Electronic circuitry development in a micropyrotechnic system for micropropulsion applications

NASA Astrophysics Data System (ADS)

Puig-Vidal, Manuel; Lopez, Jaime; Miribel, Pere; Montane, Enric; Lopez-Villegas, Jose M.; Samitier, Josep; Rossi, Carole; Camps, Thierry; Dumonteuil, Maxime

2003-04-01

An electronic circuitry is proposed and implemented to optimize the ignition process and the robustness of a microthruster. The principle is based on the integration of propellant material within a micromachined system. The operational concept is simply based on the combustion of an energetic propellant stored in a micromachined chamber. Each thruster contains three parts (heater, chamber, nozzle). Due to the one shot characteristic, microthrusters are fabricated in 2D array configuration. For the functioning of this kind of system, one critical point is the optimization of the ignition process as a function of the power schedule delivered by electronic devices. One particular attention has been paid on the design and implementation of an electronic chip to control and optimize the system ignition. Ignition process is triggered by electrical power delivered to a polysilicon resistance in contact with the propellant. The resistance is used to sense the temperature on the propellant which is in contact. Temperature of the microthruster node before the ignition is monitored via the electronic circuitry. A pre-heating process before ignition seems to be a good methodology to optimize the ignition process. Pre-heating temperature and pre-heating time are critical parameters to be adjusted. Simulation and experimental results will deeply contribute to improve the micropyrotechnic system. This paper will discuss all these point.

Two-fluid description of wave-particle interactions in strong Buneman turbulence

NASA Astrophysics Data System (ADS)

Che, H.

2014-06-01

To understand the nature of anomalous resistivity in magnetic reconnection, we investigate turbulence-induced momentum transport and energy dissipation while a plasma is unstable to the Buneman instability in force-free current sheets. Using 3D particle-in-cell simulations, we find that the macroscopic effects generated by wave-particle interactions in Buneman instability can be approximately described by a set of electron fluid equations. We show that both energy dissipation and momentum transport along electric current in the current layer are locally quasi-static, but globally dynamic and irreversible. Turbulent drag dissipates both the streaming energy of the current sheet and the associated magnetic energy. The net loss of streaming energy is converted into the electron component heat conduction parallel to the magnetic field and increases the electron Boltzmann entropy. The growth of self-sustained Buneman waves satisfies a Bernoulli-like equation that relates the turbulence-induced convective momentum transport and thermal momentum transport. Electron trapping and de-trapping drive local momentum transports, while phase mixing converts convective momentum into thermal momentum. The drag acts like a micro-macro link in the anomalous heating processes. The decrease of magnetic field maintains an inductive electric field that re-accelerates electrons, but most of the magnetic energy is dissipated and converted into the component heat of electrons perpendicular to the magnetic field. This heating process is decoupled from the heating of Buneman instability in the current sheets. Ion heating is weak but ions play an important role in assisting energy exchanges between waves and electrons. Cold ion fluid equations together with our electron fluid equations form a complete set of equations that describes the occurrence, growth, saturation and decay of the Buneman instability.

Investigation of merging/reconnection heating during solenoid-free startup of plasmas in the MAST Spherical Tokamak

NASA Astrophysics Data System (ADS)

Tanabe, H.; Yamada, T.; Watanabe, T.; Gi, K.; Inomoto, M.; Imazawa, R.; Gryaznevich, M.; Scannell, R.; Conway, N. J.; Michael, C.; Crowley, B.; Fitzgerald, I.; Meakins, A.; Hawkes, N.; McClements, K. G.; Harrison, J.; O'Gorman, T.; Cheng, C. Z.; Ono, Y.; The MAST Team

2017-05-01

We present results of recent studies of merging/reconnection heating during central solenoid (CS)-free plasma startup in the Mega Amp Spherical Tokamak (MAST). During this process, ions are heated globally in the downstream region of an outflow jet, and electrons locally around the X-point produced by the magnetic field of two internal P3 coils and of two plasma rings formed around these coils, the final temperature being proportional to the reconnecting field energy. There is an effective confinement of the downstream thermal energy, due to a thick layer of reconnected flux. The characteristic structure is sustained for longer than an ion-electron energy relaxation time, and the energy exchange between ions and electrons contributes to the bulk electron heating in the downstream region. The peak electron temperature around the X-point increases with toroidal field, but the downstream electron and ion temperatures do not change.

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

NASA Technical Reports Server (NTRS)

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

1988-01-01

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

Electron Bulk Acceleration and Thermalization at Earth's Quasiperpendicular Bow Shock.

PubMed

Chen, L-J; Wang, S; Wilson, L B; Schwartz, S; Bessho, N; Moore, T; Gershman, D; Giles, B; Malaspina, D; Wilder, F D; Ergun, R E; Hesse, M; Lai, H; Russell, C; Strangeway, R; Torbert, R B; F-Vinas, A; Burch, J; Lee, S; Pollock, C; Dorelli, J; Paterson, W; Ahmadi, N; Goodrich, K; Lavraud, B; Le Contel, O; Khotyaintsev, Yu V; Lindqvist, P-A; Boardsen, S; Wei, H; Le, A; Avanov, L

2018-06-01

Electron heating at Earth's quasiperpendicular bow shock has been surmised to be due to the combined effects of a quasistatic electric potential and scattering through wave-particle interaction. Here we report the observation of electron distribution functions indicating a new electron heating process occurring at the leading edge of the shock front. Incident solar wind electrons are accelerated parallel to the magnetic field toward downstream, reaching an electron-ion relative drift speed exceeding the electron thermal speed. The bulk acceleration is associated with an electric field pulse embedded in a whistler-mode wave. The high electron-ion relative drift is relaxed primarily through a nonlinear current-driven instability. The relaxed distributions contain a beam traveling toward the shock as a remnant of the accelerated electrons. Similar distribution functions prevail throughout the shock transition layer, suggesting that the observed acceleration and thermalization is essential to the cross-shock electron heating.

Electron Bulk Acceleration and Thermalization at Earth's Quasiperpendicular Bow Shock

NASA Astrophysics Data System (ADS)

Chen, L.-J.; Wang, S.; Wilson, L. B.; Schwartz, S.; Bessho, N.; Moore, T.; Gershman, D.; Giles, B.; Malaspina, D.; Wilder, F. D.; Ergun, R. E.; Hesse, M.; Lai, H.; Russell, C.; Strangeway, R.; Torbert, R. B.; F.-Vinas, A.; Burch, J.; Lee, S.; Pollock, C.; Dorelli, J.; Paterson, W.; Ahmadi, N.; Goodrich, K.; Lavraud, B.; Le Contel, O.; Khotyaintsev, Yu. V.; Lindqvist, P.-A.; Boardsen, S.; Wei, H.; Le, A.; Avanov, L.

2018-06-01

Electron heating at Earth's quasiperpendicular bow shock has been surmised to be due to the combined effects of a quasistatic electric potential and scattering through wave-particle interaction. Here we report the observation of electron distribution functions indicating a new electron heating process occurring at the leading edge of the shock front. Incident solar wind electrons are accelerated parallel to the magnetic field toward downstream, reaching an electron-ion relative drift speed exceeding the electron thermal speed. The bulk acceleration is associated with an electric field pulse embedded in a whistler-mode wave. The high electron-ion relative drift is relaxed primarily through a nonlinear current-driven instability. The relaxed distributions contain a beam traveling toward the shock as a remnant of the accelerated electrons. Similar distribution functions prevail throughout the shock transition layer, suggesting that the observed acceleration and thermalization is essential to the cross-shock electron heating.

Electron bulk acceleration and thermalization at Earth's quasi-perpendicular bow shock

NASA Astrophysics Data System (ADS)

Chen, L.-J.; Wang, S.; Wilson, L. B., III; Schwartz, S. J.; Bessho, N.; Moore, T. E.; Gershman, D. J.; Giles, B. L.; Malaspina, D. M.; Wilder, F. D.; Ergun, R. E.; Hesse, M.; Lai, H.; Russell, C. T.; Strangeway, R. J.; Torbert, R. B.; Vinas, A. F.-; Burch, J. L.; Lee, S.; Pollock, C.; Dorelli, J.; Paterson, W. R.; Ahmadi, N.; Goodrich, K. A.; Lavraud, B.; Le Contel, O.; Khotyaintsev, Yu. V.; Lindqvist, P.-A.; Boardsen, S.; Wei, H.; Le, A.; Avanov, L. A.

2018-05-01

Electron heating at Earth's quasiperpendicular bow shock has been surmised to be due to the combined effects of a quasistatic electric potential and scattering through wave-particle interaction. Here we report the observation of electron distribution functions indicating a new electron heating process occurring at the leading edge of the shock front. Incident solar wind electrons are accelerated parallel to the magnetic field toward downstream, reaching an electron-ion relative drift speed exceeding the electron thermal speed. The bulk acceleration is associated with an electric field pulse embedded in a whistler-mode wave. The high electron-ion relative drift is relaxed primarily through a nonlinear current-driven instability. The relaxed distributions contain a beam traveling toward the shock as a remnant of the accelerated electrons. Similar distribution functions prevail throughout the shock transition layer, suggesting that the observed acceleration and thermalization is essential to the cross-shock electron heating.

Laser-Material Interactions for Flexible Applications.

PubMed

Joe, Daniel J; Kim, Seungjun; Park, Jung Hwan; Park, Dae Yong; Lee, Han Eol; Im, Tae Hong; Choi, Insung; Ruoff, Rodney S; Lee, Keon Jae

2017-07-01

The use of lasers for industrial, scientific, and medical applications has received an enormous amount of attention due to the advantageous ability of precise parameter control for heat transfer. Laser-beam-induced photothermal heating and reactions can modify nanomaterials such as nanoparticles, nanowires, and two-dimensional materials including graphene, in a controlled manner. There have been numerous efforts to incorporate lasers into advanced electronic processing, especially for inorganic-based flexible electronics. In order to resolve temperature issues with plastic substrates, laser-material processing has been adopted for various applications in flexible electronics including energy devices, processors, displays, and other peripheral electronic components. Here, recent advances in laser-material interactions for inorganic-based flexible applications with regard to both materials and processes are presented. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Transient thermal and nonthermal electron and phonon relaxation after short-pulsed laser heating of metals

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

Giri, Ashutosh; Hopkins, Patrick E., E-mail: phopkins@virginia.edu

2015-12-07

Several dynamic thermal and nonthermal scattering processes affect ultrafast heat transfer in metals after short-pulsed laser heating. Even with decades of measurements of electron-phonon relaxation, the role of thermal vs. nonthermal electron and phonon scattering on overall electron energy transfer to the phonons remains unclear. In this work, we derive an analytical expression for the electron-phonon coupling factor in a metal that includes contributions from equilibrium and nonequilibrium distributions of electrons. While the contribution from the nonthermal electrons to electron-phonon coupling is non-negligible, the increase in the electron relaxation rates with increasing laser fluence measured by thermoreflectance techniques cannot bemore » accounted for by only considering electron-phonon relaxations. We conclude that electron-electron scattering along with electron-phonon scattering have to be considered simultaneously to correctly predict the transient nature of electron relaxation during and after short-pulsed heating of metals at elevated electron temperatures. Furthermore, for high electron temperature perturbations achieved at high absorbed laser fluences, we show good agreement between our model, which accounts for d-band excitations, and previous experimental data. Our model can be extended to other free electron metals with the knowledge of the density of states of electrons in the metals and considering electronic excitations from non-Fermi surface states.« less

Alpha heating and isotopic mass effects in JET plasmas with sawteeth

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

Budny, R. V.; Team, JET

2016-02-09

The alpha heating experiment in the Joint European Torus (JET) 1997 DTE1 campaign is re-examined. Several effects correlated with tritium content and thermal hydrogenic isotopic mass < A> weaken the conclusion that alpha heating was clearly observed. These effects delayed the occurrence of significant sawtooth crashes allowing the electron and ion temperatures T e and T i to achieve higher values. Under otherwise equal circumstances T e and T i were typically higher for discharges with higher < A >, and significant scaling of T i, T e, and total stored energy with < A > were observed. The highermore » T i led to increased ion–electron heating rates with magnitudes comparable to those computed for alpha electron heating. Rates of other heating/loss processes also had comparable magnitudes. Simulations of T e assuming the observed scaling of T i are qualitatively consistent with the measured profiles, without invoking alpha heating« less

Simplified calculation procedure of a latent heat reservoir for stabilizing the temperature of electronic devices

NASA Astrophysics Data System (ADS)

Witzman, S.; Shitzer, A.; Zvirin, Y.

A simple mathematical algorithm which facilitates the design of a latent heat reservoir for stabilizing the temperature of an inflight electronic device is developed, and the behavior of paraffin wax in a heat storage capacitor is experimentally studied. The results show that in the solidification stage the heat transfer coefficient h is smaller than 35 W/sq m - C and decreases with time. During the melting process, natural convection could significantly increase h on the internal side and thereby reduce the time required to melt the section compared to the conduction process alone. Values of h up to 60 W/sq m - C can be achieved. The correlation between experimental and theoretical results is good.

Single-molecule electronics: Cooling individual vibrational modes by the tunneling current.

PubMed

Lykkebo, Jacob; Romano, Giuseppe; Gagliardi, Alessio; Pecchia, Alessandro; Solomon, Gemma C

2016-03-21

Electronic devices composed of single molecules constitute the ultimate limit in the continued downscaling of electronic components. A key challenge for single-molecule electronics is to control the temperature of these junctions. Controlling heating and cooling effects in individual vibrational modes can, in principle, be utilized to increase stability of single-molecule junctions under bias, to pump energy into particular vibrational modes to perform current-induced reactions, or to increase the resolution in inelastic electron tunneling spectroscopy by controlling the life-times of phonons in a molecule by suppressing absorption and external dissipation processes. Under bias the current and the molecule exchange energy, which typically results in heating of the molecule. However, the opposite process is also possible, where energy is extracted from the molecule by the tunneling current. Designing a molecular "heat sink" where a particular vibrational mode funnels heat out of the molecule and into the leads would be very desirable. It is even possible to imagine how the vibrational energy of the other vibrational modes could be funneled into the "cooling mode," given the right molecular design. Previous efforts to understand heating and cooling mechanisms in single molecule junctions have primarily been concerned with small models, where it is unclear which molecular systems they correspond to. In this paper, our focus is on suppressing heating and obtaining current-induced cooling in certain vibrational modes. Strategies for cooling vibrational modes in single-molecule junctions are presented, together with atomistic calculations based on those strategies. Cooling and reduced heating are observed for two different cooling schemes in calculations of atomistic single-molecule junctions.

Influence of dimension parameters of the gravity heat pipe on the thermal performance

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

Kosa, Ľuboš, E-mail: lubos.kosa@fstroj.uniza.sk; Nemec, Patrik, E-mail: patrik.nemec@fstroj.uniza.sk; Jobb, Marián, E-mail: marian.jobb@fstroj.uniza.sk

Currently the problem with the increasing number of electronic devices is a problem with the outlet Joule heating. Joule heating, also known as ohmic heating and resistive heating, is the process by which the passage of an electric current through a conductor releases heat. Perfect dustproof cooling of electronic components ensures longer life of the equipment. One of more alternatives of heat transfer without the using of mechanical equipment is the use of the heat pipe. Heat pipes are easy to manufacture and maintenance of low input investment cost. The advantage of using the heat pipe is its use inmore » hermetic closed electronic device which is separated exchange of air between the device and the environment. This experiment deals with the influence of changes in the working tube diameter and changing the working fluid on performance parameters. Changing the working fluid and the tube diameter changes the thermal performance of the heat pipe. The result of this paper is finding the optimal diameter with ideal working substance for the greatest heat transfer for 1cm{sup 2} sectional area tube.« less

Electron temperature gradient scale at collisionless shocks.

PubMed

Schwartz, Steven J; Henley, Edmund; Mitchell, Jeremy; Krasnoselskikh, Vladimir

2011-11-18

Shock waves are ubiquitous in space and astrophysics. They transform directed flow energy into thermal energy and accelerate energetic particles. The energy repartition is a multiscale process related to the spatial and temporal structure of the electromagnetic fields within the shock layer. While large scale features of ion heating are known, the electron heating and smaller scale fields remain poorly understood. We determine for the first time the scale of the electron temperature gradient via electron distributions measured in situ by the Cluster spacecraft. Half of the electron heating coincides with a narrow layer several electron inertial lengths (c/ω(pe)) thick. Consequently, the nonlinear steepening is limited by wave dispersion. The dc electric field must also vary over these small scales, strongly influencing the efficiency of shocks as cosmic ray accelerators.

Heat pipes. [technology utilization

NASA Technical Reports Server (NTRS)

1975-01-01

The development and use of heat pipes are described, including space requirements and contributions. Controllable heat pipes, and designs for automatically maintaining a selected constant temperature, are discussed which would add to the versatility and usefulness of heat pipes in industrial processing, manufacture of integrated circuits, and in temperature stabilization of electronics.

Free suspension processing of oxides to form amorphous oxide materials, appendix B

NASA Technical Reports Server (NTRS)

Wouch, G.

1973-01-01

The processing of yttria, zirconia, and alumina under weightless conditions is discussed. The process consists of levitation or position control, heating and melting, superheating, and supercooling. The use of arc imaging furnaces, lasers, induction heating, microwave, and electron beam methods are analyzed to show the advantages and disadvantages of each.

The role of defects in Fe(II) – goethite electron transfer

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

Andrade de Notini, Luiza; Latta, Drew; Neumann, Anke

Despite accumulating experimental evidence for Fe(II)-Fe(III) oxide electron transfer, computational chemical calculations suggest that oxidation of sorbed Fe(II) is not energetically feasible unless defects are present. Here we used isotope specific 57Fe Mössbauer spectroscopy to investigate whether Fe(II)-goethite electron transfer is influenced by defects. Specifically, we heated the mineral to try to anneal the goethite surface and ground goethite to try to create defects. We found that heating goethite results in less oxidation of sorbed Fe(II) by goethite. When goethite was re-ground after heating, electron transfer was partially restored. X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) ofmore » heated and ground goethite confirm that heating and grinding alter the surface structure of the goethite. We propose that the heating process annealed the surface and decreased the number of sites where electron transfer could occur. Our experimental findings suggest that surface defects play an important role in Fe(II)-goethite electron transfer as suggested by computational calculations. Our finding that defects influence heterogeneous Fe(II)-goethite electron transfer has important implications for Fe(II) driven recrystallization of Fe oxides, as well as X and Y.« less

Adsorbate hopping via vibrational-mode coupling induced by femtosecond laser pulses

NASA Astrophysics Data System (ADS)

Ueba, H.; Hayashi, M.; Paulsson, M.; Persson, B. N. J.

2008-09-01

We study the heat transfer from femtosecond laser-heated hot electrons in a metal to adsorbates in the presence of vibrational-mode coupling. The theory is successfully applied to the experimental result of atomic oxygen hopping on a vicinal Pt(111) surface. The effective friction coupling between hot electrons and the vibrational mode relevant to the hopping motion depends on the transient temperature of the partner mode excited by hot electrons. The calculated two-pulse correlation and fluence dependence of the hopping probability reproduce the experimental results, which were previously analyzed using the hot-electron temperature (Te) -dependent friction ηa(Te) in a conventional heat transfer equation. A possible elementary process behind such a hypothetic modeling using ηa(Te) is discussed in terms of an indirect heating of the vibrational mode for hopping at the surface.

First experimental demonstration of magnetic-field assisted fast heating of a dense plasma core

NASA Astrophysics Data System (ADS)

Fujioka, Shinsuke; Sakata, Shohei; Lee, Seung Ho; Matsuo, Kazuki; Sawada, Hiroshi; Iwasa, Yuki; Law, King Fai Farley; Morita, Hitoki; Kojima, Sadaoki; Abe, Yuki; Yao, Akira; Hata, Masayasu; Johzaki, Tomoyuki; Sunahara, Atsushi; Ozaki, Tetsuo; Sakagami, Hitoshi; Morace, Alessio; Arikawa, Yasunobu; Yogo, Akifumi; Nishimura, Hiroaki; Nakai, Mitsuo; Shiraga, Hiroyuki; Sentoku, Yasuhiko; Nagatomo, Hideo; Azechi, Hiroshi; Firex Project Team

2016-10-01

Fast heating of a dense plasma core by an energetic electron beam is being studied on GEKKO-LFEX laser facility. Here, we introduce a laser-driven kilo-tesla external magnetic field to guide the diverging electron beam to the dense plasma core. This involve placing a spherical target in the magnetic field, compressing it with the GEKKO-XII laser beams and then using the LFEX laser beams injected into the dense plasma to generate the electron beam which do the fast heating. Cu-Ka emission is used to visualize transport or heating processes of a dense plasma. X-ray spectrum from a highly ionized Cu ions indicates several keV of the temperature increment induced by the LFEX.

Electron Transport Modeling of Molecular Nanoscale Bridges Used in Energy Conversion Schemes

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

Dunietz, Barry D

2016-08-09

The goal of the research program is to reliably describe electron transport and transfer processes at the molecular level. Such insight is essential for improving molecular applications of solar and thermal energy conversion. We develop electronic structure models to study (1) photoinduced electron transfer and transport processes in organic semiconducting materials, and (2) charge and heat transport through molecular bridges. We seek fundamental understanding of key processes, which lead to design new experiments and ultimately to achieve systems with improved properties.

Thomson scattering diagnostics of thermal plasmas: Laser heating of electrons and the existence of local thermodynamic equilibrium.

PubMed

Murphy, A B

2004-01-01

A number of assessments of electron temperatures in atmospheric-pressure arc plasmas using Thomson scattering of laser light have recently been published. However, in this method, the electron temperature is perturbed due to strong heating of the electrons by the incident laser beam. This heating was taken into account by measuring the electron temperature as a function of the laser pulse energy, and linearly extrapolating the results to zero pulse energy to obtain an unperturbed electron temperature. In the present paper, calculations show that the laser heating process has a highly nonlinear dependence on laser power, and that the usual linear extrapolation leads to an overestimate of the electron temperature, typically by 5000 K. The nonlinearity occurs due to the strong dependence on electron temperature of the absorption of laser energy and of the collisional and radiative cooling of the heated electrons. There are further problems in deriving accurate electron temperatures from laser scattering due to necessary averages that have to be made over the duration of the laser pulse and over the finite volume from which laser light is scattered. These problems are particularly acute in measurements in which the laser beam is defocused in order to minimize laser heating; this can lead to the derivation of electron temperatures that are significantly greater than those existing anywhere in the scattering volume. It was concluded from the earlier Thomson scattering measurements that there were significant deviations from equilibrium between the electron and heavy-particle temperatures at the center of arc plasmas of industrial interest. The present calculations indicate that such deviations are only of the order of 1000 K in 20 000 K, so that the usual approximation that arc plasmas are approximately in local thermodynamic equilibrium still applies.

Influence of the heat transfer on the thermoelastic response of metals on heating by the laser pulse

NASA Astrophysics Data System (ADS)

Sudenkov, Y. V.; Zimin, B. A.; Sventitskaya, V. E.

2018-05-01

The paper presents an analysis of the effect of the heat transfer process in metals on the parameters of thermal stresses under pulsed laser action. The dynamic problem of thermoelasticity is considered as a two-stage process. The first stage is determined by the time of action of the radiation pulse. The second stage is caused by the dynamics of the heat transfer process after the end of the laser pulse. For showing the continuity of thermoelastic and thermoelectric processes, the analysis of the electronic mechanism for the propagation of heat in metals and the results of experimental studies of these processes are presented. The results of the experiments demonstrate the high sensitivity of the parameters of thermoelastic and thermoelectric pulses to the microstructure of metals.

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

Lykkebo, Jacob; Solomon, Gemma C., E-mail: gsolomon@nano.ku.dk; Romano, Giuseppe

Electronic devices composed of single molecules constitute the ultimate limit in the continued downscaling of electronic components. A key challenge for single-molecule electronics is to control the temperature of these junctions. Controlling heating and cooling effects in individual vibrational modes can, in principle, be utilized to increase stability of single-molecule junctions under bias, to pump energy into particular vibrational modes to perform current-induced reactions, or to increase the resolution in inelastic electron tunneling spectroscopy by controlling the life-times of phonons in a molecule by suppressing absorption and external dissipation processes. Under bias the current and the molecule exchange energy, whichmore » typically results in heating of the molecule. However, the opposite process is also possible, where energy is extracted from the molecule by the tunneling current. Designing a molecular “heat sink” where a particular vibrational mode funnels heat out of the molecule and into the leads would be very desirable. It is even possible to imagine how the vibrational energy of the other vibrational modes could be funneled into the “cooling mode,” given the right molecular design. Previous efforts to understand heating and cooling mechanisms in single molecule junctions have primarily been concerned with small models, where it is unclear which molecular systems they correspond to. In this paper, our focus is on suppressing heating and obtaining current-induced cooling in certain vibrational modes. Strategies for cooling vibrational modes in single-molecule junctions are presented, together with atomistic calculations based on those strategies. Cooling and reduced heating are observed for two different cooling schemes in calculations of atomistic single-molecule junctions.« less

Tunable mega-ampere electron current propagation in solids by dynamic control of lattice melt

DOE PAGES

MacLellan, D.  A.; Carroll, D.  C.; Gray, R.  J.; ...

2014-10-31

The influence of lattice-melt-induced resistivity gradients on the transport of mega-ampere currents of fast electrons in solids is investigated numerically and experimentally using laser-accelerated protons to induce isochoric heating. Tailoring the heating profile enables the resistive magnetic fields which strongly influence the current propagation to be manipulated. This tunable laser-driven process enables important fast electron beam properties, including the beam divergence, profile, and symmetry to be actively tailored, and without recourse to complex target manufacture.

A process model for the heat-affected zone microstructure evolution in duplex stainless steel weldments: Part II. Application to electron beam welding

NASA Astrophysics Data System (ADS)

Hemmer, H.; Grong, Ø.; Klokkehaug, S.

2000-03-01

In the present investigation, a process model for electron beam (EB) welding of different grades of duplex stainless steels (i.e. SAF 2205 and 2507) has been developed. A number of attractive features are built into the original finite element code, including (1) a separate module for prediction of the penetration depth and distribution of the heat source into the plate, (2) adaptive refinement of the three-dimensional (3-D) element mesh for quick and reliable solution of the differential heat flow equation, and (3) special subroutines for calculation of the heat-affected zone (HAZ) microstructure evolution. The process model has been validated by comparison with experimental data obtained from in situ thermocouple measurements and optical microscope examinations. Subsequently, its aptness to alloy design and optimization of welding conditions for duplex stainless steels is illustrated in different numerical examples and case studies pertaining to EB welding of tubular joints.

The role of electron heat flux in guide-field magnetic reconnection

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

Hesse, Michael; Kuznetsova, Masha; Birn, Joachim

2004-12-01

A combination of analytical theory and particle-in-cell simulations are employed in order to investigate the electron dynamics near and at the site of guide field magnetic reconnection. A detailed analysis of the contributions to the reconnection electric field shows that both bulk inertia and pressure-based quasiviscous processes are important for the electrons. Analytic scaling demonstrates that conventional approximations for the electron pressure tensor behavior in the dissipation region fail, and that heat flux contributions need to be accounted for. Based on the evolution equation of the heat flux three tensor, which is derived in this paper, an approximate form ofmore » the relevant heat flux contributions to the pressure tensor is developed, which reproduces the numerical modeling result reasonably well. Based on this approximation, it is possible to develop a scaling of the electron current layer in the central dissipation region. It is shown that the pressure tensor contributions become important at the scale length defined by the electron Larmor radius in the guide magnetic field.« less

Shimmed electron beam welding process

DOEpatents

Feng, Ganjiang; Nowak, Daniel Anthony; Murphy, John Thomas

2002-01-01

A modified electron beam welding process effects welding of joints between superalloy materials by inserting a weldable shim in the joint and heating the superalloy materials with an electron beam. The process insures a full penetration of joints with a consistent percentage of filler material and thereby improves fatigue life of the joint by three to four times as compared with the prior art. The process also allows variable shim thickness and joint fit-up gaps to provide increased flexibility for manufacturing when joining complex airfoil structures and the like.

Electron holes in inhomogeneous magnetic field: Electron heating and electron hole evolution

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

Vasko, I. Y.; Space Research Institute of Russian Academy of Science, Moscow; Agapitov, O. V.

Electron holes are electrostatic non-linear structures widely observed in the space plasma. In the present paper, we analyze the process of energy exchange between electrons trapped within electron hole, untrapped electrons, and an electron hole propagating in a weakly inhomogeneous magnetic field. We show that as the electron hole propagates into the region with stronger magnetic field, trapped electrons are heated due to the conservation of the first adiabatic invariant. At the same time, the electron hole amplitude may increase or decrease in dependence on properties of distribution functions of trapped and untrapped resonant electrons. The energy gain of trappedmore » electrons is due to the energy losses of untrapped electrons and/or decrease of the electron hole energy. We stress that taking into account the energy exchange with untrapped electrons increases the lifetime of electron holes in inhomogeneous magnetic field. We illustrate the suggested mechanism for small-amplitude Schamel's [Phys. Scr. T2, 228–237 (1982)] electron holes and show that during propagation along a positive magnetic field gradient their amplitude should grow. Neglect of the energy exchange with untrapped electrons would result in the electron hole dissipation with only modest heating factor of trapped electrons. The suggested mechanism may contribute to generation of suprathermal electron fluxes in the space plasma.« less

Effect of heating on the suppression of tearing modes in tokamaks.

PubMed

Classen, I G J; Westerhof, E; Domier, C W; Donné, A J H; Jaspers, R J E; Luhmann, N C; Park, H K; van de Pol, M J; Spakman, G W; Jakubowski, M W

2007-01-19

The suppression of (neoclassical) tearing modes is of great importance for the success of future fusion reactors like ITER. Electron cyclotron waves can suppress islands, both by driving noninductive current in the island region and by heating the island, causing a perturbation to the Ohmic plasma current. This Letter reports on experiments on the TEXTOR tokamak, investigating the effect of heating, which is usually neglected. The unique set of tools available on TEXTOR, notably the dynamic ergodic divertor to create islands with a fully known driving term, and the electron cyclotron emission imaging diagnostic to provide detailed 2D electron temperature information, enables a detailed study of the suppression process and a comparison with theory.

Linking the micro and macro: L-H transition dynamics and threshold physics

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

Malkov, M. A., E-mail: mmalkov@ucsd.edu; Diamond, P. H.; Miki, K.

2015-03-15

The links between the microscopic dynamics and macroscopic threshold physics of the L → H transition are elucidated. Emphasis is placed on understanding the physics of power threshold scalings, and especially on understanding the minimum in the power threshold as a function of density P{sub thr} (n). By extending a numerical 1D model to evolve both electron and ion temperatures, including collisional coupling, we find that the decrease in P{sub thr} (n) along the low-density branch is due to the combination of an increase in collisional electron-to-ion energy transfer and an increase in the heating fraction coupled to the ions.more » Both processes strengthen the edge diamagnetic electric field needed to lock in the mean electric field shear for the L→H transition. The increase in P{sub thr} (n) along the high-density branch is due to the increase with ion collisionality of damping of turbulence-driven shear flows. Turbulence driven shear flows are needed to trigger the transition by extracting energy from the turbulence. Thus, we identify the critical transition physics components of the separatrix ion heat flux and the zonal flow excitation. The model reveals a power threshold minimum in density scans as a crossover between the threshold decrease supported by an increase in heat fraction received by ions (directly or indirectly, from electrons) and a threshold increase, supported by the rise in shear flow damping. The electron/ion heating mix emerges as important to the transition, in that it, together with electron-ion coupling, regulates the edge diamagnetic electric field shear. The importance of possible collisionless electron-ion heat transfer processes is explained.« less

40 CFR 98.92 - GHGs to report.

Code of Federal Regulations, 2012 CFR

2012-07-01

... GREENHOUSE GAS REPORTING Electronics Manufacturing § 98.92 GHGs to report. (a) You must report emissions of...). The fluorinated GHGs and fluorinated heat transfer fluids that are emitted from electronics... emitted from chemical vapor deposition and other electronics manufacturing processes. (5) Emissions of...

40 CFR 98.92 - GHGs to report.

Code of Federal Regulations, 2014 CFR

2014-07-01

... GREENHOUSE GAS REPORTING Electronics Manufacturing § 98.92 GHGs to report. (a) You must report emissions of...). The fluorinated GHGs and fluorinated heat transfer fluids that are emitted from electronics... emitted from chemical vapor deposition and other electronics manufacturing processes. (5) Emissions of...

40 CFR 98.92 - GHGs to report.

Code of Federal Regulations, 2013 CFR

2013-07-01

... GREENHOUSE GAS REPORTING Electronics Manufacturing § 98.92 GHGs to report. (a) You must report emissions of...). The fluorinated GHGs and fluorinated heat transfer fluids that are emitted from electronics... emitted from chemical vapor deposition and other electronics manufacturing processes. (5) Emissions of...

