidal rotation flow in higher collisionality regime, suggesting potential roles of plasma density. In this work, the effects of plasma density on the toroidal flow stabilization of the high- n edge localized modes have been extensively studied in linear calculations for a circular-shaped limiter H-mode tokamak, using the initial-value extended MHD code NIMROD. In the single MHD model, toroidal flow has a weak stabilizing effects on the high- n modes. Such a stabilization, however, can be significantly enhanced with the increase in plasma density. Furthermore, our calculations show that the enhanced stabilization of high- n modes from toroidal flow with higher edge plasma density persists in the 2-fluid MHD model. These findings may explain the ELM mitigation and suppression by toroidal rotation in higher collisionality regime due to the enhancement of plasma density obtained in EAST experiment. Supported by the National Magnetic Confinement Fusion Program of China under Grant Nos. 2014GB124002 and 2015GB101004, the 100 Talent Program and the President International Fellowship Initiative of Chinese Academy of Sciences.
Shape optimisation for linear stability with a RANS base-flow
NASA Astrophysics Data System (ADS)
Brewster, Jack; Juniper, Matthew
2017-11-01
A linear stability analysis of a steady flow yields a series of mode shapes and their corresponding growth rates and frequencies. The presence of modes with positive growth rates indicates that the flow will transition to another steady state or develop unsteady behaviour. Targeting the growth rate, we demonstrate shape optimisation for RANS flows. We examine the flow over a cylinder at a Reynolds number of 1000 with the Spalart-Allmaras turbulence model. A linear stability analysis yields a mode shape analogous to the low Reynolds number vortex shedding mode. Through the introduction of an adjoint global mode and an adjoint base-flow we derive the Hadamard form, a surface integral representation of the shape gradient. This gradient information is then used to modify the shape and reduce the growth rate of the mode. The cost of this approach is independent of the number of parameters and equivalent to an additional eigenvalue problem together with a linear flow calculation. In addition to the model problem of flow over a cylinder an industrial application is also presented.
Equilibrium and stability of flow-dominated Plasmas in the Big Red Ball
NASA Astrophysics Data System (ADS)
Siller, Robert; Flanagan, Kenneth; Peterson, Ethan; Milhone, Jason; Mirnov, Vladimir; Forest, Cary
2017-10-01
The equilibrium and linear stability of flow-dominated plasmas are studied numerically using a spectral techniques to model MRI and dynamo experiments in the Big Red Ball device. The equilibrium code solves for steady-state magnetic fields and plasma flows subject to boundary conditions in a spherical domain. It has been benchmarked with NIMROD (non-ideal MHD with rotation - open discussion), Two different flow scenarios are studied. The first scenario creates a differentially rotating toroidal flow that is peaked at the center. This is done to explore the onset of the magnetorotational instability (MRI) in a spherical geometry. The second scenario creates a counter-rotating von Karman-like flow in the presence of a weak magnetic field. This is done to explore the plasma dynamo instability in the limit of a weak applied field. Both scenarios are numerically modeled as axisymmetric flow to create a steady-state equilibrium solution, the stability and normal modes are studied in the lowest toroidal mode number. The details of the observed flow, and the structure of the fastest growing modes will be shown. DoE, NSF.
Stability and dynamical properties of material flow systems on random networks
NASA Astrophysics Data System (ADS)
Anand, K.; Galla, T.
2009-04-01
The theory of complex networks and of disordered systems is used to study the stability and dynamical properties of a simple model of material flow networks defined on random graphs. In particular we address instabilities that are characteristic of flow networks in economic, ecological and biological systems. Based on results from random matrix theory, we work out the phase diagram of such systems defined on extensively connected random graphs, and study in detail how the choice of control policies and the network structure affects stability. We also present results for more complex topologies of the underlying graph, focussing on finitely connected Erdös-Réyni graphs, Small-World Networks and Barabási-Albert scale-free networks. Results indicate that variability of input-output matrix elements, and random structures of the underlying graph tend to make the system less stable, while fast price dynamics or strong responsiveness to stock accumulation promote stability.
An Novel Continuation Power Flow Method Based on Line Voltage Stability Index
NASA Astrophysics Data System (ADS)
Zhou, Jianfang; He, Yuqing; He, Hongbin; Jiang, Zhuohan
2018-01-01
An novel continuation power flow method based on line voltage stability index is proposed in this paper. Line voltage stability index is used to determine the selection of parameterized lines, and constantly updated with the change of load parameterized lines. The calculation stages of the continuation power flow decided by the angle changes of the prediction of development trend equation direction vector are proposed in this paper. And, an adaptive step length control strategy is used to calculate the next prediction direction and value according to different calculation stages. The proposed method is applied clear physical concept, and the high computing speed, also considering the local characteristics of voltage instability which can reflect the weak nodes and weak area in a power system. Due to more fully to calculate the PV curves, the proposed method has certain advantages on analysing the voltage stability margin to large-scale power grid.
The effects of viscosity on the stability of a trailing-line vortex in compressible flow
NASA Technical Reports Server (NTRS)
Stott, Jillian A. K.; Duck, Peter W.
1994-01-01
We consider the effects of viscosity on the inviscid stability of the Batchelor vortex in a compressible flow. The problem is tackled asymptotically, in the limit of large (streamwise and azimuthal) wavenumbers, together with large Mach numbers. Previous studies, with viscous effects neglected, found that the nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumber. This structure persists when viscous effects are included in the analysis. In the present study the mode present in the incompressible case ceases to be unstable at high Mach numbers and a center mode forms, whose stability characteristics are determined primarily by conditions close to the vortex axis. We find generally that viscosity has a stabilizing influence on the flow, while in the case of center modes, viscous effects become important at much larger Reynolds numbers than for the first class of disturbance.
Laboratory Study of MHD Effects on Stability of Free-surface Liquid Metal Flow
NASA Astrophysics Data System (ADS)
Burin, M. J.; Ji, H.; McMurtry, K.; Peterson, L.; Giannakis, D.; Rosner, R.; Fischer, P.
2006-10-01
The dynamics of free-surface MHD shear flows is potentially important to both astrophysics (e.g. in the mixing of dense plasma accreted upon neutron star surfaces) and fusion reactors (e.g. in liquid metal ‘first walls’). To date however few relevant experiments exist. In order to study the fundamental physics of such flows, a small-scale laboratory experiment is being built using a liquid gallium alloy flowing in an open- channel geometry. The flow dimensions are nominally 10cm wide, 1cm deep, and 70cm long under an imposed magnetic field up to 7kG, leading to maximum Hartman number of 2000 and maximum Reynolds number of 4x10^5. Two basic physics issues will ultimately be addressed: (1) How do MHD effects modify the stability of the free surface? For example, is the flow more stable (through the suppression of cross-field motions), or less stable (through the introduction of new boundary layers)? We also investigate whether internal shear layers and imposed electric currents can control the surface stability. (2) How do MHD effects modify free-surface convection driven by a vertical and/or horizontal temperature gradient? We discuss aspects of both of these issues, along with detailed descriptions of the experimental device. Pertinent theoretical stability analyses and initial hydrodynamic results are presented in companion posters. This work is supported by DoE under contract #DE-AC02-76-CH03073.
NASA Astrophysics Data System (ADS)
Luzzatto-Fegiz, Paolo
2011-11-01
Steady fluid solutions play a special role in the dynamics of a flow: stable states may be realized in practice, while unstable ones may act as attractors. Unfortunately, determining stability is often a process far more laborious than finding steady states; indeed, even for simple vortex or wave flows, stability properties have often been the subject of debate. We consider here a stability idea originating with Lord Kelvin (1876), which involves using the second variation of the energy, δ2 E , to establish bounds on a perturbation. However, for numerically obtained flows, computing δ2 E explicitly is often not feasible. To circumvent this issue, Saffman & Szeto (1980) proposed an argument linking changes in δ2 E to turning points in a bifurcation diagram, for families of steady flows. Later work has shown that this argument is unreliable; the two key issues are associated with the absence of a formal turning-point theory, and with the inability to detect bifurcations (Dritschel 1995, and references therein). In this work, we build on ideas from bifurcation theory, and link turning points in a velocity-impulse diagram to changes in δ2 E ; in addition, this diagram delivers the direction of the change of δ2 E , thereby providing information as to whether stability is gained or lost. To detect hidden solution branches, we introduce to these fluid problems concepts from imperfection theory. The resulting approach, involving ``imperfect velocity-impulse'' diagrams, leads us to new and surprising results for a wide range of fundamental vortex and wave flows; we mention here the calculation of the first steady vortices without any symmetry, and the uncovering of the complete solution structure for vortex pairs. In addition, we find precise agreement with available results from linear stability analysis. Doctoral work advised by C.H.K. Williamson at Cornell University.
Fluid-structure interaction response and stability of flexible hydrofoils in cavitating flow
NASA Astrophysics Data System (ADS)
Young, Yin Lu; Ducoin, Antoine; Chae, Eun Jung
2011-11-01
There is an increasing interest in the use of passive/active control mechanisms to take advantage of the fluid-structure interaction response of flexible lifting bodies to improve propulsive efficiency and performance from ambient flow. However, design of these flexible lifting bodies are not trivial, particularly for heavily loaded and cavitating, off-design conditions, because of potential hydroelastic instability failure mechanisms such as divergence or flutter. Hence, the objectives of this research are to (i) develop and validate an efficient coupling procedure to predict the hydroelastic response of flexible hydrofoils in unsteady flows, and (ii) investigate the influence of fluid density and viscosity on the FSI response and stability of flexible hydrofoils in cavitating flows. A multiphase CFD code is coupled with a simplified 2-DOF model to represent the spanwise bending and twisting response of a flexible hydrofoil. The influence of coupling algorithms on the accuracy and stability of the numerical predictions are discussed.
NASA Astrophysics Data System (ADS)
Shelton, John; Sunkavalli, Abhishek
2017-11-01
Like the canonical, two-dimensional, square lid-driven cavity problem that serves as its cornerstone, the two-dimensional, rectangular lid-driven cavity is a well-studied extension that also generates dynamically stable, well-defined, flow structures within the laminar flow regimes. Mathematical time-dependent perturbations to these flow structures have been shown to generate a region of metastability as the system transitions towards a turbulent flow regime. By replacing the mathematically-generated, time-dependent perturbations of previous investigations into this phenomena with the particle-fluid and particle-particle interactions present within a multiphase flow, a unique perspective on the stability of these flow structures within the laminar flow regimes of the two-dimensional lid-driven cavity can be obtained. Therefore, the objective of this study is to investigate the effect varying area fractions and relative densities of suspended granular particles have on traditionally laminar and stable flows found at Reynolds numbers of 100, 400, and 1000 of a rectangular lid-driven cavity with an aspect ratio of 1.5. These studies and analyses will aid in the determination how granular materials can be used to enhance desirable flow characteristics of fluid behaviors.
Paungmali, Aatit; Henry, Leonard Joseph; Sitilertpisan, Patraporn; Pirunsan, Ubon; Uthaikhup, Sureeporn
2016-01-01
[Purpose] This study investigated the effects of lumbopelvic stabilization training on tissue blood flow changes in the lumbopelvic region and lumbopelvic stability compared to placebo treatment and controlled intervention among patients with chronic non-specific low back pain. [Subjects and Methods] A total of 25 participants (7 males, 18 females; mean age, 33.3 ± 14.4 years) participated in this within-subject, repeated-measures, double-blind, placebo-controlled comparison trial. The participants randomly underwent three types of interventions that included lumbopelvic stabilization training, placebo treatment, and controlled intervention with 48 hours between sessions. Lumbopelvic stability and tissue blood flow were measured using a pressure biofeedback device and a laser Doppler flow meter before and after the interventions. [Results] The repeated-measures analysis of variance results demonstrated a significant increase in tissue blood flow over the lumbopelvic region tissues for post- versus pre-lumbopelvic stabilization training and compared to placebo and control interventions. A significant increase in lumbopelvic stability before and after lumbopelvic stabilization training was noted, as well as upon comparison to placebo and control interventions. [Conclusion] The current study supports an increase in tissue blood flow in the lumbopelvic region and improved lumbopelvic stability after core training among patients with chronic non-specific low back pain.
The effect of finite-conductivity Hartmann walls on the linear stability of Hunt's flow
NASA Astrophysics Data System (ADS)
Arlt, Thomas; Priede, Jānis; Bühler, Leo
2017-07-01
We analyse numerically the linear stability of the fully developed liquid metal flow in a square duct with insulating side walls and thin electrically conducting horizontal walls with the wall conductance ratio $c=0.01\\cdots 1$ subject to a vertical magnetic field with the Hartmann numbers up to $Ha=10^{4}.$ In a sufficiently strong magnetic field, the flow consists of two jets at the side walls walls and a near-stagnant core with the relative velocity $\\sim(cHa)^{-1}.$ We find that for $Ha\\gtrsim300,$ the effect of wall conductivity on the stability of the flow is mainly determined by the effective Hartmann wall conductance ratio $cHa.$ For $c\\ll 1,$ the increase of the magnetic field or that of the wall conductivity has a destabilizing effect on the flow. Maximal destabilization of the flow occurs at $Ha\\approx30/c.$ In a stronger magnetic field with $cHa\\gtrsim 30,$ the destabilizing effect vanishes and the asymptotic results of Priede et al. [J. Fluid Mech. 649, 115, 2010] for the ideal Hunt's flow with perfectly conducting Hartmann walls are recovered.
Generalized Stability Analysis of Capillary Flow in Slender V-Grooves
NASA Astrophysics Data System (ADS)
White, Nicholas; Troian, Sandra
2017-11-01
Spontaneous capillary flow, an especially rapid process in slender open microchannels resembling V-grooves, is of significant importance to many applications requiring passive robust flow control. Many types of biomedical devices for point-of-care use in developing countries are being designed around this principle. Important fundamental work by Romero and Yost (1996) and Weislogel (1996) elucidated the behavior of Newtonian films in slender V-grooves driven to flow by the streamwise change in capillary pressure due to the change in radius of curvature of the circular arc describing the interface of wetting or non-wetting fluids. Self-similar solutions describing Washburn type dynamics were found but other solutions are possible. Here we extend the Romero and Yost model to include a variety of inlet and outlet boundary conditions and examine the transient growth and generalized stability of perturbations to steady state and self-similar flows. Although most cases examined for wetting fluids exhibit robust stability against small perturbations, some exceptions reveal unstable flow. In total, these results support decades of experimental work which has found this method of flow control to be especially reliable, robust and self-healing. The authors gratefully acknowledge financial support from the 2016 NASA/Jet Propulsion Laboratory President's and Director's Fund as well as a 2017 NASA Space Technology Research Fellowship.
NASA Astrophysics Data System (ADS)
ANBUKUMAR, S.; KUMAR, MUNENDRA
2017-08-01
In the present study, a flexible pipe has been considered to study the effect of ratio of visco-elastic material viscosity to fluid viscosity on the stability of flexible laminar pipe flow with axi-symmetric disturbances. The effect of thickness of visco-elastic material on the stability of flexible pipe flow with outer rigid shroud has also been studied. The stability curves are drawn for various values of the ratio of visco-elastic material viscosity to fluid viscosity. It is observed that stability of flow is increasing by decreasing the ratio of visco-elastic material viscosity to fluid viscosity.
The stability of stratified spatially periodic shear flows at low Péclet number
Garaud, Pascale; Gallet, Basile
2015-08-15
This work addresses the question of the stability of stratified, spatially periodic shear flows at low Péclet number but high Reynolds number. This little-studied limit is motivated by astrophysical systems, where the Prandtl number is often very small. Furthermore, it can be studied using a reduced set of “low-Péclet-number equations” proposed by Lignières [“The small-Péclet-number approximation in stellar radiative zones,” Astron. Astrophys. 348, 933–939 (1999)]. Through a linear stability analysis, we first determine the conditions for instability to infinitesimal perturbations. We formally extend Squire’s theorem to the low-Péclet-number equations, which shows that the first unstable mode is always two-dimensional. We then perform an energy stability analysis of the low-Péclet-number equations and prove that for a given value of the Reynolds number, above a critical strength of the stratification, any smooth periodic shear flow is stable to perturbations of arbitrary amplitude. In that parameter regime, the flow can only be laminar and turbulent mixing does not take place. Finding that the conditions for linear and energy stability are different, we thus identify a region in parameter space where finite-amplitude instabilities could exist. Using direct numerical simulations, we indeed find that the system is subject to such finite-amplitude instabilities. We determine numerically how far into the linearly stable region of parameter space turbulence can be sustained.
Flow-induced conformational changes in gelatin structure and colloidal stabilization.
Akbulut, Mustafa; Reddy, Naveen K; Bechtloff, Bernd; Koltzenburg, Sebastian; Vermant, Jan; Prud'homme, Robert K
2008-09-02
Flow can change the rate at which solutes adsorb on surfaces by changing mass transfer to the surface, but moreover, flow can induce changes in the conformation of macromolecules in solution by providing sufficient stresses to perturb the segmental distribution function. However, there are few studies where the effect of flow on macromolecules has been shown to alter the structure of macromolecules adsorbed on surfaces. We have studied how the local energy dissipation alters the adsorption of gelatin onto polystyrene nanoparticles ( r = 85 nm). The change in the nature of the adsorbed layer is manifest in the change in the ability of the nanoparticles to resist aggregation. Circular dichroism spectroscopy was used to assess conformational changes in gelatin, and dynamic light scattering was used to assess the colloid stability. Experiments were conducted in a vortex jet mixer where energy density and mixing times have been quantified; mixing of the gelatin and unstable nanoparticles occurs on the order of milliseconds. The adsorption of the gelatin provides steric stabilization to the nanoparticles. We found that the stability of the gelatin-adsorbed nanoparticles increased with increasing mixing velocities: when the mixing velocities were changed from 0.9 to 550 m/s, the radius of the nanoclusters (aggregates) formed 12 h after the mixing decreased from 2620 to 600 nm. Increasing temperature also gave rise to similar trends in the stability behavior with increasing temperature, leading to increasing colloid stability. Linear flow birefringence studies also suggested that the velocity fields in the mixer are sufficiently strong to produce conformational changes in the gelatin. These results suggest that the energy dissipation produced by mixing can activate conformational changes in gelatin to alter its adsorption on the surfaces of nanoparticles. Understanding how such conformational changes in gelatin can be driven by local fluid mechanics and how these changes
Linear stability of the Couette flow of a vibrationally excited gas. 2. viscous problem
NASA Astrophysics Data System (ADS)
Grigor'ev, Yu. N.; Ershov, I. V.
2016-03-01
Based on the linear theory, stability of viscous disturbances in a supersonic plane Couette flow of a vibrationally excited gas described by a system of linearized equations of two-temperature gas dynamics including shear and bulk viscosity is studied. It is demonstrated that two sets are identified in the spectrum of the problem of stability of plane waves, similar to the case of a perfect gas. One set consists of viscous acoustic modes, which asymptotically converge to even and odd inviscid acoustic modes at high Reynolds numbers. The eigenvalues from the other set have no asymptotic relationship with the inviscid problem and are characterized by large damping decrements. Two most unstable viscous acoustic modes (I and II) are identified; the limits of these modes were considered previously in the inviscid approximation. It is shown that there are domains in the space of parameters for both modes, where the presence of viscosity induces appreciable destabilization of the flow. Moreover, the growth rates of disturbances are appreciably greater than the corresponding values for the inviscid flow, while thermal excitation in the entire considered range of parameters increases the stability of the viscous flow. For a vibrationally excited gas, the critical Reynolds number as a function of the thermal nonequilibrium degree is found to be greater by 12% than for a perfect gas.
NASA Astrophysics Data System (ADS)
Negretti, M. Eletta; Socolofsky, Scott A.; Rummel, Andreas C.; Jirka, Gerhard H.
2005-04-01
Shallow wakes that occur in a wide range of natural flows tend to generate instabilities that develop into large, 2D coherent structures (2DCS). We present the results of an experimental study to stabilize shallow wakes by local, enhanced bottom roughness. Two successful stabilization strategies are compared to a base case of an unsteady bubble wake. First, localized bed roughness is placed in the lateral shear layers near the shoulders of the cylinder. Second, a local roughness element is placed at the end of the recirculation bubble, in the downstream region where large-scale vortices would normally shed. Dye visualization is used to assess the qualitative behavior of the wake, and two-component laser Doppler velocimetry (LDV) measurements are made to measure the Reynolds stress distributions and time-averaged velocity profiles. In both stabilization cases, a minimum patch size of the enhanced roughness elements is required for stabilization, which depends on the momentum thickness of the shear layers and the locations of enhanced Reynolds shear stresses. The main effect of the wake stabilization is a reduction in momentum exchange with the ambient flow due to damping of the large 2DCS. This reduction in eddy diffusivity results in a narrower wake and a slower decay of the centerline velocity deficit with downstream distance compared to the base case of an unsteady bubble wake.
NASA Astrophysics Data System (ADS)
Gibbs, Samuel Chad, IV
This dissertation explores the stability of beams, plates and membranes due to subsonic aerodynamic flows or solar radiation forces. Beams, plates and membranes are simple structures that may act as building blocks for more complex systems. In this dissertation we explore the stability of these simple structures so that one can predict instabilities in more complex structures. The theoretical models include both linear and nonlinear energy based models for the structural dynamics of the featureless rectangular structures. The structural models are coupled to a vortex lattice model for subsonic fluid flows or an optical reflection model for solar radiation forces. Combinations of these theoretical models are used to analyze the dynamics and stability of aeroelastic and solarelastic systems. The dissertation contains aeroelastic analysis of a cantilevered beam and a plate / membrane system with multiple boundary conditions. The dissertation includes analysis of the transition from flag-like to wing-like flutter for a cantilevered beam and experiments to quantify the post flutter fluid and structure response of the flapping flag. For the plate / membrane analysis, we show that the boundary conditions in the flow direction determine the type of instability for the system while the complete set of boundary conditions is required to accurately predict the flutter velocity and frequency. The dissertation also contains analysis of solarelastic stability of membranes for solar sail applications. For a fully restrained membrane we show that a flutter instability is possible, however the post flutter response amplitude is small. The dissertation also includes analysis of a membrane hanging in gravity. This systems is an analog to a spinning solar sail and is used to validate the structural dynamics of thin membranes on earth. A linear beam structural model is able to accurately capture the natural frequencies and mode shapes. Finally, the dissertation explores the stability
A detailed study of mean-flow solutions for stability analysis of transitional flows
NASA Technical Reports Server (NTRS)
Ramakrishnan, R.; Vatsa, V.; Otto, J.; Kumar, A.
1993-01-01
A finite-volume upwind-difference parabolized Navier-Stokes code is utilized to obtain laminar mean-flow solutions at Mach 3.5 on a half-angle cone of 5 deg at an angle-of-attack of 2 deg. A detailed study is conducted on this configuration; the main focus is the velocity profiles in the leeward and windward symmetry planes at various axial locations. Comparisons of the solution profiles are made with both a central-difference code that incorporates scalar and matrix dissipation models and another state-of-the-art upwind-difference finitevolume code. The results obtained emphasize the importance of using matrix dissipation models for schemes that require explicit artificial dissipation. These results also illustrate the accuracy and efficiency of the planeby-plane marching procedure for computing mean-flow solutions for predicting the onset of transition with linear instability.
Aeroelastic Stability of a Cylindrical Composite Shell at a Bilateral Flow
NASA Astrophysics Data System (ADS)
Bakulin, V. N.; Bokov, M. A.; Nedbai, A. Ya.
2018-01-01
The aeroelastic stability (panel flutter) of an orthotropic composite shell in supersonic and subsonic flows of a gas over its outer and inner surfaces, respectively, is investigated. The internal two-phase flow is comprised of an air portion and a portion of mixture of air and gas. The structural damping is taken into account according to the Voigt hypothesis. The solution of corresponding equations is sought in the form of trigonometric series in the longitudinal coordinate. By the Bubnov-Galerkin method, the problem is reduced to a system of algebraic equations. The characteristic equation, obtained in an explicit form by using the Lagrange polynomial, is analyzed employing the Routh-Hurwitz criterion. Relations for the critical flow speed as functions of parameters of the internal flow are constructed.
Investigating motion and stability of particles in flows using numerical models
NASA Astrophysics Data System (ADS)
Khurana, Nidhi
The phenomenon of transport of particles in a fluid is ubiquitous in nature and a detailed understanding of its mechanism continues to remain a fundamental question for physicists. In this thesis, we use numerical methods to study the dynamics and stability of particles advected in flows. First, we investigate the dynamics of a single, motile particle advected in a two-dimensional chaotic flow. The particle can be either spherical or ellipsoidal. Particle activity is modeled as a constant intrinsic swimming velocity and stochastic fluctuations in both the translational and rotational motions are also taken into account. Our results indicate that interaction of swimming with flow structures causes a reduction in long-term transport at low speeds. Swimmers can get trapped at the transport barriers of the flow. We show that elongated swimmers respond more strongly to the dynamical structures of the flow field. At low speeds, their macroscopic transport is reduced even further than in the case of spherical swimmers. However, at high speeds these elongated swimmers tend to get attracted to the stable manifolds of hyperbolic fixed points, leading to increased transport. We then investigate the collective dynamics of a system of particles. The particles may interact both with each other and with the background flow. We focus on two different cases. In the fist case, we examine the stability of aggregation models in a turbulent-like flow. We use a simple aggregation model in which a point-like particle moves with a constant intrinsic speed while its velocity vector is reoriented according to the average direction of motion of its neighbors. We generate a strongly fluctuating, spatially correlated background flow using Kinematic Simulation, and show that flocks are highly sensitive to this background flow and break into smaller clusters. Our results indicate that such environmental perturbations must be taken into account for models which aim to capture the collective
A piecewise linear mean flow model for studying stability in a lined channel
NASA Astrophysics Data System (ADS)
Marx, David
2012-07-01
Acoustic liners are used to reduce sound emission by turbofan engines. Under grazing flow they may sustain hydrodynamic instabilities and these are studied using a stability analysis, based on a simplified model: the liner is a mass-spring-damper system, the base channel flow is piecewise linear, and the inviscid, incompressible Rayleigh equation is used. The model is an extension to the channel case of a boundary layer model by Rienstra and Darau. The piecewise linear profile introduces a finite boundary layer thickness which ensures well-posedness, allowing an initial value problem to be conducted to investigate absolute stability. For typical values in aeronautics the flow above the liner is unstable. Absolute instability is obtained for somewhat extreme values of the mean flow (tiny boundary layer thickness), and under realistic conditions the flow is convectively unstable. The effect of finite channel height is investigated in both cases. In particular, for large boundary layer thicknesses associated with convective instability the channel height has little effect on the unstable mode. Favorable outcomes and failures of the model are shown by comparison to a published experimental work.
The linear stability of a core annular flow in an asymptotically corrugated tube
NASA Astrophysics Data System (ADS)
Wei, Hsien-Hung; Rumschitzki, David S.
2002-09-01
This paper examines the core annular flow of two immiscible fluids in a straight circular tube with a small corrugation, in the limit where the ratio [epsilon] of the mean undisturbed annulus thickness to the mean core radius and the corrugation (characterized by the parameter [sigma]) are both asymptotically small and where the surface tension is small. It is motivated by the problems of liquid liquid displacement in irregular rock pores such as occur in secondary oil recovery and in the evolution of the liquid film lining the bronchii in the lungs whose diameters vary over different generations of branching. We investigate the asymptotic base flow in this limit and consider the linear stability of its leading order (in the corrugation parameter) solution. For the chosen scalings of the non-dimensional parameters the core's base flow slaves that of the annulus. The equation governing the leading-order interfacial position for a given wall corrugation function shows a competition between shear and capillarity. The former tends to align the interface shape with that of the wall and the latter tends to introduce a phase shift, which can be of either sign depending on whether the circumferential or the longitudinal component of capillarity dominates. The asymptotic linear stability of this leading-order base flow reduces to a single partial differential equation with non-constant coefficients deriving from the non-uniform base flow for the time evolution of an interfacial disturbance. Examination of a single mode k wall function allows the use of Floquet theory to analyse this equation. Direct numerical solutions of the above partial differential equation agree with the predictions of the Floquet analysis. The resulting spectrum is periodic in [alpha]- space, [alpha] being the disturbance wavenumber space. The presence of a small corrugation not only modifies (at order [sigma]2) the primary eigenvalue of the system. In addition, short-wave order-one disturbances that
Stabilization of Taylor-Couette flow due to time-periodic outer cylinder oscillation
NASA Technical Reports Server (NTRS)
Murray, B. T.; Mcfadden, G. B.; Coriell, S. R.
1990-01-01
The linear stability of circular Couette flow between concentric infinite cylinders is considered for the case when the inner cylinder is rotated at a constant angular velocity and the outer cylinder is driven sinusoidally in time with zero mean rotation. This configuration was studied experimentally by Walsh and Donnelly. The critical Reynolds numbers calculated from linear stability theory agree well with the experimental values, except at large modulation amplitudes and small frequencies. The theoretical values are obtained using Floquet theory implemented in two distinct approaches: a truncated Fourier series representation in time, and a fundamental solution matrix based on a Chebyshev pseudospectral representation in space. For large amplitude, low frequency modulation, the linear eigenfunctions are temporally complex, consisting of a quiescent region followed by rapid change in the perturbed flow velocities.
Stability of flow of a thermoviscoelastic fluid between rotating coaxial circular cylinders
NASA Technical Reports Server (NTRS)
Ghandour, N. N.; Narasimhan, M. N. L.
1976-01-01
The stability problem of thermoviscoelastic fluid flow between rotating coaxial cylinders is investigated using nonlinear thermoviscoelastic constitutive equations due to Eringen and Koh. The velocity field is found to be identical with that of the classical viscous case and the case of the viscoelastic fluid, but the temperature and pressure fields are found to be different. By imposing some physically reasonable mechanical and geometrical restrictions on the flow, and by a suitable mathematical analysis, the problem is reduced to a characteristic value problem. The resulting problem is solved and stability criteria are obtained in terms of critical Taylor numbers. In general, it is found that thermoviscoelastic fluids are more stable than classical viscous fluids and viscoinelastic fluids under similar conditions.
A novel algorithm for electronic image stabilization based on improved optical flow
NASA Astrophysics Data System (ADS)
Li, Cheng-mei; Bai, Hong-yang; Guo, Hong-wei; Liang, Hua-ju
2017-11-01
Aiming at the problem of the jitter of video sequence recorded by the strapdown seeker in the terminal guidance process, a novel algorithm for electronic image stabilization based on improved optical flow is proposed. The algorithm uses Shi-Tomasi corner detection method to extract the image corner, and estimates the global motion parameters of jittery video sequence based on improved Pyramid LK optical flow which is designed. Then the Kalman smoothing global motion vector is adopted, which effectively makes compensation on the current image motion and retains the active movement while filtering random jitter parameters. Finally, stable image sequence output is achieved. The simulation test and the embedded platform for the actual test results indicate that the proposed algorithm has a good image stabilization effect on the translation, rotation and scaling motion of the random jittery video sequence recorded by the strapdown seeker, and possesses good robustness and real-time performance.
On the temporal stability of steady-state quasi-1D bubbly cavitating nozzle flow solutions
NASA Astrophysics Data System (ADS)
Pasinlioglu, Senay; Delale, Can F.; Schnerr, Gunter H.