Particle Energization via Tearing Instability with Global Self-Organization Constraints

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

Sarff, John; Guo, Fan

The presentation reviews how tearing magnetic reconnection leads to powerful ion energization in reversed field pinch (RFP) plasmas. A mature MHD model for tearing instability has been developed that captures key nonlinear dynamics from the global to intermediate spatial scales. A turbulent cascade is also present that extends to at least the ion gyroradius scale, within which important particle energization mechanisms are anticipated. In summary, Ion heating and acceleration associated with magnetic reconnection from tearing instability is a powerful process in the RFP laboratory plasma (gyro-resonant and stochastic processes are likely candidates to support the observed rapid heating and othermore » features, reconnection-driven electron heating appears weaker or even absent, energetic tail formation for ions and electrons). Global self-organization strongly impacts particle energization (tearing interactions that span to core to edge, global magnetic flux change produces a larger electric field and runaway, correlations in electric and magnetic field fluctuations needed for dynamo feedback, impact of transport processes (which can be quite different for ions and electrons), inhomogeneity on the system scale, e.g., strong edge gradients).« less

Heating power at the substrate, electron temperature, and electron density in 2.45 GHz low-pressure microwave plasma

NASA Astrophysics Data System (ADS)

Kais, A.; Lo, J.; Thérèse, L.; Guillot, Ph.

2018-01-01

To control the temperature during a plasma treatment, an understanding of the link between the plasma parameters and the fundamental process responsible for the heating is required. In this work, the power supplied by the plasma onto the surface of a glass substrate is measured using the calorimetric method. It has been shown that the powers deposited by ions and electrons, and their recombination at the surface are the main contributions to the heating power. Each contribution is estimated according to the theory commonly used in the literature. Using the corona balance, the Modified Boltzmann Plot (MBP) is employed to determine the electron temperature. A correlation between the power deposited by the plasma and the results of the MBP has been established. This correlation has been used to estimate the electron number density independent of the Langmuir probe in considered conditions.

In situ experimental formation and growth of Fe nanoparticles and vesicles in lunar soil

NASA Astrophysics Data System (ADS)

Thompson, Michelle S.; Zega, Thomas J.; Howe, Jane Y.

2017-03-01

We report the results of the first dynamic, in situ heating of lunar soils to simulate micrometeorite impacts on the lunar surface. We performed slow- and rapid-heating experiments inside the transmission electron microscope to understand the chemical and microstructural changes in surface soils resulting from space-weathering processes. Our slow-heating experiments show that the formation of Fe nanoparticles begins at 575 °C. These nanoparticles also form as a result of rapid-heating experiments, and electron energy-loss spectroscopy measurements indicate the Fe nanoparticles are composed entirely of Fe0, suggesting this simulation accurately mimics micrometeorite space-weathering processes occurring on airless body surfaces. In addition to Fe nanoparticles, rapid-heating experiments also formed vesiculated textures in the samples. Several grains were subjected to repeated thermal shocks, and the measured size distribution and number of Fe nanoparticles evolved with each subsequent heating event. These results provide insight into the formation and growth mechanisms for Fe nanoparticles in space-weathered soils and could provide a new methodology for relative age dating of individual soil grains from within a sample population.

Single-electron thermal devices coupled to a mesoscopic gate

NASA Astrophysics Data System (ADS)

Sánchez, Rafael; Thierschmann, Holger; Molenkamp, Laurens W.

2017-11-01

We theoretically investigate the propagation of heat currents in a three-terminal quantum dot engine. Electron-electron interactions introduce state-dependent processes which can be resolved by energy-dependent tunneling rates. We identify the relevant transitions which define the operation of the system as a thermal transistor or a thermal diode. In the former case, thermal-induced charge fluctuations in the gate dot modify the thermal currents in the conductor with suppressed heat injection, resulting in huge amplification factors and the possible gating with arbitrarily low energy cost. In the latter case, enhanced correlations of the state-selective tunneling transitions redistribute heat flows giving high rectification coefficients and the unexpected cooling of one conductor terminal by heating the other one. We propose quantum dot arrays as a possible way to achieve the extreme tunneling asymmetries required for the different operations.

Superthermal electron processes in the upper atmosphere of Uranus: Aurora and electroglow

NASA Technical Reports Server (NTRS)

Waite, J. H., Jr.; Chandler, M. O.; Yelle, R. V.; Sandel, B. R.

1987-01-01

Strong ultraviolet emissions from the upper atmosphere of Uranus suggest that both auroral and electroglow phenomena are of significant aeronomical consequences in the structure of the upper atmosphere. Combined modeling and data analysis were performed to determine the effect of electroglow and auroral phenomena on the global heat and atomic hydrogen budgets in the Uranus upper atmosphere. The results indicate that the auroral and electroglow heat sources are not adequate to explain the high exospheric temperature observed at Uranus, but that the atomic hydrogen supplied by these processes is more than sufficient to explain the observations. The various superthermal electron distributions modeled have significantly different efficiencies for the various processes such as UV emission, heating, ionization, and atomic hydrogen production, and produce quite different H2 band spectra. However, additional information on the UV spectra and global parameters is needed before modeling can be used to distinguish between the possible mechanisms for electroglow.

Effect of heat treatment On Microstructure of steel AISI 01 Tools

NASA Astrophysics Data System (ADS)

Dyanasari Sebayang, Melya; Yudo, Sesmaro Max; Silitonga, Charlie

2018-03-01

This study discusses the influence of quenching, normalizing, and annealing to changes in hardness, tensile, and microstructure of materials tool steel AISI 01 after the material undergo heat treatment process. This heat treatment process includes an initial warming of 600° C and a 5-minute detention time, followed by heating to an austenisation temperature of 850°C. After that a different cooling process, including annealing process, normalizing and quenching oil SAE 40. Tests performed include tensile, hard, and microstructure with shooting using SEM (Scanning Electron Microscope). This is done to see the effect of different heat treatment and cooling process. The result of this research is difference of tensile test value, hard, and micro structure from influence of difference of each process. The quenching process obtains the highest tensile and hard values followed by the normalizing process, annealing, and the lowest is in the starting material, this is because the initial material does not undergo heat treatment process. The resulting microstructure is pearlit and cementite, the difference seen from the shape and size of the grains. The larger the grain size, the greater the hardness.

Effect of Heat Treatment Process on Mechanical Properties and Microstructure of a 9% Ni Steel for Large LNG Storage Tanks

NASA Astrophysics Data System (ADS)

Zhang, J. M.; Li, H.; Yang, F.; Chi, Q.; Ji, L. K.; Feng, Y. R.

2013-12-01

In this paper, two different heat treatment processes of a 9% Ni steel for large liquefied natural gas storage tanks were performed in an industrial heating furnace. The former was a special heat treatment process consisting of quenching and intercritical quenching and tempering (Q-IQ-T). The latter was a heat treatment process only consisting of quenching and tempering. Mechanical properties were measured by tensile testing and charpy impact testing, and the microstructure was analyzed by optical microscopy, transmission electron microscopy, and x-ray diffraction. The results showed that outstanding mechanical properties were obtained from the Q-IQ-T process in comparison with the Q-T process, and a cryogenic toughness with charpy impact energy value of 201 J was achieved at 77 K. Microstructure analysis revealed that samples of the Q-IQ-T process had about 9.8% of austenite in needle-like martensite, while samples of the Q-T process only had about 0.9% of austenite retained in tempered martensite.

A comparison of superconductor and manganin technology for electronic links used in space mission applications

NASA Technical Reports Server (NTRS)

Caton, R.; Selim, R.; Buoncristiani, A. M.

1992-01-01

The electronic link connecting cryogenically cooled radiation detectors to data acquisition and signal processing electronics at higher temperatures contributes significantly to the total heat load on spacecraft cooling systems that use combined mechanical and cryogenic liquid cooling. Using high transition temperature superconductors for this link has been proposed to increase the lifetime of space missions. Herein, several YBCO (YBa2Cu3O7) superconductor-substrate combinations were examined and total heat loads were compared to manganin wire technology in current use. Using numerical solutions to the heat-flow equations, it is shown that replacing manganin technology with YBCO thick film technology can extend a 7-year mission by up to 1 year.

Spacecraft Heat Rejection Methods: Active and Passive Heat Transfer for Electronic Systems.

DTIC Science & Technology

1986-08-29

Storage in avionics, spacecraft and electronics ,;"ters. Microencapsulated phase change materials (PCMs) in a two-component water SlUrrv- were useo with...capsules was observed in the pumping process. Inaddition, both microencapsulated and pure PCM were used to passively reduce tile tempera- tuo .tremes of...conducted as a Phase I Small Business Innovation Research (SBIR) program to explore the feasibility of using microencapsulated phase change materials (PCM) in

An electronic system for measuring thermophysical properties of wind tunnel models

NASA Technical Reports Server (NTRS)

Corwin, R. R.; Kramer, J. S.

1975-01-01

An electronic system is described which measures the surface temperature of a small portion of the surface of the model or sample at high speeds using an infrared radiometer. This data is processed along with heating rate data from the reference heat gauge in a small computer and prints out the desired thermophysical properties, time, surface temperature, and reference heat rate. This system allows fast and accurate property measurements over thirty temperature increments. The technique, the details of the apparatus, the procedure for making these measurements, and the results of some preliminary tests are presented.

JPRS Report, Science & Technology, Japan

DTIC Science & Technology

1991-01-31

final test. Keywords: Spherical Pressure Hull, Titanium Alloy , Three-Dimensional Machining, Electron Beam Welding . 1. Introduction In bodies like... processed (the heat treatment involving high-temperature heating and rapid quenching in order to obtain finer grains of the titanium alloy ) and...given m Table 3. The test results were all satisfactory. Forged material of titanium alloy , manufactured by forging, beta processing , and billet

Numerical simulation of electron beam welding with beam oscillations

NASA Astrophysics Data System (ADS)

Trushnikov, D. N.; Permyakov, G. L.

2017-02-01

This research examines the process of electron-beam welding in a keyhole mode with the use of beam oscillations. We study the impact of various beam oscillations and their parameters on the shape of the keyhole, the flow of heat and mass transfer processes and weld parameters to develop methodological recommendations. A numerical three-dimensional mathematical model of electron beam welding is presented. The model was developed on the basis of a heat conduction equation and a Navier-Stokes equation taking into account phase transitions at the interface of a solid and liquid phase and thermocapillary convection (Marangoni effect). The shape of the keyhole is determined based on experimental data on the parameters of the secondary signal by using the method of a synchronous accumulation. Calculations of thermal and hydrodynamic processes were carried out based on a computer cluster, using a simulation package COMSOL Multiphysics.

Power Electronics and Electric Machines Facilities | Transportation

Science.gov Websites

current processes. Photo by Dennis Schroeder, NREL A photo of a researcher in safety glasses using a large focus in NREL's power electronics and electric machines labs. Photo by Dennis Schroeder, NREL Heat

Interaction of a neutral cloud moving through a magnetized plasma

NASA Technical Reports Server (NTRS)

Goertz, C. K.; Lu, G.

1990-01-01

Current collection by outgassing probes in motion relative to a magnetized plasma may be significantly affected by plasma processes that cause electron heating and cross field transport. Simulations of a neutral gas cloud moving across a static magnetic field are discussed. The authors treat a low-Beta plasma and use a 2-1/2 D electrostatic code linked with the authors' Plasma and Neutral Interaction Code (PANIC). This study emphasizes the understanding of the interface between the neutral gas cloud and the surrounding plasma where electrons are heated and can diffuse across field lines. When ionization or charge exchange collisions occur a sheath-like structure is formed at the surface of the neutral gas. In that region the crossfield component of the electric field causes the electron to E times B drift with a velocity of the order of the neutral gas velocity times the square root of the ion to electron mass ratio. In addition a diamagnetic drift of the electron occurs due to the number density and temperature inhomogeneity in the front. These drift currents excite the lower-hybrid waves with the wave k-vectors almost perpendicular to the neutral flow and magnetic field again resulting in electron heating. The thermal electron current is significantly enhanced due to this heating.

Heating and background plasma modification associated with large amplitude kinetic Alfv'en wave launch in LAPD

NASA Astrophysics Data System (ADS)

Carter, T. A.; Auerbach, D. W.; Brugman, B. T.

2007-11-01

Large amplitude kinetic Alfv'en waves (δB/B ˜1% > k/k) are generated in the Large Plasma Device (LAPD) at UCLA using loop antennas. Substantial electron heating is observed, localized to the wave current channels. The Poynting flux associated with the Alfv'en waves is substantial and the observed heating may be at least in part due to collisional and Landau damping of these waves. However, heating by antenna near inductive electric fields may also be responsible for the observations. A discussion of both possibilities will be presented, including measurements of near fields of the antenna. The heating structures the background plasma and results in the excitation of drift-Alfv'en waves. These drift waves then interact with the incident Alfv'en wave, causing sideband generation which results in a nearly broadband state at high wave power. This process may represent an alternate mechanism by which unidirectional kinetic Alfv'en waves can nonlinearly generate a turbulent spectrum. In addition to electron heating, evidence for background density modification and electron acceleration is observed and will be presented.

Electron energy distribution function in the divertor region of the COMPASS tokamak during neutral beam injection heating

NASA Astrophysics Data System (ADS)

Hasan, E.; Dimitrova, M.; Havlicek, J.; Mitošinková, K.; Stöckel, J.; Varju, J.; Popov, Tsv K.; Komm, M.; Dejarnac, R.; Hacek, P.; Panek, R.; the COMPASS Team

2018-02-01

This paper presents the results from swept probe measurements in the divertor region of the COMPASS tokamak in D-shaped, L-mode discharges, with toroidal magnetic field BT = 1.15 T, plasma current Ip = 180 kA and line-average electron densities varying from 2 to 8×1019 m-3. Using neutral beam injection heating, the electron energy distribution function is studied before and during the application of the beam. The current-voltage characteristics data are processed using the first-derivative probe technique. This technique allows one to evaluate the plasma potential and the real electron energy distribution function (respectively, the electron temperatures and densities). At the low average electron density of 2×1019 m-3, the electron energy distribution function is bi-Maxwellian with a low-energy electron population with temperatures 4-6 eV and a high-energy electron group 12-25 eV. As the line-average electron density is increased, the electron temperatures decrease. At line-average electron densities above 7×1019 m-3, the electron energy distribution function is found to be Maxwellian with a temperature of 6-8.5 eV. The effect of the neutral beam injection heating power in the divertor region is also studied.

The absorption of energetic electrons by molecular hydrogen gas

NASA Technical Reports Server (NTRS)

Cravens, T. E.; Victor, G. A.; Dalgarno, A.

1975-01-01

The processes by which energetic electrons lose energy in a weakly ionized gas of molecular hydrogen are analyzed, and calculations are carried out taking into account the discrete nature of the excitation processes. The excitation, ionization, and heating efficiencies are computed for electrons with energies up to 100 eV absorbed in a gas with fractional ionizations up to 0.01, and the mean energy per pair of neutral hydrogen atoms is calculated.

Influence of heat treatment on hole transfer dynamics in core-shell quantum dot/organic hole conductor hybrid films

NASA Astrophysics Data System (ADS)

Sun, Mingye; Zheng, Youjin; Zhang, Lei; Zhao, Liping; Zhang, Bing

2017-08-01

The influence of heat treatment on hole transfer (HT) processes from the CdSe/ZnS and CdSe/CdS/ZnS quantum dots (QDs) to 4,4‧,4″-Tris(carbazol-9-yl)-triphenylamine (TCTA) in QD/TCTA hybrid films has been researched with time-resolved photoluminescence (PL) spectroscopy. The PL dynamic results demonstrated a heat-treatment-temperature-dependent HT process from the core-shell CdSe QDs to TCTA. The HT rates and efficiencies can be effectively increased due to reduced distance between core-shell CdSe QDs and TCTA after heat treatment. The CdS shell exhibited a more obvious effect on HT from the core-shell CdSe QDs to TCTA than on electron transfer to TiO2, due to higher barrier for holes to tunnel through CdS shell and larger effective mass of holes in CdS than electrons. These results indicate that heat treatment would be an effective means to further optimize solid-state QD sensitized solar cells and rational design of CdS shell is significant.

Electronic measurements in an alternating magnetic field (AMF) for studying magnetic nanoparticle hyperthermia

NASA Astrophysics Data System (ADS)

Boekelheide, Z.; Hussein, Z. A.; Hartzell, S.

Magnetic nanoparticle hyperthermia is a promising cancer treatment in which magnetic nanoparticles are injected into a tumor and then exposed to an alternating magnetic field (AMF). This process releases heat and damages tumor cells, but the exact mechanisms behind the effectiveness of this therapy are still unclear. Accurate sensors are required to monitor the temperature and, potentially, other parameters such as magnetic field or mechanical stress during clinical therapy or lab research. Often, optical rather than electronic temperature sensors are used to avoid eddy current self-heating in conducting parts in the AMF. However, eddy current heating is strongly dependent on the size and geometry of the conducting part, thus micro- and nano-scale electronics are a promising possibility for further exploration into magnetic nanoparticle hyperthermia. This presentation quantitatively discusses the eddy current self-heating of thin wires (thermocouples) and will also present a proof of concept thin film resistive thermometer and magnetic field sensor along with measurements of their eddy current self-heating. The results show that electronic measurements are feasible in an AMF with both thin wires and patterned thin film sensors under certain conditions.

Tunneling of heat: Beyond linear response regime

NASA Astrophysics Data System (ADS)

Walczak, Kamil; Saroka, David

2018-02-01

We examine nanoscale processes of heat (energy) transfer as carried by electrons tunneling via potential barriers and molecular interconnects between two heat reservoirs (thermal baths). For that purpose, we use Landauer-type formulas to calculate thermal conductance and quadratic correction to heat flux flowing via quantum systems. As an input, we implement analytical expressions for transmission functions related to simple potential barriers and atomic bridges. Our results are discussed with respect to energy of tunneling electrons, temperature, the presence of resonant states, and specific parameters characterizing potential barriers as well as heat carriers. The simplicity of semi-analytical models developed by us allows to fit experimental data and extract crucial information about the values of model parameters. Further investigations are expected for more realistic transmission functions, while time-dependent aspects of nanoscale heat transfer may be addressed by using the concept of wave packets scattered on potential barriers and point-like defects within regular (periodic) nanostructures.

Comparison between off-resonance and electron Bernstein waves heating regime in a microwave discharge ion source

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

Castro, G.; Di Giugno, R.; Miracoli, R.

2012-02-15

A microwave discharge ion source (MDIS) operating at the Laboratori Nazionali del Sud of INFN, Catania has been used to compare the traditional electron cyclotron resonance (ECR) heating with an innovative mechanisms of plasma ignition based on the electrostatic Bernstein waves (EBW). EBW are obtained via the inner plasma electromagnetic-to-electrostatic wave conversion and they are absorbed by the plasma at cyclotron resonance harmonics. The heating of plasma by means of EBW at particular frequencies enabled us to reach densities much larger than the cutoff ones. Evidences of EBW generation and absorption together with X-ray emissions due to high energy electronsmore » will be shown. A characterization of the discharge heating process in MDISs as a generalization of the ECR heating mechanism by means of ray tracing will be shown in order to highlight the fundamental physical differences between ECR and EBW heating.« less

Electron heating in quasi-perpendicular shocks - A Monte Carlo simulation

NASA Technical Reports Server (NTRS)

Veltri, Pierluigi; Mangeney, Andre; Scudder, Jack D.

1990-01-01

To study the problem of electron heating in quasi-perpendicular shocks, under the combined effects of 'reversible' motion, in the shock electric potential and magnetic field, and wave-particle interactions a diffusion equation was derived, in the drift (adiabatic) approximation and it was solved by using a Monte Carlo method. The results show that most of the observations can be explained within this framework. The simulation has also definitively shown that the electron parallel temperature is determined by the dc electromagnetic field and not by any wave particle induced heating. Wave-particle interactions are effective in smoothing out the large gradients in phase space produced by the 'reversible' motion of the electrons, thus producing a 'cooling' of the electrons. Some constraints on the wave-particle interaction process may be obtained from a detailed comparison between the simulation and observations. In particular, it appears that the adiabatic approximation must be violated in order to explain the observed evolution of the perpendicular temperature.

A novel dismantling process of waste printed circuit boards using water-soluble ionic liquid.

PubMed

Zeng, Xianlai; Li, Jinhui; Xie, Henghua; Liu, Lili

2013-10-01

Recycling processes for waste printed circuit boards (WPCBs) have been well established in terms of scientific research and field pilots. However, current dismantling procedures for WPCBs have restricted the recycling process, due to their low efficiency and negative impacts on environmental and human health. This work aimed to seek an environmental-friendly dismantling process through heating with water-soluble ionic liquid to separate electronic components and tin solder from two main types of WPCBs-cathode ray tubes and computer mainframes. The work systematically investigates the influence factors, heating mechanism, and optimal parameters for opening solder connections on WPCBs during the dismantling process, and addresses its environmental performance and economic assessment. The results obtained demonstrate that the optimal temperature, retention time, and turbulence resulting from impeller rotation during the dismantling process, were 250 °C, 12 min, and 45 rpm, respectively. Nearly 90% of the electronic components were separated from the WPCBs under the optimal experimental conditions. This novel process offers the possibility of large industrial-scale operations for separating electronic components and recovering tin solder, and for a more efficient and environmentally sound process for WPCBs recycling. Copyright © 2013 Elsevier Ltd. All rights reserved.

Effects of post-weld heat treatment on microstructure and mechanical properties of laser welds in GH3535 superalloy

NASA Astrophysics Data System (ADS)

Yu, Kun; Jiang, Zhenguo; Leng, Bin; Li, Chaowen; Chen, Shuangjian; Tao, Wang; Zhou, Xingtai; Li, Zhijun

2016-07-01

In this study, the microstructure and mechanical properties of laser welds before and after post-weld heat treatment processes were studied. The results show that the tensile strength of the joints can be increased by 90 MPa by a post-weld heat treatment process at 871 °C for 6 h, exceeding the strength of the original state of the base metal. Besides, elongation of the joints are also increased to 43% by the process, whereas the elongation of as-welded joints are only 22%. In addition, the Charpy impact properties of laser welds almost do not change. Second phase precipitates, which were identified as Mo-Si rich M6C-type carbides by transmission electron diffraction and scanning electron microscope, were observed at solidification grain boundaries and solidification subgrain boundaries. These carbides can pin dislocations during the following tensile deformation, hence are responsible for the strengthening of tensile properties of the joints.

Marangoni Convection during Free Electron Laser Nitriding of Titanium

NASA Astrophysics Data System (ADS)

Höche, Daniel; Müller, Sven; Rapin, Gerd; Shinn, Michelle; Remdt, Elvira; Gubisch, Maik; Schaaf, Peter

2009-08-01

Pure titanium was treated by free electron laser (FEL) radiation in a nitrogen atmosphere. As a result, nitrogen diffusion occurs and a TiN coating was synthesized. Local gradients of interfacial tension due to the local heating lead to a Marangoni convection, which determines the track properties. Because of the experimental inaccessibility of time-dependent occurrences, finite element calculations were performed, to determine the physical processes such as heat transfer, melt flow, and mass transport. In order to calculate the surface deformation of the gas-liquid interface, the level set approach was used. The equations were modified and coupled with heat-transfer and diffusion equations. The process was characterized by dimensionless numbers such as the Reynolds, Peclet, and capillary numbers, to obtain more information about the acting forces and the coating development. Moreover, the nitrogen distribution was calculated using the corresponding transport equation. The simulations were compared with cross-sectional micrographs of the treated titanium sheets and checked for their validity. Finally, the process presented is discussed and compared with similar laser treatments.

Potential for EMU Fabric Damage by Electron Beam and Molten Metal During Space Welding for the International Space Welding Experiment

NASA Technical Reports Server (NTRS)

Fragomeni, James M.

1998-01-01

As a consequence of preparations concerning the International Space Welding Experiment (ISWE), studies were performed to better understand the effect of molten metal contact and electron beam impingement with various fabrics for space suit applications. The question arose as to what would occur if the electron beam from the Ukrainian Universal Hand Tool (UHT) designed for welding in space were to impinge upon a piece of Nextel AF-62 ceramic cloth designed to withstand temperatures up to 1427 C. The expectation was that the electron beam would lay down a static charge pattern with no damage to the ceramic fabric. The electron beam is capable of spraying the fabric with enough negative charge to repel further electrons from the fabric before significant heating occurs. The static charge pattern would deflect any further charge accumulation except for a small initial amount of leakage to the grounded surface of the welder. However, when studies were made of the effect of the electron beam on the insulating ceramic fabric it was surprisingly found that the electron beam did indeed burn through the ceramic fabric. It was also found that the shorter electron beam standoff distances had longer burnthrough times than did some greater electron beam standoff distances. A possible explanation for the longer burnthrough times for the small electron beam standoff distance would be outgassing of the fabric which caused the electron beam hand-tool to cycle on and off to provide some protection for the cathodes. The electron beam hand tool was observed to cycle off at the short standoff distance of two inches likely due to vapors being outgassed. During the electron beam welding process there is an electron leakage, or current leakage, flow from the fabric. A static charge pattern is initially laid down by the electron beam current flow. The static charge makes up the current leakage flow which initially slightly heats up the fabric. The initially laid down surface charge leaks a small amount of current. The rate at which the current charge leaks from the fabric controls how fast the fabric heats up. As the ceramic fabric is heated it begins to outgass primarily from contamination/impurities atoms or molecules on and below the fabric surface. The contaminant gases ionize to create extra charge carriers and multiply a current of electrons. The emitted gas which ionized in the electron leakage flow promotes further leakage. Thus, the small leakage of charge from the fabric surface is enhanced by outgassing. When the electron beam current makes up the lost current, the incoming electrons heat the fabric and further enhance the outgassing. The additional leakage promotes additional heating up of the ceramic fabric. The electrons bound to the ceramic fabric surface leak off more and more as the surface gets hotter promoting even greater leakage. The additional electrons that result also gain energy in the field and produce further electrons. Eventually the process becomes unstable and accelerates to the point where a hole is burned through the fabric.

Optical Sensor of Thermal Gas Flow Based on Fiber Bragg Grating.

PubMed

Jiang, Xu; Wang, Keda; Li, Junqing; Zhan, Hui; Song, Zhenan; Che, Guohang; Lyu, Guohui

2017-02-15

This paper aims at solving the problem of explosion proof in measurement of thermal gas flow using electronic sensor by presenting a new type of flow sensor by optical fiber heating. A measuring unit based on fiber Bragg grating (FBG) for fluid temperature and a unit for heat dissipation are designed to replace the traditional electronic sensors. The light in C band from the amplified spontaneous emission (ASE) light source is split, with one part used to heat the absorbing coating and the other part used in the signal processing unit. In the heating unit, an absorbing coating is introduced to replace the traditional resistance heating module to minimize the risk of explosion. The measurement results demonstrate a fine consistency between the flow and temperature difference in simulation. The method to enhance the measurement resolution of flow is also discussed.

Spin caloritronic nano-oscillator

DOE PAGES

Safranski, C.; Barsukov, I.; Lee, H. K.; ...

2017-07-18

Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic devices, and harvesting ohmic heat for signal processing is a major challenge in modern electronics. Here, we demonstrate that thermal gradients arising from ohmic heating can be utilized for excitation of coherent auto-oscillations of magnetization and for generation of tunable microwave signals. The heat-driven dynamics is observed in Y 3Fe 5O 12/Pt bilayer nanowires where ohmic heating of the Pt layer results in injection of pure spin current into the Y 3Fe 5O 12 layer. This leads to excitation of auto-oscillations of the Ymore » 3Fe 5O 12 magnetization and generation of coherent microwave radiation. Thus, our work paves the way towards spin caloritronic devices for microwave and magnonic applications.« less

Spin caloritronic nano-oscillator

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

Safranski, C.; Barsukov, I.; Lee, H. K.

Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic devices, and harvesting ohmic heat for signal processing is a major challenge in modern electronics. Here, we demonstrate that thermal gradients arising from ohmic heating can be utilized for excitation of coherent auto-oscillations of magnetization and for generation of tunable microwave signals. The heat-driven dynamics is observed in Y 3Fe 5O 12/Pt bilayer nanowires where ohmic heating of the Pt layer results in injection of pure spin current into the Y 3Fe 5O 12 layer. This leads to excitation of auto-oscillations of the Ymore » 3Fe 5O 12 magnetization and generation of coherent microwave radiation. Thus, our work paves the way towards spin caloritronic devices for microwave and magnonic applications.« less

Collisionless dissipation processes in quasi-parallel shocks. [in solar wind

NASA Technical Reports Server (NTRS)

Quest, K. B.; Forslund, D. W.; Brackbill, J. U.; Lee, K.

1983-01-01

The evolution of collisionless, quasi-parallel shocks (the angle between the shock normal and the upstream magnetic field being less than 45 deg) is examined using two dimensional particle simulations. Reflected ions upstream from the shock are observed with average guiding center velocity and gyrational energy which agree well with the prediction of simple specular reflection. Strong ion heating through the shock ramp is apparently caused by large amplitude whistler turbulence. A flux of suprathermal electrons is also the magnetic field direction. Much stronger ion heating occurs in the shock than electron heating. The relevance of this work to the earth's bow shock is discussed.

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

Berdichevskii, M.G.; Marusin, V.V.

The possible contributions of several processes to the experimentally observed heating of nitrogen plasmas in an electarodeless rf capacitive discharge at pressures of p=2.7-67 kPa are discussed. These processes are electron-rotational, vibrational--translational (V--T), and nonresonance vibrational--vibrational (V--V) energy exchange and effects due to O/sub 2/, H/sub 2/O, and NO impurities in the gas. It is shown that as the pressure is decreased the heating mechanism changes from quasiequilibrium to nonequilibrium V--T heating caused by overpopulation of high vibrational levels in the ground state of the nitrogen molecule.

Gas dynamics in the impulsive phase of solar flares. I Thick-target heating by nonthermal electrons

NASA Technical Reports Server (NTRS)

Nagai, F.; Emslie, A. G.

1984-01-01

A numerical investigation is carried out of the gas dynamical response of the solar atmosphere to a flare energy input in the form of precipitating nonthermal electrons. Rather than discussing the origin of these electrons, the spectral and temporal characteristics of the injected flux are inferred through a thick-target model of hard X-ray bremsstrahlung production. It is assumed that the electrons spiral about preexisting magnetic field lines, making it possible for a one-dimensional spatial treatment to be performed. It is also assumed that all electron energy losses are due to Coulomb collisions with ambient particles; that is, return-current ohmic effects and collective plasma processes are neglected. The results are contrasted with earlier work on conductive heating of the flare atmosphere. A local temperature peak is seen at a height of approximately 1500 km above the photosphere. This derives from a spatial maximum in the energy deposition rate from an electron beam. It is noted that such a feature is not present in conductively heated models. The associated localized region of high pressure drives material both upward and downward.

4D visualization of embryonic, structural crystallization by single-pulse microscopy

PubMed Central

Kwon, Oh-Hoon; Barwick, Brett; Park, Hyun Soon; Baskin, J. Spencer; Zewail, Ahmed H.

2008-01-01

In many physical and biological systems the transition from an amorphous to ordered native structure involves complex energy landscapes, and understanding such transformations requires not only their thermodynamics but also the structural dynamics during the process. Here, we extend our 4D visualization method with electron imaging to include the study of irreversible processes with a single pulse in the same ultrafast electron microscope (UEM) as used before in the single-electron mode for the study of reversible processes. With this augmentation, we report on the transformation of amorphous to crystalline structure with silicon as an example. A single heating pulse was used to initiate crystallization from the amorphous phase while a single packet of electrons imaged selectively in space the transformation as the structure continuously changes with time. From the evolution of crystallinity in real time and the changes in morphology, for nanosecond and femtosecond pulse heating, we describe two types of processes, one that occurs at early time and involves a nondiffusive motion and another that takes place on a longer time scale. Similar mechanisms of two distinct time scales may perhaps be important in biomolecular folding. PMID:18562291

Solar coronal loop heating by cross-field wave transport

NASA Technical Reports Server (NTRS)

Amendt, Peter; Benford, Gregory

1989-01-01

Solar coronal arches heated by turbulent ion-cyclotron waves may suffer significant cross-field transport by these waves. Nonlinear processes fix the wave-propagation speed at about a tenth of the ion thermal velocity, which seems sufficient to spread heat from a central core into a large cool surrounding cocoon. Waves heat cocoon ions both through classical ion-electron collisions and by turbulent stochastic ion motions. Plausible cocoon sizes set by wave damping are in roughly kilometers, although the wave-emitting core may be only 100 m wide. Detailed study of nonlinear stabilization and energy-deposition rates predicts that nearby regions can heat to values intermediate between the roughly electron volt foot-point temperatures and the about 100 eV core, which is heated by anomalous Ohmic losses. A volume of 100 times the core volume may be affected. This qualitative result may solve a persistent problem with current-driven coronal heating; that it affects only small volumes and provides no way to produce the extended warm structures perceptible to existing instruments.

Microencapsulated Phase-Change Materials For Storage Of Heat

NASA Technical Reports Server (NTRS)

Colvin, David P.

1989-01-01

Report describes research on engineering issues related to storage and transport of heat in slurries containing phase-change materials in microscopic capsules. Specific goal of project to develop lightweight, compact, heat-management systems used safely in inhabited areas of spacecraft. Further development of obvious potential of technology expected to lead to commercialization and use in aircraft, electronic equipment, machinery, industrial processes, and other sytems in which requirements for management of heat compete with severe restrictions on weight or volume.

Interplanetary magnetic field connection to the sun during electron heat flux dropouts in the solar wind

NASA Technical Reports Server (NTRS)

Lin, R. P.; Kahler, S. W.

1992-01-01

The paper discusses observations of 2- to 8.5-keV electrons, made by measurements aboard the ISEE 3 spacecraft during the periods of heat flux decreases (HFDs) reported by McComas et al. (1989). In at least eight of the total of 25 HFDs observed, strong streaming of electrons that were equal to or greater than 2 keV outward from the sun was recorded. In one HFD, an impulsive solar electron event was observed with an associated type III radio burst, which could be tracked from the sun to about 1 AU. It is concluded that, in many HFDs, the interplanetary field is still connected to the sun and that some energy-dependent process may produce HFDs without significantly perturbing electrons of higher energies.