2009-04-01
Quasi-1D unsteady bubbly cavitating nozzle flows are considered by employing a homogeneous bubbly liquid flow model, where the non-linear dynamics of cavitating bubbles is described by a modified Rayleigh-Plesset equation. The various damping mechanisms are considered by a single damping coefficient lumping them together in the form of viscous dissipation and by assuming a polytropic law for the expansion and compression of the gas. The complete system of equations, by appropriate uncoupling, are then reduced to two evolution equations, one for the flow speed and the other for the bubble radius when all damping mechanisms are considered by a single damping coefficient. The evolution equations for the bubble radius and flow speed are then perturbed with respect to flow unsteadiness resulting in a coupled system of linear partial differential equations (PDEs) for the radius and flow speed perturbations. This system of coupled linear PDEs is then cast into an eigenvalue problem and the exact solution of the eigenvalue problem is found by normal mode analysis in the inlet region of the nozzle. Results show that the steady-state cavitating nozzle flow solutions are stable only for perturbations with very small wave numbers. The stable regions of the stability diagram for the inlet region of the nozzle are seen to be broadened by the effect of turbulent wall shear stress.
de Croon, Guido C H E
2016-01-07
The visual cue of optical flow plays an important role in the navigation of flying insects, and is increasingly studied for use by small flying robots as well. A major problem is that successful optical flow control seems to require distance estimates, while optical flow is known to provide only the ratio of velocity to distance. In this article, a novel, stability-based strategy is proposed for monocular distance estimation, relying on optical flow maneuvers and knowledge of the control inputs (efference copies). It is shown analytically that given a fixed control gain, the stability of a constant divergence control loop only depends on the distance to the approached surface. At close distances, the control loop starts to exhibit self-induced oscillations. The robot can detect these oscillations and hence be aware of the distance to the surface. The proposed stability-based strategy for estimating distances has two main attractive characteristics. First, self-induced oscillations can be detected robustly by the robot and are hardly influenced by wind. Second, the distance can be estimated during a zero divergence maneuver, i.e., around hover. The stability-based strategy is implemented and tested both in simulation and on board a Parrot AR drone 2.0. It is shown that the strategy can be used to: (1) trigger a final approach response during a constant divergence landing with fixed gain, (2) estimate the distance in hover, and (3) estimate distances during an entire landing if the robot uses adaptive gain control to continuously stay on the 'edge of oscillation.'
Global stability and control of the confined turbulent flow past a thick flat plate
NASA Astrophysics Data System (ADS)
Carini, M.; Airiau, C.; Debien, A.; Léon, O.; Pralits, J. O.
2017-02-01
This article investigates the structural stability and sensitivity properties of the confined turbulent wake behind an elongated D-shaped cylinder of aspect-ratio 10 at Re = 32 000. The stability analysis is performed by linearising the incompressible Navier-Stokes equations around the numerically computed and the experimentally measured mean flows. We found that the vortex-shedding frequency is very well captured by the leading unstable global mode, especially when the additional turbulent diffusion is modelled in the stability equations by means of a frozen eddy-viscosity approach. The sensitivity maps derived from the computed and the measured mean flows are then compared, showing a good qualitative agreement. The careful inspection of their spatial structure highlights that the highest sensitivity is attained not only across the recirculation bubble but also at the body blunt-edge, where tiny pockets of maximum receptivity are found. The impact of the turbulent diffusion on the obtained results is investigated. Finally, we show how the knowledge of the unstable adjoint global mode of the linearised mean-flow dynamics can be exploited to design an active feedback control of the unsteady turbulent wake, which leads, under the adopted numerical framework, to completely suppress its low-frequency oscillation.
Film stability in a vertical rotating tube with a core-gas flow.
NASA Technical Reports Server (NTRS)
Sarma, G. S. R.; Lu, P. C.; Ostrach, S.
1971-01-01
The linear hydrodynamic stability of a thin-liquid layer flowing along the inside wall of a vertical tube rotating about its axis in the presence of a core-gas flow is examined. The stability problem is formulated under the conditions that the liquid film is thin, the density and viscosity ratios of gas to liquid are small and the relative (axial) pressure gradient in the gas is of the same order as gravity. The resulting eigenvalue problem is first solved by a perturbation method appropriate to axisymmetric long-wave disturbances. The damped nature (to within the thin-film and other approximations made) of the nonaxisymmetric and short-wave disturbances is noted. In view of the limitations on a truncated perturbation solution when the disturbance wavenumber is not small, an initial value method using digital computer is presented. Stability characteristics of neutral, growing, and damped modes are presented showing the influences of rotation, surface tension, and the core-gas flow. Energy balance in a neutral mode is also illustrated.
Silver nanoparticle colloids with γ-cyclodextrin: enhanced stability and Gibbs-Marangoni flow
NASA Astrophysics Data System (ADS)
Amiri, Setareh; Duroux, Laurent; Larsen, Kim Lambertsen
2015-01-01
Although cyclodextrins (CD) are effective stabilizers for metal nanoparticle colloids, differences between α-, β- and γ-CD in stabilizing such colloids have not been previously reported. In this study, silver nanoparticles (AgNP) were synthesized using NaBH4 as reducing agent and cyclodextrins as stabilizers. Long-term stability of AgNP colloids in equilibrium conditions showed no marked differences between CD types. Transmission electron microscopy and quantitative image analysis revealed only marginal differences in particle sizes for CD-AgNP, although statistically significant. CD-AgNP colloids showed dispersed particles with average diameters of 7.3 ± 2.2, 6.3 ± 2.9 and 4.9 ± 1.9 nm for α-, β- and γ-CD, respectively, and with similar ζ-potentials about -25 to -30 mV. AgNP without CD showed bigger and aggregated particles of 15.0 ± 2.0 nm with lower ζ-potentials of about -40 mV. When subjected to centrifugal forces, i.e. non-equilibrium conditions, γ-CD was markedly more efficient than α- and β-CD in stabilizing the colloids. Drying patterns of colloid droplets showed a typical self-pinned coffee ring for all but the colloid stabilized by γ-CD, which showed a pattern resulting from a dominant Gibbs-Marangoni flow inside the drying droplet. Calculations using the Derjaguin, Landau, Verwey and Overbeek (DLVO) theory supported the stabilizing effect of CD in equilibrium conditions; it however did not provide clues for the superior stabilization by γ-CD in conditions of hydrodynamic stress.
Stability of a premixed flame in stagnation-point flow against general disturbances
NASA Technical Reports Server (NTRS)
Jackson, Thomas L.; Matalon, Moshe
1992-01-01
Previously, the stability of a premixed flame in a stagnation flow was discussed for a restricted class of disturbances that are self-similar to the basic undisturbed flow; thus, flame fronts with corrugations only in the cross stream direction were considered. Here, we consider a more general class of three-dimensional flame front perturbations which also permits corrugations in the streamwise direction. It is shown that, because of the stretch experienced by the flame, the hydrodynamic instability is limited only to disturbances of short wavelength. If in addition diffusion effects have a stabilizing influence, as would be the case of mixtures with Lewis number greater than one, a stretched flame could be absolutely stable. Instabilities occur when the Lewis number is below some critical value less than one. Neutral stability boundaries are presented in terms of the Lewis number, the strain rate, and the appropriate wavenumbers. Beyond the stability threshold, the two-dimensional self-similar modes always grow first. However, if disturbances of long wavelength are excluded, it is possible for the three-dimensional modes to be the least stable one. Accordingly, the pattern that will be observed on the flame front, at the onset of instability, will consist of either ridges in the direction of stretch or the more common three-dimensional cellular structure.
Asymptotic theory of neutral stability of the Couette flow of a vibrationally excited gas
NASA Astrophysics Data System (ADS)
Grigor'ev, Yu. N.; Ershov, I. V.
2017-01-01
An asymptotic theory of the neutral stability curve for a supersonic plane Couette flow of a vibrationally excited gas is developed. The initial mathematical model consists of equations of two-temperature viscous gas dynamics, which are used to derive a spectral problem for a linear system of eighth-order ordinary differential equations within the framework of the classical linear stability theory. Unified transformations of the system for all shear flows are performed in accordance with the classical Lin scheme. The problem is reduced to an algebraic secular equation with separation into the "inviscid" and "viscous" parts, which is solved numerically. It is shown that the thus-calculated neutral stability curves agree well with the previously obtained results of the direct numerical solution of the original spectral problem. In particular, the critical Reynolds number increases with excitation enhancement, and the neutral stability curve is shifted toward the domain of higher wave numbers. This is also confirmed by means of solving an asymptotic equation for the critical Reynolds number at the Mach number M ≤ 4.
Ground effects on the stability of separated flow around an airfoil at low Reynolds numbers
NASA Astrophysics Data System (ADS)
He, Wei; Yu, Peng; Li, Larry K. B.
2017-11-01
We perform a BiGlobal stability analysis on the separated flow around a NACA 4415 airfoil at low Reynolds numbers (Re = 300 - 1000) and a high angle of attack α =20° with a focus on the effect of the airfoil's proximity to a moving ground. The results show that the most dominant perturbation is the Kelvin-Helmholtz mode and that this traveling mode becomes less unstable as the airfoil approaches the ground, although this stabilizing effect diminishes with increasing Reynolds number. By performing a Floquet analysis, we find that this ground effect can also stabilize secondary instabilities. This numerical-theoretical study shows that the ground can have a significant influence on the stability of separated flow around an airfoil at low Reynolds numbers, which could have implications for the design of micro aerial vehicles and for the understanding of natural flyers such as insects and birds. This work was supported by the Research Grants Council of Hong Kong (Project No. 16235716 and 26202815) and the Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund (the second phase) under Grant No.U1501501.
Odier, Philippe; Ecke, Robert E.
2017-02-21
Stratified shear flows occur in many geophysical contexts, from oceanic overflows and river estuaries to wind-driven thermocline layers. In this study, we explore a turbulent wall-bounded shear flow of lighter miscible fluid into a quiescent fluid of higher density with a range of Richardson numbersmore » $$0.05\\lesssim Ri\\lesssim 1$$. In order to find a stability parameter that allows close comparison with linear theory and with idealized experiments and numerics, we investigate different definitions of$Ri$$. We find that a gradient Richardson number defined on fluid interface sections where there is no overturning at or adjacent to the maximum density gradient position provides an excellent stability parameter, which captures the Miles–Howard linear stability criterion. For small $$Ri$$ the flow exhibits robust Kelvin–Helmholtz instability, whereas for larger $$Ri$$ interfacial overturning is more intermittent with less frequent Kelvin–Helmholtz events and emerging Holmboe wave instability consistent with a thicker velocity layer compared with the density layer. We compute the perturbed fraction of interface as a quantitative measure of the flow intermittency, which is approximately 1 for the smallest $$Ri$$ but decreases rapidly as $$Ri$ increases, consistent with linear theory. For the perturbed regions, we use the Thorpe scale to characterize the overturning properties of these flows. The probability distribution of the non-zero Thorpe length yields a universal exponential form, suggesting that much of the overturning results from increasingly intermittent Kelvin–Helmholtz instability events. Finally, the distribution of turbulent kinetic energy, conditioned on the intermittency fraction, has a similar form, suggesting an explanation for the universal scaling collapse of the Thorpe length distribution.« less
Linear stability of layered two-phase flows through parallel soft-gel-coated walls
NASA Astrophysics Data System (ADS)
Dinesh, B.; Pushpavanam, S.
2017-07-01
The linear stability of layered two-phase Poiseuille flows through soft-gel-coated parallel walls is studied in this work. The focus is on determining the effect of the elastohydrodynamic coupling between the fluids and the soft-gel layers on the different instabilities observed in flows between parallel plates. The fluids are assumed Newtonian and incompressible, while the soft gels are modeled as linear viscoelastic solids. A long-wave asymptotic analysis is used to obtain an analytical expression for the growth rate of the disturbances. A Chebyshev collocation method is used to numerically solve the general linearized equations. Three distinct instability modes are identified in the flow: (a) a liquid-liquid long-wave mode; (b) a liquid-liquid short-wave mode; (c) a gel-liquid short-wave mode. The effect of deformability of the soft gels on these three modes is analyzed. From the long-wave analysis of the liquid-liquid mode a stability map is obtained, in which four different regions are clearly demarcated. It is shown that introducing a gel layer near the more viscous fluid has a predominantly stabilizing effect on this mode seen in flows between rigid plates. For parameters where this mode is stable for flow between rigid plates, introducing a gel layer near the less viscous and thinner fluid has a predominantly destabilizing effect. The liquid-liquid short-wave mode is destabilized by the introduction of soft-gel layers. Additional instability modes at the gel-liquid interfaces induced by the deformability of the soft-gel layers are identified. We show that these can be controlled by varying the thickness of the gel layers. Insights into the physical mechanism driving different instabilities are obtained using an energy budget analysis.
Dynamics and stability of two-potential flows in the porous media.
Markicevic, B; Bijeljic, B; Navaz, H K
2011-11-01
The experimental and numerical results of the capillary-force-driven climb of wetting liquid in porous media, which is opposed by the gravity force, are analyzed with respect to the emergence of a multiphase flow front and flow stability of the climbing liquid. Two dynamic characteristics are used: (i) the multiphase flow front thickness as a function of time, and (ii) the capillary number as a function of Bond number, where both numbers are calculated from the harmonic average of pores radii. Throughout the climb, the influence of capillary, gravity, and viscous force variations on the flow behavior is investigated for different porous media. For a specific porous medium, a unique flow front power law function of time is observed for the capillary flow climbs with or without gravity force. Distinct dynamic flow front power law functions are found for different porous media. However, for capillary climb in different porous media, one is able to predict a unique behavior for the wetting height (the interface between wetted and dry regions of porous medium) using the capillary and Bond number. It is found that these two numbers correlate as a unique exponential function, even for porous media whose permeabilities vary for two orders of magnitude. For climbs without the gravity force (capillary spreads), the initial climb dynamics follows this exponential law, but for later flow times and when a significant flow front is developed, one observes a constant value of the capillary number. Using this approach to describe the capillary climb, only the capillary versus Bond number correlation is needed, which is completely measureable from the experiments.
Stability and sensitivity analysis of hypersonic flow past a blunt cone
NASA Astrophysics Data System (ADS)
Nichols, Joseph W.; Cook, David; Brock, Joseph M.; Candler, Graham V.
2017-11-01
We investigate the effects of nosetip bluntness and low-level distributed roughness on instabilities leading to transition on a 7 degree half-angle blunt cone at Mach 10. To study the sensitivity of boundary layer instabilities to bluntness and roughness, we numerically extract Jacobian matrices directly from the unstructured hypersonic flow solver US3D. These matrices govern the dynamics of small perturbations about otherwise laminar base flows. We consider the frequency response of the resulting linearized dynamical system between different input and output locations along the cone, including close to the nosetip. Using adjoints, our method faithfully captures effects of complex geometry such as strong curvature and roughness that lead to flow acceleration and localized heating in this region. These effects violate the assumption of a slowly-varying base flow that underpins traditional linear stability analyses. We compare our results, which do not rely upon this assumption, to experimental measurements of a Mach 10 blunt cone taken at the AEDC Hypervelocity Ballistic Range G facility. In particular, we assess whether effects of complex geometry can explain discrepancies previously noted between traditional stability analysis and observations. This work is supported by the Office of Naval Research through Grant Number N00014-17-1-2496.
NASA Astrophysics Data System (ADS)
Rastegari, Amirreza; Akhavan, Rayhaneh
2017-11-01
The stability of the liquid/gas interfaces on SuperHydrophobic (SH) Longitudinal MicroGrooves (LMGs) in high Reynolds number turbulent flows of practical interest is investigated by analytical extrapolation of DNS results in turbulent channel flow at Reτ0 222 and 442 with SH LMGs at protrusion angle of θ = -30o . Given that the magnitude of pressure fluctuations in turbulent channel flow scales as prms+ √{ ln(Reτ) } , it is found that the stability limits of SH LMGs diminishes by factors of 4 when the Reynolds number of the base flow increases from Reτ0 200 of DNS to Reτ0 105 -106 of practical applications. For SH LMGs operating at Weber numbers of We+0 ≡ μuτ0 / σ 3 ×10-3 - 1.5 ×10-2 , corresponding to friction velocities of uτ0 0.2 - 1 m/s, this limits the size of stable LMGs to g+0 5 - 30 at Reτ0 105 and g+0 4 - 20 at Reτ0 106 , and the maximum drag reductions to DRmax 20 - 30 % at Reτ0 105 and DRmax 10 - 20 % at Reτ0 106 .