Cluster/Peace Electrons Velocity Distribution Function: Modeling the Strahl in the Solar Wind

NASA Technical Reports Server (NTRS)

Figueroa-Vinas, Adolfo; Gurgiolo, Chris; Goldstein, Melvyn L.

2008-01-01

We present a study of kinetic properties of the strahl electron velocity distribution functions (VDF's) in the solar wind. These are used to investigate the pitch-angle scattering and stability of the population to interactions with electromagnetic (whistler) fluctuations. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer. Our study focuses on the mechanisms that control and regulate the pitch-angle and stability of strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the electron heat-flux and temperature anisotropy. The goal is to check whether the strahl electrons are constrained by some instability (e.g., the whistler instability), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by fitting the VDF's to a spectral spherical harmonic model from which the moments are derived directly from the model coefficients.

Role of the heat accumulation effect in the multipulse modes of the femtosecond laser microstructuring of silicon

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

Guk, I. V., E-mail: corchand@gmail.com; Shandybina, G. D.; Yakovlev, E. B.

2016-05-15

The results of quantitative evaluation of the heat accumulation effect during the femtosecond laser microstructuring of the surface of silicon are presented for discussion. In the calculations, the numerical–analytical method is used, in which the dynamics of electronic processes and lattice heating are simulated by the numerical method, and the cooling stage is described on the basis of an analytical solution. The effect of multipulse irradiation on the surface temperature is studied: in the electronic subsystem, as the dependence of the absorbance on the excited carrier density and the dependence of the absorbance on the electron-gas temperature; in the latticemore » subsystem, as the variation in the absorbance from pulse to pulse. It was shown that, in the low-frequency pulse-repetition mode characteristic of the femtosecond microstructuring of silicon, the heat accumulation effect is controlled not by the residual surface temperature by the time of the next pulse arrival, which corresponds to conventional concepts, but by an increase in the maximum temperature from pulse to pulse, from which cooling begins. The accumulation of the residual temperature of the surface can affect the microstructuring process during irradiation near the evaporation threshold or with increasing pulse-repetition rate.« less

Thermal electron heating rate: A derivation

NASA Technical Reports Server (NTRS)

Hoegy, W. R.

1983-01-01

The thermal electron heating rate is an important heat source term in the ionospheric electron energy balance equation, representing heating by photoelectrons or by precipitating higher energy electrons. A formula for the thermal electron heating rate is derived from the kinetic equation using the electron-electron collision operator as given by the unified theory of Kihara and Aono. This collision operator includes collective interactions to produce a finite collision operator with an exact Coulomb logarithm term. The derived heating rate O(e) is the sum of three terms, O(e) = O(p) + S + O(int), which are respectively: (1) primary electron production term giving the heating from newly created electrons that have not yet suffered collisions with the ambient electrons; (2) a heating term evaluated on the energy surface m(e)/2 = E(T) at the transition between Maxwellian and tail electrons at E(T); and (3) the integral term representing heating of Maxwellian electrons by energetic tail electrons at energies ET. Published ionospheric electron temperature studies used only the integral term O(int) with differing lower integration limits. Use of the incomplete heating rate could lead to erroneous conclusions regarding electron heat balance, since O(e) is greater than O(int) by as much as a factor of two.

Analysis of microstructure in electro-spark deposited IN718 superalloy

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

Anisimov, E.; Khan, A.K.; Ojo, O.A., E-mail: olanr

2016-09-15

The microstructure of electro-spark deposited (ESD) superalloy IN718 was studied by the use of scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. In converse to general assumption, the extremely high cooling rate involved in the ESD process did not produce partitionless solidification that is devoid of second phase microconstituents in the material, nano-sized Laves phase and MC carbide particles were observed within the deposited layer. Notwithstanding the several thermal cycles involved in the process, the extremely low heat input of the process produced a deposited region that is free ofmore » the main strengthening phase of the alloy, γ″ phase precipitates, which is in contrast to what have been reported on laser deposition. Nevertheless, application of the standard full heat treatment of the alloy resulted in extensive formation of the γ″ phase precipitates and δ phase precipitates, the most stable secondary phase of the alloy, with nearly, if not complete, dissolution of the Laves phase particles. Furthermore, the XPS analysis done in the study revealed the formation of nano-oxides within the deposited layer, which increased the microhardness of the superalloy in the as-deposited condition and inhibited its grain growth during post-process heat treatment. The microstructure analysis done in this work is crucial to the understanding of properties of the superalloy processed by the ESD technique. - Highlights: •Electron microscopy analyses of electro-spark deposited IN 718 superalloy were performed. •Nano-sized secondary phase particles were observed within the deposited layer. •The study shows that the ESD did not produce partitionless solidification of the alloy.« less

Viking heat sterilization - Progress and problems

NASA Technical Reports Server (NTRS)

Daspit, L. P.; Cortright, E. M.; Stern, J. A.

1974-01-01

The Viking Mars landers to be launched in 1975 will carry experiments in biology, planetology, and atmospheric physics. A terminal dry-heat sterilization process using an inert gas was chosen to meet planetary quarantine requirements and preclude contamination of the biology experiment by terrestrial organisms. Deep sterilization is performed at the component level and terminal surface sterilization at the system level. Solutions to certain component problems relating to sterilization are discussed, involving the gyroscope, tape recorder, battery, electronic circuitry, and outgassing. Heat treatment placed special requirements on electronic packaging, including fastener preload monitoring and solder joints. Chemical and physical testing of nonmetallic materials was performed to establish data on their behavior in heat-treatment and vacuum environments. A Thermal Effects Test Model and a Proof Test Capsule were used. It is concluded that a space vehicle can be designed and fabricated to withstand heat sterilization requirements.

Experimental metrology to obtain thermal phonon transmission coefficients at solid interfaces

NASA Astrophysics Data System (ADS)

Hua, Chengyun; Chen, Xiangwen; Ravichandran, Navaneetha K.; Minnich, Austin J.

2017-05-01

Interfaces play an essential role in phonon-mediated heat conduction in solids, impacting applications ranging from thermoelectric waste heat recovery to heat dissipation in electronics. From the microscopic perspective, interfacial phonon transport is described by transmission coefficients that link vibrational modes in the materials composing the interface. However, direct experimental determination of these coefficients is challenging because most experiments provide a mode-averaged interface conductance that obscures the microscopic detail. Here, we report a metrology to extract thermal phonon transmission coefficients at solid interfaces using ab initio phonon transport modeling and a thermal characterization technique, time-domain thermoreflectance. In combination with transmission electron microscopy characterization of the interface, our approach allows us to link the atomic structure of an interface to the spectral content of the heat crossing it. Our work provides a useful perspective on the microscopic processes governing interfacial heat conduction.

Numerical simulation of plasma processes driven by transverse ion heating

NASA Technical Reports Server (NTRS)

Singh, Nagendra; Chan, C. B.

1993-01-01

The plasma processes driven by transverse ion heating in a diverging flux tube are investigated with numerical simulation. The heating is found to drive a host of plasma processes, in addition to the well-known phenomenon of ion conics. The downward electric field near the reverse shock generates a doublestreaming situation consisting of two upflowing ion populations with different average flow velocities. The electric field in the reverse shock region is modulated by the ion-ion instability driven by the multistreaming ions. The oscillating fields in this region have the possibility of heating electrons. These results from the simulations are compared with results from a previous study based on a hydrodynamical model. Effects of spatial resolutions provided by simulations on the evolution of the plasma are discussed.

Development of silicon growth techniques from melt with surface heating

NASA Astrophysics Data System (ADS)

Kravtsov, Anatoly

2018-05-01

The paper contains literary and personal data on the development history of silicon-growing technology with volumetric and surface melt heating. It discusses the advantages and disadvantages of surface-heating technology. Examples are given of the implementation of such processes in the 60s-70s of the last century, and the reasons for the discontinuation of the relevant work. It describes the main solutions for the implementation of crystal growth process with the electron-beam heating of the melt surface, implemented by KEPP EU (Latvia). It discusses differences in the management of the growth process for the crystals with constant diameters compared to the Czochralski method. It lists geometrical and electro-physical properties of the obtained crystals. It describes the possible use of such crystals and the immediate challenges of technology development.

Enhanced O2 Loss at Mars Due to an Ambipolar Electric Field from Electron Heating

NASA Technical Reports Server (NTRS)

Ergun, R. E.; Andersson, L. A.; Fowler, C. M.; Woodson, A. K.; Weber, T. D.; Delory, G. T.; Andrews, D. J.; Eriksson, A. I.; Mcenulty, T.; Morooka, M. W.;

Plasma Heating and Ultrafast Semiconductor Laser Modulation Through a Terahertz Heating Field

NASA Technical Reports Server (NTRS)

Li, Jian-Zhong; Ning, C. Z.

2000-01-01

Electron-hole plasma heating and ultrafast modulation in a semiconductor laser under a terahertz electrical field are investigated using a set of hydrodynamic equations derived from the semiconductor Bloch equations. The self-consistent treatment of lasing and heating processes leads to the prediction of a strong saturation and degradation of modulation depth even at moderate terahertz field intensity. This saturation places a severe limit to bandwidth achievable with such scheme in ultrafast modulation. Strategies for increasing modulation depth are discussed.

Plasma dynamics near critical density inferred from direct measurements of laser hole boring

NASA Astrophysics Data System (ADS)

Gong, Chao; Tochitsky, Sergei Ya.; Fiuza, Frederico; Pigeon, Jeremy J.; Joshi, Chan

2016-06-01

We have used multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, vHB, of the density cavity pushed forward by a train of C O2 laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the vHB falls rapidly as the laser pulse intensity falls at the back of the laser pulse train. A heuristic theory is presented that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. The measured values of vHB, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.

Plasma dynamics near critical density inferred from direct measurements of laser hole boring

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

Gong, Chao; Tochitsky, Sergei Ya.; Fiuza, Frederico

Here, we use multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, vHB, of the density cavity pushed forward by a train of CO 2 laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the vHB falls rapidly as the laser pulse intensity falls at the back of the laser pulsemore » train. We present a heuristic theory that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. Furthermore, the measured values of v HB, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.« less

Plasma dynamics near critical density inferred from direct measurements of laser hole boring.

PubMed

Gong, Chao; Tochitsky, Sergei Ya; Fiuza, Frederico; Pigeon, Jeremy J; Joshi, Chan

2016-06-01

We have used multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, v_{HB}, of the density cavity pushed forward by a train of CO_{2} laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the v_{HB} falls rapidly as the laser pulse intensity falls at the back of the laser pulse train. A heuristic theory is presented that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. The measured values of v_{HB}, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.

Plasma dynamics near critical density inferred from direct measurements of laser hole boring

DOE PAGES

Gong, Chao; Tochitsky, Sergei Ya.; Fiuza, Frederico; ...

2017-06-24

Here, we use multiframe picosecond optical interferometry to make direct measurements of the hole boring velocity, vHB, of the density cavity pushed forward by a train of CO 2 laser pulses in a near critical density helium plasma. As the pulse train intensity rises, the increasing radiation pressure of each pulse pushes the density cavity forward and the plasma electrons are strongly heated. After the peak laser intensity, the plasma pressure exerted by the heated electrons strongly impedes the hole boring process and the vHB falls rapidly as the laser pulse intensity falls at the back of the laser pulsemore » train. We present a heuristic theory that allows the estimation of the plasma electron temperature from the measurements of the hole boring velocity. Furthermore, the measured values of v HB, and the estimated values of the heated electron temperature as a function of laser intensity are in reasonable agreement with those obtained from two-dimensional numerical simulations.« less

Heat currents in electronic junctions driven by telegraph noise

NASA Astrophysics Data System (ADS)

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

2017-11-01

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

Use of beam deflection to control an electron beam wire deposition process

NASA Technical Reports Server (NTRS)

Taminger, Karen M. (Inventor); Hofmeister, William H. (Inventor); Hafley, Robert A. (Inventor)

2013-01-01

A method for controlling an electron beam process wherein a wire is melted and deposited on a substrate as a molten pool comprises generating the electron beam with a complex raster pattern, and directing the beam onto an outer surface of the wire to thereby control a location of the wire with respect to the molten pool. Directing the beam selectively heats the outer surface of the wire and maintains the position of the wire with respect to the molten pool. An apparatus for controlling an electron beam process includes a beam gun adapted for generating the electron beam, and a controller adapted for providing the electron beam with a complex raster pattern and for directing the electron beam onto an outer surface of the wire to control a location of the wire with respect to the molten pool.

A Concept for Measuring Electron Distribution Functions Using Collective Thomson Scattering

NASA Astrophysics Data System (ADS)

Milder, A. L.; Froula, D. H.

2017-10-01

A.B. Langdon proposed that stable non-Maxwellian distribution functions are realized in coronal inertial confinement fusion plasmas via inverse bremsstrahlung heating. For Zvosc2 Zvosc2 vth2 > 1 , vth2 > 1 , the inverse bremsstrahlung heating rate is sufficiently fast to compete with electron-electron collisions. This process preferentially heats the subthermal electrons leading to super-Gaussian distribution functions. A method to identify the super-Gaussian order of the distribution functions in these plasmas using collective Thomson scattering will be proposed. By measuring the collective Thomson spectra over a range of angles the density, temperature and super-Gaussian order can be determined. This is accomplished by fitting non-Maxwellian distribution data with a super-Gaussian model; in order to match the density and electron temperature to within 10%, the super-Gaussian order must be varied. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Modelling of pulsed electron beam induced graphite ablation: Sublimation versus melting

NASA Astrophysics Data System (ADS)

Ali, Muddassir; Henda, Redhouane

2017-12-01

Pulsed electron beam ablation (PEBA) has recently emerged as a very promising technique for the deposition of thin films with superior properties. Interaction of the pulsed electron beam with the target material is a complex process, which consists of heating, phase transition, and erosion of a small portion from the target surface. Ablation can be significantly affected by the nature of thermal phenomena taking place at the target surface, with subsequent bearing on the properties, stoichiometry and structure of deposited thin films. A two stage, one-dimensional heat conduction model is presented to describe two different thermal phenomena accounting for interaction of a graphite target with a polyenergetic electron beam. In the first instance, the thermal phenomena are comprised of heating, melting and vaporization of the target surface, while in the second instance the thermal phenomena are described in terms of heating and sublimation of the graphite surface. In this work, the electron beam delivers intense electron pulses of ∼100 ns with energies up to 16 keV and an electric current of ∼400 A to a graphite target. The temperature distribution, surface recession velocity, ablated mass per unit area, and ablation depth for the graphite target are numerically simulated by the finite element method for each case. Based on calculation findings and available experimental data, ablation appears to occur mainly in the regime of melting and vaporization from the surface.

Electron Fluid Description of Wave-Particle Interactions in Strong Buneman Turbulence

NASA Astrophysics Data System (ADS)

Che, Haihong

2013-10-01

To understand the nature of anomalous resistivity in magnetic reconnection, we investigate turbulence-induced momentum transport and energy dissipation associated with electron heating in Buneman instability. Using 3D particle-in-cell simulations, we find that the macroscopic effects generated by wave-particle interactions can be described by a set of electron fluid equations. These equations show that the energy dissipation and momentum transports in Buneman instability are locally quasi-static but globally non-static and irreversible. Turbulence drag dissipates both the bulk energy of electron streams and the associated magnetic energy. The decrease of magnetic field maintains an inductive electric field that re-accelerates electrons. The net loss of streaming energy is converted into electron heat and increases the electron Boltzmann entropy. The growth of self-sustained Buneman waves satisfies a Bernoulli-like equation which relates the turbulence-induced convective momentum transport and thermal momentum transport. Electron trapping and de-trapping drives local momentum transports, while phase mixing converts convective momentum into thermal momentum.These two local momentum transports sustain the Buneman waves and act as the micro-macro link in the anomalous heating process. This research is supported by the NASA Postdoctoral Program at NASA/GSFC administered by Oak Ridge Associated Universities through a contract with NASA.

Propagation of resist heating mask error to wafer level

NASA Astrophysics Data System (ADS)

Babin, S. V.; Karklin, Linard

2006-10-01

As technology is approaching 45 nm and below the IC industry is experiencing a severe product yield hit due to rapidly shrinking process windows and unavoidable manufacturing process variations. Current EDA tools are unable by their nature to deliver optimized and process-centered designs that call for 'post design' localized layout optimization DFM tools. To evaluate the impact of different manufacturing process variations on final product it is important to trace and evaluate all errors through design to manufacturing flow. Photo mask is one of the critical parts of this flow, and special attention should be paid to photo mask manufacturing process and especially to mask tight CD control. Electron beam lithography (EBL) is a major technique which is used for fabrication of high-end photo masks. During the writing process, resist heating is one of the sources for mask CD variations. Electron energy is released in the mask body mainly as heat, leading to significant temperature fluctuations in local areas. The temperature fluctuations cause changes in resist sensitivity, which in turn leads to CD variations. These CD variations depend on mask writing speed, order of exposure, pattern density and its distribution. Recent measurements revealed up to 45 nm CD variation on the mask when using ZEP resist. The resist heating problem with CAR resists is significantly smaller compared to other types of resists. This is partially due to higher resist sensitivity and the lower exposure dose required. However, there is no data yet showing CD errors on the wafer induced by CAR resist heating on the mask. This effect can be amplified by high MEEF values and should be carefully evaluated at 45nm and below technology nodes where tight CD control is required. In this paper, we simulated CD variation on the mask due to resist heating; then a mask pattern with the heating error was transferred onto the wafer. So, a CD error on the wafer was evaluated subject to only one term of the mask error budget - the resist heating CD error. In simulation of exposure using a stepper, variable MEEF was considered.

Gap length effect on electron energy distribution in capacitive radio frequency discharges

NASA Astrophysics Data System (ADS)

You, S. J.; Kim, S. S.; Kim, Jung-Hyung; Seong, Dae-Jin; Shin, Yong-Hyeon; Chang, H. Y.

2007-11-01

A study on the dependence of electron energy distribution function (EEDF) on discharge gap size in capacitive rf discharges was conducted. The evolution of the EEDF over a gap size range from 2.5to7cm in 65mTorr Ar discharges was investigated both experimentally and theoretically. The measured EEDFs exhibited typical bi-Maxwellian forms with low energy electron groups. A significant depletion in the low energy portion of the bi-Maxwellian was found with decreasing gap size. The results show that electron heating by bulk electric fields, which is the main heating process of the low-energy electrons, is greatly enhanced as the gap size decreases, resulting in the abrupt change of the EEDF. The calculated EEDFs based on nonlocal kinetic theory are in good agreement with the experiments.

Apparatus and method of direct water cooling several parallel circuit cards each containing several chip packages

DOEpatents

Cipolla, Thomas M [Katonah, NY; Colgan, Evan George [Chestnut Ridge, NY; Coteus, Paul W [Yorktown Heights, NY; Hall, Shawn Anthony [Pleasantville, NY; Tian, Shurong [Mount Kisco, NY

2011-12-20

A cooling apparatus, system and like method for an electronic device includes a plurality of heat producing electronic devices affixed to a wiring substrate. A plurality of heat transfer assemblies each include heat spreaders and thermally communicate with the heat producing electronic devices for transferring heat from the heat producing electronic devices to the heat transfer assemblies. The plurality of heat producing electronic devices and respective heat transfer assemblies are positioned on the wiring substrate having the regions overlapping. A heat conduit thermally communicates with the heat transfer assemblies. The heat conduit circulates thermally conductive fluid therethrough in a closed loop for transferring heat to the fluid from the heat transfer assemblies via the heat spreader. A thermally conductive support structure supports the heat conduit and thermally communicates with the heat transfer assemblies via the heat spreader transferring heat to the fluid of the heat conduit from the support structure.

Resolving the role of femtosecond heated electrons in ultrafast spin dynamics.

PubMed

Mendil, J; Nieves, P; Chubykalo-Fesenko, O; Walowski, J; Santos, T; Pisana, S; Münzenberg, M

2014-02-05

Magnetization manipulation is essential for basic research and applications. A fundamental question is, how fast can the magnetization be reversed in nanoscale magnetic storage media. When subject to an ultrafast laser pulse, the speed of the magnetization dynamics depends on the nature of the energy transfer pathway. The order of the spin system can be effectively influenced through spin-flip processes mediated by hot electrons. It has been predicted that as electrons drive spins into the regime close to almost total demagnetization, characterized by a loss of ferromagnetic correlations near criticality, a second slower demagnetization process takes place after the initial fast drop of magnetization. By studying FePt, we unravel the fundamental role of the electronic structure. As the ferromagnet Fe becomes more noble in the FePt compound, the electronic structure is changed and the density of states around the Fermi level is reduced, thereby driving the spin correlations into the limit of critical fluctuations. We demonstrate the impact of the electrons and the ferromagnetic interactions, which allows a general insight into the mechanisms of spin dynamics when the ferromagnetic state is highly excited, and identifies possible recording speed limits in heat-assisted magnetization reversal.

Observation of collisionless heating of low energy electrons in low pressure inductively coupled argon plasmas

NASA Astrophysics Data System (ADS)

Lee, Min-Hyong; Lee, Hyo-Chang; Chung, Chin-Wook

2008-12-01

Collisionless heating of low energy electrons was observed in low pressure argon rf-biased inductively coupled plasmas (ICPs) by measurement of the electron energy distribution function (EEDF). When only capacitive power (bias) was supplied, the EEDF in the discharge was a bi-Maxwellian distribution with two electron groups. It was found that the low energy electrons were heated up significantly even with a little inductive power (<20 W) even when the discharge was in E mode. Due to the low gas pressure and low temperature of low energy electrons (close to the energy of the Ramsauer minimum), the collisional heating of low energy electrons appears to be negligible. Therefore, this effective heating of the low energy electrons showed a direct experimental evidence of the collisionless heating by inductive field. The significant heating of low energy electrons in E mode indicates that collisionless heating in the skin layer is an important electron heating mechanism of low pressure ICP even when the discharge is in E mode.

Experimental Characterization of Electron Beam Welded SAE 5137H Thick Steel Plate

NASA Astrophysics Data System (ADS)

Kattire, Prakash; Bhawar, Valmik; Thakare, Sandeep; Patil, Sachin; Mane, Santosh; Singh, Rajkumar, Dr.

2017-09-01

Electron beam welding is known for its narrow weld zone with high depth to width ratio, less heat affected zone, less distortion and contamination. Electron beam welding is fusion welding process, where high velocity electrons impinge on material joint to be welded and kinetic energy of this electron is transformed into heat upon impact to fuse the material. In the present work electron beam welding of 60 mm thick SAE 5137H steel is studied. Mechanical and metallurgical properties of electron beam welded joint of SAE 5137H were evaluated. Mechanical properties are analysed by tensile, impact and hardness test. Metallurgical properties are investigated through optical and scanning electron microscope. The hardness traverse across weld zone shows HV 370-380, about 18% increase in the tensile strength and very low toughness of weld joint compared to parent metal. Microstructural observation shows equiaxed dendrite in the fusion zone and partial grain refinement was found in the HAZ.

Combined Modeling of Acceleration, Transport, and Hydrodynamic Response in Solar Flares. 1; The Numerical Model

NASA Technical Reports Server (NTRS)

Liu, Wei; Petrosian, Vahe; Mariska, John T.

2009-01-01

Acceleration and transport of high-energy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares, but for convenience and simplicity they were artificially separated in the past. We present here self consistently combined Fokker-Planck modeling of particles and hydrodynamic simulation of flare plasma. Energetic electrons are modeled with the Stanford unified code of acceleration, transport, and radiation, while plasma is modeled with the Naval Research Laboratory flux tube code. We calculated the collisional heating rate directly from the particle transport code, which is more accurate than those in previous studies based on approximate analytical solutions. We repeated the simulation of Mariska et al. with an injection of power law, downward-beamed electrons using the new heating rate. For this case, a -10% difference was found from their old result. We also used a more realistic spectrum of injected electrons provided by the stochastic acceleration model, which has a smooth transition from a quasi-thermal background at low energies to a non thermal tail at high energies. The inclusion of low-energy electrons results in relatively more heating in the corona (versus chromosphere) and thus a larger downward heat conduction flux. The interplay of electron heating, conduction, and radiative loss leads to stronger chromospheric evaporation than obtained in previous studies, which had a deficit in low-energy electrons due to an arbitrarily assumed low-energy cutoff. The energy and spatial distributions of energetic electrons and bremsstrahlung photons bear signatures of the changing density distribution caused by chromospheric evaporation. In particular, the density jump at the evaporation front gives rise to enhanced emission, which, in principle, can be imaged by X-ray telescopes. This model can be applied to investigate a variety of high-energy processes in solar, space, and astrophysical plasmas.

New Evidence for Efficient Collisionless Heating of Electrons at the Reverse Shock of a Young Supernova Remnant

NASA Technical Reports Server (NTRS)

Yamaguchi, Hiroya; Eriksen, Kristoffer A.; Badenes, Carles; Hughes, John P.; Brickhouse, Nancy S.; Foster, Adam R.; Patnaude, Daniel J.; Petre, Robert; Slane, Patrick O.; Smith, Randall K.

2013-01-01

Although collisionless shocks are ubiquitous in astrophysics, certain key aspects of them are not well understood. In particular, the process known as collisionless electron heating, whereby electrons are rapidly energized at the shock front, is one of the main open issues in shock physics. Here, we present the first clear evidence for efficient collisionless electron heating at the reverse shock of Tycho's supernova remnant (SNR), revealed by Fe K diagnostics using high-quality X-ray data obtained by the Suzaku satellite. We detect K beta (3p yields 1s) fluorescence emission from low-ionization Fe ejecta excited by energetic thermal electrons at the reverse shock front, which peaks at a smaller radius than Fe K alpha (2p yields 1s) emission dominated by a relatively highly ionized component. Comparisons with our hydrodynamical simulations imply instantaneous electron heating to a temperature 1000 times higher than expected from Coulomb collisions alone. The unique environment of the reverse shock, which is propagating with a high Mach number into rarefied ejecta with a low magnetic field strength, puts strong constraints on the physical mechanism responsible for this heating and favors a cross-shock potential created by charge deflection at the shock front. Our sensitive observation also reveals that the reverse shock radius of this SNR is about 10% smaller than the previous measurement using the Fe K alpha morphology from the Chandra observations. Since strong Fe K beta fluorescence is expected only from low-ionization plasma where Fe ions still have many 3p electrons, this feature is key to diagnosing the plasma state and distribution of the immediate postshock ejecta in a young SNR.

Texture-Induced Anisotropy in an Inconel 718 Alloy Deposited Using Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Tayon, W.; Shenoy, R.; Bird, R.; Hafley, R.; Redding, M.

2014-01-01

A test block of Inconel (IN) 718 was fabricated using electron beam freeform fabrication (EBF(sup 3)) to examine how the EBF(sup 3) deposition process affects the microstructure, crystallographic texture, and mechanical properties of IN 718. Tests revealed significant anisotropy in the elastic modulus for the as-deposited IN 718. Subsequent tests were conducted on specimens subjected to a heat treatment designed to decrease the level of anisotropy. Electron backscatter diffraction (EBSD) was used to characterize crystallographic texture in the as-deposited and heat treated conditions. The anisotropy in the as-deposited condition was strongly affected by texture as evidenced by its dependence on orientation relative to the deposition direction. Heat treatment resulted in a significant improvement in modulus of the EBF(sup 3) product to a level nearly equivalent to that for wrought IN 718 with reduced anisotropy; reduction in texture through recrystallization; and production of a more homogeneous microstructure.

Rapid, in Situ Synthesis of High Capacity Battery Anodes through High Temperature Radiation-Based Thermal Shock.

PubMed

Chen, Yanan; Li, Yiju; Wang, Yanbin; Fu, Kun; Danner, Valencia A; Dai, Jiaqi; Lacey, Steven D; Yao, Yonggang; Hu, Liangbing

2016-09-14

High capacity battery electrodes require nanosized components to avoid pulverization associated with volume changes during the charge-discharge process. Additionally, these nanosized electrodes need an electronically conductive matrix to facilitate electron transport. Here, for the first time, we report a rapid thermal shock process using high-temperature radiative heating to fabricate a conductive reduced graphene oxide (RGO) composite with silicon nanoparticles. Silicon (Si) particles on the order of a few micrometers are initially embedded in the RGO host and in situ transformed into 10-15 nm nanoparticles in less than a minute through radiative heating. The as-prepared composites of ultrafine Si nanoparticles embedded in a RGO matrix show great performance as a Li-ion battery (LIB) anode. The in situ nanoparticle synthesis method can also be adopted for other high capacity battery anode materials including tin (Sn) and aluminum (Al). This method for synthesizing high capacity anodes in a RGO matrix can be envisioned for roll-to-roll nanomanufacturing due to the ease and scalability of this high-temperature radiative heating process.

Deposition of diamond-like films by ECR microwave plasma

NASA Technical Reports Server (NTRS)

Shing, Yuh-Han (Inventor); Pool, Frederick S. (Inventor)

1995-01-01

Hard amorphous hydrogenated carbon, diamond-like films are deposited using an electron cyclotron resonance microwave plasma with a separate radio frequency power bias applied to a substrate stage. The electron cyclotron resonance microwave plasma yields low deposition pressure and creates ion species otherwise unavailable. A magnetic mirror configuration extracts special ion species from a plasma chamber. Different levels of the radio frequency power bias accelerate the ion species of the ECR plasma impinging on a substrate to form different diamond-like films. During the deposition process, a sample stage is maintained at an ambient temperature of less than 100.degree. C. No external heating is applied to the sample stage. The deposition process enables diamond-like films to be deposited on heat-sensitive substrates.

Strategy for Texture Management in Metals Additive Manufacturing

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

Kirka, Michael M.; Lee, Yousub; Greeley, Duncan A.

Additive manufacturing (AM) technologies have long been recognized for their ability to fabricate complex geometric components directly from models conceptualized through computers, allowing for complicated designs and assemblies to be fabricated at lower costs, with shorter time to market, and improved function. Lacking behind the design complexity aspect is the ability to fully exploit AM processes for control over texture within AM components. Currently, standard heat-fill strategies utilized in AM processes result in largely columnar grain structures. Here, we propose a point heat source fill for the electron beam melting (EBM) process through which the texture in AM materials canmore » be controlled. Using this point heat source strategy, the ability to form either columnar or equiaxed grain structures upon solidification through changes in the process parameters associated with the point heat source fill is demonstrated for the nickel-base superalloy, Inconel 718. Mechanically, the material is demonstrated to exhibit either anisotropic properties for the columnar-grained material fabricated through using the standard raster scan of the EBM process or isotropic properties for the equiaxed material fabricated using the point heat source fill.« less

Strategy for Texture Management in Metals Additive Manufacturing

DOE PAGES

Kirka, Michael M.; Lee, Yousub; Greeley, Duncan A.; ...

2017-01-31

Additive manufacturing (AM) technologies have long been recognized for their ability to fabricate complex geometric components directly from models conceptualized through computers, allowing for complicated designs and assemblies to be fabricated at lower costs, with shorter time to market, and improved function. Lacking behind the design complexity aspect is the ability to fully exploit AM processes for control over texture within AM components. Currently, standard heat-fill strategies utilized in AM processes result in largely columnar grain structures. Here, we propose a point heat source fill for the electron beam melting (EBM) process through which the texture in AM materials canmore » be controlled. Using this point heat source strategy, the ability to form either columnar or equiaxed grain structures upon solidification through changes in the process parameters associated with the point heat source fill is demonstrated for the nickel-base superalloy, Inconel 718. Mechanically, the material is demonstrated to exhibit either anisotropic properties for the columnar-grained material fabricated through using the standard raster scan of the EBM process or isotropic properties for the equiaxed material fabricated using the point heat source fill.« less

The integration of liquid cryogen cooling and cryocoolers withsuperconducting electronic systems

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

Green, Michael A.

2003-07-09

The need for cryogenic cooling has been a critical issuethat has kept superconducting electronic devices from reaching the marketplace. Even though the performance of many of the superconductingcircuits is superior to silicon electronics, the requirement forcryogenic cooling has put the superconducting devices at a seriousdisadvantage. This report discusses the process of refrigeratingsuperconducting devices with cryogenic liquids and small cryocoolers.Three types of cryocoolers are compared for vibration, efficiency, andreliability. The connection of a cryocooler to the load is discussed. Acomparison of using flexible copper straps to carry the heat load andusing heat pipe is shown. The type of instrumentation needed formonitoringmore » and controlling the cooling is discussed.« less

Artificial muscles on heat

NASA Astrophysics Data System (ADS)

McKay, Thomas G.; Shin, Dong Ki; Percy, Steven; Knight, Chris; McGarry, Scott; Anderson, Iain A.

2014-03-01

Many devices and processes produce low grade waste heat. Some of these include combustion engines, electrical circuits, biological processes and industrial processes. To harvest this heat energy thermoelectric devices, using the Seebeck effect, are commonly used. However, these devices have limitations in efficiency, and usable voltage. This paper investigates the viability of a Stirling engine coupled to an artificial muscle energy harvester to efficiently convert heat energy into electrical energy. The results present the testing of the prototype generator which produced 200 μW when operating at 75°C. Pathways for improved performance are discussed which include optimising the electronic control of the artificial muscle, adjusting the mechanical properties of the artificial muscle to work optimally with the remainder of the system, good sealing, and tuning the resonance of the displacer to minimise the power required to drive it.

Measurements of plasma sheath heat flux in the Alcator C-Mod divertor

NASA Astrophysics Data System (ADS)

Brunner, Dan; Labombard, Brian; Terry, Jim; Reinke, Matt

2010-11-01

Heat flux is one of the most important parameters controlling the lifetime of first-wall components in fusion experiments and reactors. The sheath heat flux coefficient (γ) is a parameter relating heat flux (from a plasma to a material surface) to the electron temperature and ion saturation current. Being such a simple expression for a kinetic process, it is of great interest to plasma edge fluid modelers. Under the assumptions of equal ion and electron temperatures, no secondary electron emission, and no net current to the surface the value of γ is approximately 7 [1]. Alcator C-Mod provides a unique opportunity among today's experiments to measure reactor-relevant heat fluxes (100's of MW/m^2 parallel to the magnetic field) in reactor-like divertor geometry. Motivated by the DoE 2010 joint milestone to measure heat flux footprints, the lower outer divertor of Alcator has been instrumented with a suite of Langmuir probes, novel surface thermocouples, and calorimeters in tiles purposefully ramped to eliminate shadowing; all within view of an IR camera. Initial results indicate that the experimentally inferred values of γ are found to agree with simple theory in the sheath limited regime and diverges to lower values as the density increases.

Space Station - The base for tomorrow's electronic industry

NASA Technical Reports Server (NTRS)

Naumann, Robert J.

1985-01-01

The potential value of space material processing on the Space Station for the electronics industry is examined. The primary advantages of the space environment for producing high-purity semiconductors and electrooptical materials are identified as the virtual absence of gravity (suppressing buoyancy-driven convection in melts and density segregation of alloys) and the availabilty of high vacuum (with high pumping speed and heat rejection). The recent history of material development and processing technology in the electronics industry is reviewed, and the principal features of early space experiments are outlined.

Effect of heat input on the microstructure, residual stresses and corrosion resistance of 304L austenitic stainless steel weldments

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

Unnikrishnan, Rahul, E-mail: rahulunnikrishnannair@gmail.com; Idury, K.S.N. Satish, E-mail: satishidury@gmail.com; Ismail, T.P., E-mail: tpisma@gmail.com

Austenitic stainless steels are widely used in high performance pressure vessels, nuclear, chemical, process and medical industry due to their very good corrosion resistance and superior mechanical properties. However, austenitic stainless steels are prone to sensitization when subjected to higher temperatures (673 K to 1173 K) during the manufacturing process (e.g. welding) and/or certain applications (e.g. pressure vessels). During sensitization, chromium in the matrix precipitates out as carbides and intermetallic compounds (sigma, chi and Laves phases) decreasing the corrosion resistance and mechanical properties. In the present investigation, 304L austenitic stainless steel was subjected to different heat inputs by shielded metalmore » arc welding process using a standard 308L electrode. The microstructural developments were characterized by using optical microscopy and electron backscattered diffraction, while the residual stresses were measured by X-ray diffraction using the sin{sup 2}ψ method. It was observed that even at the highest heat input, shielded metal arc welding process does not result in significant precipitation of carbides or intermetallic phases. The ferrite content and grain size increased with increase in heat input. The grain size variation in the fusion zone/heat affected zone was not effectively captured by optical microscopy. This study shows that electron backscattered diffraction is necessary to bring out changes in the grain size quantitatively in the fusion zone/heat affected zone as it can consider twin boundaries as a part of grain in the calculation of grain size. The residual stresses were compressive in nature for the lowest heat input, while they were tensile at the highest heat input near the weld bead. The significant feature of the welded region and the base metal was the presence of a very strong texture. The texture in the heat affected zone was almost random. - Highlights: • Effect of heat input on microstructure, residual stresses and corrosion is studied. • HAZ and width of dendrite in the welded region increase with heat input. • Residual stresses are tensile near the welded region after the highest heat input. • Welded region has the highest pit density after highest heat input. • Dendrites and δ-ferrite were highly oriented in the welded region.« less

Analysis of counter flow of corona wind for heat transfer enhancement

NASA Astrophysics Data System (ADS)

Shin, Dong Ho; Baek, Soo Hong; Ko, Han Seo

2018-03-01

A heat sink for cooling devices using the counter flow of a corona wind was developed in this study. Detailed information about the numerical investigations of forced convection using the corona wind was presented. The fins of the heat sink using the counter flow of a corona wind were also investigated. The corona wind generator with a wire-to-plate electrode arrangement was used for generating the counter flow to the fin. The compact and simple geometric characteristics of the corona wind generator facilitate the application of the heat sink using the counter flow, demonstrating the heat sink is effective for cooling electronic devices. Parametric studies were performed to analyze the effect of the counter flow on the fins. Also, the velocity and temperature were measured experimentally for the test mock-up of the heat sink with the corona wind generator to verify the numerical results. From a numerical study, the type of fin and its optimal height, length, and pitch were suggested for various heat fluxes. In addition, the correlations to calculate the mass of the developed heat sink and its cooling performance in terms of the heat transfer coefficient were derived. Finally, the cooling efficiencies corresponding to the mass, applied power, total size, and noise of the devices were compared with the existing commercial central processing unit (CPU) cooling devices with rotor fans. As a result, it was confirmed that the heat sink using the counter flow of the corona wind showed appropriate efficiencies for cooling electronic devices, and is a suitable replacement for the existing cooling device for high power electronics.

Improvement of efficiency and temperature control of induction heating vapor source on electron cyclotron resonance ion source.

PubMed

Takenaka, T; Kiriyama, R; Muramatsu, M; Kitagawa, A; Uchida, T; Kurisu, Y; Nozaki, D; Yano, K; Yoshida, Y; Sato, F; Kato, Y; Iida, T

2012-02-01

An electron cyclotron resonance ion source (ECRIS) is used to generate multicharged ions for many kinds of the fields. We have developed an evaporator by using induction heating method that can generate pure vapor from solid state materials in ECRIS. We develop the new matching and protecting circuit by which we can precisely control the temperature of the induction heating evaporator. We can control the temperature within ±15 °C around 1400 °C under the operation pressure about 10(-4) Pa. We are able to use this evaporator for experiment of synthesizing process to need pure vapor under enough low pressure, e.g., experiment of generation of endohedral Fe-fullerene at the ECRIS.

Impact of Gas Heating in Inductively Coupled Plasmas

NASA Technical Reports Server (NTRS)

Hash, D. B.; Bose, D.; Rao, M. V. V. S.; Cruden, B. A.; Meyyappan, M.; Sharma, S. P.; Biegel, Bryan (Technical Monitor)

2001-01-01

Recently it has been recognized that the neutral gas in inductively coupled plasma reactors heats up significantly during processing. The resulting gas density variations across the reactor affect reaction rates, radical densities, plasma characteristics, and uniformity within the reactor. A self-consistent model that couples the plasma generation and transport to the gas flow and heating has been developed and used to study CF4 discharges. A Langmuir probe has been used to measure radial profiles of electron density and temperature. The model predictions agree well with the experimental results. As a result of these comparisons along with the poorer performance of the model without the gas-plasma coupling, the importance of gas heating in plasma processing has been verified.

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

Tsytovich, Vadim, E-mail: tsytov@lpi.ru; Max Planck Institute for Extraterrestrial Physics, Garching; Gusein-zade, Namik

Dust structuring is a natural and universal process in complex plasmas. The scattering of electromagnetic waves by dust structures is governed by the factor of coherency, i.e., the total number of coherent electrons in a single structure. In the present paper, we consider how the factor of coherency changes due to additional pulse electron heating and show that it obeys a hysteresis. After the end of the pulse heating, the scattering intensity differs substantially from that before heating. There are three necessary conditions for scattering hysteresis: first, the radiation wavelength should be larger than the pattern (structure) size; second, themore » total number of coherent electrons confined by the structure should be large; and third, the heating pulse duration should be shorter than the characteristic time of dust structure formation. We present the results of numerical calculations using existing models of self-consistent dust structures with either positively or negatively charged dust grains. It is shown that, depending on the grain charge and the ionization rate, two types of hysteresis are possible: one with a final increase of the scattering and the other with a final decrease of the scattering. It is suggested that the hysteresis of coherent scattering can be used as a tool in laboratory experiments and that it can be a basic mechanism explaining the observed hysteresis in radar scattering by noctilucent clouds during active experiments on electron heating in mesosphere.« less

Inner Magnetospheric Superthermal Electron Transport: Photoelectron and Plasma Sheet Electron Sources

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Liemohn, M. W.; Kozyra, J. U.; Moore, T. E.

1998-01-01

Two time-dependent kinetic models of superthermal electron transport are combined to conduct global calculations of the nonthermal electron distribution function throughout the inner magnetosphere. It is shown that the energy range of validity for this combined model extends down to the superthermal-thermal intersection at a few eV, allowing for the calculation of the en- tire distribution function and thus an accurate heating rate to the thermal plasma. Because of the linearity of the formulas, the source terms are separated to calculate the distributions from the various populations, namely photoelectrons (PEs) and plasma sheet electrons (PSEs). These distributions are discussed in detail, examining the processes responsible for their formation in the various regions of the inner magnetosphere. It is shown that convection, corotation, and Coulomb collisions are the dominant processes in the formation of the PE distribution function and that PSEs are dominated by the interplay between the drift terms. Of note is that the PEs propagate around the nightside in a narrow channel at the edge of the plasmasphere as Coulomb collisions reduce the fluxes inside of this and convection compresses the flux tubes inward. These distributions are then recombined to show the development of the total superthermal electron distribution function in the inner magnetosphere and their influence on the thermal plasma. PEs usually dominate the dayside heating, with integral energy fluxes to the ionosphere reaching 10(exp 10) eV/sq cm/s in the plasmasphere, while heating from the PSEs typically does not exceed 10(exp 8) eV/sq cm/s. On the nightside, the inner plasmasphere is usually unheated by superthermal electrons. A feature of these combined spectra is that the distribution often has upward slopes with energy, particularly at the crossover from PE to PSE dominance, indicating that instabilities are possible.

Electron-phonon interaction model and prediction of thermal energy transport in SOI transistor.

PubMed

Jin, Jae Sik; Lee, Joon Sik

2007-11-01

An electron-phonon interaction model is proposed and applied to thermal transport in semiconductors at micro/nanoscales. The high electron energy induced by the electric field in a transistor is transferred to the phonon system through electron-phonon interaction in the high field region of the transistor. Due to this fact, a hot spot occurs, which is much smaller than the phonon mean free path in the Si-layer. The full phonon dispersion model based on the Boltzmann transport equation (BTE) with the relaxation time approximation is applied for the interactions among different phonon branches and different phonon frequencies. The Joule heating by the electron-phonon scattering is modeled through the intervalley and intravalley processes for silicon by introducing average electron energy. The simulation results are compared with those obtained by the full phonon dispersion model which treats the electron-phonon scattering as a volumetric heat source. The comparison shows that the peak temperature in the hot spot region is considerably higher and more localized than the previous results. The thermal characteristics of each phonon mode are useful to explain the above phenomena. The optical mode phonons of negligible group velocity obtain the highest energy density from electrons, and resides in the hot spot region without any contribution to heat transport, which results in a higher temperature in that region. Since the acoustic phonons with low group velocity show the higher energy density after electron-phonon scattering, they induce more localized heating near the hot spot region. The ballistic features are strongly observed when phonon-phonon scattering rates are lower than 4 x 10(10) S(-1).

Electron energy deposition in N2 gas

NASA Technical Reports Server (NTRS)

Fox, J. L.; Victor, G. A.

1988-01-01

The processes by which energetic electrons lose energy in a weakly ionized gas of molecular nitrogen are analyzed and calculations are carried out taking into account the discrete nature of the excitation processes. The excitation, ionization, dissociation and heating efficiencies are computed for energies up to 200 eV absorbed in a gas with fractional ionizations varying from 10(-6) to 10(-2). Individual vibrational excitations up to the seventh vibrational level are presented.

Numerical study of plasma generation process and internal antenna heat loadings in J-PARC RF negative ion source

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

Shibata, T., E-mail: shibat@post.j-parc.jp; Ueno, A.; Oguri, H.

A numerical model of plasma transport and electromagnetic field in the J-PARC (Japan Proton Accelerator Research Complex) radio frequency ion source has been developed to understand the relation between antenna coil heat loadings and plasma production/transport processes. From the calculation, the local plasma density increase is observed in the region close to the antenna coil. Electrons are magnetized by the magnetic field line with absolute magnetic flux density 30–120 Gauss which leads to high local ionization rate. The results suggest that modification of magnetic configuration can be made to reduce plasma heat flux onto the antenna.

Sequential control of step-bunching during graphene growth on SiC (0001)

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

Bao, Jianfeng; Kusunoki, Michiko; Yasui, Osamu

2016-08-22

We have investigated the relation between the step-bunching and graphene growth phenomena on an SiC substrate. We found that only a minimum amount of step-bunching occurred during the graphene growth process with a high heating rate. On the other hand, a large amount of step-bunching occurred using a slow heating process. These results indicated that we can control the degree of step-bunching during graphene growth by controlling the heating rate. We also found that graphene coverage suppressed step bunching, which is an effective methodology not only in the graphene technology but also in the SiC-based power electronics.

Study of heating capacity of focused IR light soldering systems.

PubMed

Anguiano, C; Félix, M; Medel, A; Bravo, M; Salazar, D; Márquez, H

2013-10-07

An experimental study about four optical setups used for developing a Focused IR Light Soldering System (FILSS) for Surface Mount Technology (SMT) lead-free electronic devices specifically for Ball Grid Arrays (BGA) is presented. An analysis of irradiance and infrared thermography at BGA surface is presented, as well as heat transfer by radiation and conduction process from the surface of the BGA to the solder balls. The results of this work show that the heating provided by our proposed optical setups, measured at the BGA under soldering process, meets the high temperature and uniform thermal distribution requirements, which are defined by the reflow solder method for SMT devices.

Heating of Solar Wind Ions via Cyclotron Resonance

NASA Astrophysics Data System (ADS)

Navarro, R.; Moya, P. S.; Figueroa-Vinas, A.; Munoz, V.; Valdivia, J. A.

2017-12-01

Remote and in situ observations in the solar wind show that ion and electron velocity distributions persistently deviate from thermal equilibrium in the form of relative streaming between species components, temperature anisotropy, etc. These non-thermal features represent a source of free energy for the excitation of kinetic instabilities and fluctuations in the plasma. In this regard, it is believed that plasma particles can be heated, through a second order Fermi acceleration process, by multiple resonances with unstable counter-propagating field-aligned Ion-cyclotron waves. For multi-species plasmas, several collective wave modes participate in this process. In this work, we test this model by studying the percentage of ions that resonate with the waves modes described by the proper kinetic multi-species dispersion relation in a solar-wind-like plasma composed of electrons, protons, and alpha particles. Numerical results are compared with WIND spacecraft data to test its relevance for the existence of thresholds for the preferential perpendicular heating of He+2 ions as observed in the solar wind fast streams.

Heat- and electron-beam-induced transport of gold particles into silicon oxide and silicon studied by in situ high-resolution transmission electron microscopy.

PubMed

Biskupek, Johannes; Kaiser, Ute; Falk, Fritz

2008-06-01

In this study, we describe the transport of gold (Au) nanoparticles from the surface into crystalline silicon (Si) covered by silicon oxide (SiO(2)) as revealed by in situ high-resolution transmission electron microscopy. Complete crystalline Au nanoparticles sink through the SiO(2) layer into the Si substrate when high-dose electron irradiation is applied and temperature is raised above 150 degrees C. Above temperatures of 250 degrees C, the Au nanoparticles finally dissolve into fragments accompanied by crystallization of the amorphized Si substrate around these fragments. The transport process is explained by a wetting process followed by Stokes motion. Modelling this process yields boundaries for the interface energies involved.

Investigation of the relevant kinetic processes in the initial stage of a double-arcing instability in oxygen plasmas

NASA Astrophysics Data System (ADS)

Mancinelli, B.; Prevosto, L.; Chamorro, J. C.; Minotti, F. O.; Kelly, H.

2018-05-01

A numerical investigation of the kinetic processes in the initial (nanosecond range) stage of the double-arcing instability was developed. The plasma-sheath boundary region of an oxygen-operated cutting torch was considered. The energy balance and chemistry processes in the discharge were described. It is shown that the double-arcing instability is a sudden transition from a diffuse (glow-like) discharge to a constricted (arc-like) discharge in the plasma-sheath boundary region arising from a field-emission instability. A critical electric field value of ˜107 V/m was found at the cathodic part of the nozzle wall under the conditions considered. The field-emission instability drives in turn a fast electronic-to-translational energy relaxation mechanism, giving rise to a very fast gas heating rate of at least ˜109 K/s, mainly due to reactions of preliminary dissociation of oxygen molecules via the highly excited electronic state O2(B3Σu-) populated by electron impact. It is expected that this fast oxygen heating rate further stimulates the discharge contraction through the thermal instability mechanism.

Development of optimum process for electron beam cross-linking of high density polyethylene thermal energy storage pellets, process scale-up and production of application qualities of material

NASA Technical Reports Server (NTRS)

Salyer, I. O.

1980-01-01

The electron irradiation conditions required to prepare thermally from stable high density polyethylene (HDPE) were defined. The conditions were defined by evaluating the heat of fusion and the melting temperature of several HDPE specimens. The performance tests conducted on the specimens, including the thermal cycling tests in the thermal energy storage unit are described. The electron beam irradiation tests performed on the specimens, in which the total radiation dose received by the pellets, the electron beam current, the accelerating potential, and the atmospheres were varied, are discussed.

Thermally assisted nanosecond laser generation of ferric nanoparticles

NASA Astrophysics Data System (ADS)

Kurselis, K.; Kozheshkurt, V.; Kiyan, R.; Chichkov, B.; Sajti, L.

2018-03-01

A technique to increase nanosecond laser based production of ferric nanoparticles by elevating temperature of the iron target and controlling its surface exposure to oxygen is reported. High power near-infrared laser ablation of the iron target heated up to 600 °C enhances the particle generation efficiency by more than tenfold exceeding 6 μg/J. Temporal and thermal dependencies of the particle generation process indicate correlation of this enhancement with the oxidative processes that take place on the iron surface during the per spot interpulse delay. Nanoparticles, produced using the heat-assisted ablation technique, are examined using scanning electron and transmission electron microscopy confirming the presence of 1-100 nm nanoparticles with an exponential size distribution that contain multiple randomly oriented magnetite nanocrystallites. The described process enables the application of high power lasers and facilitates precise, uniform, and controllable direct deposition of ferric nanoparticle coatings at the industry-relevant rates.

Influence of heat input in electron beam process on microstructure and properties of duplex stainless steel welded interface

NASA Astrophysics Data System (ADS)

Zhang, Zhiqiang; Jing, Hongyang; Xu, Lianyong; Han, Yongdian; Zhao, Lei; Lv, Xiaoqing; Zhang, Jianyang

2018-03-01

The influence of heat input in electron beam (EB) process on microstructure, mechanical properties, and pitting corrosion resistance of duplex stainless steel (DSS) welded interface was investigated. The rapid cooling in EB welding resulted in insufficient austenite formation. The austenite mainly consisted of grain boundary austenite and intragranular austenite, and there was abundant Cr2N precipitation in the ferrite. The Ni, Mo, and Si segregation indicated that the dendritic solidification was primarily ferrite in the weld. The weld exhibited higher hardness, lower toughness, and poorer pitting corrosion resistance than the base metal. The impact fractures of the welds were dominated by the transgranular cleavage failure of the ferrite. The ferrite was selectively attacked because of its lower pitting resistance equivalent number than that of austenite. The Cr2N precipitation accelerated the pitting corrosion. In summary, the optimised heat input slightly increased the austenite content, reduced the segregation degree and ferrite texture intensity, decreased the hardness, and improved the toughness and pitting corrosion resistance. However, the effects were limited. Furthermore, optimising the heat input could not suppress the Cr2N precipitation. Taking into full consideration the microstructure and properties, a heat input of 0.46 kJ/mm is recommended for the EB welding of DSS.

Observation of auroral secondary electrons in the Jovian magnetosphere

NASA Technical Reports Server (NTRS)

Mcnutt, Ralph L., Jr.; Bagenal, Fran; Thorne, Richard M.

1990-01-01

Localized enhancements in the flux of suprathermal electrons were observed by the Voyager 1 Plasma Science instrument near the outer boundary of the Io plasma torus between L = 7.5 and l = 10. This localization, which occurs within the general region of hot electrons noted by Sittler and Strobel (1987), and the spectral characteristics of the observed electrons are consistent with secondary (backscattered) electron production by intense Jovian auroral energetic particle precipitation and support the hypothesis that such electrons may contribute to the processes that heat the plasma in this region of the magnetosphere.

Direct heating of a laser-imploded core using ultraintense laser LFEX

NASA Astrophysics Data System (ADS)

Kitagawa, Y.; Mori, Y.; Ishii, K.; Hanayama, R.; Nishimura, Y.; Okihara, S.; Nakayama, S.; Sekine, T.; Takagi, M.; Watari, T.; Satoh, N.; Kawashima, T.; Komeda, O.; Hioki, T.; Motohiro, T.; Azuma, H.; Sunahara, A.; Sentoku, Y.; Arikawa, Y.; Abe, Y.; Miura, E.; Ozaki, T.

2017-07-01

A CD shell was preimploded by two counter-propagating green beams from the GEKKO laser system GXII (based at the Institute of Laser Engineering, Osaka University), forming a dense core. The core was predominantly heated by energetic ions driven by the laser for fast-ignition-fusion experiment, an extremely energetic ultrashort pulse laser, that is illuminated perpendicularly to the GXII axis. Consequently, we observed the D(d, n)3 He-reacted neutrons (DD beam-fusion neutrons) at a yield of 5× {{10}8} n/4π sr. The beam-fusion neutrons verified that the ions directly collided with the core plasma. Whereas the hot electrons heated the whole core volume, the energetic ions deposited their energies locally in the core. As evidenced in the spectrum, the process simultaneously excited thermal neutrons with a yield of 6× {{10}7} n/4π sr, raising the local core temperature from 0.8 to 1.8 keV. The shell-implosion dynamics (including the beam fusion and thermal fusion initiated by fast deuterons and carbon ions) can be explained by the one-dimensional hydrocode STAR 1D. Meanwhile, the core heating due to resistive processes driven by hot electrons, and also the generation of fast ions were well-predicted by the two-dimensional collisional particle-in-cell code. Together with hot electrons, the ion contribution to fast ignition is indispensable for realizing high-gain fusion. By virtue of its core heating and ignition, the proposed scheme can potentially achieve high-gain fusion.

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

Takahashi, Masayuki, E-mail: m.takahashi@al.t.u-tokyo.ac.jp; Ohnishi, Naofumi

A filamentary plasma is reproduced based on a fully kinetic model of electron and ion transports coupled with electromagnetic wave propagation. The discharge plasma transits from discrete to diffusive patterns at a 110-GHz breakdown, with decrease in the ambient pressure, because of the rapid electron diffusion that occurs during an increase in the propagation speed of the ionization front. A discrete plasma is obtained at low pressures when a low-frequency microwave is irradiated because the ionization process becomes more dominant than the electron diffusion, when the electrons are effectively heated by the low-frequency microwave. The propagation speed of the plasmamore » increases with decrease in the incident microwave frequency because of the higher ionization frequency and faster plasma diffusion resulting from the increase in the energy-absorption rate. An external magnetic field is applied to the breakdown volume, which induces plasma filamentation at lower pressures because the electron diffusion is suppressed by the magnetic field. The thrust performance of a microwave rocket is improved by the magnetic fields corresponding to the electron cyclotron resonance (ECR) and its higher-harmonic heating, because slower propagation of the ionization front and larger energy-absorption rates are obtained at lower pressures. It would be advantageous if the fundamental mode of ECR heating is coupled with a lower frequency microwave instead of combining the higher-harmonic ECR heating with the higher frequency microwave. This can improve the thrust performance with smaller magnetic fields even if the propagation speed increases because of the decrease in the incident microwave frequency.« less

Creation of high-energy electron tails by means of the modified two-stream instability

NASA Technical Reports Server (NTRS)

Tanaka, M.; Papadopoulos, K.

1983-01-01

Particle simulations of the modified two-stream instability demonstrate strong electron acceleration rather than bulk heating when the relative drift speed is below a critical speed Vc. A very interesting nonlinear mode transition and autoresonance acceleration process is observed which accelerates the electrons much above the phase speed of the linearly unstable modes. Simple criteria are presented that predict the value of Vc and the number density of the accelerated electrons.

Effects of design parameters and puff topography on heating coil temperature and mainstream aerosols in electronic cigarettes

NASA Astrophysics Data System (ADS)

Zhao, Tongke; Shu, Shi; Guo, Qiuju; Zhu, Yifang

2016-06-01

Emissions from electronic cigarettes (ECs) may contribute to both indoor and outdoor air pollution and the number of users is increasing rapidly. ECs operate based on the evaporation of e-liquid by a high-temperature heating coil. Both puff topography and design parameters can affect this evaporation process. In this study, both mainstream aerosols and heating coil temperature were measured concurrently to study the effects of design parameters and puff topography. The heating coil temperatures and mainstream aerosols varied over a wide range across different brands and within same brand. The peak heating coil temperature and the count median diameter (CMD) of EC aerosols increased with a longer puff duration and a lower puff flow rate. The particle number concentration was positively associated with the puff duration and puff flow rate. These results provide a better understanding of how EC emissions are affected by design parameters and puff topography and emphasize the urgent need to better regulate EC products.

Relativistic-Electron-Dominated Solar Flares Observed by Fermi/GBM

NASA Astrophysics Data System (ADS)

Shih, A. Y.; Schwartz, R. A.; Dennis, B. R.

2013-12-01

Up to tens of percent of the energy released in solar flares goes into accelerating electrons above ~10 keV and ions above ~1 MeV, and the impulsive heating of the ambient solar atmosphere by these particles is partially or wholly responsible for the production of hot flare plasmas (up to ~50 MK). Although flares can accelerate electrons to relativistic energies, in even large flares the typical falling power-law energy spectrum means that the plasma is primarily heated by the much larger number of low-energy electrons. However, there have been flares observed where the electron energy spectra have high low-energy cutoffs (well above ~100 keV), which significantly changes the electron energies responsible for heating and modifies the usual conception of energy transport in a flare. A systematic study of a range of relativistic-electron-dominated flares can improve our understanding of the relevant acceleration processes and how they may differ from those in "typical" flares. We search the Fermi/GBM data set for such flares based on the electron-associated X-ray/gamma-ray bremsstrahlung emission, making use of an improved background-subtraction approach to improve the ability to detect weaker flares. We present the fitted parameters for the relativistic-electron spectrum and their evolution over time, and compare against RHESSI observations and other instruments when available. We also discuss these events in the context of previously observed correlations between relativistic-electron acceleration and ion acceleration in flares.

Ion and Electron Heating Characteristics of Magnetic Re- Connection in Mast Tokamak Merging Experiment

NASA Astrophysics Data System (ADS)

Tanabe, Hiroshi; Inomoto, Michiaki; Ono, Yasushi; Yamada, Takuma; Imazawa, Ryota; Cheng, Chio-Zong

2016-07-01

We present results of recent studies of high power heating of magnetic reconnection, the fundamental process of several astrophysical events such as solar flare, in the Mega Amp Spherical Tokamak (MAST) - the world largest merging experiment. In addition to the previously reported significant reconnection heating up to ˜1keV [1], detailed local profiles of electron and ion temperature have been measured using a ultra-fine 300 channel Ruby- and a 130 channel YAG-Thomson scattering and a new 32 channel ion Doppler tomography diagnostics [2]. 2D profile measurement of electron temperature revealed highly localized heating structure at the X point with the characteristic scale length of 0.02-0.05m0.3T), a thick layer of closed flux surface surrounding the current sheet sustains the temperature profile for longer time than the electron and ion energy relaxation time ˜4-10ms, finally forming triple peak structures of ion and electron temperatures at the X point and in the downstream. While the peak electron temperature at the X point increases with toroidal field, the bulk electron temperature and the ion temperature in the downstream are unaffected. [1] Y. Ono et.al., Plasma Phys. Control. Fusion 54, 124039 (2012) [2] H. Tanabe et. al., Nucl. Fusion 53, 093027 (2013). [3] H. Tanabe et.al., Phys. Rev. Lett. 115, 215004 (2015)

ELECTRON-CAPTURE AND β-DECAY RATES FOR sd-SHELL NUCLEI IN STELLAR ENVIRONMENTS RELEVANT TO HIGH-DENSITY O–NE–MG CORES

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

Suzuki, Toshio; Toki, Hiroshi; Nomoto, Ken’ichi, E-mail: suzuki@phys.chs.nihon-u.ac.jp

Electron-capture and β-decay rates for nuclear pairs in the sd-shell are evaluated at high densities and high temperatures relevant to the final evolution of electron-degenerate O–Ne–Mg cores of stars with initial masses of 8–10 M{sub ⊙}. Electron capture induces a rapid contraction of the electron-degenerate O–Ne–Mg core. The outcome of rapid contraction depends on the evolutionary changes in the central density and temperature, which are determined by the competing processes of contraction, cooling, and heating. The fate of the stars is determined by these competitions, whether they end up with electron-capture supernovae or Fe core-collapse supernovae. Since the competing processes aremore » induced by electron capture and β-decay, the accurate weak rates are crucially important. The rates are obtained for pairs with A = 20, 23, 24, 25, and 27 by shell-model calculations in the sd-shell with the USDB Hamiltonian. Effects of Coulomb corrections on the rates are evaluated. The rates for pairs with A = 23 and 25 are important for nuclear Urca processes that determine the cooling rate of the O–Ne–Mg core, while those for pairs with A = 20 and 24 are important for the core contraction and heat generation rates in the core. We provide these nuclear rates at stellar environments in tables with fine enough meshes at various densities and temperatures for studies of astrophysical processes sensitive to the rates. In particular, the accurate rate tables are crucially important for the final fates of not only O–Ne–Mg cores but also a wider range of stars, such as C–O cores of lower-mass stars.« less

High-energy electron beams for ceramic joining

NASA Astrophysics Data System (ADS)

Turman, Bob N.; Glass, S. J.; Halbleib, J. A.; Helmich, D. R.; Loehman, Ron E.; Clifford, Jerome R.

1995-03-01

Joining of structural ceramics is possible using high melting point metals such as Mo and Pt that are heated with a high energy electron beam, with the potential for high temperature joining. A 10 MeV electron beam can penetrate through 1 cm of ceramic, offering the possibility of buried interface joining. Because of transient heating and the lower heat capacity of the metal relative to the ceramic, a pulsed high power beam has the potential for melting the metal without decomposing or melting the ceramic. We have demonstrated the feasibility of the process with a series of 10 MeV, 1 kW electron beam experiments. Shear strengths up to 28 MPa have been measured. This strength is comparable to that reported in the literature for bonding silicon nitride (Si3N4) to molybdenum with copper-silver-titanium braze, but weaker than that reported for Si3N4 - Si3N4 with gold-nickel braze. The bonding mechanism appears to be formation of a thin silicide layer. Beam damage to the Si3N4 was also assessed.

Plasma ignition and steady state simulations of the Linac4 H- ion source

NASA Astrophysics Data System (ADS)

Mattei, S.; Ohta, M.; Yasumoto, M.; Hatayama, A.; Lettry, J.; Grudiev, A.

2014-02-01

The RF heating of the plasma in the Linac4 H- ion source has been simulated using a particle-in-cell Monte Carlo collision method. This model is applied to investigate the plasma formation starting from an initial low electron density of 1012 m-3 and its stabilization at 1018 m-3. The plasma discharge at low electron density is driven by the capacitive coupling with the electric field generated by the antenna, and as the electron density increases the capacitive electric field is shielded by the plasma and induction drives the plasma heating process. Plasma properties such as e-/ion densities and energies, sheath formation, and shielding effect are presented and provide insight to the plasma properties of the hydrogen plasma.

Room Temperature Deposition Processes Mediated By Ultrafast Photo-Excited Hot Electrons

DTIC Science & Technology

2014-01-30

mechanical through resonant energy transfer. The average electron temperature (Tel) during τ2 evolves as energy is lost through optical and acoustic ...through ballistic collisions and acoustic phonons. The large difference in heat capacities between electrons and the substrate leads to negligible...temperature pyrometer indicated only a ~30oC temperature gradient between the thermocouple location and the topside of the sample which faced the

TURBULENCE AND PROTON–ELECTRON HEATING IN KINETIC PLASMA

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

Matthaeus, William H; Parashar, Tulasi N; Wu, P.

2016-08-10

Analysis of particle-in-cell simulations of kinetic plasma turbulence reveals a connection between the strength of cascade, the total heating rate, and the partitioning of dissipated energy into proton heating and electron heating. A von Karman scaling of the cascade rate explains the total heating across several families of simulations. The proton to electron heating ratio increases in proportion to total heating. We argue that the ratio of gyroperiod to nonlinear turnover time at the ion kinetic scales controls the ratio of proton and electron heating. The proposed scaling is consistent with simulations.