Stability of Brillouin flow in the presence of slow-wave structure
Simon, D. H.; Lau, Y. Y.; Greening, G.
2016-09-15
Including a slow-wave structure (SWS) on the anode in the conventional, planar, and inverted magnetron, we systematically study the linear stability of Brillouin flow, which is the prevalent flow in crossed-field devices. The analytic treatment is fully relativistic and fully electromagnetic, and it incorporates the equilibrium density profile, flow profile, and electric field and magnetic field profiles in the linear stability analysis. Using parameters similar to the University of Michigan's recirculating planar magnetron, the numerical data show that the resonant interaction of the vacuum circuit mode and the corresponding smooth-bore diocotron-like mode is the dominant cause for instability. This resonantmore » interaction is far more important than the intrinsic negative (positive) mass property of electrons in the inverted (conventional) magnetron geometry. It is absent in either the smooth-bore magnetron or under the electrostatic assumption, one or both of which was almost always adopted in prior analytical formulation. This resonant interaction severely restricts the wavenumber for instability to the narrow range in which the cold tube frequency of the SWS is within a few percent of the corresponding smooth bore diocotron-like mode in the Brillouin flow.« less
Shape and stability of dry spots left inside a flowing film
NASA Astrophysics Data System (ADS)
Limat, Laurent; Podgorski, Thomas; Flesselles, Jean-Marc; Jenffer, Patrice
1997-11-01
The stability to dewetting of liquid films spread on solid surfaces is of central importance in many technical applications. The case of ``static'' films (i.e. at rest when dewetting occurs) is now well known: condition of appearance of dry spots, growth kinetics... On the other hand, in many cases (heat exchangers for instance), dewetting occurs in presence of a mean flow (films driven by gravity). One observes in this case dry spots with well defined stationary shapes. We present experimental studies of dewetting of films flowing on inclined plates in situation of partial wetting (low Reynolds number, very low capillary number). These results point out evidences of a critical flow rate above which these dry spots become unstable (``healing'' or coating condition). We also discuss the shape and stability of the dry domains with a simple model based on an equilibrium between surface tension and the weight of the rim formed around each dry spot. Both the model and the experiment suggest a critical flow rate per unit length proportional to the capillary length times the capillary velocity.
NASA Astrophysics Data System (ADS)
Markeviciute, Vilda; White, Nicholas; Troian, Sandra
2017-11-01
Although spontaneous capillary flow can be an especially rapid process in slender open microchannels resembling V-grooves, enhanced flow control is possible through implementation of electric field distributions which generate opposing electrohydrodynamic pressures along the air/liquid interface to modulate the capillary pressures. Important fundamental work by Romero and Yost (1996) and Weislogel(1996) has elucidated the behavior of Newtonian films in slender V-grooves driven to flow solely by the streamwise change in capillary pressure due to the change in radius of curvature of the circular arc describing the interface of wetting or non-wetting fluids. Here we augment the Romero and Yost model with inclusion of Maxwell stresses for perfectly conducting wetting films and examine which electric field distributions allow formation of steady state film shapes for various inlet and outlet boundary conditions. We investigate the stability of these steady solutions to small perturbations in film thickness using a generalized stability analysis. These results reveal how the ratio of Maxwell to capillary stresses influences the degree of linearized transient growth or decay for thin films confined to flow within an open V-groove. Funding from the 2017 Caltech Summer Undergraduate Research Fellowship Program (Markeviciute) as well as a 2017 NASA Space Technology Research Fellowship (White) is gratefully acknowledged.
Stability of Brillouin flow in the presence of slow-wave structure
NASA Astrophysics Data System (ADS)
Simon, D. H.; Lau, Y. Y.; Greening, G.; Wong, P.; Hoff, B.; Gilgenbach, R. M.
2016-09-01
Including a slow-wave structure (SWS) on the anode in the conventional, planar, and inverted magnetron, we systematically study the linear stability of Brillouin flow, which is the prevalent flow in crossed-field devices. The analytic treatment is fully relativistic and fully electromagnetic, and it incorporates the equilibrium density profile, flow profile, and electric field and magnetic field profiles in the linear stability analysis. Using parameters similar to the University of Michigan's recirculating planar magnetron, the numerical data show that the resonant interaction of the vacuum circuit mode and the corresponding smooth-bore diocotron-like mode is the dominant cause for instability. This resonant interaction is far more important than the intrinsic negative (positive) mass property of electrons in the inverted (conventional) magnetron geometry. It is absent in either the smooth-bore magnetron or under the electrostatic assumption, one or both of which was almost always adopted in prior analytical formulation. This resonant interaction severely restricts the wavenumber for instability to the narrow range in which the cold tube frequency of the SWS is within a few percent of the corresponding smooth bore diocotron-like mode in the Brillouin flow.
Effect of pulse pressure on borehole stability during shear swirling flow vibration cementing.
Cui, Zhihua; Ai, Chi; Lv, Lei; Yin, Fangxian
2017-01-01
The shear swirling flow vibration cementing (SSFVC) technique rotates the downhole eccentric cascade by circulating cementing fluid. It makes the casing eccentrically revolve at high speed around the borehole axis. It produces strong agitation action to the annulus fluid, makes it in the state of shear turbulent flow, and results in the formation of pulse pressure which affects the surrounding rock stress. This study was focused on 1) the calculation of the pulse pressure in an annular turbulent flow field based on the finite volume method, and 2) the analysis of the effect of pulse pressure on borehole stability. On the upside, the pulse pressure is conducive to enhancing the liquidity of the annulus fluid, reducing the fluid gel strength, and preventing the formation of fluid from channeling. But greater pulse pressure may cause lost circulation and even formation fracturing. Therefore, in order to ensure smooth cementing during SSFVC, the effect of pulse pressure should be considered when cementing design.
NASA Technical Reports Server (NTRS)
Wernet, Mark P.; Skoch, Gary J.; Wernet, Judith H.
1995-01-01
Laser anemometry enables the measurement of complex flow fields via the light scattered from small particles entrained in the flow. In the study of turbomachinery, refractory seed materials are required for seeding the flow due to the high temperatures encountered. In this work we present a pH stabilization technique commonly employed in ceramic processing to obtain stable dispersions for generating aerosols of refractory seed material. By adding submicron alumina particles to a preadjusted pH solution of ethanol, a stable dispersion is obtained which when atomized, produces a high quality aerosol. Commercial grade alumina powder is used with a moderate size distribution. Other metal oxide powders in various polar solvents could also be used once the point of zero charge (pH(pzc)) of the powder in the solvent has been determined. Laser anemometry measurements obtained using the new seeding technique are compared to measurements obtained using Polystyrene Latex (PSL) spheres as the seed material.
A neural network-based power system stabilizer using power flow characteristics
Park, Y.M.; Choi, M.S.; Lee, K.Y.
1996-06-01
A neural network-based Power System Stabilizer (Neuro-PSS) is designed for a generator connected to a multi-machine power system utilizing the nonlinear power flow dynamics. The uses of power flow dynamics provide a PSS for a wide range operation with reduced size neutral networks. The Neuro-PSS consists of two neutral networks: Neuro-Identifier and Neuro-Controller. The low-frequency oscillation is modeled by the Neuro-Identifier using the power flow dynamics, then a Generalized Backpropagation-Thorough-Time (GBTT) algorithm is developed to train the Neuro-Controller. The simulation results show that the Neuro-PSS designed in this paper performs well with good damping in a wide operation range comparedmore » with the conventional PSS.« less
On the stability of a solid-body-rotation flow in a finite-length pip
NASA Astrophysics Data System (ADS)
Wang, Shixiao; Rusak, Zvi; Gong, Rui; Liu, Feng
2015-11-01
The three-dimensional, inviscid and viscous flow instability modes that appear on a solid-body rotation flow in a finite-length, straight, circular pipe are analyzed. This study is a direct extension of the Wang & Rusak (1996) analysis of axisymmetric instabilities on inviscid swirling flows in a pipe. We study a general mode of perturbation that satisfies the inlet, outlet and wall conditions of a flow in a finite-length pipe with a fixed-in-time and in-space vortex generator ahead of it. The eigenvalue problem for the growth rate and the shape of the perturbations for any azimuthal wave number m is solved numerically for all azimuthal wave number m. In the inviscid flow case, the m = 1 modes are the first to become unstable as the swirl ratio is increased and dominate the perturbation's growth in a certain range of swirl levels. In the viscous flow case, the neutral stability line is presented in a Reynolds number (Re) versus swirl ratio (ω) diagram and can be used to predict the first appearance of of axisymmetric or spiral instabilities as a function of Re and L. We will discuss and demonstrate the physical mechanism and evidences of the onset of the instability.
Non-modal stability in Hagen-Poiseuille flow of a Bingham fluid
NASA Astrophysics Data System (ADS)
Liu, Rong; Liu, Qiu Sheng
2014-01-01
Linear stability in Hagen-Poiseuille flow of a Bingham fluid is considered. Bingham fluid exhibits a yield stress in addition to a plastic viscosity. A Bingham number B, which describes the ratio of yield and viscous stresses, is used to characterize the behavior of Bingham-Hagen-Poiseuille flow. The effects of B on the stability are investigated using the energy method and the non-modal stability theory. The energy analysis shows that the non-axisymmetric disturbance has the lowest critical energy Reynolds number for all B. The global critical energy Reynolds number Reg increases with B. At sufficient large B, Reg has the order of B1/2. For the non-modal stability, we focus on response to external excitations and initial conditions. The former is studied by examining the ɛ-pseudospectrum, and the latter is by examining the energy growth function G(t). For the problem of response to external excitations, the maximum response is achieved by non-axisymmetric and streamwise uniform disturbances at the frequency of ω = 0, with a possible choice of the azimuthal wavenumbers of n = 1, 2, or 3. For the problem of response to initial conditions, it is found that there can be a rather large transient growth even though the linear operator of the Bingham-Hagen-Poiseuille flow has no unstable eigenvalue. For small B, the optimal disturbance is in the form of streamwise uniform vortices and streaks. For large B, the optimal disturbance is in the form of oblique waves. The optimal energy growth decreases and the optimal azimuthal wavenumber increases with the increase of B.
The stability of stratified spatially periodic shear flows at low Péclet number
Garaud, Pascale, E-mail: pgaraud@ucsc.edu; Gallet, Basile; Bischoff, Tobias
2015-08-15
This work addresses the question of the stability of stratified, spatially periodic shear flows at low Péclet number but high Reynolds number. This little-studied limit is motivated by astrophysical systems, where the Prandtl number is often very small. Furthermore, it can be studied using a reduced set of “low-Péclet-number equations” proposed by Lignières [“The small-Péclet-number approximation in stellar radiative zones,” Astron. Astrophys. 348, 933–939 (1999)]. Through a linear stability analysis, we first determine the conditions for instability to infinitesimal perturbations. We formally extend Squire’s theorem to the low-Péclet-number equations, which shows that the first unstable mode is always two-dimensional. Wemore » then perform an energy stability analysis of the low-Péclet-number equations and prove that for a given value of the Reynolds number, above a critical strength of the stratification, any smooth periodic shear flow is stable to perturbations of arbitrary amplitude. In that parameter regime, the flow can only be laminar and turbulent mixing does not take place. Finding that the conditions for linear and energy stability are different, we thus identify a region in parameter space where finite-amplitude instabilities could exist. Using direct numerical simulations, we indeed find that the system is subject to such finite-amplitude instabilities. We determine numerically how far into the linearly stable region of parameter space turbulence can be sustained.« less
Jet stability and wall impingement flow field in a thermal striping experiment
Lomperski, S.; Obabko, A.; Merzari, E.; Fischer, P.; Pointer, W. D.
2017-08-10
We present velocity and temperature field measurements for a 0.9 x 0.9 x 1.7 m glass tank in which two air jets at Re=10000 mix and impinge upon the lid at ambient temperature and pressure. Flow patterns are characterized across a 350 x 200 mm plane located 3 mm below the lid for two inlet geometries: 1) “extended”, in which inlet channels protrude above the tank base, and 2) “flush”, a flat base without protrusions. This minor geometry variation produced distinct changes in the lid flow field, appearing as three stagnant regions for the extended case and only one for flush. The dichotomy is attributed to system stability characteristics: jets are stable in the extended case and unstable for flush. In a separate set of nonisothermal tests, the impingement temperature field was measured for inlet temperature mismatches of 4 oC and jets near Re=10000. A 50 m-long fiber optic distributed temperature sensor positioned 2 mm below the lid measured at 1350 locations. Like the velocity fields, the temperature fields differ for the two inlet geometries: good thermal mixing for the flush case and subdued mixing for the extended case. Simulations with the spectral element code Nek5000 replicated the observed stability dichotomy, duplicating the number of stagnant regions observed in the experiment and matching their locations within ±10 mm. Simulation data suggests that flush case instability is due to interactions between jets and wall flows at the bottom of the tank. The clear flow dichotomy exhibited by this two-jet setup presents an unambiguous case to test the ability of CFD tools to predict subtle flow field changes driven by minor modifications in geometry in the context of thermal striping.
Jet stability and wall impingement flow field in a thermal striping experiment
Lomperski, S.; Obabko, A.; Merzari, E.; ...
2017-08-10
We present velocity and temperature field measurements for a 0.9 x 0.9 x 1.7 m glass tank in which two air jets at Re=10000 mix and impinge upon the lid at ambient temperature and pressure. Flow patterns are characterized across a 350 x 200 mm plane located 3 mm below the lid for two inlet geometries: 1) “extended”, in which inlet channels protrude above the tank base, and 2) “flush”, a flat base without protrusions. This minor geometry variation produced distinct changes in the lid flow field, appearing as three stagnant regions for the extended case and only one formore » flush. The dichotomy is attributed to system stability characteristics: jets are stable in the extended case and unstable for flush. In a separate set of nonisothermal tests, the impingement temperature field was measured for inlet temperature mismatches of 4 oC and jets near Re=10000. A 50 m-long fiber optic distributed temperature sensor positioned 2 mm below the lid measured at 1350 locations. Like the velocity fields, the temperature fields differ for the two inlet geometries: good thermal mixing for the flush case and subdued mixing for the extended case. Simulations with the spectral element code Nek5000 replicated the observed stability dichotomy, duplicating the number of stagnant regions observed in the experiment and matching their locations within ±10 mm. Simulation data suggests that flush case instability is due to interactions between jets and wall flows at the bottom of the tank. The clear flow dichotomy exhibited by this two-jet setup presents an unambiguous case to test the ability of CFD tools to predict subtle flow field changes driven by minor modifications in geometry in the context of thermal striping.« less
On the stability of surfactant-laden interfaces in thin-film shear flows
NASA Astrophysics Data System (ADS)
Kalogirou, Anna; Blyth, Mark
2017-11-01
In this study, we investigate the stability of a two-fluid shear flow with a surfactant-populated interface. The two fluids have in general different densities, viscosities and depths, but here we consider the case with one of the layers being very thin compared to the other. We therefore derive an asymptotic model in the thin-layer approximation, consisting of a set of nonlinear PDEs to describe the evolution of the film and interfacial surfactant disturbances. A novel feature is the presence of a nonlocal term due to multiphase coupling. Interfacial instabilities are induced due to the acting forces of gravity and inertia, as well as the action of Marangoni forces generated as a result of the dependence of surface tension on the local surfactant concentration. We find that in the inertialess limit, a stably stratified flow can become unstable if an insoluble surfactant is present at the interface. Inertial flows are known to be unstable in the absence of surfactant (due to density and viscosity stratification); yet, we identify regions in parameter space where stability is supported due to the existence of the surfactant monolayer at the interface. The destabilising mechanism related to the Marangoni forces will also be discussed. The work was funded by a Leverhulme Trust Early Career Fellowship.