Comprehensive stabilization mechanism of electron-beam irradiated polyacrylonitrile fibers to shorten the conventional thermal treatment

PubMed Central

Park, Sejoon; Yoo, Seung Hwa; Kang, Ha Ri; Jo, Seong Mu; Joh, Han-Ik; Lee, Sungho

2016-01-01

An electron beam was irradiated on polyacrylonitrile (PAN) fibers prior to thermal stabilization. The electron-beam irradiation effectively shortened the thermal stabilization process by one fourth compared with the conventional thermal stabilization process. A comprehensive mechanistic study was conducted regarding this shortening of the thermal stabilization by electron-beam irradiation. Various species of chain radicals were produced in PAN fibers by electron-beam irradiation and existed for a relatively long duration, as observed by electron spin resonance spectroscopy. Subsequently, these radicals were gradually oxidized to peroxy radicals in the presence of oxygen under storage or heating. We found that these peroxy radicals (CO) enabled such an effective shortcut of thermal stabilization by acting as intermolecular cross-linking and partial aromatization points in the low temperature range (100–130 °C) and as earlier initiation seeds of successive cyclization reactions in the next temperature range (>130–140 °C) of thermal stabilization. Finally, even at a low irradiation dose (200 kGy), followed by a short heat treatment (230 °C for 30 min), the PAN fibers were sufficiently stabilized to produce carbon fibers with tensile strength and modulus of 2.3 and 216 GPa, respectively, after carbonization. PMID:27349719

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

NASA Astrophysics Data System (ADS)

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

2017-12-01

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

Status and future trends of radiation processing in Brazil

NASA Astrophysics Data System (ADS)

Lugão, A. B.; Andrade, E.; Silva, L. G.

1998-06-01

Electron-beam and gamma irradiation of polymers are widely applied in Brazil today. The main applications are: - radio-induced crosslinking of wire and cable for automobile and appliance industry; - heat shrinkable tubes for appliance, automobile and electronic; - heat shrinkable packing for food processing industry; - sterilization of medical supplies and so on. Nevertheless, there are only a few industrial facilities about 20 years old in full operation at present and there are some new low energy machines for food packing. The reason for such absence of investment in this area was studied and the relation between automobile and appliance production with radiation processing was fully demonstrated for Brazil case. In conclusion, it was shown that the industry of radiation processing of polymers is likely to experience a strong growth based on the continuous increase in the production of automobiles and appliances. The R&D activities of IPEN are an important support for developing the necessary technology and developing the necessary confidence in the radiation as tool for economical and social growth.

Thermal runaway of metal nano-tips during intense electron emission

NASA Astrophysics Data System (ADS)

Kyritsakis, A.; Veske, M.; Eimre, K.; Zadin, V.; Djurabekova, F.

2018-06-01

When an electron emitting tip is subjected to very high electric fields, plasma forms even under ultra high vacuum conditions. This phenomenon, known as vacuum arc, causes catastrophic surface modifications and constitutes a major limiting factor not only for modern electron sources, but also for many large-scale applications such as particle accelerators, fusion reactors etc. Although vacuum arcs have been studied thoroughly, the physical mechanisms that lead from intense electron emission to plasma ignition are still unclear. In this article, we give insights to the atomic scale processes taking place in metal nanotips under intense field emission conditions. We use multi-scale atomistic simulations that concurrently include field-induced forces, electron emission with finite-size and space-charge effects, Nottingham and Joule heating. We find that when a sufficiently high electric field is applied to the tip, the emission-generated heat partially melts it and the field-induced force elongates and sharpens it. This initiates a positive feedback thermal runaway process, which eventually causes evaporation of large fractions of the tip. The reported mechanism can explain the origin of neutral atoms necessary to initiate plasma, a missing key process required to explain the ignition of a vacuum arc. Our simulations provide a quantitative description of in the conditions leading to runaway, which shall be valuable for both field emission applications and vacuum arc studies.

Microwave Assisted Helicon Plasmas

NASA Astrophysics Data System (ADS)

McKee, John; Caron, David; Jemiolo, Andrew; Scime, Earl

2017-10-01

The use of two (or more) rf sources at different frequencies is a common technique in the plasma processing industry to control ion energy characteristics separately from plasma generation. A similar approach is presented here with the focus on modifying the electron population in argon and helium plasmas. The plasma is generated by a helicon source at a frequency f0 = 13.56 MHz. Microwaves of frequency f1 = 2.45 GHz are then injected into the helicon source chamber perpendicular to the background magnetic field. The microwaves damp on the electrons via X-mode Electron Cyclotron Heating (ECH) at the upper hybrid resonance, providing additional energy input into the electrons. The effects of this secondary-source heating on electron density, temperature, and energy distribution function are examined and compared to helicon-only single source plasmas as well as numeric models suggesting that the heating is not evenly distributed. Optical Emission Spectroscopy (OES) is used to examine the impact of the energetic tail of the electron distribution on ion and neutral species via collisional excitation. Large enhancements of neutral spectral lines are observed in both Ar and He. While small enhancement of ion lines is seen in Ar, ion lines not normally present in He are observed during microwave injection. U.S. National Science Foundation Grant No. PHY-1360278.

Low-Temperature Oxidation-Free Selective Laser Sintering of Cu Nanoparticle Paste on a Polymer Substrate for the Flexible Touch Panel Applications.

PubMed

Kwon, Jinhyeong; Cho, Hyunmin; Eom, Hyeonjin; Lee, Habeom; Suh, Young Duk; Moon, Hyunjin; Shin, Jaeho; Hong, Sukjoon; Ko, Seung Hwan

2016-05-11

Copper nanomaterials suffer from severe oxidation problem despite the huge cost effectiveness. The effect of two different processes for conventional tube furnace heating and selective laser sintering on copper nanoparticle paste is compared in the aspects of chemical, electrical and surface morphology. The thermal behavior of the copper thin films by furnace and laser is compared by SEM, XRD, FT-IR, and XPS analysis. The selective laser sintering process ensures low annealing temperature, fast processing speed with remarkable oxidation suppression even in air environment while conventional tube furnace heating experiences moderate oxidation even in Ar environment. Moreover, the laser-sintered copper nanoparticle thin film shows good electrical property and reduced oxidation than conventional thermal heating process. Consequently, the proposed selective laser sintering process can be compatible with plastic substrate for copper based flexible electronics applications.

Assembly of opto-electronic module with improved heat sink

DOEpatents

Chan, Benson; Fortier, Paul Francis; Freitag, Ladd William; Galli, Gary T.; Guindon, Francois; Johnson, Glen Walden; Letourneau, Martial; Sherman, John H.; Tetreault, Real

2004-11-23

A heat sink for a transceiver optoelectronic module including dual direct heat paths and a structure which encloses a number of chips having a central web which electrically isolates transmitter and receiver chips from each other. A retainer for an optical coupler having a port into which epoxy is poured. An overmolded base for an optoelectronic module having epoxy flow controller members built thereon. Assembly methods for an optoelectronic module including gap setting and variation of a TAB bonding process.

Evolution of Inclusions During the 1473 K (1200 °C) Heating Process of EH36 Shipbuilding Steel

NASA Astrophysics Data System (ADS)

Wang, Qiyu; Zou, Xiaodong; Matsuura, Hiroyuki; Wang, Cong

2018-02-01

Evolution behaviors of inclusions of EH36 shipbuilding steel during 1473 K (1200 °C) heating have been studied in conjunction with ex situ scanning electron microscope (SEM) examination and in situ confocal scanning laser microscopy (CSLM) observations. It has been found that Al-Ca-O-S complex inclusions dominate the particles in the cast billet. However, TiN inclusions are profusely populated after heating. Moreover, possible strategies governing austenite growth are offered here.

Detection of Heating Processes in Coronal Loops by Soft X-ray Spectroscopy

NASA Astrophysics Data System (ADS)

Kawate, Tomoko; Narukage, Noriyuki; Ishikawa, Shin-nosuke; Imada, Shinsuke

2017-08-01

Imaging and Spectroscopic observations in the soft X-ray band will open a new window of the heating/acceleration/transport processes in the solar corona. The soft X-ray spectrum between 0.5 and 10 keV consists of the electron thermal free-free continuum and hot coronal lines such as O VIII, Fe XVII, Mg XI, Si XVII. Intensity of free-free continuum emission is not affected by the population of ions, whereas line intensities especially from highly ionized species have a sensitivity of the timescale of ionization/recombination processes. Thus, spectroscopic observations of both continuum and line intensities have a capability of diagnostics of heating/cooling timescales. We perform a 1D hydrodynamic simulation coupled with the time-dependent ionization, and calculate continuum and line intensities under different heat input conditions in a coronal loop. We also examine the differential emission measure of the coronal loop from the time-integrated soft x-ray spectra. As a result, line intensity shows a departure from the ionization equilibrium and shows different responses depending on the frequency of the heat input. Solar soft X-ray spectroscopic imager will be mounted in the sounding rocket experiment of the Focusing Optics X-ray Solar Imager (FOXSI). This observation will deepen our understanding of heating processes to solve the “coronal heating problem”.

Demonstration of Efficient Core Heating of Magnetized Fast Ignition in FIREX project

NASA Astrophysics Data System (ADS)

Johzaki, Tomoyuki

2017-10-01

Extensive theoretical and experimental research in the FIREX ``I project over the past decade revealed that the large angular divergence of the laser generated electron beam is one of the most critical problems inhibiting efficient core heating in electron-driven fast ignition. To solve this problem, beam guiding using externally applied kilo-tesla class magnetic field was proposed, and its feasibility has recently been numerically demonstrated. In 2016, integrated experiments at ILE Osaka University demonstrated core heating efficiencies reaching > 5 % and heated core temperatures of 1.7 keV. In these experiments, a kilo-tesla class magnetic field was applied to a cone-attached Cu(II) oleate spherical solid target by using a laser-driven capacitor-coil. The target was then imploded by G-XII laser and heated by the PW-class LFEX laser. The heating efficiency was evaluated by measuring the number of Cu-K- α photons emitted. The heated core temperature was estimated by the X-ray intensity ratio of Cu Li-like and He-like emission lines. To understand the detailed dynamics of the core heating process, we carried out integrated simulations using the FI3 code system. Effects of magnetic fields on the implosion and electron beam transport, detailed core heating dynamics, and the resultant heating efficiency and core temperature will be presented. I will also discuss the prospect for an ignition-scale design of magnetized fast ignition using a solid ball target. This work is partially supported by JSPA KAKENHI Grant Number JP16H02245, JP26400532, JP15K21767, JP26400532, JP16K05638 and is performed with the support and the auspices of the NIFS Collaboration Research program (NIFS12KUGK057, NIFS15KUGK087).

Powder bed charging during electron-beam additive manufacturing

DOE PAGES

Cordero, Zachary C.; Meyer, Harry M.; Nandwana, Peeyush; ...

2016-11-18

Electrons injected into the build envelope during powder-bed electron-beam additive manufacturing can accumulate on the irradiated particles and cause them to repel each other. Furthermore, these electrostatic forces can grow so large that they drive the particles out of the build envelope in a process known as smoking. Here, a model of powder bed charging is formulated and used to develop criteria that predict the conditions under which the powder bed will smoke. These criteria suggest dependences on particle size, pre-heat temperature, and process parameters that align closely with those observed in practice.

Fluoroalkylsilane-Modified Textile-Based Personal Energy Management Device for Multifunctional Wearable Applications.

PubMed

Guo, Yinben; Li, Kerui; Hou, Chengyi; Li, Yaogang; Zhang, Qinghong; Wang, Hongzhi

2016-02-01

The rapid development of wearable electronics in recent years has brought increasing energy consumption, making it an urgent need to focus on personal energy harvesting, storage and management. Herein, a textile-based personal energy management device with multilayer-coating structure was fabricated by encapsulating commercial nylon cloth coated with silver nanowires into polydimethylsiloxane using continuous and facile dip-coating method. This multilayer-coating structure can not only harvest mechanical energy from human body motion to power wearable electronics but also save energy by keeping people warm without losing heat to surroundings and wasting energy to heat empty space and inanimate objects. Fluoroalkylsilanes (FAS) were grafted onto the surface of the film through one single dip-coating process to improve its energy harvesting performance, which has hardly adverse effect to heat insulation and Joule heating property. In the presence of FAS modification, the prepared film harvested mechanical energy to reach a maximum output power density of 2.8 W/m(2), charged commercial capacitors and lighted LEDs, showing its potential in powering wearable electronics. Furthermore, the film provided 8% more thermal insulation than normal cloth at 37 °C and efficiently heated to 40 °C within 4 min when applied the voltage of only 1.5 V due to Joule heating effect. The high flexibility and stability of the film ensures its wide and promising application in the wearable field.

Thermal Modeling and Simulation of Electron Beam Melting for Rapid Prototyping on Ti6Al4V Alloys

NASA Astrophysics Data System (ADS)

Neira Arce, Alderson

To be a viable solution for contemporary engineering challenges, the use of titanium alloys in a wider range of applications requires the development of new techniques and processes that are able to decrease production cost and delivery times. As a result, the use of material consolidation in a near-net-shape fashion, using dynamic techniques like additive manufacturing by electron beam selective melting EBSM represents a promising method for part manufacturing. However, a new product material development can be cost prohibitive, requiring the use of computer modeling and simulation as a way to decrease turnaround time. To ensure a proper representation of the EBSM process, a thermophysical material characterization and comparison was first performed on two Ti6Al4V powder feedstock materials prepared by plasma (PREP) and gas atomized (GA) processes. This evaluation comprises an evaluation on particle size distribution, density and powder surface area, collectively with the temperature dependence on properties such as heat capacity, thermal diffusivity, thermal conductivity and surface emissivity. Multiple techniques were employed in this evaluation, including high temperature differential scanning calorimetry (HT-DSC), laser flash analysis (LFA), infrared remote temperature analysis (IR-Thermography), laser diffraction, liquid and gas pycnometry using mercury and krypton adsorption respectively. This study was followed by the review of complementary strategies to simulate the temperature evolution during the EBSM process, using a finite element analysis package called COMSOL Multiphysics. Two alternatives dedicated to representing a moving heat source (electron beam) and the powder bed were developed using a step-by-step approximation initiative. The first method consisted of the depiction of a powder bed discretized on an array of domains, each one representing a static melt pool, where the moving heat source was illustrated by a series of time dependant selective heating and cooling steps. The second method consisted of the solution of a prescribed domain, where each powder layer is discretized by an individual 3D element and the heat source is represented by a 1D element displaced by a temperature-coupling extrapolation routine. Two validation strategies were presented here; the first was used to confirm the accuracy of the proposed model strategy by setting up a controlled experiment; the second was used to validate the post-processing data obtained by the simulation by comparison with in-situ measured EBSM process temperature. Finally, a post-process part evaluation on surface finishing and part porosity was discussed including an assessment of the use of non-destructive inspection techniques such as 3D profilometry by axial chromatism for surface roughness, partial section analysis by serial block-face scanning electron microscopy (SBFSEM) and micro computed tomography (CT-Scan) for pore and inclusion detection.

Electron cyclotron resonance heating by magnetic filter field in a negative hydrogen ion source.

PubMed

Kim, June Young; Cho, Won-Hwi; Dang, Jeong-Jeung; Chung, Kyoung-Jae; Hwang, Y S

2016-02-01

The influence of magnetic filter field on plasma properties in the heating region has been investigated in a planar-type inductively coupled radio-frequency (RF) H(-) ion source. Besides filtering high energy electrons near the extraction region, the magnetic filter field is clearly observed to increase the electron temperature in the heating region at low pressure discharge. With increasing the operating pressure, enhancement of electron temperature in the heating region is reduced. The possibility of electron cyclotron resonance (ECR) heating in the heating region due to stray magnetic field generated by a filter magnet located at the extraction region is examined. It is found that ECR heating by RF wave field in the discharge region, where the strength of an axial magnetic field is approximately ∼4.8 G, can effectively heat low energy electrons. Depletion of low energy electrons in the electron energy distribution function measured at the heating region supports the occurrence of ECR heating. The present study suggests that addition of axial magnetic field as small as several G by an external electromagnet or permanent magnets can greatly increase the generation of highly ro-vibrationally excited hydrogen molecules in the heating region, thus improving the performance of H(-) ion generation in volume-produced negative hydrogen ion sources.

Electron beams in research and technology

NASA Astrophysics Data System (ADS)

Mehnert, R.

1995-11-01

Fast electrons lose their energy by inelastic collisions with electrons of target molecules forming secondary electrons and excited molecules. Coulomb interaction of secondary electrons with valence electrons of neighboring molecules leads to the formation of radical cations, thermalized electrons, excited molecular states and radicals. The primary reactive species initiate chemical reactions in the materials irradiated. Polymer modifications using accelerated electrons such as cross-linking of cable insulation, tubes, pipes and moldings, vulcanization of elastomers, grafting of polymer surfaces, processing of foamed plastics and heat shrinkable materials have gained wide industrial acceptance. A steadily growing electron beam technology is curing of paints, lacquers, printing inks and functional coatings. Electron beam processing offers high productivity, the possibility to treat the materials at normal temperature and pressure, excellent process control and clean production conditions. On an industrial scale the most important application of fast electrons is curing of 100% reactive monomer/prepolymer systems. Mainly acrylates and epoxides are used to formulate functional coatings on substrates such as paper, foil, wood, fibre board and high pressure laminates. A survey is given about the reaction mechanism of curing, the characterization of cured coatings, and of some industrial application.

Unraveling Main Limiting Sites of Photosynthesis under Below- and Above-Ground Heat Stress in Cucumber and the Alleviatory Role of Luffa Rootstock.

PubMed

Li, Hao; Ahammed, Golam J; Zhou, Guona; Xia, Xiaojian; Zhou, Jie; Shi, Kai; Yu, Jingquan; Zhou, Yanhong

2016-01-01

Photosynthesis is one of the most thermo-sensitive processes in plants. Although the severity of heat stress could be attenuated by grafting approach, the primary damaged site of photosynthesis system under heat stress and the regulatory mechanism of rootstock-mediated heat tolerance are poorly understood. In the current study, cucumber plants grafted onto their own roots and heat-tolerant luffa roots were exposed to root-zone heat (25/40°C) and aerial heat (40/25°C) individually and in combination (40/40°C) to understand the response of photosynthetic process by investigating energy absorption and distribution, electron transport in photosystem (PS) II and I, and CO2 assimilation. According to the results, root-zone heat stress inhibited photosynthesis mainly through decreasing Rubisco activity, while aerial heat stress mainly through inhibiting PSII acceptor side. The imbalance in light absorption and utilization resulted in accumulation of reactive oxygen species that caused damage to photosynthetic apparatus, forming a vicious cycle. On the contrary, grafting cucumber onto heat-tolerant luffa rootstock alleviated heat-induced photosynthetic inhibition and oxidative stress by maintaining higher root vitality, HSP70 accumulation, and antioxidant potential.

SYNCHROTRON HEATING BY A FAST RADIO BURST IN A SELF-ABSORBED SYNCHROTRON NEBULA AND ITS OBSERVATIONAL SIGNATURE

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

Yang, Yuan-Pei; Dai, Zi-Gao; Zhang, Bing, E-mail: zhang@physics.unlv.edu

Fast radio bursts (FRBs) are mysterious transient sources. If extragalactic, as suggested by their relative large dispersion measures, their brightness temperatures must be extremely high. Some FRB models (e.g., young pulsar model, magnetar giant flare model, or supra-massive neutron star collapse model) suggest that they may be associated with a synchrotron nebula. Here we study a synchrotron-heating process by an FRB in a self-absorbed synchrotron nebula. If the FRB frequency is below the synchrotron self-absorption frequency of the nebula, electrons in the nebula would absorb FRB photons, leading to a harder electron spectrum and enhanced self-absorbed synchrotron emission. In themore » meantime, the FRB flux is absorbed by the nebula electrons. We calculate the spectra of FRB-heated synchrotron nebulae, and show that the nebula spectra would show a significant hump in several decades near the self-absorption frequency. Identifying such a spectral feature would reveal an embedded FRB in a synchrotron nebula.« less

First results from the energetic particle instrument on the OEDIPUS-C sounding rocket

NASA Astrophysics Data System (ADS)

Gough, M. P.; Hardy, D. A.; James, H. G.

The Canadian / US OEDIPUS-C rocket was flown from the Poker Flat Rocket Range November 6th 1995 as a mother-son sounding rocket. It was designed to study auroral ionospheric plasma physics using active wave sounding and prove tether technology. The payload separated into two sections reaching a separation of 1200m along the Earth's magnetic field. One section included a frequency stepped HF transmitter and the other included a synchronised HF receiver. Both sections included Energetic Particle Instruments, EPI, stepped in energy synchronously with the transmitter steps. On-board EPI particle processing in both payloads provided direct measurements of electron heating, wave-particle interactions via particle correlators, and a high resolution measurement of wave induced particle heating via transmitter synchronised fast sampling. Strong electron heating was observed at times when the HF transmitter frequency was equal to a harmonic of the electron gyrofrequency, f_ce, or equal to the upper hybrid frequency, f_uh.

Reflection and backscattering of microwaves under doubling of the plasma density and displacement of the gyroresonance region during electron cyclotron resonance heating of plasma in the l-2M stellarator

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

Batanov, G. M.; Borzosekov, V. D.; Vasilkov, D. G.

Reflection and backscattering of high-power (400 kW) gyrotron radiation creating and heating plasma at the second harmonic of the electronic cyclotron frequency in the L-2M stellarator have been investigated experimentally. The effect of the displacement of the gyroresonance region from the axis of the plasma column under doubling of the plasma density on the processes of reflection and backscattering of microwave radiation has been examined. A near doubling of short-wavelength (k{sub ⊥} ≈ 30 cm{sup –1}) turbulent density fluctuations squared is observed. The change in the energy confinement time under variations of plasma parameters and characteristics of short-wavelength turbulence ismore » discussed. A discrepancy between the measured values of the reflection coefficient from the electron cyclotron resonance heating region and predictions of the one-dimensional model is revealed.« less

Features of Afterbody Radiative Heating for Earth Entry

NASA Technical Reports Server (NTRS)

Johnston, Christopher O.; Brandis, Aaron

2014-01-01

Radiative heating is identified as a major contributor to afterbody heating for Earth entry capsules at velocities above 10 km/s. Because of rate-limited electron-ion recombination processes, a large fraction of the electronically-excited N and O atoms produced in the high temperature/pressure forebody remain as they expand into the afterbody region, which results in significant afterbody radiation. Large radiative heating sensitivities to electron-impact ionization rates and escape factors are identified. Ablation products from a forebody ablator are shown to increase the afterbody radiation by as much as 40%. The tangent-slab radiation transport approach is shown to over-predict the radiative flux by as much as 40% in the afterbody, therefore making the more computationally expensive ray-tracing approach necessary for accurate radiative flux predictions. For the Stardust entry, the afterbody radiation is predicted to be nearly twice as large as the convective heating during the peak heating phase of the trajectory. Comparisons between simulations and the Stardust Echelle observation measurements, which are shown to be dominated by afterbody emission, indicate agreement within 20% for various N and O lines. Similarly, calorimeter measurements from the Fire II experiment are identified as a source of validation data for afterbody radiation. For the afterbody calorimeter measurement closest to the forebody, which experiences the largest afterbody radiative heating component, the convective heating alone is shown to under-predict the measurement, even for the fullycatalytic assumption. Agreement with the measurements is improved with the addition of afterbody radiation. These comparisons with Stardust and Fire II measurements provide validation that the significant afterbody radiation values proposed in this work are legitimate.

Generation of ionizing radiation from lithium niobate crystals

NASA Astrophysics Data System (ADS)

Orlikov, L. N.; Orlikov, N. L.; Arestov, S. I.; Mambetova, K. M.; Shandarov, S. M.

2017-01-01

The work done experimentally explores generation of electron and x-ray radiation in the process of heating and cooling monolithic and iron-doped crystals of lithium niobate. Iron doping to the concentrations in the range of 1023 m3 was carried out by adding ferric oxide into the melt during the process of crystal growth. The research into radiation generation was performed at 1-10 Pa. The speed of heating from -10 to 1070 C was 10-20 degrees a minute. Current pulses appeared at 17, 38, 56, 94, 98, 100, 105, 106, 1070 C with the interval of 1-3 minutes. The obtained electron current increased in direct proportion to the crystal surface area. The maximum current was 3mA at the design voltage 11 kV on the crystal with 14,5x10,5x10 mm3 surface area. The article describes the possibility to control the start of generation by introducing priming pulse. The results achieved are explained by the domain repolarization while heating the crystal and the appearance of electric field local strength. Bias and overcharge currents contribute to the appearance of electric strength, which stimulates breakdown and plasma formation. X-ray radiation appears both at the stage of discharge formation and during electron deceleration on gas and target material.

An Integrated Experimental and Computational Study of Heating due to Surface Catalysis under Hypersonic Conditions

DTIC Science & Technology

2012-08-01

17 1.1.1 Mass production / destruction terms . . . . . . . . . . . . . . . . . . . . 18 1.1.2 Energy exchange terms...that US3D does not cur- rently model electronic energy . If the US3D solution is post-processed to account for electronic energy modes, the computed...nonequilibrium model for electronic energy to the 12 Distribution A: Approved for public release; distribution is unlimited. Figure 9: (left) jet profile solution

COMBINED MODELING OF ACCELERATION, TRANSPORT, AND HYDRODYNAMIC RESPONSE IN SOLAR FLARES. I. THE NUMERICAL MODEL

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

Liu Wei; Petrosian, Vahe; Mariska, John T.

2009-09-10

Acceleration and transport of high-energy particles and fluid dynamics of atmospheric plasma are interrelated aspects of solar flares, but for convenience and simplicity they were artificially separated in the past. We present here self-consistently combined Fokker-Planck modeling of particles and hydrodynamic simulation of flare plasma. Energetic electrons are modeled with the Stanford unified code of acceleration, transport, and radiation, while plasma is modeled with the Naval Research Laboratory flux tube code. We calculated the collisional heating rate directly from the particle transport code, which is more accurate than those in previous studies based on approximate analytical solutions. We repeated themore » simulation of Mariska et al. with an injection of power law, downward-beamed electrons using the new heating rate. For this case, a {approx}10% difference was found from their old result. We also used a more realistic spectrum of injected electrons provided by the stochastic acceleration model, which has a smooth transition from a quasi-thermal background at low energies to a nonthermal tail at high energies. The inclusion of low-energy electrons results in relatively more heating in the corona (versus chromosphere) and thus a larger downward heat conduction flux. The interplay of electron heating, conduction, and radiative loss leads to stronger chromospheric evaporation than obtained in previous studies, which had a deficit in low-energy electrons due to an arbitrarily assumed low-energy cutoff. The energy and spatial distributions of energetic electrons and bremsstrahlung photons bear signatures of the changing density distribution caused by chromospheric evaporation. In particular, the density jump at the evaporation front gives rise to enhanced emission, which, in principle, can be imaged by X-ray telescopes. This model can be applied to investigate a variety of high-energy processes in solar, space, and astrophysical plasmas.« less

Numerical modeling of heat-transfer and the influence of process parameters on tailoring the grain morphology of IN718 in electron beam additive manufacturing

DOE PAGES

Raghavan, Narendran; Dehoff, Ryan; Pannala, Sreekanth; ...

2016-04-26

The fabrication of 3-D parts from CAD models by additive manufacturing (AM) is a disruptive technology that is transforming the metal manufacturing industry. The correlation between solidification microstructure and mechanical properties has been well understood in the casting and welding processes over the years. This paper focuses on extending these principles to additive manufacturing to understand the transient phenomena of repeated melting and solidification during electron beam powder melting process to achieve site-specific microstructure control within a fabricated component. In this paper, we have developed a novel melt scan strategy for electron beam melting of nickel-base superalloy (Inconel 718) andmore » also analyzed 3-D heat transfer conditions using a parallel numerical solidification code (Truchas) developed at Los Alamos National Laboratory. The spatial and temporal variations of temperature gradient (G) and growth velocity (R) at the liquid-solid interface of the melt pool were calculated as a function of electron beam parameters. By manipulating the relative number of voxels that lie in the columnar or equiaxed region, the crystallographic texture of the components can be controlled to an extent. The analysis of the parameters provided optimum processing conditions that will result in columnar to equiaxed transition (CET) during the solidification. Furthermore, the results from the numerical simulations were validated by experimental processing and characterization thereby proving the potential of additive manufacturing process to achieve site-specific crystallographic texture control within a fabricated component.« less

Light-induced electronic non-equilibrium in plasmonic particles.

PubMed

Kornbluth, Mordechai; Nitzan, Abraham; Seideman, Tamar

2013-05-07

We consider the transient non-equilibrium electronic distribution that is created in a metal nanoparticle upon plasmon excitation. Following light absorption, the created plasmons decohere within a few femtoseconds, producing uncorrelated electron-hole pairs. The corresponding non-thermal electronic distribution evolves in response to the photo-exciting pulse and to subsequent relaxation processes. First, on the femtosecond timescale, the electronic subsystem relaxes to a Fermi-Dirac distribution characterized by an electronic temperature. Next, within picoseconds, thermalization with the underlying lattice phonons leads to a hot particle in internal equilibrium that subsequently equilibrates with the environment. Here we focus on the early stage of this multistep relaxation process, and on the properties of the ensuing non-equilibrium electronic distribution. We consider the form of this distribution as derived from the balance between the optical absorption and the subsequent relaxation processes, and discuss its implication for (a) heating of illuminated plasmonic particles, (b) the possibility to optically induce current in junctions, and (c) the prospect for experimental observation of such light-driven transport phenomena.

The controllable electron-heating by external magnetic fields at relativistic laser-solid interactions in the presence of large scale pre-plasmas

NASA Astrophysics Data System (ADS)

Wu, D.; Luan, S. X.; Wang, J. W.; Yu, W.; Gong, J. X.; Cao, L. H.; Zheng, C. Y.; He, X. T.

2017-06-01

The two-stage electron acceleration/heating model (Wu et al 2017 Nucl. Fusion 57 016007 and Wu et al 2016 Phys. Plasmas 23 123116) is extended to the study of laser magnetized-plasmas interactions at relativistic intensities and in the presence of large-scale preformed plasmas. It is shown that the electron-heating efficiency is a controllable value by the external magnetic fields. Detailed studies indicate that for a right-hand circularly polarized laser, the electron heating efficiency depends on both strength and directions of external magnetic fields. The electron-heating is dramatically enhanced when the external magnetic field is of B\\equiv {ω }c/{ω }0> 1. When magnetic field is of negative direction, i.e. B< 0, it trends to suppress the electron heating. The underlining physics—the dependences of electron-heating on both the strength and directions of the external magnetic fields—is uncovered. With -∞ < B< 1, the electron-heating is explained by the synergetic effects by longitudinal charge separation electric field and the reflected ‘envelop-modulated’ CP laser. It is indicated that the ‘modulation depth’ of reflected CP laser is significantly determined by the external magnetic fields, which will in turn influence the efficiency of the electron-heating. While with B> 1, a laser front sharpening mechanism is identified at relativistic laser magnetized-plasmas interactions, which is responsible for the dramatical enhancement of electron-heating.

The NBS: Processing/Microstructure/Property Relationships in 2024 Aluminum Alloy Plates

NASA Technical Reports Server (NTRS)

Ives, L. K.; Swartzendruber, W. J.; Boettinger, W. J.; Rosen, M.; Ridder, S. D.

1983-01-01

As received plates of 2024 aluminum alloy were examined. Topics covered include: solidification segregation studies; microsegregation and macrosegregation in laboratory and commercially cast ingots; C-curves and nondestructive evaluation; time-temperature precipitation diagrams and the relationships between mechanical properties and NDE measurements; transmission electron microscopy studies; the relationship between microstructure and properties; ultrasonic characterization; eddy-current conductivity characterization; the study of aging process by means of dynamic eddy current measurements; and Heat flow-property predictions, property degradations due to improve quench from the solution heat treatment temperature.

Two temperature approach to femtosecond laser oxidation of molybdenum and morphological study

NASA Astrophysics Data System (ADS)

Kotsedi, L.; Kaviyarasu, K.; Fuku, X. G.; Eaton, S. M.; Amara, E. H.; Bireche, F.; Ramponi, R.; Maaza, M.

2017-11-01

The two-temperature model was used to gain insight into the thermal evolution of the hot electrons and the crystal lattice of the molybdenum thin coating during femtosecond laser treatment. The heat from the laser raised the bulk temperature of the sample through heat transfer from the hot electron to the crystal lattice of the material, which then led to the melting of the top layer of the film. This process resulted in the hot melt reacting ambient oxygen, which in turn oxidized the surface of molybdenum coating. The topological study and morphology of the oxidized film was conducted using high-resolution scanning electron microscope, with micrographs taken in both the cross-sectional geometry and normal incidence to the electron beam. The molybdenum oxide nanorods were clearly observed and the x-ray diffraction patterns showed the diffraction peaks due to molybdenum oxide.

In situ transmission electron microscopy of transistor operation and failure.

PubMed

Wang, Baoming; Islam, Zahabul; Haque, Aman; Chabak, Kelson; Snure, Michael; Heller, Eric; Glavin, Nicholas

2018-08-03

Microscopy is typically used as a post-mortem analytical tool in performance and reliability studies on nanoscale materials and devices. In this study, we demonstrate real time microscopy of the operation and failure of AlGaN/GaN high electron mobility transistors inside the transmission electron microscope. Loading until failure was performed on the electron transparent transistors to visualize the failure mechanisms caused by self-heating. At lower drain voltages, thermo-mechanical stresses induce irreversible microstructural deformation, mostly along the AlGaN/GaN interface, to initiate the damage process. At higher biasing, the self-heating deteriorates the gate and catastrophic failure takes place through metal/semiconductor inter-diffusion and/or buffer layer breakdown. This study indicates that the current trend of recreating the events, from damage nucleation to catastrophic failure, can be replaced by in situ microscopy for a quick and accurate account of the failure mechanisms.

Structural, microstructural and magnetic evolution in cryo milled carbon doped MnAl.

PubMed

Fang, Hailiang; Cedervall, Johan; Hedlund, Daniel; Shafeie, Samrand; Deledda, Stefano; Olsson, Fredrik; von Fieandt, Linus; Bednarcik, Jozef; Svedlindh, Peter; Gunnarsson, Klas; Sahlberg, Martin

2018-02-06

The low cost, rare earth free τ-phase of MnAl has high potential to partially replace bonded Nd 2 Fe 14 B rare earth permanent magnets. However, the τ-phase is metastable and it is experimentally difficult to obtain powders suitable for the permanent magnet alignment process, which requires the fine powders to have an appropriate microstructure and high τ-phase purity. In this work, a new method to make high purity τ-phase fine powders is presented. A high purity τ-phase Mn 0.55 Al 0.45 C 0.02 alloy was synthesized by the drop synthesis method. The drop synthesized material was subjected to cryo milling and  followed by a flash heating process. The crystal structure and microstructure of the drop synthesized, cryo milled and flash heated samples were studied by X-ray in situ powder diffraction, scanning electron microscopy, X-ray energy dispersive spectroscopy and electron backscatter diffraction. Magnetic properties and magnetic structure of the drop synthesized, cryo milled, flash heated  samples were characterized by magnetometry and neutron powder diffraction, respectively. The results reveal that the 2 and 4 hours cryo milled and flash heated samples both exhibit high τ-phase purity and micron-sized round particle shapes. Moreover, the flash heated samples display high saturation magnetization as well as increased coercivity.

[Effect of different heat treatment on mechanical properties and microstructure of laser welding CoCr-NiCr dissimilar alloys].

PubMed

Liang, Rui-ying; Li, Chang-yi; Han, Ya-jing; Hu, Xin; Zhang, Lian-yun

2008-11-01

To evaluate the effect of heat treatment and porcelain-fused-to-metal (PFM) processing on mechanical properties and microstructure of laser welding CoCr-NiCr dissimilar alloys. Samples of CoCr-NiCr dissimilar alloys with 0.5 mm thickness were laser-welded single-side under the setting parameters of 280 V, 10 ms pulse duration. After being welded, samples were randomly assigned to three groups, 10 each. Group1 and 2 received heat treatment and PFM processing, respectively. Group 3 was control group without any treatment. Tensile strength, microstructure and element distribution of samples in the three groups were tested and observed using tensile test, metallographic examinations, scanning electron microscope (SEM), and energy dispersive spectroscopy (EDS) analysis. After heat treatment and PFM processing, tensile strength of the samples were (537.15 +/- 43.91) MPa and (534.58 +/- 48.47) MPa respectively, and elongation rates in Group 1 and 2 were (7.65 +/- 0.73)% and (7.40 +/- 0.45)%. Ductile structure can be found on tensile fracture surface of samples and it was more obvious in heat treatment group than in PFM group. The results of EDS analysis indicated that certain CoCr alloy diffused towards fusion zone and NiCr side after heat treatment and PFM processing. Compared with PFM processing group, the diffusion in the heat treatment group was more obvious. Heat treatment and PFM processing can improve the mechanical properties and microstructure of welded CoCr-NiCr dissimilar alloy to a certain degree. The improvements are more obvious with heat treatment than with porcelain treatment.

Novel Chemical Process for Producing Chrome Coated Metal

PubMed Central

Pelar, Christopher; Greenaway, Karima; Zea, Hugo; Wu, Chun-Hsien

2018-01-01

This work demonstrates that a version of the Reduction Expansion Synthesis (RES) process, Cr-RES, can create a micron scale Cr coating on an iron wire. The process involves three steps. I. A paste consisting of a physical mix of urea, chrome nitrate or chrome oxide, and water is prepared. II. An iron wire is coated by dipping. III. The coated, and dried, wire is heated to ~800 °C for 10 min in a tube furnace under a slow flow of nitrogen gas. The processed wires were then polished and characterized, primarily with scanning electron microscopy (SEM). SEM indicates the chrome layer is uneven, but only on the scale of a fraction of a micron. The evidence of porosity is ambiguous. Elemental mapping using SEM electron microprobe that confirmed the process led to the formation of a chrome metal layer, with no evidence of alloy formation. Additionally, it was found that thickness of the final Cr layer correlated with the thickness of the precursor layer that was applied prior to the heating step. Potentially, this technique could replace electrolytic processing, a process that generates carcinogenic hexavalent chrome, but further study and development is needed. PMID:29303977

Novel Chemical Process for Producing Chrome Coated Metal.

PubMed

Pelar, Christopher; Greenaway, Karima; Zea, Hugo; Wu, Chun-Hsien; Luhrs, Claudia C; Phillips, Jonathan

2018-01-05

This work demonstrates that a version of the Reduction Expansion Synthesis (RES) process, Cr-RES, can create a micron scale Cr coating on an iron wire. The process involves three steps. I. A paste consisting of a physical mix of urea, chrome nitrate or chrome oxide, and water is prepared. II. An iron wire is coated by dipping. III. The coated, and dried, wire is heated to ~800 °C for 10 min in a tube furnace under a slow flow of nitrogen gas. The processed wires were then polished and characterized, primarily with scanning electron microscopy (SEM). SEM indicates the chrome layer is uneven, but only on the scale of a fraction of a micron. The evidence of porosity is ambiguous. Elemental mapping using SEM electron microprobe that confirmed the process led to the formation of a chrome metal layer, with no evidence of alloy formation. Additionally, it was found that thickness of the final Cr layer correlated with the thickness of the precursor layer that was applied prior to the heating step. Potentially, this technique could replace electrolytic processing, a process that generates carcinogenic hexavalent chrome, but further study and development is needed.

Control Mechanisms of the Electron Heat Flux in the Solar Wind: Observations in Comparison to Numerical Simulations

NASA Astrophysics Data System (ADS)

Stverak, S.; Hellinger, P.; Landi, S.; Travnicek, P. M.; Maksimovic, M.

2017-12-01

Recent understanding of the heat transport and dissipation in the expanding solar wind propose number of complex control mechanisms down to the electron kinetic scales. We investigate the evolution of electron heat flux properties and constraints along the expansion using in situ observations from Helios spacecraft in comparison to numerical kinetic simulations. In particular we focus on the roles of Coulomb collisions and wave-particle interactions in shaping the electron velocity distribution functions and thus controlling the heat transported by the electron heat flux. We show the general evolution of the electron heat flux to be driven namely by the Coulomb collisions. Locally we demonstrate the wave-particle interactions related to the kinetic plasma instabilities to be providing effective constraints in case of extreme heat flux levels.

A Non Local Electron Heat Transport Model for Multi-Dimensional Fluid Codes

NASA Astrophysics Data System (ADS)

Schurtz, Guy

2000-10-01

Apparent inhibition of thermal heat flow is one of the most ancient problems in computational Inertial Fusion and flux-limited Spitzer-Harm conduction has been a mainstay in multi-dimensional hydrodynamic codes for more than 25 years. Theoretical investigation of the problem indicates that heat transport in laser produced plasmas has to be considered as a non local process. Various authors contributed to the non local theory and proposed convolution formulas designed for practical implementation in one-dimensional fluid codes. Though the theory, confirmed by kinetic calculations, actually predicts a reduced heat flux, it fails to explain the very small limiters required in two-dimensional simulations. Fokker-Planck simulations by Epperlein, Rickard and Bell [PRL 61, 2453 (1988)] demonstrated that non local effects could lead to a strong reduction of heat flow in two dimensions, even in situations where a one-dimensional analysis suggests that the heat flow is nearly classical. We developed at CEA/DAM a non local electron heat transport model suitable for implementation in our two-dimensional radiation hydrodynamic code FCI2. This model may be envisionned as the first step of an iterative solution of the Fokker-Planck equations; it takes the mathematical form of multigroup diffusion equations, the solution of which yields both the heat flux and the departure of the electron distribution function to the Maxwellian. Although direct implementation of the model is straightforward, formal solutions of it can be expressed in convolution form, exhibiting a three-dimensional tensor propagator. Reduction to one dimension retrieves the original formula of Luciani, Mora and Virmont [PRL 51, 1664 (1983)]. Intense magnetic fields may be generated by thermal effects in laser targets; these fields, as well as non local effects, will inhibit electron conduction. We present simulations where both effects are taken into account and shortly discuss the coupling strategy between them.

Ion and electron heating characteristics of magnetic reconnection in tokamak plasma merging experiments

NASA Astrophysics Data System (ADS)

Ono, Y.; Tanabe, H.; Yamada, T.; Inomoto, M.; T, Ii; Inoue, S.; Gi, K.; Watanabe, T.; Gryaznevich, M.; Scannell, R.; Michael, C.; Cheng, C. Z.

2012-12-01

Recently, the TS-3 and TS-4 tokamak merging experiments revealed significant plasma heating during magnetic reconnection. A key question is how and where ions and electrons are heated during magnetic reconnection. Two-dimensional measurements of ion and electron temperatures and plasma flow made clear that electrons are heated inside the current sheet mainly by the Ohmic heating and ions are heated in the downstream areas mainly by the reconnection outflows. The outflow kinetic energy is thermalized by the fast shock formation and viscous damping. The magnetic reconnection converts the reconnecting magnetic field energy mostly to the ion thermal energy in the outflow region whose size is much larger than the current sheet size for electron heating. The ion heating energy is proportional to the square of the reconnection magnetic field component B_p^2 . This scaling of reconnection heating indicates the significant ion heating effect of magnetic reconnection, which leads to a new high-field reconnection heating experiment for fusion plasmas.

Combined action of corrugation and Weibel instabilities from electron-beam interaction with laser-irradiated plasma

NASA Astrophysics Data System (ADS)

Bai, Yafeng; Tian, Ye; Zhang, Zhijun; Cao, Lihua; Liu, Jiansheng

2018-03-01

The combined action of corrugation and Weibel instabilities was experimentally observed in the interaction between energetic electrons and a laser-irradiated insulated target. The energetic electron beam, driven by an ultrashort laser pulse, splits into filaments with a diameter of ˜10 μm while traversing an insulated target, owing to the corrugation instability. The filaments continued to split into thinner filaments owing to the Weibel instability if a preplasma was induced by a heating beam on the rear side of the target. When the time delay between the heating beam and electron beam was larger than 1 ps, a merging of the current filaments was observed. The characteristic filamentary structures disappeared when the time delay between the two beams was larger than 3 ps. A simplified model was developed to analyze this process; the obtained results were in good agreement with the experiment. Two-dimensional particle-in-cell simulations supported our analysis and reproduced the filamentation of the electron beam inside the plasma.

Thermal reaction of sonochemically prepared amorphous Fe/C

NASA Astrophysics Data System (ADS)

Miyatani, R.; Kobayashi, Y.; Yamada, Y.

2017-11-01

An amorphous iron/carbon mixture was prepared by sonolysis of ferrocene in diphenylmethane. Heating of the amorphous mixture at 900 or 1200 °C produced nanoparticles, which were then analyzed using Mössbauer spectroscopy, X-ray diffraction, and transmission electron microscopy. The nanoparticles obtained after heating were spherical with diameters of about 50 nm. The sample obtained after heating at 900 °C consisted of α-Fe and Fe 3C, whereas the sample obtained after heating at 1200 °C consisted of α-Fe and γ-Fe. The reaction of the mixture during the heating process was accompanied by the formation of carbon nanotubes catalyzed by the iron or iron carbide nanoparticles.

Momentum transport and nonlocality in heat-flux-driven magnetic reconnection in high-energy-density plasmas.

PubMed

Liu, Chang; Fox, William; Bhattacharjee, Amitava; Thomas, Alexander G R; Joglekar, Archis S

2017-10-01

Recent theory has demonstrated a novel physics regime for magnetic reconnection in high-energy-density plasmas where the magnetic field is advected by heat flux via the Nernst effect. Here we elucidate the physics of the electron dissipation layer in this regime. Through fully kinetic simulation and a generalized Ohm's law derived from first principles, we show that momentum transport due to a nonlocal effect, the heat-flux-viscosity, provides the dissipation mechanism for magnetic reconnection. Scaling analysis, and simulations show that the reconnection process comprises a magnetic field compression stage and quasisteady reconnection stage, and the characteristic width of the current sheet in this regime is several electron mean-free paths. These results show the important interplay between nonlocal transport effects and generation of anisotropic components to the distribution function.

THEMIS Observations of the Magnetopause Electron Diffusion Region: Large Amplitude Waves and Heated Electrons

NASA Technical Reports Server (NTRS)

Tang, Xiangwei; Cattell, Cynthia; Dombeck, John; Dai, Lei; Wilson, Lynn B. III; Breneman, Aaron; Hupack, Adam

2013-01-01

We present the first observations of large amplitude waves in a well-defined electron diffusion region based on the criteria described by Scudder et al at the subsolar magnetopause using data from one Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite. These waves identified as whistler mode waves, electrostatic solitary waves, lower hybrid waves, and electrostatic electron cyclotron waves, are observed in the same 12 s waveform capture and in association with signatures of active magnetic reconnection. The large amplitude waves in the electron diffusion region are coincident with abrupt increases in electron parallel temperature suggesting strong wave heating. The whistler mode waves, which are at the electron scale and which enable us to probe electron dynamics in the diffusion region were analyzed in detail. The energetic electrons (approx. 30 keV) within the electron diffusion region have anisotropic distributions with T(sub e(right angle))/T(sub e(parallel)) > 1 that may provide the free energy for the whistler mode waves. The energetic anisotropic electrons may be produced during the reconnection process. The whistler mode waves propagate away from the center of the "X-line" along magnetic field lines, suggesting that the electron diffusion region is a possible source region of the whistler mode waves.

Momentum transport and non-local transport in heat-flux-driven magnetic reconnection in HEDP

NASA Astrophysics Data System (ADS)

Liu, Chang; Fox, Will; Bhattacharjee, Amitava

2016-10-01

Strong magnetic fields are readily generated in high-energy-density plasmas and can affect the heat confinement properties of the plasma. Magnetic reconnection can in turn be important as an inverse process, which destroys or reconfigures the magnetic field. Recent theory has demonstrated a novel physics regime for reconnection in high-energy-density plasmas where the magnetic field is advected into the reconnection layer by plasma heat flux via the Nernst effect. In this work we elucidate the physics of the electron dissipation layer in this heat-flux-driven regime. Through fully kinetic simulation and a new generalized Ohm's law, we show that momentum transport due to the heat-flux-viscosity effect provides the dissipation mechanism to allow magnetic field line reconnection. Scaling analysis and simulations show that the characteristic width of the current sheet in this regime is several electron mean-free-paths. These results additionally show a coupling between non-local transport and momentum transport, which in turn affects the dynamics of the magnetic field. This work was supported by the U.S. Department of Energy under Contract No. DE-SC0008655.

Role of Magnetic Reconnection in Heating Astrophysical Plasmas

NASA Astrophysics Data System (ADS)

Hammoud, M. M.; El Eid, M.; Darwish, M.; Dayeh, M. A.

2017-12-01

The description of plasma in the context of a fluid model reveals the important phenomenon of magnetic reconnection (MGR). This process is thought to be the cause of particle heating and acceleration in various astrophysical phenomena. Examples are geomagnetic storms, solar flares, or heating the solar corona, which is the focus of the present contribution. The magnetohydrodynamic approach (MHD) provides a basic description of MGR. However, the simulation of this process is rather challenging. Although it is not yet established whether waves or reconnection play the dominant role in heating the solar atmosphere, the present goal is to examine the tremendous increase of the temperature between the solar chromosphere and the corona in a very narrow transition region. Since we are dealing with very-high temperature plasma, the modeling of such heating process seems to require a two-fluid description consisting of ions and electrons. This treatment is an extension of the one-fluid model of resistive MHD that has been recently developed by [Hammoud et al., 2017] using the modern numerical openfoam toolbox. In this work, we outline the two-fluid approach using coronal conditions, show evidence of MGR in the two-fluid description, and investigate the temperature increase as a result of this MGR process.

Materials Development for Auxiliary Components for Large Compact Mo/Au TES Arrays

NASA Technical Reports Server (NTRS)

Finkbeiner, F. m.; Chervenak, J. A.; Bandler, S. R.; Brekosky, R.; Brown, A. D.; Figueroa-Feliciano, E.; Iyomoto, N.; Kelley, R. L.; Kilbourne, C. A.; Porter, F. S.;

Kinetic Alfven turbulence: Electron and ion heating by particle-in-cell simulations

NASA Astrophysics Data System (ADS)

Gary, S. P.; Hughes, R. S.; Wang, J.; Parashar, T. N.

2017-12-01

Three-dimensional particle-in-cell simulations of the forward cascade of decaying kinetic Alfvén turbulence have been carried out as an initial-value problem on a collisionless, homogeneous, magnetized, electron-ion plasma model with betae = betai =0.50 and mi/me=100 where subscripts e and i represent electrons and ions respectively. Initial anisotropic narrowband spectra of relatively long wavelength modes with approximately gyrotropic distributions in kperp undergo a forward cascade to broadband spectra of magnetic fluctuations at shorter wavelengths. Maximum electron and ion heating rates are computed as functions of the initial fluctuating magnetic field energy density eo on the range 0.05 < eo < 0.50. In contrast to dissipation by whistler turbulence, the maximum ion heating rate due to kinetic Alfvén turbulence is substantially greater than the maximum electron heating rate. Furthermore, ion heating as well as electron heating due to kinetic Alfvén turbulence scale approximately with eo. Finally, electron heating leads to anisotropies of the type T||e> Tperpe where the parallel and perpendicular symbols refer to directions parallel and perpendicular, respectively, to the background magnetic field, whereas the heated ions remain relatively isotropic. This implies that, for the range of eo values considered, the Landau wave-particle resonance is a likely heating mechanism for the electrons and may also contribute to ion heating.

Incubation behavior of silicon nanowire growth investigated by laser-assisted rapid heating

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

Ryu, Sang-gil; Kim, Eunpa; Grigoropoulos, Costas P., E-mail: cgrigoro@berkeley.edu

2016-08-15

We investigate the early stage of silicon nanowire growth by the vapor-liquid-solid mechanism using laser-localized heating combined with ex-situ chemical mapping analysis by energy-filtered transmission electron microscopy. By achieving fast heating and cooling times, we can precisely determine the nucleation times for nanowire growth. We find that the silicon nanowire nucleation process occurs on a time scale of ∼10 ms, i.e., orders of magnitude faster than the times reported in investigations using furnace processes. The rate-limiting step for silicon nanowire growth at temperatures in the vicinity of the eutectic temperature is found to be the gas reaction and/or the silicon crystalmore » growth process, whereas at higher temperatures it is the rate of silicon diffusion through the molten catalyst that dictates the nucleation kinetics.« less

Silicon Chemical Vapor Deposition Process Using a Half-Inch Silicon Wafer for Minimal Manufacturing System

NASA Astrophysics Data System (ADS)

Li, Ning; Habuka, Hitoshi; Ikeda, Shin-ichi; Hara, Shiro

A chemical vapor deposition reactor for producing thin silicon films was designed and developed for achieving a new electronic device production system, the Minimal Manufacturing, using a half-inch wafer. This system requires a rapid process by a small footprint reactor. This was designed and verified by employing the technical issues, such as (i) vertical gas flow, (ii) thermal operation using a highly concentrated infrared flux, and (iii) reactor cleaning by chlorine trifluoride gas. The combination of (i) and (ii) could achieve a low heating power and a fast cooling designed by the heat balance of the small wafer placed at a position outside of the reflector. The cleaning process could be rapid by (iii). The heating step could be skipped because chlorine trifluoride gas was reactive at any temperature higher than room temperature.

Low-Heat-Leak Electrical Leads For Cryogenic Systems

NASA Technical Reports Server (NTRS)

Wise, Stephanie A.; Hooker, Matthew W.

1994-01-01

Electrical leads offering high electrical conductivity and low thermal conductivity developed for use in connecting electronic devices inside cryogenic systems to power supplies, signal-processing circuits, and other circuitry located in nearby warmer surroundings. Strip of superconductive leads on ceramic substrate, similar to ribbon cable, connects infrared detectors at temperature of liquid helium with warmer circuitry. Electrical leads bridging thermal gradient at boundary of cryogenic system designed both to minimize conduction of heat from surroundings through leads into system and to minimize resistive heating caused by electrical currents flowing in leads.

PROCESS FOR COLORING DIAMONDS

DOEpatents

Dugdale, R.A.

1960-07-19

A process is given for coloring substantially colorless diamonds in the blue to blue-green range and comprises the steps of irradiating the colorless diamonds with electrons having an energy within the range 0.5 to 2 Mev to obtain an integrated electron flux of between 1 and 2 x 10/sup 18/ thc diamonds may be irradiated 1 hr when they take on a blue color with a slight green tint: After being heated at about 500 deg C for half an hour they become pure blue. Electrons within this energy range contam sufficient energy to displace the diamond atoms from their normal lattice sites into interstitial sites, thereby causing the color changes.

DSMC simulation of rarefied gas flows under cooling conditions using a new iterative wall heat flux specifying technique

NASA Astrophysics Data System (ADS)

Akhlaghi, H.; Roohi, E.; Myong, R. S.

2012-11-01

Micro/nano geometries with specified wall heat flux are widely encountered in electronic cooling and micro-/nano-fluidic sensors. We introduce a new technique to impose the desired (positive/negative) wall heat flux boundary condition in the DSMC simulations. This technique is based on an iterative progress on the wall temperature magnitude. It is found that the proposed iterative technique has a good numerical performance and could implement both positive and negative values of wall heat flux rates accurately. Using present technique, rarefied gas flow through micro-/nanochannels under specified wall heat flux conditions is simulated and unique behaviors are observed in case of channels with cooling walls. For example, contrary to the heating process, it is observed that cooling of micro/nanochannel walls would result in small variations in the density field. Upstream thermal creep effects in the cooling process decrease the velocity slip despite of the Knudsen number increase along the channel. Similarly, cooling process decreases the curvature of the pressure distribution below the linear incompressible distribution. Our results indicate that flow cooling increases the mass flow rate through the channel, and vice versa.

Laser-Matter Interaction in Dielectrics: Insight from Picosecond-Pulsed Second-Harmonic Generation in Periodically Poled LiTaO3

NASA Astrophysics Data System (ADS)

Louchev, Oleg A.; Wada, Satoshi; Panchenko, Vladislav Ya.

2017-08-01

We develop a modified two-temperature (2T) model of laser-matter interaction in dielectrics based on experimental insight from picosecond-pulsed high-frequency temperature-controlled second-harmonic (515 nm) generation in periodically poled stoichiometric LiTaO3 crystal and required for computational treatment of short-pulsed nonlinear optics and materials processing applications. We show that the incorporation of an extended set of recombination-kinetics-related energy-release and heat-exchange processes following short-pulsed photoionization by two-photon absorption of the second harmonic allows accurate simulation of the electron-lattice relaxation dynamics and electron-lattice temperature evolution in LiTaO3 crystal in nonlinear laser-frequency conversion. Our experimentally confirmed model and detailed simulation study show that two-photon ionization with the recombination mechanism via ion-electron-lattice interaction followed by a direct transfer of the recombination energy to the lattice is the main laser-matter energy-transfer pathway responsible for the majority of the crystal lattice heating (approximately 90%) continuing for approximately 50 ps after laser-pulse termination and competing with effect of electron-phonon energy transfer from the free electrons. This time delay is due to a recombination bottleneck which hinders faster relaxation to thermal equilibrium in photoionized dielectric crystal. Generally, our study suggests that in dielectrics photoionized by short-pulsed radiation with intensity range used in nonlinear laser-frequency conversion, the electron-lattice relaxation period is defined by the recombination-stage bottleneck of a few tens of picoseconds and not by the time of the electron-phonon energy transfer. This modification of the 2T model can be applied to a broad range of processes involving laser-matter interactions in dielectrics and semiconductors for charge density reaching the range of 1021- 1022 cm-3 .

Mathematical modelling of convective processes in a weld pool under electric arc surfacing

NASA Astrophysics Data System (ADS)

Sarychev, V. D.; Granovskii, A. Yu; Nevskii, S. A.; Konovalov, S. V.

2017-01-01

The authors develop the mathematical model of convective processes in a molten pool under electric arc surfacing with flux-cored wire. The model is based on the ideas of how convective flows appear due to temperature gradient and action of electromagnetic forces. Influence of alloying elements in the molten metal was modeled as a non-linear dependence of surface tension upon temperature. Surface tension and its temperature coefficient were calculated according to the electron density functional method with consideration to asymmetric electron distribution at the interface “molten metal / shielding gas”. Simultaneous solution of Navier-Stokes and Maxwell equations according to finite elements method with consideration to the moving heat source at the interface showed that there is a multi-vortex structure in the molten metal. This structure gives rise to a downward heat flux which, at the stage of heating, moves from the centre of the pool and stirs it full width. At the cooling stage this flux moves towards the centre of the pool and a single vortex is formed near the symmetry centre. This flux penetration is ∼ 10 mm. Formation of the downward heat flux is determined by sign reversal of the temperature coefficient of surface tension due to the presence of alloying elements.

A theory of heating of quiet solar corona

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

Wu, C. S., E-mail: cszcwu@msn.com; Institute of Space Science, National Central University, Zhongli 32001, Taiwan; Insitute for Physical Sciences and Technology, University of Maryland, College Park, Maryland 20742

A theory is proposed to discuss the creation of hot solar corona. We pay special attention to the transition region and the low corona, and consider that the sun is quiet. The proposed scenario suggests that the protons are heated by intrinsic Alfvénic turbulence, while the ambient electrons are heated by the hot protons via collisions. The theory contains two prime components: the generation of the Alfvénic fluctuations by the heavy minor ions in the transition region and second, the explanation of the temperature profile in the low solar atmosphere. The proposed heating process operates continuously in time and globallymore » in space.« less

Method for Fabricating Composite Structures Using Pultrusion Processing

NASA Technical Reports Server (NTRS)

Farley, Gary L. (Inventor)

2000-01-01

A method for fabricating composite structures at a low-cost, moderate-to-high production rate. A first embodiment of the method includes employing a continuous press forming fabrication process. A second embodiment of the method includes employing a pultrusion process for obtaining composite structures. The methods include coating yarns with matrix material, weaving the yarn into fabric to produce a continuous fabric supply and feeding multiple layers of net-shaped fabrics having optimally oriented fibers into a debulking tool to form an undebulked preform. The continuous press forming fabrication process includes partially debulking the preform, cutting the partially debulked preform and debulking the partially debulked preform to form a net-shape. An electron-beam or similar technique then cures the structure. The pultrusion fabric process includes feeding the undebulked preform into a heated die and gradually debulking the undebulked preform. The undebulked preform in the heated die changes dimension until a desired cross-sectional dimension is achieved. This process further includes obtaining a net-shaped infiltrated uncured preform, cutting the uncured preform to a desired length and electron-beam curing (or similar technique) the uncured preform. These fabrication methods produce superior structures formed at higher production rates, resulting in lower cost and high structural performance.

Abnormal electron-heating mode and formation of secondary-energetic electrons in pulsed microwave-frequency atmospheric microplasmas

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

Kwon, H. C.; Research and Development Division, SK Hynix Semiconductor Inc., Icheon 467-701; Jung, S. Y.

2014-03-15

The formation of secondary energetic electrons induced by an abnormal electron-heating mode in pulsed microwave-frequency atmospheric microplasmas was investigated using particle-in-cell simulation. We found that additional high electron heating only occurs during the first period of the ignition phase after the start of a second pulse at sub-millimeter dimensions. During this period, the electrons are unable to follow the abruptly retreating sheath through diffusion alone. Thus, a self-consistent electric field is induced to drive the electrons toward the electrode. These behaviors result in an abnormal electron-heating mode that produces high-energy electrons at the electrode with energies greater than 50 eV.

ZnO sublimation using a polyenergetic pulsed electron beam source: numerical simulation and validation

NASA Astrophysics Data System (ADS)

Tricot, S.; Semmar, N.; Lebbah, L.; Boulmer-Leborgne, C.

2010-02-01

This paper details the electro-thermal study of the sublimation phase on a zinc oxide surface. This thermodynamic process occurs when a ZnO target is bombarded by a pulsed electron beam source composed of polyenergetic electrons. The source delivers short pulses of 180 ns of electrons with energies up to 16 keV. The beam total current reaches 800 A and is focused onto a spot area 2 mm in diameter. The Monte Carlo CASINO program is used to study the first stage of the interaction and to define the heat source space distribution inside the ZnO target. Simulation of the second stage of interaction is developed in a COMSOL multiphysics project. The simulated thermal field induced by space and time heat conduction is presented. Typically for a pulsed electron beam 2 mm in diameter of electrons having energies up to 16 keV, the surface temperature reaches a maximum of 7000 K. The calculations are supported by SEM pictures of the target irradiated by various beam energies and numbers of pulses.

Electron kinetics in capacitively coupled plasmas modulated by electron injection

NASA Astrophysics Data System (ADS)

Zhang, Ya; Peng, Yanli; Innocenti, Maria Elena; Jiang, Wei; Wang, Hong-yu; Lapenta, Giovanni

2017-09-01

The controlling effect of an electron injection on the electron energy distribution function (EEDF) and on the energetic electron flux, in a capacitive radio-frequency argon plasma, is studied using a one-dimensional particle-in-cell/Monte Carlo collisions model. The input power of the electron beam is as small as several tens of Watts with laboratory achievable emission currents and energies. With the electron injection, the electron temperature decreases but with a significant high energy tail. The electron density, electron temperature in the sheath, and electron heating rate increase with the increasing emission energy. This is attributed to the extra heating of the energetic electrons in the EEDF tail. The non-equilibrium EEDF is obtained for strong non-local distributions of the electric field, electron heating rate, excitation, and ionization rate, indicating the discharge has transited from a volume heating (α-mode dominated) into a sheath heating (γ-mode dominated) type. In addition, the electron injection not only modifies the self-bias voltage, but also enhances the electron flux that can reach the electrodes. Moreover, the relative population of energetic electrons significantly increases with the electron injection compared to that without the electron injection, relevant for modifying the gas and surface chemistry reactions.

Coalescence of two current loops with a kink instability simulated by a three-dimensional electromagnetic particle code

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Sakai, J.-I.; Zhao, Jie; Neubert, T.; Buneman, Oscar

1994-01-01

We have studied the dynamics of a coalescence of current loops using three-dimensional electromagnetic (EM) particle simulation code. Our focus is the investigation of such kinetic processes as energy trasnfer, heating particles, and electromagnetic emissions associated with a current loop coalescence which cannot be studied by MHD simulations. First, the two loops undergo a pinching oscillation due to a pressure imbalance between the inside and outside of the current loop. During the pinching oscillation, a kinetic kink instability is excited and electrons in the loops are heated perpendicularly to an ambient magnetic field. Next, the two current loops collide and coalesce, while at the same time a helical structure grows further. Subsequently, the perturbed current, which is due to these helically bunched electrons, can drive a whistler instability. It should be noted in this case that the whistler wave is excited by the kinetic kink instability and not a beam instability. After the coalescence of two helical loops, tilting motions can be observed in the direction of left-hand rotation, and the helical structure will relax resulting in strong plasma heating mostly in the direction perpendicular to the ambient magnetic field. It is also shown that high-frequency electromagnetic waves can be emitted from the region where the two loops coalesce and propagate strongly in the direction of the electron drift velocity. These processes may be important in understanding heating mechansims for coronal loops as well as radio wave emission mechanisms from active regions of solar plasmas.

The ultrafast dynamics and conductivity of photoexcited graphene at different Fermi energies

PubMed Central

Turchinovich, Dmitry; Kläui, Mathias; Hendry, Euan; Polini, Marco

2018-01-01

For many of the envisioned optoelectronic applications of graphene, it is crucial to understand the subpicosecond carrier dynamics immediately following photoexcitation and the effect of photoexcitation on the electrical conductivity—the photoconductivity. Whereas these topics have been studied using various ultrafast experiments and theoretical approaches, controversial and incomplete explanations concerning the sign of the photoconductivity, the occurrence and significance of the creation of additional electron-hole pairs, and, in particular, how the relevant processes depend on Fermi energy have been put forward. We present a unified and intuitive physical picture of the ultrafast carrier dynamics and the photoconductivity, combining optical pump–terahertz probe measurements on a gate-tunable graphene device, with numerical calculations using the Boltzmann equation. We distinguish two types of ultrafast photo-induced carrier heating processes: At low (equilibrium) Fermi energy (EF ≲ 0.1 eV for our experiments), broadening of the carrier distribution involves interband transitions (interband heating). At higher Fermi energy (EF ≳ 0.15 eV), broadening of the carrier distribution involves intraband transitions (intraband heating). Under certain conditions, additional electron-hole pairs can be created [carrier multiplication (CM)] for low EF, and hot carriers (hot-CM) for higher EF. The resultant photoconductivity is positive (negative) for low (high) EF, which in our physical picture, is explained using solely electronic effects: It follows from the effect of the heated carrier distributions on the screening of impurities, consistent with the DC conductivity being mostly due to impurity scattering. The importance of these insights is highlighted by a discussion of the implications for graphene photodetector applications. PMID:29756035

Heat flux measurements of Tb3M series (M=Co, Rh and Ru): Specific heat and magnetocaloric properties

NASA Astrophysics Data System (ADS)

Monteiro, J. C. B.; Lombardi, G. A.; dos Reis, R. D.; Freitas, H. E.; Cardoso, L. P.; Mansanares, A. M.; Gandra, F. G.