Linear stability of the cylindrical Couette flow of a rarefied gas.
Yoshida, Hiroaki; Aoki, Kazuo
2006-02-01
A rarefied gas between two coaxial circular cylinders of infinite length, rotating with different angular velocities and kept at a common temperature, is considered. The stability of the circumferentially as well as axially uniform flow (cylindrical Couette flow) for circumferentially uniform small disturbances is investigated on the basis of kinetic theory. The linear-stability analysis is performed using the Bhatnagar-Gross-Krook model of the Boltzmann equation and the diffuse reflection condition on the cylinders. The maximum growth rate of the disturbances is determined numerically by solving the initial and boundary value problem for the disturbances for relatively small Knudsen numbers and wide ranges of angular velocities of the cylinders. As a result, the parameter range where the cylindrical Couette flow is unstable is clarified. The result is compared with the corresponding result based on the continuum model of the compressible Navier-Stokes type. A comparison is also made with the result of a direct numerical analysis of the original Boltzmann system, obtained by the direct simulation Monte Carlo method in previous papers as well as in the present study.
F-111 natural laminar flow glove flight test data analysis and boundary layer stability analysis
NASA Technical Reports Server (NTRS)
Runyan, L. J.; Navran, B. H.; Rozendaal, R. A.
1984-01-01
An analysis of 34 selected flight test data cases from a NASA flight program incorporating a natural laminar flow airfoil into partial wing gloves on the F-111 TACT airplane is given. This analysis determined the measured location of transition from laminar to turbulent flow. The report also contains the results of a boundary layer stability analysis of 25 of the selected cases in which the crossflow (C-F) and Tollmien-Schlichting (T-S) disturbance amplification factors are correlated with the measured transition location. The chord Reynolds numbers for these cases ranges from about 23 million to 29 million, the Mach numbers ranged from 0.80 to 0.85, and the glove leading-edge sweep angles ranged from 9 deg to 25 deg. Results indicate that the maximum extent of laminar flow varies from 56% chord to 9-deg sweep on the upper surface, and from 51% chord at 16-deg sweep to 6% chord at 25-deg sweep on the lower. The results of the boundary layer stability analysis indicate that when both C-F and T-S disturbances are amplified, an interaction takes place which reduces the maximum amplification factor of either type of disturbance that can be tolerated without causing transition.
Stability of haline density-driven flows in saturated heterogeneous media
NASA Astrophysics Data System (ADS)
Musuuza, Jude; Attinger, Sabine; Radu, Florin
2010-05-01
Density-driven flows occur in deep aquifers due to temperature differences and in coastal aquifers and refuse dumps due to solute concentration differences. Its relevance cuts across many practical applications like (normal and nuclear) waste repository management, exploitation of geothermal energy resources, enhanced oil recovery from aquifers and remediation of contaminated sites. A typical feature of density dependent flow problems is that they can become unstable (physically or numerically). A big challenge has been the absence of a general criterion that states whether flow is physically stable or unstable and the optimum computational grid resolution needed to solve the problem without creating numerical (artificial) instabilities. The homogenization theory ideas from [1] were extended in [2] to derive a stability criterion for density-driven flows in saturated homogeneous porous media. The criterion included the effects of density, viscosity and velocity but could not adequately predict the onset of fingering when velocity was varied. That study is extended here to include dispersive and medium heterogeneity effects. The specific objective is to answer the question: under what conditions do heterogeneities stabilise or destabilise flow? The homogenization theory ideas from [1] are again used to derive expressions for the elements of the macrodispersion tensor for flow aligned parallel to gravity. The dependency of the temporal evolution of the coefficients on the density contrast, heterogeneity variance, transverse dispersivity, anisotropy and correlation length are then investigated and the results checked against numerical simulations performed with the software toolbox d3 f. The work will be extended to include temperature effects and it is hoped that the ideas can be extended to flow in unsaturated soils. REFERENCES [1]Held, R., S. Attinger, and W. Kinzelbach (2005), Homogenization and effective parameters for the Henry problem in heterogeneous
Cockerham, L.G.; Doyle, T.F.; Pautler, E.L.; Hampton, J.D.
1986-01-01
Early transient incapacitation (ETI) is the complete cessation of performance during the first 30 min after radiation exposure, and performance decrement (PD) is a reduction in performance at the same time. Supralethal doses of radiation have been shown to produce a marked decrease in regional cerebral blood flow in primates concurrent with systemic hypotension and a dramatic release of mast-cell histamine. In an attempt to elucidate mechanisms underlying the radiation-induced ETI/PD phenomena and the postradiation decrease in cerebral blood flow, primates were given the mast-cell stabilizers disodium cromoglycate (DSCG) or BRL 22321 before exposure to 100 Gy whole-body gamma radiation. Hypothalamic and cortical blood flows were measured by hydrogen clearance, before and after radiation exposure. Systemic blood pressures were determined simultaneously. The data indicated that DSCG was successful in diminishing postradiation decrease in cerebral blood flow. Irradiated animals pretreated with DSCG, showed only a 10% decrease in hypothalamic blood flow 60 min postradiation, while untreated, irradiated animals showed a 57% decrease. The cortical blood flow of DSCG treated, irradiated animals showed a triphasic response, with a decrease of 38% at 10 min postradiation, then a rise to 1% below baseline at 20 min, followed by a fall to 42% below baseline by 50 min postradiation. In contrast, the untreated, irradiated animals showed a steady decrease in cortical blood flow to 79% below baseline by 50 min postradiation. There was no significant difference in blood-pressure response between the treated and untreated, irradiated animals. Systemic blood pressure showed a 60% decrease at 10 min postradiation, falling to a 71% decrease by 60 min.
NASA Astrophysics Data System (ADS)
Rostami, Ali Bakhshandeh; Fernandes, Antonio Carlos
2018-03-01
This paper is dedicated to develop a mathematical model that can simulate nonlinear phenomena of a hinged plate which places into the fluid flow (1 DOF). These phenomena are fluttering (oscillation motion), autorotation (continuous rotation) and chaotic motion (combination of fluttering and autorotation). Two mathematical models are developed for 1 DOF problem using two eminent mathematical models which had been proposed for falling plates (3 DOF). The procedures of developing these models are elaborated and then these results are compared to experimental data. The best model in the simulation of the phenomena is chosen for stability and bifurcation analysis. Based on these analyses, this model shows a transcritical bifurcation and as a result, the stability diagram and threshold are presented. Moreover, an analytical expression is given for finding the boundary of bifurcation from the fluttering to the autorotation.
Tutty, O.
2015-01-01
With the goal of providing the first example of application of a recently proposed method, thus demonstrating its ability to give results in principle, global stability of a version of the rotating Couette flow is examined. The flow depends on the Reynolds number and a parameter characterizing the magnitude of the Coriolis force. By converting the original Navier–Stokes equations to a finite-dimensional uncertain dynamical system using a partial Galerkin expansion, high-degree polynomial Lyapunov functionals were found by sum-of-squares of polynomials optimization. It is demonstrated that the proposed method allows obtaining the exact global stability limit for this flow in a range of values of the parameter characterizing the Coriolis force. Outside this range a lower bound for the global stability limit was obtained, which is still better than the energy stability limit. In the course of the study, several results meaningful in the context of the method used were also obtained. Overall, the results obtained demonstrate the applicability of the recently proposed approach to global stability of the fluid flows. To the best of our knowledge, it is the first case in which global stability of a fluid flow has been proved by a generic method for the value of a Reynolds number greater than that which could be achieved with the energy stability approach. PMID:26730219
Huang, D; Chernyshenko, S; Goulart, P; Lasagna, D; Tutty, O; Fuentes, F
2015-11-08
With the goal of providing the first example of application of a recently proposed method, thus demonstrating its ability to give results in principle, global stability of a version of the rotating Couette flow is examined. The flow depends on the Reynolds number and a parameter characterizing the magnitude of the Coriolis force. By converting the original Navier-Stokes equations to a finite-dimensional uncertain dynamical system using a partial Galerkin expansion, high-degree polynomial Lyapunov functionals were found by sum-of-squares of polynomials optimization. It is demonstrated that the proposed method allows obtaining the exact global stability limit for this flow in a range of values of the parameter characterizing the Coriolis force. Outside this range a lower bound for the global stability limit was obtained, which is still better than the energy stability limit. In the course of the study, several results meaningful in the context of the method used were also obtained. Overall, the results obtained demonstrate the applicability of the recently proposed approach to global stability of the fluid flows. To the best of our knowledge, it is the first case in which global stability of a fluid flow has been proved by a generic method for the value of a Reynolds number greater than that which could be achieved with the energy stability approach.
Solution techniques for transient stability-constrained optimal power flow – Part II
Geng, Guangchao; Abhyankar, Shrirang; Wang, Xiaoyu
2017-06-28
Transient stability-constrained optimal power flow is an important emerging problem with power systems pushed to the limits for economic benefits, dense and larger interconnected systems, and reduced inertia due to expected proliferation of renewable energy resources. In this study, two more approaches: single machine equivalent and computational intelligence are presented. Also discussed are various application areas, and future directions in this research area. In conclusion, a comprehensive resource for the available literature, publicly available test systems, and relevant numerical libraries is also provided.
Unique laminar-flow stability limit based shallow-water theory
Chen, Cheng-lung
1993-01-01
Two approaches are generally taken in deriving the stability limit for the Froude member (Fs) for laminar sheet flow. The first approach used the Orr-Sommerfeld equation, while the second uses the cross-section-averaged equations of continuity and motion. Because both approaches are based on shallow-water theory, the values of Fs obtained from both approaches should be identical, yet in the literature they are not. This suggests that a defect exists in at least one of the two approaches. After examining the governing equations used in both approaches, one finds that the existing cross-section -averaged equation of motion is dependent on the frame of reference.
Effects of Gravity and Shear on the Dynamics and Stability of Particulate and Multiphase Flows
NASA Technical Reports Server (NTRS)
Sangani, Ashor S.
1996-01-01
The main objectives of this project are to understand the differing particulate and multiphase flow behaviors that will occur in space and in Earth's gravity. More specifically, the project is concerned with understanding the effect of shear and gravity on two relatively ideal suspensions with significant inertial effects. The first is a gas-solid suspension at small Reynolds numbers and finite Stokes numbers. In this type of suspensions the inertia of the particle phase is significant while the hydrodynamic interactions are dominated by viscous forces in the suspending fluid. The other is a bubble suspension at small Weber and large Reynolds numbers. The hydrodynamic interactions in such suspensions are dominated by the inertial effects in the suspending fluid, but these inertial interactions can be described using potential flow theory. Our main objective is to examine the effects of shear and gravity on the average properties and stability of these two suspensions.
Stability and structure of fields of a flow with a hydrodynamic discontinuity
NASA Astrophysics Data System (ADS)
Ilyin, Dv; Goddard, Wa, III; Fukumoto, Y.; Abarzhi, Si
2017-10-01
We consider from a far field the evolution of a hydrodynamic discontinuity separating incompressible ideal fluids of different densities, with mass flow across this interface. By solving the boundary value problem and finding fundamental solutions of linearized dynamics, we directly link interface stability to structure of the flow fields. We find that classic Landau's system of equations for the Landau-Darrieus instability has a degenerate and singular character. Eliminating this degeneracy leads to appearance of a neutrally stable solution whose vortical field can seed the instability. We further find that the interface is stable if the flux of energy fluctuations produced by the perturbed interface is small compared to the flux of kinetic energy across the planar interface. The interface is unstable otherwise. Landau's solution is consistent with the latter case.
Stability and structure of fields in a flow with a hydrodynamic discontinuity
NASA Astrophysics Data System (ADS)
Ilyin, Daniil; Fukumoto, Yasuhide; Goddard, William; Abarzhi, Snezhana
2017-10-01
We consider from a far field the evolution of a hydrodynamic discontinuity separating incompressible ideal fluids of different densities, with mass flow across this interface. By solving the boundary value problem and finding fundamental solutions of linearized dynamics, we directly link interface stability to structure of the flow fields. We find that the classic Landau system of equations for the Landau-Darrieus instability has a degenerate and singular character. Eliminating this degeneracy leads to appearance of a neutrally stable solution whose vortical field can seed the instability. We further find that the interface is stable if the flux of energy fluctuations produced by the perturbed interface is small compared to the flux of specific kinetic energy across the planar interface. The interface is unstable if the energy fluctuations flux is large compared to the kinetic energy flux. Landau's solution is consistent with the latter case. Keywords: hydrodynamic instabilities, interfacial dynamics, mixing.
On the Nonlinear Stability of Plane Parallel Shear Flow in a Coplanar Magnetic Field
NASA Astrophysics Data System (ADS)
Xu, Lanxi; Lan, Wanli
2017-12-01
Lyapunov direct method has been used to study the nonlinear stability of laminar flow between two parallel planes in the presence of a coplanar magnetic field for streamwise perturbations with stress-free boundary planes. Two Lyapunov functions are defined. By means of the first, it is proved that the transverse components of the perturbations decay unconditionally and asymptotically to zero for all Reynolds numbers and magnetic Reynolds numbers. By means of the second, it is showed that the other components of the perturbations decay conditionally and exponentially to zero for all Reynolds numbers and the magnetic Reynolds numbers below π ^2/2M, where M is the maximum of the absolute value of the velocity field of the laminar flow.
A parametric study of supersonic laminar flow for swept wings using linear stability analysis
NASA Technical Reports Server (NTRS)
Cummings, Russell M.; Garcia, Joseph A.; Tu, Eugene L.
1995-01-01
A parametric study to predict the extent of laminar flow on the upper surface of a generic swept-back wing (NACA 64A010 airfoil section) at supersonic speeds was conducted. The results were obtained by using surface pressure predictions from an Euler/Navier-Stokes computational fluid dynamics code coupled with a boundary layer code, which predicts detailed boundary layer profiles, and finally with a linear stability code to determine the extent of laminar flow. The parameters addressed are Reynolds number, angle of attack, and leading-edge wing sweep. The results of this study show that an increase in angle of attack, for specific Reynolds numbers, can actually delay transition. Therefore, higher lift capability, caused by the increased angle of attack, as well as a reduction in viscous drag due to the delay in transition is possible for certain flight conditions.
NASA Astrophysics Data System (ADS)
Suttle, Lee; Lebedev, Sergey; Swadling, George; Suzuki-Vidal, Francisco; Burdiak, Guy; Bennett, Matthew; Hare, Jack; Burgess, David; Clemens, Adam; Niasse, Nicholas; Chittenden, Jerry; Smith, Roland; Bland, Simon; Patankar, Siddharth; Stuart, Nic
2014-10-01
We present first results from a new experimental platform designed to study the quasi-1D collision of counter-streaming plasma flows produced by the ablation from a pair of inverse wire array z pinches at the MAGPIE pulsed power facility. The flows are magnetized (B ~ 2 T, ReM ~ 100) and enter the interaction region with supersonic velocity (MS > 5, MMS > 3). The advected magnetic fields are perpendicular to the flow and aligned in anti-parallel directions, allowing studies of magnetic reconnection in a strongly driven regime. The setup allows parameters of the plasma to be measured in the reconnection region with a set of diagnostics which includes Thomson scattering, Faraday rotation, interferometry and detectors of energetic particles. The collisionality of the interaction and the relative role of the radiative cooling can be varied by choice of material of the colliding flows (e.g. Al or W).
Odier, Philippe; Ecke, Robert E.
2017-02-21
Stratified shear flows occur in many geophysical contexts, from oceanic overflows and river estuaries to wind-driven thermocline layers. In this study, we explore a turbulent wall-bounded shear flow of lighter miscible fluid into a quiescent fluid of higher density with a range of Richardson numbers
Montgomery, D.R.; Schmidt, K.M.; Dietrich, W.E.; McKean, J.