2016-12-01

We report on the magnetic properties and magnetocaloric effect (MCE) for the Tb3M series, with M=Co, Rh and Ru, obtained using a heat flux technique. The specific heat of Tb3Co and Tb3Rh are very similar, with a first order type transition occurring around 6 K below the magnetic ordering temperature without any corresponding feature on the magnetization. The slightly enhanced electronic specific heat, the Debye temperature around 150 K and the presence of the magnetic specific heat well above the ordering temperature are also characteristic of many other compounds of the R3M family (R=Rare Earth). The specific heat for Tb3Ru, however, presents two peaks at 37 K and 74 K. The magnetization shows that below the first peak the system presents an antiferromagnetic behavior and is paramagnetic above 74 K. We obtained a magnetocaloric effect for M=Co and Rh, -∆S=12 J/kg K, but for Tb3Ru it is less than 3 J/kg K (μ0∆H=5 T). We believe that the experimental results show that the MCE is directly related with the process of hybridization of the (R)5d-(M)d electrons that occurs in the R3M materials.

Needleless Electrospinning Experimental Study and Nanofiber Application in Semiconductor Packaging

NASA Astrophysics Data System (ADS)

Sun, Tianwei

Electronics especially mobile electronics such as smart phones, tablet PCs, notebooks and digital cameras are undergoing rapid development nowadays and have thoroughly changed our lives. With the requirement of more transistors, higher power, smaller size, lighter weight and even bendability, thermal management of these devices became one of the key challenges. Compared to active heat management system, heat pipe, which is a passive fluidic system, is considered promising to solve this problem. However, traditional heat pipes have size, weight and capillary limitation. Thus new type of heat pipe with smaller size, lighter weight and higher capillary pressure is needed. Nanofiber has been proved with superior properties and has been applied in multiple areas. This study discussed the possibility of applying nanofiber in heat pipe as new wick structure. In this study, a needleless electrospinning device with high productivity rate was built onsite to systematically investigate the effect of processing parameters on fiber properties as well as to generate nanofiber mat to evaluate its capability in electronics cooling. Polyethylene oxide (PEO) and Polyvinyl Alcohol (PVA) nanofibers were generated. Tensiometer was used for wettability measurement. The results show that independent parameters including spinneret type, working distance, solution concentration and polymer type are strongly correlated with fiber morphology compared to other parameters. The results also show that the fabricated nanofiber mat has high capillary pressure.

Particle Acceleration and Heating Processes at the Dayside Magnetopause

NASA Astrophysics Data System (ADS)

Berchem, J.; Lapenta, G.; Richard, R. L.; El-Alaoui, M.; Walker, R. J.; Schriver, D.

2017-12-01

It is well established that electrons and ions are accelerated and heated during magnetic reconnection at the dayside magnetopause. However, a detailed description of the actual physical mechanisms driving these processes and where they are operating is still incomplete. Many basic mechanisms are known to accelerate particles, including resonant wave-particle interactions as well as stochastic, Fermi, and betatron acceleration. In addition, acceleration and heating processes can occur over different scales. We have carried out kinetic simulations to investigate the mechanisms by which electrons and ions are accelerated and heated at the dayside magnetopause. The simulation model uses the results of global magnetohydrodynamic (MHD) simulations to set the initial state and the evolving boundary conditions of fully kinetic implicit particle-in-cell (iPic3D) simulations for different solar wind and interplanetary magnetic field conditions. This approach allows us to include large domains both in space and energy. In particular, some of these regional simulations include both the magnetopause and bow shock in the kinetic domain, encompassing range of particle energies from a few eV in the solar wind to keV in the magnetospheric boundary layer. We analyze the results of the iPic3D simulations by discussing wave spectra and particle velocity distribution functions observed in the different regions of the simulation domain, as well as using large-scale kinetic (LSK) computations to follow particles' time histories. We discuss the relevance of our results by comparing them with local observations by the MMS spacecraft.

Trends for Electron Beam Accelerator Applications in Industry

NASA Astrophysics Data System (ADS)

Machi, Sueo

2011-02-01

Electron beam (EB) accelerators are major pieces of industrial equipment used for many commercial radiation processing applications. The industrial use of EB accelerators has a history of more than 50 years and is still growing in terms of both its economic scale and new applications. Major applications involve the modification of polymeric materials to create value-added products, such as heat-resistant wires, heat-shrinkable sheets, automobile tires, foamed plastics, battery separators and hydrogel wound dressing. The surface curing of coatings and printing inks is a growing application for low energy electron accelerators, resulting in an environmentally friendly and an energy-saving process. Recently there has been the acceptance of the use of EB accelerators in lieu of the radioactive isotope cobalt-60 as a source for sterilizing disposable medical products. Environmental protection by the use of EB accelerators is a new and important field of application. A commercial plant for the cleaning flue gases from a coal-burning power plant is in operation in Poland, employing high power EB accelerators. In Korea, a commercial plant uses EB to clean waste water from a dye factory.

Natural convection of Al2O3-water nanofluid in a wavy enclosure

NASA Astrophysics Data System (ADS)

Leonard, Mitchell; Mozumder, Aloke K.; Mahmud, Shohel; Das, Prodip K.

2017-06-01

Natural convection heat transfer and fluid flow inside enclosures filled with fluids, such as air, water or oil, have been extensively analysed for thermal enhancement and optimisation due to their applications in many engineering problems, including solar collectors, electronic cooling, lubrication technologies, food processing and nuclear reactors. In comparison, little effort has been given to the problem of natural convection inside enclosures filled with nanofluids, while the addition of nanoparticles into a fluid base to alter thermal properties can be a feasible solution for many heat transfer problems. In this study, the problem of natural convection heat transfer and fluid flow inside a wavy enclosure filled with Al2O3-water nanofluid is investigated numerically using ANSYS-FLUENT. The effects of surface waviness and aspect ratio of the wavy enclosure on the heat transfer and fluid flow are analysed for various concentrations of Al2O3 nanoparticles in water. Flow fields and temperature fields are investigated and heat transfer rate is examined for different values of Rayleigh number. Results show that heat transfer within the enclosure can be enhanced by increasing surface waviness, aspect ratio or nanoparticles volume fraction. Changes in surface waviness have little effect on the heat transfer rate at low Rayleigh numbers, but when Ra ≥ 105 heat transfer increases with the increase of surface waviness from zero to higher values. Increasing the aspect ratio causes an increase in heat transfer rate, as the Rayleigh number increases the effect of changing aspect ratio is more apparent with the greatest heat transfer enhancement seen at higher Rayleigh numbers. Nanoparticles volume fraction has a little effect on the average Nusselt number at lower Rayleigh numbers when Ra ≥ 105 average Nusselt number increases with the increase of volume fraction. These findings provide insight into the heat transfer effects of using Al2O3-water nanofluid as a heat transfer medium and the effects of changing geometrical parameters, which will help in developing novel geometries with enhanced and controlled heat-transfer for solar collectors, electronic cooling, and food processing industries.

Infrared thermography with non-uniform heat flux boundary conditions on the rotor endwall of an axial turbine

NASA Astrophysics Data System (ADS)

Lazzi Gazzini, S.; Schädler, R.; Kalfas, A. I.; Abhari, R. S.

2017-02-01

It is technically challenging to measure heat fluxes on the rotating components of gas turbines, yet accurate knowledge of local heat loads under engine-representative conditions is crucial for ensuring the reliability of the designs. In this work, quantitative image processing tools were developed to perform fast and accurate infrared thermography measurements on 3D-shaped film-heaters directly deposited on the turbine endwalls. The newly developed image processing method and instrumentation were used to measure the heat load on the rotor endwalls of an axial turbine. A step-transient heat flux calibration technique is applied to measure the heat flux generated locally by the film heater, thus eliminating the need for a rigorously iso-energetic boundary condition. On-board electronics installed on the rotor record the temperature readings of RTDs installed in the substrate below the heaters in order to evaluate the conductive losses in the solid. Full maps of heat transfer coefficient and adiabatic wall temperature are produced for two different operating conditions, demonstrating the sensitivity of the technique to local flow features and variations in heat transfer due to Reynolds number effect.

A COLD FLARE WITH DELAYED HEATING

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

Fleishman, Gregory D.; Pal'shin, Valentin D.; Lysenko, Alexandra L.

2016-05-10

Recently, a number of peculiar flares have been reported that demonstrate significant nonthermal particle signatures with low, if any, thermal emission, which implies a close association of the observed emission with the primary energy release/electron acceleration region. This paper presents a flare that appears “cold” at the impulsive phase, while displaying delayed heating later on. Using hard X-ray data from Konus- Wind , microwave observations by SSRT, RSTN, NoRH, and NoRP, context observations, and three-dimensional modeling, we study the energy release, particle acceleration, and transport, and the relationships between the nonthermal and thermal signatures. The flaring process is found tomore » involve the interaction between a small loop and a big loop with the accelerated particles divided roughly equally between them. Precipitation of the electrons from the small loop produced only a weak thermal response because the loop volume was small, while the electrons trapped in the big loop lost most of their energy in the coronal part of the loop, which resulted in coronal plasma heating but no or only weak chromospheric evaporation, and thus unusually weak soft X-ray emission. The energy losses of the fast electrons in the big tenuous loop were slow, which resulted in the observed delay of the plasma heating. We determined that the impulsively accelerated electron population had a beamed angular distribution in the direction of the electric force along the magnetic field of the small loop. The accelerated particle transport in the big loop was primarily mediated by turbulent waves, which is similar to other reported cold flares.« less

Heat budget of ionospheric electrons

NASA Technical Reports Server (NTRS)

Prasad, S. S.; Schneck, L. J.

1976-01-01

Heat input calculations were detached from solar extreme UV data and monatomic oxygen densities were derived from simultaneously measured data sets (ion composition 146-191 km) in a study of the heat budget of ionosphere electrons. Earlier inferences that cooling predominates over heating are supported. A search for additional heat sources or a revision of the cooling rates is recommended, by way of balancing the heat budget. Importance is attached to electron cooling by fine structure excitation of monatomic oxygen.

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

Cordero, Zachary C.; Meyer, Harry M.; Nandwana, Peeyush

Electrons injected into the build envelope during powder-bed electron-beam additive manufacturing can accumulate on the irradiated particles and cause them to repel each other. Furthermore, these electrostatic forces can grow so large that they drive the particles out of the build envelope in a process known as smoking. Here, a model of powder bed charging is formulated and used to develop criteria that predict the conditions under which the powder bed will smoke. These criteria suggest dependences on particle size, pre-heat temperature, and process parameters that align closely with those observed in practice.

Catastrophic cooling and cessation of heating in the solar corona

NASA Astrophysics Data System (ADS)

Peter, H.; Bingert, S.; Kamio, S.

2012-01-01

Context. Condensations in the more than 106 K hot corona of the Sun are commonly observed in the extreme ultraviolet (EUV). While their contribution to the total solar EUV radiation is still a matter of debate, these condensations certainly provide a valuable tool for studying the dynamic response of the corona to the heating processes. Aims: We investigate different distributions of energy input in time and space to investigate which process is most relevant for understanding these coronal condensations. Methods: For a comparison to observations we synthesize EUV emission from a time-dependent, one-dimensional model for coronal loops, where we employ two heating scenarios: simply shutting down the heating and a model where the heating is very concentrated at the loop footpoints, while keeping the total heat input constant. Results: The heating off/on model does not lead to significant EUV count rates that one observes with SDO/AIA. In contrast, the concentration of the heating near the footpoints leads to thermal non-equilibrium near the loop top resulting in the well-known catastrophic cooling. This process gives a good match to observations of coronal condensations. Conclusions: This shows that the corona needs a steady supply of energy to support the coronal plasma, even during coronal condensations. Otherwise the corona would drain very fast, too fast to even form a condensation. Movies are available in electronic form at http://www.aanda.org

One step sintering of homogenized bauxite raw material and kinetic study

NASA Astrophysics Data System (ADS)

Gao, Chang-he; Jiang, Peng; Li, Yong; Sun, Jia-lin; Zhang, Jun-jie; Yang, Huan-ying

2016-10-01

A one-step sintering process of bauxite raw material from direct mining was completed, and the kinetics of this process was analyzed thoroughly. The results show that the sintering kinetics of bauxite raw material exhibits the liquid-phase sintering behavior. A small portion of impurities existed in the raw material act as a liquid phase. After X-ray diffraction analyses, scanning electron microscopy observations, and kinetics calculations, sintering temperature and heating duration were determined as the two major factors contributing to the sintering process and densification of bauxite ore. An elevated heating temperature and longer duration favor the densification process. The major obstacle for the densification of bauxite material is attributed to the formation of the enclosed blowhole during liquid-phase sintering.

Solar Wind Strahl Observations and Their Implication to the Core-Halo Formation due to Scattering

NASA Technical Reports Server (NTRS)

Vinas, Adolfo F.

2011-01-01

A study of the kinetic properties of the strahl electron velocity distribution functions (VDF?s) in the solar wind is presented. This study focuses on the mechanisms that control and regulate the electron VDF?s and the stability of the strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the strahl-electron density, temperature anisotropy, and electron heat-flux. These parameters are used to investigate the stability of the strahl population. The analysis check for whether the strahl electrons are constrained by some instability (e.g., the whistler or KAW instabilities), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by modeling of the 3D-VDF?s from which the moments properties of the various populations are obtained. The results of this study have profound implication on the current hypothesis about the probable formation of the solar wind halo electrons produced from the scattering of the strahl population. This hypothesis is strengthened by direct observations of the strahl electrons being scattered into the core-halo in an isolated event. The observation implies that the scattering of the strahl is not a continuous process but occurs in bursts in regions where conditions for wave growth providing the scattering are optimum. Sometimes, observations indicate that the strahl component is anisotropic (Tper/Tpal approx. 2). This provides a possible free energy source for the excitation of whistler waves as a possible scattering mechanism, however this condition is not always observed. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer.

Evaluation of the Low Heat Input Process for Weld Repair of Nickel-Base Superalloys

NASA Astrophysics Data System (ADS)

Durocher, J.; Richards, N. L.

2011-10-01

The repair of turbine blades and vanes commonly involves gas tungsten arc welding or an equivalent process, but unfortunately these components are often susceptible to heat-affected zone (HAZ) cracking during the weld repair process. This is a major problem especially in cast alloys due to their coarse-grain size and where the (Al + Ti) contents is in excess of 3-4%; vacuum brazing is also used but mainly on low stress non-rotating components such as vanes. Micro-welding has the potential to deposit small amounts of filler at low heat input levels with minimum HAZ and thus is an attractive process for depositing a quality weld. As with conventional fusion processes, the filler alloy is deposited by the generation of a low power arc between a consumable electrode and the substrate. The low heat input of this process offers unique advantages over more common welding processes such as gas tungsten arc, plasma arc, laser, and electron beam welding. In this study, the low heat input characteristic of micro-welding has been used to simulate weld repair using Inconel (IN) (Inconel and IN are trademarks of INCO Alloys International) 625, Rene (Rene is a trademark of General Electric Company) 41, Nimonic (Nimonic is a trademark of INCO Alloys International) 105 and Inconel 738LC filler alloys, to a cast Inconel 738LC substrate. The effect of micro-welding process parameters on the deposition rate, coating quality, and substrate has been investigated.

Miniature Heat Pipes

NASA Technical Reports Server (NTRS)

1997-01-01

Small Business Innovation Research contracts from Goddard Space Flight Center to Thermacore Inc. have fostered the company work on devices tagged "heat pipes" for space application. To control the extreme temperature ranges in space, heat pipes are important to spacecraft. The problem was to maintain an 8-watt central processing unit (CPU) at less than 90 C in a notebook computer using no power, with very little space available and without using forced convection. Thermacore's answer was in the design of a powder metal wick that transfers CPU heat from a tightly confined spot to an area near available air flow. The heat pipe technology permits a notebook computer to be operated in any position without loss of performance. Miniature heat pipe technology has successfully been applied, such as in Pentium Processor notebook computers. The company expects its heat pipes to accommodate desktop computers as well. Cellular phones, camcorders, and other hand-held electronics are forsible applications for heat pipes.

Momentum transport and nonlocality in heat-flux-driven magnetic reconnection in high-energy-density plasmas

DOE PAGES

Liu, Chang; Fox, William; Bhattacharjee, Amitava; ...

2017-10-06

Recent theory has demonstrated a novel physics regime for magnetic reconnection in high-energy-density plasmas where the magnetic field is advected by heat flux via the Nernst effect. In this paper, we elucidate the physics of the electron dissipation layer in this regime. Through fully kinetic simulation and a generalized Ohm's law derived from first principles, we show that momentum transport due to a nonlocal effect, the heat-flux-viscosity, provides the dissipation mechanism for magnetic reconnection. Scaling analysis, and simulations show that the reconnection process comprises a magnetic field compression stage and quasisteady reconnection stage, and the characteristic width of the currentmore » sheet in this regime is several electron mean-free paths. Finally, these results show the important interplay between nonlocal transport effects and generation of anisotropic components to the distribution function.« less

Anomalous Behavior of Electronic Heat Capacity of Strongly Correlated Iron Monosilicide

NASA Astrophysics Data System (ADS)

Povzner, A. A.; Volkov, A. G.; Nogovitsyna, T. A.

2018-04-01

The paper deals with the electronic heat capacity of iron monosilicide FeSi subjected to semiconductor-metal thermal transition during which the formation of its spintronic properties is observed. The proposed model which considers pd-hybridization of strongly correlated d-electrons with non-correlated p-electrons, demonstrates a connection of their contribution to heat capacity in the insulator phase with paramagnon effects and fluctuations of occupation numbers for p- and d-states. In a slitless state, the temperature curve of heat capacity is characterized by a maximum appeared due to normalization of the electron density of states using fluctuating exchange fields. At higher temperatures, a linear growth in heat capacity occurs due to paramagnon effects. The correlation between the model parameters and the first-principles calculation provides the electron contribution to heat capacity, which is obtained from the experimental results on phonon heat capacity. Anharmonicity of phonons is connected merely with the thermal expansion of the crystal lattice.

Fast wave direct electron heating in advanced inductive and ITER baseline scenario discharges in DIII-D

DOE PAGES

Pinsker, R. I.; Austin, M. E.; Diem, S. J.; ...

2014-02-12

Fast Wave (FW) heating and electron cyclotron heating (ECH) are used in the DIII-D tokamak to study plasmas with low applied torque and dominant electron heating characteristic of burning plasmas. FW heating via direct electron damping has reached the 2.5 MW level in high performance ELMy H-mode plasmas. In Advanced Inductive (AI) plasmas, core FW heating was found to be comparable to that of ECH, consistent with the excellent first-pass absorption of FWs predicted by ray-tracing models at high electron beta. FW heating at the ~2 MW level to ELMy H-mode discharges in the ITER Baseline Scenario (IBS) showed unexpectedlymore » strong absorption of FW power by injected neutral beam (NB) ions, indicated by significant enhancement of the D-D neutron rate, while the intended absorption on core electrons appeared rather weak. As a result, the AI and IBS discharges are compared in an effort to identify the causes of the different response to FWs.« less

Fast wave direct electron heating in advanced inductive and ITER baseline scenario discharges in DIII-D

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

Pinsker, R. I.; Jackson, G. L.; Luce, T. C.

Fast Wave (FW) heating and electron cyclotron heating (ECH) are used in the DIII-D tokamak to study plasmas with low applied torque and dominant electron heating characteristic of burning plasmas. FW heating via direct electron damping has reached the 2.5 MW level in high performance ELMy H-mode plasmas. In Advanced Inductive (AI) plasmas, core FW heating was found to be comparable to that of ECH, consistent with the excellent first-pass absorption of FWs predicted by ray-tracing models at high electron beta. FW heating at the ∼2 MW level to ELMy H-mode discharges in the ITER Baseline Scenario (IBS) showed unexpectedlymore » strong absorption of FW power by injected neutral beam (NB) ions, indicated by significant enhancement of the D-D neutron rate, while the intended absorption on core electrons appeared rather weak. The AI and IBS discharges are compared in an effort to identify the causes of the different response to FWs.« less

Fast wave direct electron heating in advanced inductive and ITER baseline scenario discharges in DIII-D

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

Pinsker, R. I.; Austin, M. E.; Diem, S. J.

Fast Wave (FW) heating and electron cyclotron heating (ECH) are used in the DIII-D tokamak to study plasmas with low applied torque and dominant electron heating characteristic of burning plasmas. FW heating via direct electron damping has reached the 2.5 MW level in high performance ELMy H-mode plasmas. In Advanced Inductive (AI) plasmas, core FW heating was found to be comparable to that of ECH, consistent with the excellent first-pass absorption of FWs predicted by ray-tracing models at high electron beta. FW heating at the ~2 MW level to ELMy H-mode discharges in the ITER Baseline Scenario (IBS) showed unexpectedlymore » strong absorption of FW power by injected neutral beam (NB) ions, indicated by significant enhancement of the D-D neutron rate, while the intended absorption on core electrons appeared rather weak. As a result, the AI and IBS discharges are compared in an effort to identify the causes of the different response to FWs.« less

Surface heating of electrons in atomic clusters irradiated by ultrashort laser pulses

NASA Astrophysics Data System (ADS)

Krainov, V. P.; Sofronov, A. V.

2014-04-01

We consider a mechanism for electron heating in atomic clusters at the reflections of free electrons from the cluster surface. Electrons acquire energy from the external laser field during these reflections. A simple analytical expression has been obtained for acquired electron kinetic energy during the laser pulse. We find conditions when this mechanism dominates compared to the electron heating due to the well-known induced inverse bremsstrahlung at the electron-ion collisions inside clusters.

Measurement of electron-ion relaxation in warm dense copper

DOE PAGES

Cho, B. I.; Ogitsu, T.; Engelhorn, K.; ...

2016-01-06

Experimental investigation of electron-ion coupling and electron heat capacity of copper in warm and dense states are presented. From time-resolved x-ray absorption spectroscopy, the temporal evolution of electron temperature is obtained for non-equilibrium warm dense copper heated by an intense femtosecond laser pulse. Electron heat capacity and electron-ion coupling are inferred from the initial electron temperature and its decrease over 10 ps. As a result, data are compared with various theoretical models.

Particle Demagnetization in Collisionless Magnetic Reconnection

NASA Technical Reports Server (NTRS)

Hesse, Michael

2006-01-01

The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. In this presentation, we present analytical theory results, as well as 2.5 and three-dimensional PIC simulations of guide field magnetic reconnection. We will show that diffusion region scale sizes in moderate and large guide field cases are determined by electron Larmor radii, and that analytical estimates of diffusion region dimensions need to include description of the heat flux tensor. The dominant electron dissipation process appears to be based on thermal electron inertia, expressed through nongyrotropic electron pressure tensors. We will argue that this process remains viable in three dimensions by means of a detailed comparison of high resolution particle-in-cell simulations.

Method for Fabricating Composite Structures Using Continuous Press Forming

NASA Technical Reports Server (NTRS)

Farley, Gary L. (Inventor)

1997-01-01

A method for fabricating composite structures at a low-cost. moderate-to-high production rate. A first embodiment of the method includes employing a continuous press forming fabrication process. A second embodiment of the method includes employing a pultrusion process for obtaining composite structures. The methods include coating yarns with matrix material, weaving the yarn into fabric to produce a continuous fabric supply and feeding multiple layers of net-shaped fabrics having optimally oriented fibers into a debulking tool to form an undebulked preform. The continuous press forming fabrication process includes partially debulking the preform, cutting the partially debulked preform and debulking the partially debulked preform to form a net-shape. An electron-beam or similar technique then cures the structure. The pultrusion fabric process includes feeding the undebulked preform into a heated die and gradually debulking the undebulked preform. The undebulked preform in the heated die changes dimension until a desired cross-sectional dimension is achieved. This process further includes obtaining a net-shaped infiltrated uncured preform, cutting the uncured preform to a desired length and electron-beam curing (or similar technique) the uncured preform. These fabrication methods produce superior structures formed at higher production rates. resulting in lower cost and high structural performance.

Model of convection mass transfer in titanium alloy at low energy high current electron beam action

NASA Astrophysics Data System (ADS)

Sarychev, V. D.; Granovskii, A. Yu; Nevskii, S. A.; Konovalov, S. V.; Gromov, V. E.

2017-01-01

The convection mixing model is proposed for low-energy high-current electron beam treatment of titanium alloys, pre-processed by heterogeneous plasma flows generated via explosion of carbon tape and powder TiB2. The model is based on the assumption vortices in the molten layer are formed due to the treatment by concentrated energy flows. These vortices evolve as the result of thermocapillary convection, arising because of the temperature gradient. The calculation of temperature gradient and penetration depth required solution of the heat problem with taking into account the surface evaporation. However, instead of the direct heat source the boundary conditions in phase transitions were changed in the thermal conductivity equation, assuming the evaporated material takes part in the heat exchange. The data on the penetration depth and temperature distribution are used for the thermocapillary model. The thermocapillary model embraces Navier-Stocks and convection heat transfer equations, as well as the boundary conditions with the outflow of evaporated material included. The solution of these equations by finite elements methods pointed at formation of a multi-vortices structure when electron-beam treatment and its expansion over new zones of material. As the result, strengthening particles are found at the depth exceeding manifold their penetration depth in terms of the diffusion mechanism.

Numerical study on characteristics of radio-frequency discharge at atmospheric pressure in argon with small admixtures of oxygen

NASA Astrophysics Data System (ADS)

Wang, Yinan; Liu, Yue

2017-07-01

In this paper, a 1D fluid model is developed to study the characteristics of a discharge in argon with small admixtures of oxygen at atmospheric pressure. This model consists of a series of equations, including continuity equations for electrons, positive ions, negative ions and neutral particles, the energy equation, and the Poisson equation for electric potential. Special attention has been paid to the electron energy dissipation and the mechanisms of electron heating, while the admixture of oxygen is in the range of 0.1%-0.6%. It is found that when the oxygen-to-argon ratio grows, the discharge is obviously divided into three stages: electron growth, electron reduction and the electron remaining unchanged. Furthermore, the cycle-averaged electric field, electron temperature, electron Ohmic heating, electron collisionless heating, electron energy dissipation and the net electron production are also studied in detail, and when the oxygen-to-argon ratio is relatively larger (R = 0.6%), double value peaks of electron Ohmic heating appear in the sheath. According to the results of the numerical simulation, various oxygen-to-argon ratios result in different amounts of electron energy dissipation and electron heating.

Transmission electron microscopy characterization of microstructural features of Al-Li-Cu alloys

NASA Technical Reports Server (NTRS)

Avalos-Borja, M.; Pizzo, P. P.; Larson, L. A.

1983-01-01

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitation events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significant alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations.

Transmission electron microscopy characterization of microstructural features in aluminum-lithium-copper alloys

NASA Technical Reports Server (NTRS)

Avalos-Borja, M.; Larson, L. A.; Pizzo, P. P.

1984-01-01

A transmission electron microscopy (TEM) examination of aluminum-lithium-copper alloys was conducted. The principal purpose is to characterize the nature, size, and distribution of stringer particles which result from the powder metallurgy (P/M) processing of these alloys. Microstructural features associated with the stringer particles are reported that help explain the stress corrosion susceptibility of the powder metallurgy-processed Al-Li-Cu alloys. In addition, matrix precipitaton events are documented for a variety of heat treatments and process variations. Hot rolling is observed to significantly alter the nature of matrix precipitation, and the observations are correlated with concomitant mechanical property variations.

Artificial plasma cusp generated by upper hybrid instabilities in HF heating experiments at HAARP

NASA Astrophysics Data System (ADS)

Kuo, Spencer; Snyder, Arnold

2013-05-01

High Frequency Active Auroral Research Program digisonde was operated in a fast mode to record ionospheric modifications by the HF heating wave. With the O mode heater of 3.2 MHz turned on for 2 min, significant virtual height spread was observed in the heater off ionograms, acquired beginning the moment the heater turned off. Moreover, there is a noticeable bump in the virtual height spread of the ionogram trace that appears next to the plasma frequency (~ 2.88 MHz) of the upper hybrid resonance layer of the HF heating wave. The enhanced spread and the bump disappear in the subsequent heater off ionograms recorded 1 min later. The height distribution of the ionosphere in the spread situation indicates that both electron density and temperature increases exceed 10% over a large altitude region (> 30 km) from below to above the upper hybrid resonance layer. This "mini cusp" (bump) is similar to the cusp occurring in daytime ionograms at the F1-F2 layer transition, indicating that there is a small ledge in the density profile reminiscent of F1-F2 layer transitions. Two parametric processes exciting upper hybrid waves as the sidebands by the HF heating waves are studied. Field-aligned purely growing mode and lower hybrid wave are the respective decay modes. The excited upper hybrid and lower hybrid waves introduce the anomalous electron heating which results in the ionization enhancement and localized density ledge. The large-scale density irregularities formed in the heat flow, together with the density irregularities formed through the parametric instability, give rise to the enhanced virtual height spread. The results of upper hybrid instability analysis are also applied to explain the descending feature in the development of the artificial ionization layers observed in electron cyclotron harmonic resonance heating experiments.

Solar flare model atmospheres

NASA Technical Reports Server (NTRS)

Hawley, Suzanne L.; Fisher, George H.

1993-01-01

Solar flare model atmospheres computed under the assumption of energetic equilibrium in the chromosphere are presented. The models use a static, one-dimensional plane parallel geometry and are designed within a physically self-consistent coronal loop. Assumed flare heating mechanisms include collisions from a flux of non-thermal electrons and x-ray heating of the chromosphere by the corona. The heating by energetic electrons accounts explicitly for variations of the ionized fraction with depth in the atmosphere. X-ray heating of the chromosphere by the corona incorporates a flare loop geometry by approximating distant portions of the loop with a series of point sources, while treating the loop leg closest to the chromospheric footpoint in the plane-parallel approximation. Coronal flare heating leads to increased heat conduction, chromospheric evaporation and subsequent changes in coronal pressure; these effects are included self-consistently in the models. Cooling in the chromosphere is computed in detail for the important optically thick HI, CaII and MgII transitions using the non-LTE prescription in the program MULTI. Hydrogen ionization rates from x-ray photo-ionization and collisional ionization by non-thermal electrons are included explicitly in the rate equations. The models are computed in the 'impulsive' and 'equilibrium' limits, and in a set of intermediate 'evolving' states. The impulsive atmospheres have the density distribution frozen in pre-flare configuration, while the equilibrium models assume the entire atmosphere is in hydrostatic and energetic equilibrium. The evolving atmospheres represent intermediate stages where hydrostatic equilibrium has been established in the chromosphere and corona, but the corona is not yet in energetic equilibrium with the flare heating source. Thus, for example, chromospheric evaporation is still in the process of occurring.

Effect of Heat Treatment on the Hardness and Wear of Grinding Balls

NASA Astrophysics Data System (ADS)

Aissat, Sahraoui; Sadeddine, Abdelhamid; Bradai, Mohand Amokrane; Younes, Rassim; Bilek, Ali; Benabbas, Abderrahim

2017-09-01

The effect quenching and tempering by different regimes on Rockwell hardness and wear processes of grinding balls 50 and 70 mm in diameter made of two melts of chromium-molybdenum cast iron is studied. The heating temperature for quenching is 850, 950, and 1050°C; the tempering temperature is 250, 400, and 600°C. Iron is analyzed in an electron microscope. Diffraction patterns are obtained. A model of cast iron wear is suggested and compared to the Davis model and to experimental results. An optimum heat treatment regime is proposed.

Engineering aspects of the HT-6M Tokamak

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

Not Available

1986-05-01

The HT-6M is a medium-sized tokamak being built in China. The principal aim of the project is to study high-power auxiliary heating (1-MW neutral beam injection, 1-MW ion cyclotron resonance heating, and 100-kW electron cyclotron resonance heating), high-..beta.. experiments, the transport process, and the formation and diffusion process of impurities. The main device parameters are: major plasma radius R = 65 cm, minor plasma radius a = 20 cm, plasma current I/subP/ = 150 kA, discharge time tau = 150 ms, toroidal field B/subT/ = 15 kG. Simplicity of construction, accessibility to the plasma, reliability in operation, and convenience formore » maintenance were particularly emphasized in the design. The important design features of the device and power supply system are described.« less

5 MV 30 mA industrial electron processing system

NASA Astrophysics Data System (ADS)

Hoshi, Y.; Mizusawa, K.

1991-05-01

Industrial electron beam processing systems have been in use in various application fields such as: improving heat resistivity of wire insulation; controlling quality of automobile rubber tires and melt index characteristics of PE foams; and curing paintings or printing inks. Recently, there has come up a need for electron beam with an energy higher than 3 MV in order to disinfect salmonella in chicken meat, to kill bugs in fruits, and to sterilize medical disposables. To meet this need we developed a 5 MV 30 mA electron processing system with an X-ray conversion target. The machine was tested in NHV's plant in Kyoto at continuous operation of full voltage and full current. It proved to be very steady in operation with a high efficiency (as much as 72%). Also, the X-ray target was tested in a continuous run of 5 MV 30 mA (150 kW). It proved to be viable in industrial utilization. This paper introduces the process and the results of the development.