2009-01-01
The middle of a hillslope hollow in the Oregon Coast Range failed and mobilized as a debris flow during heavy rainfall in November 1996. Automated pressure transducers recorded high spatial variability of pore water pressure within the area that mobilized as a debris flow, which initiated where local upward flow from bedrock developed into overlying colluvium. Postfailure observations of the bedrock surface exposed in the debris flow scar reveal a strong spatial correspondence between elevated piezometric response and water discharging from bedrock fractures. Measurements of apparent root cohesion on the basal (Cb) and lateral (Cl) scarp demonstrate substantial local variability, with areally weighted values of Cb = 0.1 and Cl = 4.6 kPa. Using measured soil properties and basal root strength, the widely used infinite slope model, employed assuming slope parallel groundwater flow, provides a poor prediction of hydrologie conditions at failure. In contrast, a model including lateral root strength (but neglecting lateral frictional strength) gave a predicted critical value of relative soil saturation that fell within the range defined by the arithmetic and geometric mean values at the time of failure. The 3-D slope stability model CLARA-W, used with locally observed pore water pressure, predicted small areas with lower factors of safety within the overall slide mass at sites consistent with field observations of where the failure initiated. This highly variable and localized nature of small areas of high pore pressure that can trigger slope failure means, however, that substantial uncertainty appears inevitable for estimating hydrologie conditions within incipient debris flows under natural conditions. Copyright 2009 by the American Geophysical Union.
NASA Astrophysics Data System (ADS)
Stubbington, Rachel; Wood, Paul J.; Reid, Ian
2010-05-01
In lotic ecosystems, the most common disturbance events occur at the extremes of the hydrological continuum, i.e. spates and streambed drying. During spates, high flow velocities can mobilise sediments and displace invertebrates, and during streambed drying, loss of free water can cause mass mortality of many aquatic taxa. In both cases, invertebrates inhabiting the surface sediments are subject to a greater frequency and magnitude of disturbance than those in the hyporheic zone, and this habitat may therefore act as a refugium. Between extreme events, stable hydrological conditions allow competitive species to thrive, which can cause biotic interactions to increase. We compared the effects of flow extremes and hydrological stability on benthic and hyporheic invertebrate communities. Hydrological conditions included spates, flow recession, and localised streambed drying. During flow recession, competitive benthic taxa, particularly Gammarus pulex (Amphipoda) increased in abundance in surface sediments, causing community diversity to decline. A concurrent increase in the hyporheic abundance of G. pulex indicated that the hyporheic zone may act as a refugium from increasing biotic pressures in the benthic sediments. In contrast, spate events caused severe reductions in both benthic and hyporheic invertebrate abundance, and declines in G. pulex abundance were particularly pronounced; spate events were therefore important in increasing both benthic and hyporheic community diversity.
Stability of a density-change flow in the solidification of a ternary alloy
NASA Astrophysics Data System (ADS)
Guba, Peter; Anderson, Daniel
2017-11-01
We consider phase-change driven flow and solidification of a ternary (three-component) alloy. The ternary system is characterized by the formation of two distinct mushy layers (primary and secondary), distinguished by the number of components present in their solid phases. A primary layer has the solid phase composed of a single component and, beneath the primary layer, a secondary layer has the solid phase composed of two components. Generally, the densities of the liquid, primary solid and secondary solid phases during solidification are different, and these differences give rise to a flow of the interstitial liquid. We identify four different flow regimes dependent upon whether the two solid phases shrink or expand upon solidification. The stability of this density-change flow in the absence of buoyancy is studied numerically applying a spectral method. A simple power law is employed to describe the permeability of the ternary mushy layers, with a sensitivity of permeability to changes in porosity used as the control parameter. An instability is found to occur not only in the case of expansion but also contraction, an option that is apparently unavailable for the binary case. A reduced model is derived which contains the bare essentials required to capture this instability.
The stability of two-phase flow over a swept-wing
NASA Technical Reports Server (NTRS)
Coward, Adrian; Hall, Philip
1994-01-01
We use numerical and asymptotic techniques to study the stability of a two-phase air/water flow above a flat porous plate. This flow is a model of the boundary layer which forms on a yawed cylinder and can be used as a useful approximation to the air flow over swept wings during heavy rainfall. We show that the interface between the water and air layers can significantly destabilize the flow, leading to traveling wave disturbances which move along the attachment line. This instability occurs for lower Reynolds numbers than in the case of the absence of a water layer. We also investigate the instability of inviscid stationary modes. We calculate the effective wavenumber and orientation of the stationary disturbance when the fluids have identical physical properties. Using perturbation methods we obtain corrections due to a small stratification in viscosity, thus quantifying the interfacial effects. Our analytical results are in agreement with the numerical solution which we obtain for arbitrary fluid properties.
The stability of variable Atwood number flows with preferential heating in the lower layer
NASA Astrophysics Data System (ADS)
Kaiser, Bryan; Canfield, Jesse; Reisner, Jon
2017-11-01
The conditions for instability in a flow consisting of two miscible, horizontal fluid strata when the lower fluid is preferentially heated by volumetric energy deposition (VED) is insufficiently understood. The flow is an approximation of the mechanical behavior of fuel capsule plasma during the compression phase of inertial confinement fusion (ICF). If the plasma becomes unstable then ignition ceases. The motivation for this study is not only to assist ICF research, but also to explore the stability of a variable Atwood number flow that develops features resembling both Rayleigh-Taylor instability and Rayleigh-Bénard instability (RBI). We use simulations to show that the instability observed in experiments can be reproduced by a stationary, spatially-variable thermal forcing and we show that the observed RBI in the bottom layer is a flow feature rather than a byproduct of imperfect experimental conditions. Paradoxically, a model by other researchers predicted the time of instability in an experiment with 2% error using a model that assumes stationary forcing in the upper layer and linearly-growing-in-time forcing the lower layer. We discuss the paradox and present a new model for predicting the time of instability that accounts for spatially-variable VED.
Influence of foam on the stability characteristics of immiscible flow in porous media
NASA Astrophysics Data System (ADS)
van der Meer, J. M.; Farajzadeh, R.; Rossen, W. R.; Jansen, J. D.
2018-01-01
Accurate field-scale simulations of foam enhanced oil recovery are challenging, due to the sharp transition between gas and foam. Hence, unpredictable numerical and physical behavior is often observed, casting doubt on the validity of the simulation results. In this paper, a thorough stability analysis of the foam model is presented to validate the simulation results. We study the effect of a strongly non-monotonous total mobility function arising from foam models on the stability characteristics of the flow. To this end, we apply the linear stability analysis to nearly discontinuous relative permeability functions and compare the results with those of highly accurate numerical simulations. In addition, we present a qualitative analysis of the effect of different reservoir and fluid properties on the foam fingering behavior. In particular, we consider the effect of heterogeneity of the reservoir, injection rates, and foam quality. Relative permeability functions play an important role in the onset of fingering behavior of the injected fluid. Hence, we can deduce that stability properties are highly dependent on the non-linearity of the foam transition. The foam-water interface is governed by a very small total mobility ratio, implying a stable front. The transition between gas and foam, however, exhibits a huge total mobility ratio, leading to instabilities in the form of viscous fingering. This implies that there is an unstable pattern behind the front. We deduce that instabilities are able to grow behind the front but are later absorbed by the expanding wave. Moreover, the stability analysis, validated by numerical simulations, provides valuable insights about the important scales and wavelengths of the foam model. In this way, we remove the ambiguity regarding the effect of grid resolution on the convergence of the solutions. This insight forms an essential step toward the design of a suitable computational solver that captures all the appropriate scales, while
NASA Astrophysics Data System (ADS)
Craik, A. D. D.
1989-01-01
An account is given of those flows influenced by body forces that admit exact solutions similar to those identified by Craik and Criminale (1986) when body forces are absent. Bayly's (1986) inviscid Floquet stability analysis of elliptical flows is extended to incorporate a Coriolis force. With the exception of a narrow band of rotation speeds, it is found that elliptical-vortex flows are inviscidly unstable to three-dimensional plane-wave disturbances.
Field of Flow About a Jet and Effect of Jets on Stability of Jet-Propelled Airplanes
NASA Technical Reports Server (NTRS)
Ribner, Herbert S.
1946-01-01
A theoretical investigation was conducted on jet-induced flow deviation. Analysis is given of flow inclination induced outside cold and hot jets and jet deflection caused by angle of attack. Applications to computation of effects of jet on longitudinal stability and trim are explained. Effect of jet temperature on flow inclination was found small when thrust coefficient is used as criterion for similitude. The average jet-induced downwash over tail plane was obtained geometrically.
Using web-based observations to identify thresholds of a person's stability in a flow
NASA Astrophysics Data System (ADS)
Milanesi, L.; Pilotti, M.; Bacchi, B.
2016-10-01
Flood risk assessment and mitigation are important tasks that should take advantage of rational vulnerability models to increase their effectiveness. These models are usually identified through a relevant set of laboratory experiments. However, there is growing evidence that these tests are not fully representative of the variety of conditions that characterize real flood hazard situations. This paper suggests a citizen science-based and innovative approach to obtain information from web resources for the calibration of people's vulnerability models. A comprehensive study employing commonly used web engines allowed the collection of a wide set of documents showing real risk situations for people impacted by floods, classified according to the stability of the involved subjects. A procedure to extrapolate the flow depth and velocity from the video frames is developed and its reliability is verified by comparing the results with observation. The procedure is based on the statistical distribution of the population height employing a direct uncertainty propagation method. The results complement the experimental literature data and conceptual models. The growing availability of online information will progressively increase the sample size on which the procedure is based and will eventually lead to the identification of a probability surface describing the transition between stability and instability conditions of individuals in a flow.
NASA Technical Reports Server (NTRS)
Rozendaal, R. A.
1986-01-01
The linear boundary layer stability analyses and their correlation with data of 18 cases from a natural laminar flow (NLF) flight test program using a Cessna Citation 3 business jet are described. The transition point varied from 5% to 35% chord for these conditions, and both upper and lower wing surfaces were included. Altitude varied from 10,000 to 43,000 ft and Mach number from 0.3 to 0.8. Four cases were at nonzero sideslip. Although there was much scatter in the results, the analyses of boundary layer stability at the 18 conditions led to the conclusion that crossflow instability was the primary cause of transition. However, the sideslip cases did show some interaction of crossflow and Tollmien-Schlichting disturbances. The lower surface showed much lower Tollmien-Schlichting amplification at transition than the upper surface, but similar crossflow amplifications. No relationship between Mach number and disturbance amplification at transition could be found. The quality of these results is open to question from questionable wing surface quality, inadequate density of transition sensors on the wing upper surface, and an unresolved pressure shift in the wing pressure data. The results of this study show the need for careful preparation for transition experiments. Preparation should include flow analyses of the test surface, boundary layer disturbance amplification analyses, and assurance of adequate surface quality in the test area. The placement of necessary instruments and usefulness of the resulting data could largely be determined during the pretest phase.
NASA Astrophysics Data System (ADS)
Chatterjee, Krishnashis; Staples, Anne
2014-11-01
The effects of sinusoidal perturbations of the inner cylinder radius in the axial direction in a Taylor-Couette flow apparatus are studied. The base flow solution in the apparatus is derived and then linear stability analysis is performed using the wide gap approximation. The stability criteria are established based on the critical Taylor numbers which mark the transition from the purely circular base flow to the Taylor Vortex flow regime. The effects of varying the forcing wavelength and modulation amplitude on the stability criteria are investigated. The studies are conducted for different instability wave numbers and inner and outer cylinder rotational velocity combinations. The results are compared with those obtained in the same apparatus using a narrow gap assumption, and with the classical Taylor-Couette case.
Stability of Shapes Held by Surface Tension and Subjected to Flow
NASA Technical Reports Server (NTRS)
Chen, Yi-Ju; Robinson, Nathaniel D.; Steen, Paul H.
1999-01-01
Results of three problems are summarized in this contribution. Each involves the fundamental capillary instability of an interfacial bridge and is an extension of previous work. The first two problems concern equilibrium shapes of liquid bridges near the stability boundary corresponding to maximum length (Plateau-Rayleigh limit). For the first problem, a previously formulated nonlinear theory to account for imposed gravity and interfacial shear disturbances in an isothermal environment is quantitatively tested in experiment. For the second problem, the liquid bridge is subjected to a shear that models the effect of a thermocapillary flow generated by a ring heater in a liquid encapsulated float-zone configuration. In the absence of gravity, this symmetric perturbation can stabilize the bridge to lengths on the order of 30 percent beyond the Plateau-Rayleigh limit, which is on the order of heretofore unexplained Shuttle observations. The third problem considers the dynamics of collapse and pinchoff of a film bridge (no gravity), which happens in the absence of stabilization. Here, we summarize experimental efforts to measure the self-similar cone-and-crater structure predicted by a previous theory.
Stability of viscous film flow coating the interior of a vertical tube with a porous wall
NASA Astrophysics Data System (ADS)
Liu, Rong; Ding, Zijing
2017-05-01
The stability of the gravity-driven flow of a viscous film coating the inside of a tube with a porous wall is studied theoretically. We used Darcy's law to describe the motion of fluids in a porous medium. The Beaver-Joseph condition is used to describe the discontinuity of velocity at the porous-fluid interface. We derived an evolution equation for the film thickness using a long-wave approximation. The effect of velocity slip at the porous wall is identified by a parameter β . We examine the effect of β on the temporal stability, the absolute-convective instability (AI-CI), and the nonlinear evolution of the interface deformation. The results of the temporal stability reveal that the effect of velocity slip at the porous wall is destabilizing. The parameter β plays an important role in determining the AI-CI behavior and the nonlinear evolution of the interface. The presence of the porous wall promotes the absolute instability and the formation of the plug in the tube.
Stability and accuracy of free surface time integration in viscous flows
NASA Astrophysics Data System (ADS)
Rose, Ian; Buffett, Bruce; Heister, Timo
2017-01-01
Geodynamic simulations increasingly rely on models with a true free surface to investigate questions of dynamic topography, tectonic deformation, gravity perturbations, and global mantle convection. However, implementations of free surface boundary conditions have proven challenging from a standpoint of accuracy, robustness, and stability. In particular, time integration of a free surface tends to suffer from a numerical instability that manifests as sloshing surface motions, also known as the "drunken sailor" instability. This instability severely limits stable timestep sizes to those much smaller than can be used in geodynamic simulations without a free surface. Several schemes have been proposed in the literature to deal with these instabilities. Here we analyze the problem of creeping viscous flow with a free surface and discuss the origin of these instabilities. We demonstrate their cause and how existing stabilization schemes work to damp them out. We also propose a new scheme for removing instabilities from free surface calculations. It does not require modifications to the system matrix, nor additional variables, but is instead an explicit scheme based on nonstandard finite differences. It relies on a single stabilization parameter which may be identified with the smallest relaxation timescale of the free surface. Finally, we present numerical results to show the effectiveness of the new approach and discuss the free surface implementation in the open source, community based mantle convection software ASPECT.
NASA Astrophysics Data System (ADS)
Flemings, P. B.
2010-12-01
Integrated Ocean Drilling Program Expepedition 308 used direct measurements of pore pressure, analysis of hydromechanical properties, and geological analysis to illuminate how sedimentation, flow focusing, overpressure, and slope stability couple beneath the seafloor on the deepwater continental slope in the Gulf of Mexico. We used pore pressure penetrometers to measure severe overpressures (60% of the difference between lithostatic stress and hydrostatic pressure) that extend from the seafloor for 100’s of meters. We ran uniaxial consolidation experiments on whole core and found that although permeability is relatively high near the seafloor, the sediments are highly compressible. As a result, the coefficient of consolidation (the hydraulic diffusivity) is remarkably constant over a large range of effective stresses. This behavior accounts for the high overpressure that begins near the seafloor and extends to depth. Forward modeling suggests that flow is driven laterally along a permeable unit called the Blue Unit. Calculations suggest that soon after deposition, lateral flow lowered the effective stress and triggered the submarine landslides that we observe. Later in the evolution of this system, overpressure may have pre-conditioned the slope to failure by earthquakes. Results from IODP Expedition 308 illustrate how pore pressure and sedimentation control the large-scale form of continental margins, how submarine landslides form, and provide strategies for designing stable drilling programs.
Lehoucq, Richard B.; Salinger, Andrew G.
1999-08-01
We present an approach for determining the linear stability of steady states of PDEs on massively parallel computers. Linearizing the transient behavior around a steady state leads to a generalized eigenvalue problem. The eigenvalues with largest real part are calculated using Arnoldi's iteration driven by a novel implementation of the Cayley transformation to recast the problem as an ordinary eigenvalue problem. The Cayley transformation requires the solution of a linear system at each Arnoldi iteration, which must be done iteratively for the algorithm to scale with problem size. A representative model problem of 3D incompressible flow and heat transfer in a rotating disk reactor is used to analyze the effect of algorithmic parameters on the performance of the eigenvalue algorithm. Successful calculations of leading eigenvalues for matrix systems of order up to 4 million were performed, identifying the critical Grashof number for a Hopf bifurcation.
Stabilized Alumina/Ethanol Colloidal Dispersion for Seeding High Temperature Air Flows
NASA Technical Reports Server (NTRS)
Wernet, Judith H.; Wernet, Mark P.
1994-01-01
Seeding air flows with particles to enable measurements of gas velocities via laser anemometry and/or particle image velocimetry techniques can be quite exasperating. The seeding requirements are compounded when high temperature environments are encountered and special care must be used in selecting a refractory seed material. The pH stabilization techniques commonly employed in ceramic processing are used to obtain stable dispersions for generating aerosols of refractory seed material. By adding submicron alumina particles to a preadjusted pH solution of ethanol, a stable dispersion is obtained which when atomized produces a high quality aerosol. Commercial grade alumina powder is used with a moderate size distribution. The technique is not limited to alumina/ethanol and is also demonstrated with an alumina/H2O system. Other ceramic powders in various polar solvents could also be used once the point of zero charge (pH(sub pzc)) of the powder in the solvent has been determined.
On the transient settling of spheres and the stability of viscously heated viscoelastic flows
NASA Astrophysics Data System (ADS)
Becker, Leif Eric
This thesis is composed of three separate projects in the field of Non-Newtonian fluid mechanics. The first project consists of an experimental investigation of the motion of a sphere accelerating from rest along the centerline of a cylindrical tube filled with a polyisobutylene Boger fluid. Deborah numbers in the range 0.4/le De/le 11.7 are obtained, and the experimental results show transient velocity overshoots of up to fifty percent before the spheres approach their final constant settling velocity. Independent measurements of this settling velocity indicate significant drag increases at high De. In the second project, a reciprocal theorem is used to predict the steady three-dimensional creeping motion of a sphere sedimenting near a single vertical plane wall. Weak Non-Newtonian effects up to second order in Deborah number are calculated as are inertial effects up to first order in Reynolds number. At low Deborah numbers, the theoretical calculations indicate that fluid elasticity results in a migration of the sphere away from the wall and a drag decrease greater than that predicted in the unbounded case. Shear thinning in the fluid viscosity tends to cause the sphere to rotate more slowly, which may lead to 'anomalous' rotation at higher Deborah numbers. Inertial effects, on the other hand, cause no modification to the rotation speed, but do produce a drift velocity away from the wall. In addition, illustrative experiments are performed with spheres sedimenting through a polyacrylamide solution in a sufficiently large tank to focus on the interaction with a single vertical boundary. The third and final project provides an investigation of the linear stability of creeping plane Couette and Poiseuille flow with viscous heating for a non-isothermal formulation of the FENE-P constitutive model. Viscous heating is observed to have a destabilizing tendency at long to moderate disturbance wavelengths, and a stabilizing effect at short wavelengths, but no
Kolb, Gregory J [Albuquerque, NM
2012-02-07
A suction-recirculation device for stabilizing the flow of a curtain of blackened heat absorption particles falling inside of a solar receiver with an open aperture. The curtain of particles absorbs the concentrated heat from a solar mirror array reflected up to the receiver on a solar power tower. External winds entering the receiver at an oblique angle can destabilize the particle curtain and eject particles. A fan and ductwork is located behind the back wall of the receiver and sucks air out through an array of small holes in the back wall. Any entrained particles are separated out by a conventional cyclone device. Then, the air is recirculated back to the top of the receiver by injecting the recycled air through an array of small holes in the receiver's ceiling and upper aperture front wall. Since internal air is recirculated, heat losses are minimized and high receiver efficiency is maintained. Suction-recirculation velocities in the range of 1-5 m/s are sufficient to stabilize the particle curtain against external wind speeds in excess of 10 m/s.
Zhang, Jingjing; Shkrob, Ilya A.; Assary, Rajeev S.; Tung, Siu on; Silcox, Benjamin; Curtiss, Larry A.; Thompson, Levi; Zhang, Lu
2017-10-16
Catholyte materials are used to store positive charge in energized fluids circulating through redox flow batteries (RFBs) for electric grid and vehicle applications. Energy-rich radical cations (RCs) are being considered for use as catholyte materials, but to be practically relevant, these RCs (that are typically unstable, reactive species) need to have long lifetimes in liquid electrolytes under the ambient conditions. Only few families of such energetic RCs possess stabilities that are suitable for their use in RFBs; currently, the derivatives of 1,4- dialkoxybenzene look the most promising. In this study, we examine factors that define the chemical and electrochemical stabilities for RCs in this family. To this end, we engineered rigid bis-annulated molecules that by design avoid the two main degradation pathways for such RCs, viz. their deprotonation and radical addition. The decay of the resulting RCs are due to the single remaining reaction: O-dealkylation. We establish the mechanism for this reaction and examine factors controlling its rate. In particular, we demonstrate that this reaction is initiated by the nucleophile attack of the counter anion on the RC partner. The reaction proceeds through the formation of the aroxyl radicals whose secondary reactions yield the corresponding quinones. The O-dealkylation accelerates considerably when the corresponding quinone has poor solubility in the electrolyte, and the rate depends strongly on the solvent polarity. Our mechanistic insights suggest new ways of improving the RC catholytes through molecular engineering and electrolyte optimization.
Stability of finite difference approximations of two fluid, two phase flow equations
Holmes, Mark Alan
1995-01-01
It is well known that the basic single pressure, two fluid model for two phase flow has complex characteristics and is dynamically unstable. Nevertheless, common nuclear reactor thermal-hydraulics codes use variants of this model for reactor safety calculations. In these codes, the non-physical instabilities of the model may be damped by the numerical method and/or additional momentum interchange terms. Both of these effects are investigated using the linearized Von Neumann stability analysis. The stability of the semi-implicit method is of primary concern, because of its computational efficiency and popularity. It is shown that there is likely no completely stable numerical method, including fully implicit methods, for the basic single pressure model. Additionally, the momentum interchange terms commonly added to the basic single pressure model do not result in stable numerical methods for all the physically interesting reference conditions. Although practical stable approximations may be realized on a coarse computational grid, it is concluded that the assumption of instantaneously equilibrated phasic pressures must be relaxed in order to develop a generally stable numerical solution of a two fluid model. The numerical stability of the semi-implicit discretization of the true two pressure models of Ransom and Hicks, and Holm and Kupershmidt is analyzed. The semi-implicit discretization of these models, which possess real characteristics, are found to be numerically stable as long as certain convective limits are satisfied. Based on the form of these models, the general form of a numerically stable, basic two pressure model is proposed. The evolution equation required for closure is a volume fraction transport equation, which may possibly be determined based on void wave propagation considerations.
NASA Astrophysics Data System (ADS)
Douglas, Christopher; Smith, Travis; Emerson, Benjamin; Lieuwen, Timothy
2017-11-01
This work considers the linear hydrodynamic stability framework for reacting swirling jets in a premixed swirl combustor. In typical local stability analyses of such flows, a significant amount of the base flow field information is neglected by the parallel flow assumption, despite the often highly non-parallel nature of such flows. Implementation of a global stability analysis addresses this issue. However, global stability analysis requires suitable streamwise boundary conditions which are often non-trivial and/or physically dubious. Additionally, global stability methods are significantly more costly than weakly-global techniques which are based on solutions to a sequence of locally-parallel problems and linked using WKBJ theory. This motivates an effort to identify the pitfalls of locally-parallel methods and establish techniques for improved hydrodynamic modeling of spreading swirling jets without requiring the imposition of streamwise boundary conditions. Therefore, we analyze experimental combustor data to demonstrate the effects of non-parallelism that a locally-parallel analysis would neglect, and we propose a modified framework to address this issue. Air Force Office of Scientific Research (contract #FA9550-16-1-0442), contract monitor Dr. Chiping Li.
Stability of a gravity-driven thin electrolyte film flowing over a heated substrate.
Kumawat, Tara Chand; Vikram, Ajit; Tiwari, Naveen
2017-05-01
The stability of a thin electrolyte liquid film driven by gravity over a vertical substrate is presented. A film thickness evolution equation is derived and solved numerically. The substrate is non-uniformly heated from below which is modeled by imposing a temperature profile at the liquid-solid interface. The electrohydrodynamics is included in the model with Maxwell's stress tensor. The governing flow and energy equations are simplified using the lubrication approximation. The Poisson-Boltzmann equation with Debye-Hückel approximation is used for the potential which is generated inside the film due to a charged layer at the liquid-solid interface. The positive temperature gradient at the substrate leads to the formation of a thermocapillary ridge due to an opposing Marangoni stress. This thermocapillary ridge becomes unstable beyond critical parameters related to Marangoni stress and convective energy loss at the free surface. The electroosmotic flow has no effect on the base profile of the film, but enhances its instability. A parameter space is presented delineating the stable and unstable regimes for the film dynamics.
NASA Astrophysics Data System (ADS)
Aguilar-López, Juan Pablo; Bogaard, Thom
2017-04-01
The stability of soil composed dikes is often affected by high water and rainfall events. These loading conditions are often included in the stability assessment performed by designers and managers. These assessments are performed often by limit equilibrium methods such as Bishop or Spencer's as they have proven to be simpler to calculate and faster to compute with respect to finite element methods. However, the time dependent preferential flow effects cannot be included in the limit equilibrium methods as they do not allow the inclusion of the porous media flow effects. In addition, the initial conditions such as permeability anisotropy, initial water content and infiltration capacity are recognized as important features which may also influence the dike stability. The present study aimed to understand the effects of preferential flow in the stability assessment of a riverine dike. This was done by simulating a riverine dike as dual permeability conceptualization of the soil, based on a 2D Darcy-Richards numerical solution. With this model it was possible to identify which of the initial conditions affects the dike stability the most and how much it differs when compared to the results obtained with a limit equilibrium assessment. The results showed that the stability assessment may differ by as much as 10% when dual permeability effects are included and that changes in the permeability anisotropy influence the results the most.
Studies of Antarctic Ice Shelf Stability: Surface Melting, Basal Melting, and Ice Flow Dynamics
NASA Astrophysics Data System (ADS)
Alley, Karen E.
Floating extensions of ice sheets, known as ice shelves, play a vital role in regulating the rate of ice flow into the Southern Ocean from the Antarctic Ice Sheet. Shear stresses imparted by contact with islands, embayment walls, and other obstructions transmit "backstress" to grounded ice. Ice shelf collapse reduces or eliminates this backstress, increasing mass flux to the ocean and therefore rates of sea level rise. This dissertation presents studies that address three main factors that regulate ice shelf stability: surface melt, basal melt, and ice flow dynamics. The first factor, surface melt, is assessed using active microwave backscatter. Combined with measurements of annual melt, backscatter values provide insights into the state of the upper layers of the ice shelf, indicating whether melt ponds, which can destabilize ice shelves, are likely to form on the ice shelf surface. We present a map of the relative vulnerability of ice shelves to hydrofracture collapse caused by surface melt ponding. As many authors have recently performed large-scale assessments of basal melt, the second factor is addressed at a smaller scale, through the study of channels that form on the undersides of ice shelves. These basal channels are mapped using visible-band imagery, and shown statistically to be related to the presence of warm ocean water. Landsat imagery and ICESat laser altimetry provide evidence that basal channels can in some cases change very rapidly and cause weakening of ice shelf structures. The final study addresses the calculation of surface strain rates from velocity fields. This common calculation, which is integral to understanding of flow patterns and stresses on both grounded and floating ice, can be achieved using a variety of approaches. We examine two commonly used algorithms and the differences in results produced by the different methods. We also present a Matlab code for calculating strain rates and a data product of strain rates across the Antarctic
van der Linden, H J; Jellema, L C; Holwerda, M; Verpoorte, E
2006-08-01
In this paper we present our first results on the realization of stable water/octanol, two-phase flows inside poly(dimethylsiloxane) (PDMS) microchannels. Native PDMS microchannels were coated with high molecular weight polymers to change the surface properties of the microchannels and thus stabilize the laminar flow profile. The polymers poly(2-hydroxyethyl methacrylate), poly(vinyl pyrrolidone), poly(ethylene oxide), poly(ethylene glycol), and poly(vinyl alcohol) were assessed for their quality as stabilization coatings after deposition from flowing and stationary solutions. Additionally, the influence of coating the microchannels homogeneously with a single kind of polymer or heterogeneously with two different polymers was investigated. From the experimental observations, it can be concluded that homogeneous polymer coatings with poly(2-hydroxyethyl methacrylate) and poly(vinyl pyrrolidone) led to the effective stabilization of laminar water/octanol flows. Furthermore, heterogeneous coatings led to two-phase flows which had a better-defined and more stable interface over long distances (i.e., 40-mm-long microchannels). Finally, the partitioning of fuchsin dye in the coated microchannels was demonstrated, establishing the feasibility of the use of the polymer-coated PDMS microchannels for determination of logP values in laminar octanol/water flows.
Massively Parallel Linear Stability Analysis with P_ARPACK for 3D Fluid Flow Modeled with MPSalsa
Lehoucq, R.B.; Salinger, A.G.
1998-10-13
We are interested in the stability of three-dimensional fluid flows to small dkturbances. One computational approach is to solve a sequence of large sparse generalized eigenvalue problems for the leading modes that arise from discretizating the differential equations modeling the flow. The modes of interest are the eigenvalues of largest real part and their associated eigenvectors. We discuss our work to develop an effi- cient and reliable eigensolver for use by the massively parallel simulation code MPSalsa. MPSalsa allows simulation of complex 3D fluid flow, heat transfer, and mass transfer with detailed bulk fluid and surface chemical reaction kinetics.
NASA Astrophysics Data System (ADS)
Deng, Q.; Ginting, V.; McCaskill, B.; Torsu, P.
2017-10-01
We study the application of a stabilized continuous Galerkin finite element method (CGFEM) in the simulation of multiphase flow in poroelastic subsurfaces. The system involves a nonlinear coupling between the fluid pressure, subsurface's deformation, and the fluid phase saturation, and as such, we represent this coupling through an iterative procedure. Spatial discretization of the poroelastic system employs the standard linear finite element in combination with a numerical diffusion term to maintain stability of the algebraic system. Furthermore, direct calculation of the normal velocities from pressure and deformation does not entail a locally conservative field. To alleviate this drawback, we propose an element based post-processing technique through which local conservation can be established. The performance of the method is validated through several examples illustrating the convergence of the method, the effectivity of the stabilization term, and the ability to achieve locally conservative normal velocities. Finally, the efficacy of the method is demonstrated through simulations of realistic multiphase flow in poroelastic subsurfaces.
Linear stability of a circular Couette flow under a radial thermoelectric body force.
Yoshikawa, H N; Meyer, A; Crumeyrolle, O; Mutabazi, I
2015-03-01
The stability of the circular Couette flow of a dielectric fluid is analyzed by a linear perturbation theory. The fluid is confined between two concentric cylindrical electrodes of infinite length with only the inner one rotating. A temperature difference and an alternating electric tension are applied to the electrodes to produce a radial dielectrophoretic body force that can induce convection in the fluid. We examine the effects of superposition of this thermoelectric force with the centrifugal force including its thermal variation. The Earth's gravity is neglected to focus on the situations of a vanishing Grashof number such as microgravity conditions. Depending on the electric field strength and of the temperature difference, critical modes are either axisymmetric or nonaxisymmetric, occurring in either stationary or oscillatory states. An energetic analysis is performed to determine the dominant destabilizing mechanism. When the inner cylinder is hotter than the outer one, the circular Couette flow is destabilized by the centrifugal force for weak and moderate electric fields. The critical mode is steady axisymmetric, except for weak fields within a certain range of the Prandtl number and of the radius ratio of the cylinders, where the mode is oscillatory and axisymmetric. The frequency of this oscillatory mode is correlated with a Brunt-Väisälä frequency due to the stratification of both the density and the electric permittivity of the fluid. Under strong electric fields, the destabilization by the dielectrophoretic force is dominant, leading to oscillatory nonaxisymmetric critical modes with a frequency scaled by the frequency of the inner-cylinder rotation. When the outer cylinder is hotter than the inner one, the instability is again driven by the centrifugal force. The critical mode is axisymmetric and either steady under weak electric fields or oscillatory under strong electric fields. The frequency of the oscillatory mode is also correlated with the
NASA Technical Reports Server (NTRS)
Chambers, J. R.; Grafton, S. B.; Lutze, F. H.
1981-01-01
The test capabilities of the Stability Wind Tunnel of the Virginia Polytechnic Institute and State University are described, and calibrations for curved and rolling flow techniques are given. Oscillatory snaking tests to determine pure yawing derivatives are considered. Representative aerodynamic data obtained for a current fighter configuration using the curved and rolling flow techniques are presented. The application of dynamic derivatives obtained in such tests to the analysis of airplane motions in general, and to high angle of attack flight conditions in particular, is discussed.
Martoïa, F; Dumont, P J J; Orgéas, L; Belgacem, M N; Putaux, J-L
2016-02-14
In this study, we characterized and modeled the rheology of TEMPO-oxidized cellulose nanofibril (NFC) aqueous suspensions with electrostatically stabilized and unflocculated nanofibrous structures. These colloidal suspensions of slender and wavy nanofibers exhibited a yield stress and a shear thinning behavior at low and high shear rates, respectively. Both the shear yield stress and the consistency of these suspensions were power-law functions of the NFC volume fraction. We developed an original multiscale model for the prediction of the rheology of these suspensions. At the nanoscale, the suspensions were described as concentrated systems where NFCs interacted with the Newtonian suspending fluid through Brownian motion and long range fluid-NFC hydrodynamic interactions, as well as with each other through short range hydrodynamic and repulsive colloidal interaction forces. These forces were estimated using both the experimental results and 3D networks of NFCs that were numerically generated to mimic the nanostructures of NFC suspensions under shear flow. They were in good agreement with theoretical and measured forces for model colloidal systems. The model showed the primary role played by short range hydrodynamic and colloidal interactions on the rheology of NFC suspensions. At low shear rates, the origin of the yield stress of NFC suspensions was attributed to the combined contribution of repulsive colloidal interactions and the topology of the entangled NFC networks in the suspensions. At high shear rates, both concurrent colloidal and short (in some cases long) range hydrodynamic interactions could be at the origin of the shear thinning behavior of NFC suspensions.
Studies on stability in three-layer Hele-Shaw flows
NASA Astrophysics Data System (ADS)
Daripa, Prabir
2008-11-01
We consider a setup in a Hele-Shaw cell where a fluid of constant viscosity μl occupying a near-half-plane pushes a fluid of constant viscosity μ >μl occupying a layer of length L which in turn pushes another fluid of constant viscosity μr>μ occupying the right half-plane. The fluid upstream has a velocity U. Careful analysis of the dispersion relation arising from linear stability of the three-layer Hele-Shaw flow problem leads to the following specific analytical results all of which are strikingly independent of the length (L) of the middle layer: (i) a necessary and sufficient condition for modal instability; (ii) a critical viscosity of the middle layer that gives the shortest bandwidth of unstable waves; and (iii) a strict upper bound on the growth rate of instabilities, meaning that this upper bound is never reached and hence this upper bound can be improved upon. Results based on exact growth rates are presented which provides some insight into the instability transfer mechanism between interfaces as the parameters of the problem are varied. Numerical evidence that supports the effectiveness of the upper bound is also presented.
Yang, Yang; Zhou, Dandan; Xu, Zhengxue; Li, Aijun; Gao, Hang; Hou, Dianxun
2014-06-01
In this study, the possibility of using backwashed biofilm as seed in an aerobic granular sludge continuous-flow airlift fluidized bed (CAFB) reactor was investigated. After the addition of the inoculated backwashed biofilm, the start-up period of this reactor fed with municipal wastewater was reduced to 25 days, and aerobic granulation and stabilization were enhanced. At steady state, the chemical oxygen demand (COD) removal efficiency and nitrification efficiency were as high as 80-90 and 60 %, respectively. The CAFB was operated continuously and totally for 90 days, and its performance was much more stable when compared with system inoculated with activated sludge. Microbial distribution analyzed by fluorescence in situ hybridization (FISH) showed that the nitrite-oxidizing bacteria (NOB) and ammonium-oxidizing bacteria (AOB) were compatible with heterotrophic bacteria and distributed evenly throughout the granules. Such unique population distribution might be attributed to the low COD level and abundant dissolved oxygen in the entire granule as simulated by the mathematic models. Moreover, scanning electron microscopy revealed broad holes in the granules, which might promote the mass transfer of the nutrients from the surface to the center and enable simultaneous COD removal and nitrification. In conclusion, backwashed biofilm is an alternative seed of the conventional flocculent activated sludge in the aerobic granular sludge system to enhance carbonaceous oxidization and nitrification.
Zhang, Jingjing; Shkrob, Ilya A.; Assary, Rajeev S.
2017-10-16
Catholyte materials are used to store positive charge in energized fluids circulating through redox flow batteries (RFBs) for electric grid and vehicle applications. Energy-rich radical cations (RCs) are being considered for use as catholyte materials, but to be practically relevant, these RCs (that are typically unstable, reactive species) need to have long lifetimes in liquid electrolytes under the ambient conditions. Only few families of such energetic RCs possess stabilities that are suitable for their use in RFBs; currently, the derivatives of 1,4- dialkoxybenzene look the most promising. In this study, we examine factors that define the chemical and electrochemical stabilitiesmore » for RCs in this family. To this end, we engineered rigid bis-annulated molecules that by design avoid the two main degradation pathways for such RCs, viz. their deprotonation and radical addition. The decay of the resulting RCs are due to the single remaining reaction: O-dealkylation. We establish the mechanism for this reaction and examine factors controlling its rate. In particular, we demonstrate that this reaction is initiated by the nucleophile attack of the counter anion on the RC partner. The reaction proceeds through the formation of the aroxyl radicals whose secondary reactions yield the corresponding quinones. The O-dealkylation accelerates considerably when the corresponding quinone has poor solubility in the electrolyte, and the rate depends strongly on the solvent polarity. Our mechanistic insights suggest new ways of improving the RC catholytes through molecular engineering and electrolyte optimization.« less
NASA Technical Reports Server (NTRS)
Fowle, A. A.; Soto, L.; Strong, P. F.; Wang, C. A.
1980-01-01
A low Bond number simulation technique was used to establish the stability limits of cylindrical and conical floating liquid columns under conditions of isorotation, equal counter rotation, rotation of one end only, and parallel axis offset. The conditions for resonance in cylindrical liquid columns perturbed by axial, sinusoidal vibration of one end face are also reported. All tests were carried out under isothermal conditions with water and silicone fluids of various viscosities. A technique for the quantitative measurement of stream velocity within a floating, isothermal, liquid column confined between rotatable disks was developed. In the measurement, small, light scattering particles were used as streamline markers in common arrangement, but the capability of the measurement was extended by use of stereopair photography system to provide quantitative data. Results of velocity measurements made under a few selected conditions, which established the precision and accuracy of the technique, are given. The general qualitative features of the isothermal flow patterns under various conditions of end face rotation resulting from both still photography and motion pictures are presented.
NASA Astrophysics Data System (ADS)
Krishna Swamy, Aditya; Verma, Deepak; Ganesh, Rajaraman; Brunner, Stephan; Villard, Laurent
2016-10-01
Turbulent transport of energy, particles and momentum is one of the important limiting factors for long time plasma confinement. Modern study using gyrokinetic formalism and simulation has progressed to identify several microinstabilities that cause ion and electron thermal transport. Typically, these have been ballooning parity modes (φ is even and Ã∥ is odd) such as Ion Temperature Gradient mode (ITG), Kinetic Ballooning Mode (KBM) and Electron Temperature Gradient mode (ETG) which cause transport through fluctuations or tearing parity modes (φ is odd and Ã∥ is even) such as Microtearing modes (MTM) which change the local magnetic topology and cause transport through stochastization of the magnetic field. Here, the role of global safety factor profile variation on the MTM instability and global mode structure is studied in large aspect ratio tokamaks. Multiple subdominant branches of MTM are linearly unstable in several shear profiles. At lower shear, linearly unstable Mixed Parity Modes are found to exist. The growth rate spectrum, β-scaling in reverse shear profiles and the role of equilibrium flow on the stability and global mode structures of these modes will be presented.
NASA Astrophysics Data System (ADS)
Gogoi, Bidyut B.
2016-07-01
We have recently analyzed the global two-dimensional (2D) stability of the staggered lid-driven cavity (LDC) flow with a higher order compact (HOC) approach. In the analysis, critical parameters are determined for both the parallel and anti-parallel motion of the lids and a detailed analysis has been carried out on either side of the critical values. In this article, we carry out an investigation of flow stabilities inside a two-sided cross lid-driven cavity with a pair of opposite lids moving in both parallel and anti-parallel directions. On discretization, the governing 2D Navier-Stokes (N-S) equations describing the steady flow and flow perturbations results in a generalized eigenvalue problem which is solved for determining the critical parameters on four different grids. Elaborate computation is performed for a wide range of Reynolds numbers (Re) on either side of the critical values in the range 200 ⩽ Re ⩽ 10000. For flows below the critical Reynolds number Rec, our numerical results are compared with established steady-state results and excellent agreement is obtained in all the cases. For Reynolds numbers above Rec, phase plane and spectral density analysis confirmed the existence of periodic, quasi-periodic, and stable flow patterns.
Saeid Khalafvand, Seyed; Han, Hai-Chao
2015-06-01
It has been shown that arteries may buckle into tortuous shapes under lumen pressure, which in turn could alter blood flow. However, the mechanisms of artery instability under pulsatile flow have not been fully understood. The objective of this study was to simulate the buckling and post-buckling behaviors of the carotid artery under pulsatile flow using a fully coupled fluid-structure interaction (FSI) method. The artery wall was modeled as a nonlinear material with a two-fiber strain-energy function. FSI simulations were performed under steady-state flow and pulsatile flow conditions with a prescribed flow velocity profile at the inlet and different pressures at the outlet to determine the critical buckling pressure. Simulations were performed for normal (160 ml/min) and high (350 ml/min) flow rates and normal (1.5) and reduced (1.3) axial stretch ratios to determine the effects of flow rate and axial tension on stability. The results showed that an artery buckled when the lumen pressure exceeded a critical value. The critical mean buckling pressure at pulsatile flow was 17-23% smaller than at steady-state flow. For both steady-state and pulsatile flow, the high flow rate had very little effect (<5%) on the critical buckling pressure. The fluid and wall stresses were drastically altered at the location with maximum deflection. The maximum lumen shear stress occurred at the inner side of the bend and maximum tensile wall stresses occurred at the outer side. These findings improve our understanding of artery instability in vivo.
Saeid Khalafvand, Seyed; Han, Hai-Chao
2015-01-01
It has been shown that arteries may buckle into tortuous shapes under lumen pressure, which in turn could alter blood flow. However, the mechanisms of artery instability under pulsatile flow have not been fully understood. The objective of this study was to simulate the buckling and post-buckling behaviors of the carotid artery under pulsatile flow using a fully coupled fluid–structure interaction (FSI) method. The artery wall was modeled as a nonlinear material with a two-fiber strain-energy function. FSI simulations were performed under steady-state flow and pulsatile flow conditions with a prescribed flow velocity profile at the inlet and different pressures at the outlet to determine the critical buckling pressure. Simulations were performed for normal (160 ml/min) and high (350 ml/min) flow rates and normal (1.5) and reduced (1.3) axial stretch ratios to determine the effects of flow rate and axial tension on stability. The results showed that an artery buckled when the lumen pressure exceeded a critical value. The critical mean buckling pressure at pulsatile flow was 17–23% smaller than at steady-state flow. For both steady-state and pulsatile flow, the high flow rate had very little effect (<5%) on the critical buckling pressure. The fluid and wall stresses were drastically altered at the location with maximum deflection. The maximum lumen shear stress occurred at the inner side of the bend and maximum tensile wall stresses occurred at the outer side. These findings improve our understanding of artery instability in vivo. PMID:25761257
Stability of an accretion disk: nonlinear small-scale analysis of a quasi-Keplerian shear flow
NASA Astrophysics Data System (ADS)
Miquel, Benjamin; Knobloch, Edgar; Julien, Keith
2015-11-01
We model the background flow in the equatorial plane of an accretion disk with a radially stratified, non-magnetic zonal flow in a quasi-Keplerian balance (i.e. small pressure corrections are taken into account in the radial balance). The dynamics of the perturbations around this background flow obey a set of equations which main ingredients are: (i) a radial shear, (ii) a radial stratification, and (iii) a coupling between the flow and the background entropy gradient. The inviscid linear stability of this set of equation is first discussed: perturbations are decomposed into Kelvin modes (also known as the shearing sheet approximation) which amplitudes are determined analytically as a function of the radial stratification. Then, using as well a Kelvin modes decomposition, the viscous linear problem exhibits potentially transient growth, yet features unconditional stability as t --> ∞ . Finally, we demonstrate with 2D simulations of the viscous nonlinear problem that nonlinearities provide an energy transfer mechanism through modes that compensates the transfer induced by the linear shear. This mechanism allows for a sustained instability scenario despite the stability of the linear viscous problem.
NASA Astrophysics Data System (ADS)
Akcabay, Deniz Tolga; Xiao, Jian; Young, Yin Lu
2017-08-01
The growing interest to examine the hydroelastic dynamics and stabilities of lightweight and flexible materials requires robust and accurate fluid-structure interaction (FSI) models. Classically, partitioned fluid and structure solvers are easier to implement compared to monolithic methods; however, partitioned FSI models are vulnerable to numerical ("virtual added mass") instabilities for cases when the solid to fluid density ratio is low and if the flow is incompressible. As a partitioned method, the loosely hybrid coupled (LHC) method, which was introduced and validated in Young et al. (Acta Mech. Sin. 28:1030-1041, 2012), has been successfully used to efficiently and stably model lightweight and flexible structures. The LHC method achieves its numerical stability by, in addition to the viscous fluid forces, embedding potential flow approximations of the fluid induced forces to transform the partitioned FSI model into a semi-implicit scheme. The objective of this work is to derive and validate the numerical stability boundary of the LHC. The results show that the stability boundary of the LHC is much wider than traditional loosely coupled methods for a variety of numerical integration schemes. The results also show that inclusion of an estimate of the fluid inertial forces is the most critical to ensure the numerical stability when solving for fluid-structure interaction problems involving cases with a solid to fluid-added mass ratio less than one.
Combining slope stability and groundwater flow models to assess stratovolcano collapse hazard
NASA Astrophysics Data System (ADS)
Ball, J. L.; Taron, J.; Reid, M. E.; Hurwitz, S.; Finn, C.; Bedrosian, P.
2016-12-01
Flank collapses are a well-documented hazard at volcanoes. Elevated pore-fluid pressures and hydrothermal alteration are invoked as potential causes for the instability in many of these collapses. Because