Investigation of Third Gyro-harmonic Heating at HAARP Using Stimulated Radio Emissions, the MUIR and SuperDARN Radars

NASA Astrophysics Data System (ADS)

Mahmoudian, Alireza; Bernhardt, Paul; Ruohoniemi, J. Michael; Isham, Brett; Watkins, Brenton; Scales, Wayne

2016-07-01

Use of high frequency (HF) heating experiments has been extended in recent years as a useful methodology for plasma physicists wishing to remotely study the properties and behavior of the ionosphere as well as nonlinear plasma processes. Our recent work using high latitude heating experiments has lead to several important discoveries that have enabled assessment of active geomagnetic conditions, determination of minor ion species and their densities, ion mass spectrometry, electron temperature measurements in the heating ionosphere, as well a deeper understanding of physical processes associated with electron acceleration and formation of field aligned irregularities. The data recorded during two campaigns at HAARP in 2011 and 2012 will be presented. Several diagnostic instruments have been used to detect HAARP heater-generated ionospheric irregularities and plasma waves. These diagnostics include an ionosonde, MUIR (Modular UHF Ionospheric Radar at 446 MHz), SuperDARN HF backscatter radar and ground-based SEE receivers. Variation of the wideband/ narrowband SEE features, SuperDARN echoes, and enhanced ion lines were studied with pump power variation, pump frequency stepping near 3fce as well as changing beam angle relative to the magnetic zenith. In particular, formation of field-aligned irregularities (FAIs) and upper hybrid (UH) waves through oscillating two-stream instability (OSTI) and resonance instability is studied. During heating, Narrowband SEE (NSEE) showed enhancements that correlated with the enhanced MUIR radar ion lines. IA MSBS (Magnetized Stimulated Brillouin Scatter) lines are much narrower than Wideband SEE (WSEE) lines and as a result electron temperature calculated using NSEE line offset has potential to be more accurate. This technique may therefore complement the electron temperature calculation using ISR spectra. Strength of IA MSBS lines correlate with EHIL in the MUIR spectrum during HF pump frequency variation near 3fce. Therefore, NSEE could be used for similar diagnostic information, particularly temperature assessment during heating. More detailed physics-based modeling of such SEE is expected to provide further diagnostic information/capabilities. This work has demonstrated the tremendous future potential of Narrowband SEE (NSEE) as a powerful untapped ionospheric diagnostic which could provide complementary measurements for locations that ISR facilities are not available or as a complementary measurement for the waves and irregularities that cannot be observed by ISR.

Impact excitation and electron-hole multiplication in graphene and carbon nanotubes.

PubMed

Gabor, Nathaniel M

2013-06-18

In semiconductor photovoltaics, photoconversion efficiency is governed by a simple competition: the incident photon energy is either transferred to the crystal lattice (heat) or transferred to electrons. In conventional materials, energy loss to the lattice is more efficient than energy transferred to electrons, thus limiting the power conversion efficiency. Quantum electronic systems, such as quantum dots, nanowires, and two-dimensional electronic membranes, promise to tip the balance in this competition by simultaneously limiting energy transfer to the lattice and enhancing energy transfer to electrons. By exploring the optical, thermal, and electronic properties of quantum materials, we may perhaps find an ideal optoelectronic material that provides low cost fabrication, facile systems integration, and a means to surpass the standard limit for photoconversion efficiency. Nanoscale carbon materials, such as graphene and carbon nanotubes, provide ideal experimental quantum systems in which to explore optoelectronic behavior for applications in solar energy harvesting. Within essentially the same material, researchers can achieve a broad spectrum of energetic configurations, from a gapless semimetal to a large band-gap semiconducting nanowire. Owing to their nanoscale dimensions, graphene and carbon nanotubes exhibit electronic and optical properties that reflect strong electron-electron interactions. Such strong interactions may lead to exotic low-energy electron transport behavior and high-energy electron scattering processes such as impact excitation and the inverse process of Auger recombination. High-energy processes, which become very important under photoexcitation, may be particularly efficient in nanoscale carbon materials due to the relativistic-like, charged particle band structure and sensitivity to the dielectric environment. In addition, due to the covalently bonded carbon framework that makes up these materials, electron-phonon coupling is very weak. In carbon nanomaterials, strong electron-electron interactions combined with weak electron-phonon interactions results in excellent optical, thermal and electronic properties, the exploration of which promises to reveal fundamentally new physical processes and deliver advanced nanotechnologies. In this Account, we review the results of novel optoelectronic experiments that explore the intrinsic photoresponse of carbon nanomaterials integrated into nanoscale devices. By fabricating gate voltage-controlled photodetectors composed of atomically thin sheets of graphene and individual carbon nanotubes, we are able to fully explore electron transport in these systems under optical illumination. We find that strong electron-electron interactions play a key role in the intrinsic photoresponse of both materials, as evidenced by hot carrier transport in graphene and highly efficient multiple electron-hole pair generation in nanotubes. In both of these quantum systems, photoexcitation leads to high-energy electron-hole pairs that relax energy predominantly into the electronic system, rather than heating the lattice. Due to highly efficient energy transfer from photons into electrons, graphene and carbon nanotubes may be ideal materials for solar energy harvesting devices with efficiencies that could exceed the Shockley-Queisser limit.

Improvement of Electropolishing of 1100 Al Alloy for Solar Thermal Applications

NASA Astrophysics Data System (ADS)

Aguilar-Sierra, Sara María; Echeverría E, Félix

2018-03-01

Aluminum sheets-based mirrors are finding applicability in high-temperature solar concentrating technologies because they are cost-effective, lightweight and have high mechanical properties. Nonetheless, the reflectance percentages obtained by electropolishing are not close to the reflectance values of the currently used evaporated films. Therefore, controlling key factors affecting electropolishing processes became essential in order to achieve highly reflective aluminum surfaces. This study investigated the effect of both the electropolishing process and previous heat treatment on the total reflectance of the AA 1100 aluminum alloy. An acid electrolyte and a modified Brytal process were evaluated. Total reflectance was measured by means of UV-Vis spectrophotometry. Reflectance values higher than 80% at 600 nm were achieved for both electrolytes. Optical microscopy and scanning electron microscopy images showed uneven dissolution for the acid electropolished samples causing a reflectance drop in the 200-450 nm region. The influence of heat treatment, previously to electropolishing, was tested at two different temperatures and various holding times. It was found that reflectance increases around 15% for the heat-treated and electropolished samples versus the non-heat-treated ones. A heat treatment at low temperature combined with a short holding time was enough to improve the sample total reflectance.

Effects of heat treatments on microstructure and properties of Ti-6Al-4V ELI alloy fabricated by electron beam melting (EBM)

DOE PAGES

Galarraga, Haize; Warren, Robert J.; Lados, Diana A.; ...

2017-01-06

Electron beam melting (EBM) is a metal powder bed fusion additive manufacturing (AM) technology that is used to fabricate three-dimensional near-net-shaped parts directly from computer models. Ti-6Al-4V is the most widely used and studied alloy for this technology and is the focus of this work in its ELI (Extra Low Interstitial) variation. The mechanisms of microstructure formation, evolution, and its subsequent influence on mechanical properties of the alloy in as-fabricated condition have been documented by various researchers. In the present work, the thermal history resulting in the formation of the as-fabricated microstructure was analyzed and studied by a thermal simulation.more » Subsequently different heat treatments were performed based on three approaches in order to study the effects of heat treatments on the singular and exclusive microstructure formed during the EBM fabrication process. In the first approach, the effect of cooling rate after the solutionizing process was studied. In the second approach, the variation of α lath thickness during annealing treatment and correlation with mechanical properties was established. In the last approach, several solutionizing and aging experiments were conducted.« less

Micromechanical Characterization and Texture Analysis of Direct Cast Titanium Alloys Strips

NASA Technical Reports Server (NTRS)

2000-01-01

This research was conducted to determine a post-processing technique to optimize mechanical and material properties of a number of Titanium based alloys and aluminides processed via Melt Overflow Solidification Technique (MORST). This technique was developed by NASA for the development of thin sheet titanium and titanium aluminides used in high temperature applications. The materials investigated in this study included conventional titanium alloy strips and foils, Ti-1100, Ti-24Al-11Nb (Alpha-2), and Ti-48Al-2Ta (Gamma). The methodology used included micro-characterization, heat-treatment, mechanical processing and mechanical testing. Characterization techniques included optical, electron microscopy, and x-ray texture analysis. The processing included heat-treatment and mechanical deformation through cold rolling. The initial as-cast materials were evaluated for their microstructure and mechanical properties. Different heat-treatment and rolling steps were chosen to process these materials. The properties were evaluated further and a processing relationship was established in order to obtain an optimum processing condition. The results showed that the as-cast material exhibited a Widmanstatten (fine grain) microstructure that developed into a microstructure with larger grains through processing steps. The texture intensity showed little change for all processing performed in this investigation.

Thermodynamic Study on Plasma Expansion along a Divergent Magnetic Field.

PubMed

Zhang, Yunchao; Charles, Christine; Boswell, Rod

2016-01-15

Thermodynamic properties are revisited for electrons that are governed by nonlocal electron energy probability functions in a plasma of low collisionality. Measurements in a laboratory helicon double layer experiment have shown that the effective electron temperature and density show a polytropic correlation with an index of γ_{e}=1.17±0.02 along the divergent magnetic field, implying a nearly isothermal plasma (γ_{e}=1) with heat being brought into the system. However, the evolution of electrons along the divergent magnetic field is essentially an adiabatic process, which should have a γ_{e}=5/3. The reason for this apparent contradiction is that the nearly collisionless plasma is very far from local thermodynamic equilibrium and the electrons behave nonlocally. The corresponding effective electron enthalpy has a conservation relation with the potential energy, which verifies that there is no heat transferred into the system during the electron evolution. The electrons are shown in nonlocal momentum equilibrium under the electric field and the gradient of the effective electron pressure. The convective momentum of ions, which can be assumed as a cold species, is determined by the effective electron pressure and the effective electron enthalpy is shown to be the source for ion acceleration. For these nearly collisionless plasmas, the use of traditional thermodynamic concepts can lead to very erroneous conclusions regarding the thermal conductivity.

Characterization of the α phase nucleation in a two-phase metastable β titanium alloy

NASA Astrophysics Data System (ADS)

Lenain, A.; Clément, N.; Jacques, P. J.; Véron, M.

2005-12-01

Beta titanium alloys are increasingly the best choice for automotive and aerospace applications due to their high performance-to-density ratio. Among these alloys, the TIMETAL Ti-LCB is already used in the automotive industry because it presents excellent mechanical properties and a lower cost compared with other Ti alloys. The current study deals with the characterization of the nucleation and growth of the α phase in several thermomechanical processes, because the distribution and size of the α phase strongly influence the mechanical properties of the resulting microstructures. Several heat treatments were conducted after either cold rolling or annealing. The resulting microstructures were characterized by scanning electron microscopy, transmission electron microscopy, x-ray diffraction, or electron backscatter diffraction. It was observed that the morphology and the volume fraction of the α phase are strongly dependent on the holding temperature, on the heating or cooling rate, and on the β grain size.

Electron Energy Distribution function in a weakly magnetized expanding helicon plasma discharge

NASA Astrophysics Data System (ADS)

Sirse, Nishant; Harvey, Cleo; Gaman, Cezar; Ellingboe, Bert

2016-09-01

Helicon wave heating is well known to produce high-density plasma source for application in plasma thrusters, plasma processing and many more. Our previous study (B Ellingboe et al. APS Gaseous Electronics Conference 2015, abstract #KW2.005) has shown observation of helicon wave in a weakly magnetized inductively coupled plasma source excited by m =0 antenna at 13.56 MHz. In this paper, we investigated the Electron Energy Distribution Function (EEDF) in the same setup by using an RF compensated Langmuir probe. The ac signal superimposition technique (second harmonic technique) is used to determine EEDF. The EEDF is measured for 5-100 mTorr gas pressure, 100 W - 1.5 kW rf power and at different locations in the source chamber, boundary and diffusion chamber. This paper will discuss the change in the shape of EEDF for various heating mode transitions.

Diffusion, convection, and solidification in cw-mode free electron laser nitrided titanium

NASA Astrophysics Data System (ADS)

Höche, Daniel; Shinn, Michelle; Müller, Sven; Schaaf, Peter

2009-04-01

Titanium sheets were irradiated by free electron laser radiation in cw mode in pure nitrogen. Due to the interaction, nitrogen diffusion occurs and titanium nitride was synthesized in the tracks. Overlapping tracks have been utilized to create coatings in order to improve the tribological properties of the sheets. Caused by the local heating and the spatial dimension of the melt pool, convection effects were observed and related to the track properties. Stress, hardness, and nitrogen content were investigated with x-ray diffraction, nanoindention, and resonant nuclear reaction analysis. The measured results were correlated with the scan parameters, especially to the lateral track shift. Cross section micrographs were prepared and investigated by means of scanning electron microscopy. They show the solidification behavior, phase formation, and the nitrogen distribution. The experiments give an insight into the possibilities of materials processing using such a unique heat source.

[Study of the effect of heat source separation distance on plasma physical properties in laser-pulsed GMAW hybrid welding based on spectral diagnosis technique].

PubMed

Liao, Wei; Hua, Xue-Ming; Zhang, Wang; Li, Fang

2014-05-01

In the present paper, the authors calculated the plasma's peak electron temperatures under different heat source separation distance in laser- pulse GMAW hybrid welding based on Boltzmann spectrometry. Plasma's peak electron densities under the corresponding conditions were also calculated by using the Stark width of the plasma spectrum. Combined with high-speed photography, the effect of heat source separation distance on electron temperature and electron density was studied. The results show that with the increase in heat source separation distance, the electron temperatures and electron densities of laser plasma did not changed significantly. However, the electron temperatures of are plasma decreased, and the electron densities of are plasma first increased and then decreased.

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

Minami, R., E-mail: minami@prc.tsukuba.ac.jp; Imai, T.; Kariya, T.

Temporally and spatially resolved soft x-ray and end-loss-electron analyses of the electron cyclotron heated plasmas are carried out by using a semiconductor detector array and an electrostatic energy analyzer in the GAMMA 10 tandem mirror. The flux and the energy spectrum of the end loss electrons are measured by a multi-grid energy analyzer. Recently, the electron cyclotron heating power modulation experiments have been started in order to generate and control the high heat flux and to make the edge localized mode-like intermittent heat load pattern for the divertor simulation studies by the use of these detectors for electron properties.

Parameter study of r-process lanthanide production and heating rates in kilonovae

NASA Astrophysics Data System (ADS)

Lippuner, Jonas; Roberts, Luke F.

2015-04-01

Explosive r-process nucleosynthesis in material ejected during compact object mergers may lead to radioactively powered transients called kilonovae. The timescale and peak luminosity of these transients are sensitive to the composition of the material after nuclear burning ceases, as the composition determines the local heating rate from nuclear decays and the opacity. The presence of lanthanides in the ejecta can drastically increase the opacity. We use the new general-purpose nuclear reaction network SkyNet to run a parameter study of r-process nucleosynthesis for a range of initial electron fractions Ye, initial entropies s, and density decay timescales τ. We find that the ejecta is lanthanide-free for Ye >~ 0 . 22 - 0 . 3 , depending on s and τ. The heating rate is insensitive to s and τ, but certain, larger values of Ye lead to reduced heating rates, because single nuclides dominate the heating. With a simple model we estimate the luminosity, time, and effective temperature at the peak of the light curve. Since the opacity is much lower in the lanthanide-free case, we find the luminosity peaks much earlier at ~ 1 day vs. ~ 15 days in the lanthanide-rich cases. Although there is significant variation in the heating rate with Ye, changes in the heating rate do not mitigate the effect of the lanthanides. This research is partially supported by NSF under Award Numbers AST-1333520 and AST-1205732.

Tracking the ultrafast XUV optical properties of x-ray free-electron-laser heated matter with high-order harmonics

NASA Astrophysics Data System (ADS)

Williams, Gareth O.; Künzel, S.; Daboussi, S.; Iwan, B.; Gonzalez, A. I.; Boutu, W.; Hilbert, V.; Zastrau, U.; Lee, H. J.; Nagler, B.; Granados, E.; Galtier, E.; Heimann, P.; Barbrel, B.; Dovillaire, G.; Lee, R. W.; Dunn, J.; Recoules, V.; Blancard, C.; Renaudin, P.; de la Varga, A. G.; Velarde, P.; Audebert, P.; Merdji, H.; Zeitoun, Ph.; Fajardo, M.

2018-02-01

We present measurements of photon absorption by free electrons as a solid is transformed to plasma. A femtosecond x-ray free-electron laser is used to heat a solid, which separates the electron and ion heating time scales. The changes in absorption are measured with an independent probe pulse created through high-order-harmonic generation. We find an increase in electron temperature to have a relatively small impact on absorption, contrary to several predictions, whereas ion heating increases absorption. We compare the data to current theoretical and numerical approaches and find that a smoother electronic structure yields a better fit to the data, suggestive of a temperature-dependent electronic structure in warm dense matter.

In-Process Thermal Imaging of the Electron Beam Freeform Fabrication Process

NASA Technical Reports Server (NTRS)

Taminger, Karen M.; Domack, Christopher S.; Zalameda, Joseph N.; Taminger, Brian L.; Hafley, Robert A.; Burke, Eric R.

2016-01-01

Researchers at NASA Langley Research Center have been developing the Electron Beam Freeform Fabrication (EBF3) metal additive manufacturing process for the past 15 years. In this process, an electron beam is used as a heat source to create a small molten pool on a substrate into which wire is fed. The electron beam and wire feed assembly are translated with respect to the substrate to follow a predetermined tool path. This process is repeated in a layer-wise fashion to fabricate metal structural components. In-process imaging has been integrated into the EBF3 system using a near-infrared (NIR) camera. The images are processed to provide thermal and spatial measurements that have been incorporated into a closed-loop control system to maintain consistent thermal conditions throughout the build. Other information in the thermal images is being used to assess quality in real time by detecting flaws in prior layers of the deposit. NIR camera incorporation into the system has improved the consistency of the deposited material and provides the potential for real-time flaw detection which, ultimately, could lead to the manufacture of better, more reliable components using this additive manufacturing process.

Method for Fabricating Composite Structures Including Continuous Press Forming and Pultrusion Processing

NASA Technical Reports Server (NTRS)

Farley, Gary L. (Inventor)

1995-01-01

A method for fabricating composite structures at a low-cost, moderate-to-high production rate is disclosed. A first embodiment of the method includes employing a continuous press forming fabrication process. A second embodiment of the method includes employing a pultrusion process for obtaining composite structures. The methods include coating yarns with matrix material, weaving the yarn into fabric to produce a continuous fabric supply, and feeding multiple layers of net-shaped fabrics having optimally oriented fibers into a debulking tool to form an undebulked preform. The continuous press forming fabrication process includes partially debulking the preform, cutting the partially debulked preform, and debulking the partially debulked preform to form a netshape. An electron-beam or similar technique then cures the structure. The pultrusion fabric process includes feeding the undebulked preform into a heated die and gradually debulking the undebulked preform. The undebulked preform in the heated die changes dimension until a desired cross-sectional dimension is achieved. This process further includes obtaining a net-shaped infiltrated uncured preform, cutting the uncured preform to a desired length, and electron-beam curing (or similar technique) the uncured preform. These fabrication methods produce superior structures formed at higher production rates, resulting in lower cost and high structural performance.

Effect of Post-Braze Heat Treatment on the Microstructure and Shear Strength of Cemented Carbide and Steel Using Ag-Based Alloy

NASA Astrophysics Data System (ADS)

Winardi, Y.; Triyono; Muhayat, N.

2018-03-01

The aim of the present study was to investigate the effect temperature of heat treatment process on the interfacial microstructure and mechanical properties of cemented carbide/carbon steel single lap joint brazed using Ag based alloy filler metal. The brazing process was carried out using torch brazing. Heat treatment process was carried out in induction furnace on the temperature of 700, 725, and 750°C, for 30 minutes. Microstructural examinations and phase analysis were performed using scanning electron microscopy (SEM) equipped with energy dispersion spectrometry (EDS). Shear strength of the joints was measured by the universal testing machine. The results of the microstructural analyses of the brazed area indicate that the increase temperature of treatment lead to the increase of solid solution phase of enrichted Cu. Based on EDS test, the carbon elements spread to all brazed area, which is disseminated by base metals. Shear strength joint is increased with temperature treatment. The highest shear strength of the brazed joint was 214,14 MPa when the heated up at 725°C.

Evolution and Control of 2219 Aluminum Microstructural Features Through Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Taminger, Karen M.; Hafley, Robert A.; Domack, Marcia S.

2006-01-01

The layer-additive nature of the electron beam freeform fabrication (EBF3) process results in a tortuous thermal path producing complex microstructures including: small homogeneous equiaxed grains; dendritic growth contained within larger grains; and/or pervasive dendritic formation in the interpass regions of the deposits. Several process control variables contribute to the formation of these different microstructures, including translation speed, wire feed rate, beam current and accelerating voltage. In electron beam processing, higher accelerating voltages embed the energy deeper below the surface of the substrate. Two EBF3 systems have been established at NASA Langley, one with a low-voltage (10-30kV) and the other a high-voltage (30-60 kV) electron beam gun. Aluminum alloy 2219 was processed over a range of different variables to explore the design space and correlate the resultant microstructures with the processing parameters. This report is specifically exploring the impact of accelerating voltage. Of particular interest is correlating energy to the resultant material characteristics to determine the potential of achieving microstructural control through precise management of the heat flux and cooling rates during deposition.

Heterogeneous catalysis with lasers

NASA Astrophysics Data System (ADS)

George, T. F.

1986-06-01

Theoretical techniques have been developed to describe a variety of laser-induced molecular rate processes occurring at solid surfaces which are involved in heterogeneous catalysis. Such processes include adsorption, migration, chemical reactions and desorption. The role of surface phonons in laser-selective processes and laser heating has been analyzed. The importance of electronic degrees of freedom has been considered for semiconductor and metal substrates, with special emphasis on the laser excitation of surface states. Surface-modified photochemistry has also been investigated, where the effect of a metal surface on the resonance fluorescence spectrum of a laser-driven atom/molecule has been assessed by means of surface-dressed optical Bloch equations. It is seen that the spectrum can be significantly different from the gas-phase case. Two related gas-surface collision processes have also been studied. First, the feasibility of the formation of the electron-hole pairs in a semiconductor by vibrationally excited molecules has been explored. Second, charge transfer in ion-surface collisions has been examined for both one-electron and two-electron transfer processes. Work has been initiated on microstructures and rough structures, including clusters and surface gratings.

Anisotropic Electron Tail Generation during Tearing Mode Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Dubois, Ami

2017-10-01

Magnetic reconnection (MR) plays an important role in particle transport, energization, and acceleration in space, astrophysical, and laboratory plasmas. In the MST RFP, discrete MR events release large amounts of energy from the equilibrium magnetic field, a large fraction of which is transferred to the ions in a non-collisional process. Key features are anisotropic heating, mass and charge dependence, and energetic ion tail formation. Unlike the ions, the thermal electron temperature decreases at MR events, which is consistent with enhanced electron heat transport due to increased magnetic stochasticity. However, new high-speed x-ray spectrum measurements reveal transient formation of a non-Maxwellian energetic electron tail during MR. The energetic tail is characterized by a power-law, E-γ, with the spectral index (γ) decreasing from 4.2 to 2.2 at MR, and then increasing rapidly to 6.8 due to increased stochastic transport. The x-ray emission peaks in a radial view and is symmetric in the toroidal direction, indicating an anisotropic electron tail is generated. The toroidal symmetry of the electron tail implies runaway acceleration is not a dominant process, consistent with the net emf, ηJll, being smaller than the Dreicer field. Modeling of bremsstrahlung emission shows that a power-law electron tail distribution that is localized near the magnetic axis will yield strong perpendicular anisotropy, consistent with x-ray measurements in the radial and toroidal views. A strong correlation between high energy x-ray flux and tearing mode dynamics suggests a turbulent mechanism is active. This implies that the electron tail formation most likely results from a turbulent wave-particle interaction. This work is supported by the US DOE and NSF.

JPRS Report, Science & Technology, Japan

DTIC Science & Technology

1988-11-10

stage of microbial culture and fermentation through the stage of product isolation and purification. The information is expected to become an...controlled so that a process can be manipulated normally and safely. For example, in a bioreactor process mainly involving fermentation , the author and his...10) Electron microscope (11) Jar fermenter Continuous centrifuge Examples of equipment used in cell fusion research (1) Autotable Heated vibrating

Organic/Inorganic Polymeric Composites for Heat-Transfer Reduction

NASA Technical Reports Server (NTRS)

Smith, Trent; Williams, Martha

2008-01-01

Organic/inorganic polymeric composite materials have been invented with significant reduction in heat-transfer properties. Measured decreases of 20-50 percent in thermal conductivity versus that of the unmodified polymer matrix have been attained. These novel composite materials also maintain mechanical properties of the unmodified polymer matrix. The present embodiments are applicable, but not limited to: racing applications, aerospace applications, textile industry, electronic applications, military hardware improvements, and even food service industries. One specific application of the polymeric composition is for use in tanks, pipes, valves, structural supports, and components for hot or cold fluid process systems where heat flow through materials is problematic and not desired. With respect to thermal conductivity and physical properties, these materials are superior alternatives to prior composite materials. These materials may prove useful as substitutes for metals in some cryogenic applications. A material of this type can be made from a blend of thermoplastics, elastomers, and appropriate additives and processed on normal polymer processing equipment. The resulting processed organic/inorganic composite can be made into fibers, molded, or otherwise processed into useable articles.

[Arc spectrum diagnostic and heat coupling mechanism analysis of double wire pulsed MIG welding].

PubMed

Liu, Yong-qiang; Li, Huan; Yang, Li-jun; Zheng, Kai; Gao, Ying

2015-01-01

A double wire pulsed MIG welding test system was built in the present paper, in order to analyze the heat-coupling mechanism of double wire pulsed MIG welding, and study are temperature field. Spectroscopic technique was used in diagnostic analysis of the are, plasma radiation was collected by using hollow probe method to obtain the arc plasma optical signal The electron temperature of double wire pulsed MIG welding arc plasma was calculated by using Boltzmann diagram method, the electron temperature distribution was obtained, a comprehensive analysis of the arc was conducted combined with the high speed camera technology and acquisition means of electricity signal. The innovation of this paper is the combination of high-speed camera image information of are and optical signal of arc plasma to analyze the coupling mechanism for dual arc, and a more intuitive analysis for are temperature field was conducted. The test results showed that a push-pull output was achieved and droplet transfer mode was a drop in a pulse in the welding process; Two arcs attracted each other under the action of a magnetic field, and shifted to the center of the arc in welding process, so a new heat center was formed at the geometric center of the double arc, and flowing up phenomenon occurred on the arc; Dual arc electronic temperature showed an inverted V-shaped distribution overall, and at the geometric center of the double arc, the arc electron temperature at 3 mm off the workpiece surface was the highest, which was 16,887.66 K, about 4,900 K higher than the lowest temperature 11,963.63 K.

Tracking the ultrafast XUV optical properties of x-ray free-electron-laser heated matter with high-order harmonics

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

Williams, Gareth O.; Künzel, S.; Daboussi, S.

We present measurements of photon absorption by free electrons as a solid is transformed to plasma. A femtosecond x-ray free-electron laser is used to heat a solid, which separates the electron and ion heating time scales. The changes in absorption are measured with an independent probe pulse created through high-order-harmonic generation. We find an increase in electron temperature to have a relatively small impact on absorption, contrary to several predictions, whereas ion heating increases absorption. Here, we compare the data to current theoretical and numerical approaches and find that a smoother electronic structure yields a better fit to the data,more » suggestive of a temperature-dependent electronic structure in warm dense matter.« less

Tracking the ultrafast XUV optical properties of x-ray free-electron-laser heated matter with high-order harmonics

DOE PAGES

Williams, Gareth O.; Künzel, S.; Daboussi, S.; ...

2018-02-14

We present measurements of photon absorption by free electrons as a solid is transformed to plasma. A femtosecond x-ray free-electron laser is used to heat a solid, which separates the electron and ion heating time scales. The changes in absorption are measured with an independent probe pulse created through high-order-harmonic generation. We find an increase in electron temperature to have a relatively small impact on absorption, contrary to several predictions, whereas ion heating increases absorption. Here, we compare the data to current theoretical and numerical approaches and find that a smoother electronic structure yields a better fit to the data,more » suggestive of a temperature-dependent electronic structure in warm dense matter.« less

Martian Electron Temperatures in the Sub Solar Region.

NASA Astrophysics Data System (ADS)

Fowler, C. M.; Peterson, W. K.; Andersson, L.; Thiemann, E.; Mayyasi, M.; Yelle, R. V.; Benna, M.; Espley, J. R.

2017-12-01

Observations from Viking, and MAVEN have shown that the observed ionospheric electron temperatures are systematically higher than those predicted by many models. Because electron temperature is a balance between heating, cooling, and heat transport, we systematically compare the magnitude of electron heating from photoelectrons, electron cooling and heat transport, as a function of altitude within 30 degrees of the sub solar point. MAVEN observations of electron temperature and density, EUV irradiance, neutral and ion composition are used to evaluate terms in the heat equation following the framework of Matta et al. (Icarus, 2014, doi:10.1016/j.icarus.2013.09.006). Our analysis is restricted to inbound orbits where the magnetic field is within 30 degrees of horizontal. MAVEN sampled the sub solar region in May 2015 and again in May 2017, in near northern spring equinoctial conditions. Solar activity was higher and the spacecraft sampled altitudes down to 120 km in 2015, compared to 160 km in 2017. We find that between 160 and 200 km the Maven electron temperatures are in thermal equilibrium, in the sub solar region, on field lines inclined less than 30 degrees to the horizontal. Above 200km the data suggest that heating from other sources, such as wave heating are significant. Below 160 km some of the discrepancy comes from measurement limitations. This is because the MAVEN instrument cannot resolve the lowest electron temperatures, and because some cooling rates scale as the difference between the electron and neutral temperatures.

Coordinated Radio, Electron, and Waves Experiment (CREWE) for the NASA Comet Rendezvous and Asteroid Flyby (CRAF) instrument

NASA Technical Reports Server (NTRS)

Scudder, Jack D.

1992-01-01

The Coordinated Radio, Electron, and Waves Experiment (CREWE) was designed to determine density, bulk velocity and temperature of the electrons for the NASA Comet Rendezvous and Asteroid Flyby Spacecraft, to define the MHD-SW IMF flow configuration; to clarify the role of impact ionization processes, to comment on the importance of anomalous ionization phenomena (via wave particle processes), to quantify the importance of wave turbulence in the cometary interaction, to establish the importance of photoionization via the presence of characteristic lines in a structured energy spectrum, to infer the presence and grain size of significant ambient dust column density, to search for the theoretically suggested 'impenetrable' contact surface, and to quantify the flow of heat (in the likelihood that no surface exists) that will penetrate very deep into the atmosphere supplying a good deal of heat via impact and charge exchange ionization. This final report provides an instrument description, instrument test plans, list of deliverables/schedule, flight and support equipment and software schedule, CREWE accommodation issues, resource requirements, status of major contracts, an explanation of the non-NASA funded efforts, status of EIP and IM plan, descope options, and Brinton questions.

Electron backscatter diffraction applied to lithium sheets prepared by broad ion beam milling.

PubMed

Brodusch, Nicolas; Zaghib, Karim; Gauvin, Raynald

2015-01-01

Due to its very low hardness and atomic number, pure lithium cannot be prepared by conventional methods prior to scanning electron microscopy analysis. Here, we report on the characterization of pure lithium metallic sheets used as base electrodes in the lithium-ion battery technology using electron backscatter diffraction (EBSD) and X-ray microanalysis using energy dispersive spectroscopy (EDS) after the sheet surface was polished by broad argon ion milling (IM). No grinding and polishing were necessary to achieve the sufficiently damage free necessary for surface analysis. Based on EDS results the impurities could be characterized and EBSD revealed the microsctructure and microtexture of this material with accuracy. The beam damage and oxidation/hydration resulting from the intensive use of IM and the transfer of the sample into the microscope chamber was estimated to be <50 nm. Despite the fact that the IM process generates an increase of temperature at the specimen surface, it was assumed that the milling parameters were sufficient to minimize the heating effect on the surface temperature. However, a cryo-stage should be used if available during milling to guaranty a heating artefact free surface after the milling process. © 2014 Wiley Periodicals, Inc.

Science Objectives of the FOXSI Small Explorer Mission Concept

NASA Astrophysics Data System (ADS)

Shih, Albert Y.; Christe, Steven; Alaoui, Meriem; Allred, Joel C.; Antiochos, Spiro K.; Battaglia, Marina; Buitrago-Casas, Juan Camilo; Caspi, Amir; Dennis, Brian R.; Drake, James; Fleishman, Gregory D.; Gary, Dale E.; Glesener, Lindsay; Grefenstette, Brian; Hannah, Iain; Holman, Gordon D.; Hudson, Hugh S.; Inglis, Andrew R.; Ireland, Jack; Ishikawa, Shin-Nosuke; Jeffrey, Natasha; Klimchuk, James A.; Kontar, Eduard; Krucker, Sam; Longcope, Dana; Musset, Sophie; Nita, Gelu M.; Ramsey, Brian; Ryan, Daniel; Saint-Hilaire, Pascal; Schwartz, Richard A.; Vilmer, Nicole; White, Stephen M.; Wilson-Hodge, Colleen

2016-05-01

Impulsive particle acceleration and plasma heating at the Sun, from the largest solar eruptive events to the smallest flares, are related to fundamental processes throughout the Universe. While there have been significant advances in our understanding of impulsive energy release since the advent of RHESSI observations, there is a clear need for new X-ray observations that can capture the full range of emission in flares (e.g., faint coronal sources near bright chromospheric sources), follow the intricate evolution of energy release and changes in morphology, and search for the signatures of impulsive energy release in even the quiescent Sun. The FOXSI Small Explorer (SMEX) mission concept combines state-of-the-art grazing-incidence focusing optics with pixelated solid-state detectors to provide direct imaging of hard X-rays for the first time on a solar observatory. We present the science objectives of FOXSI and how its capabilities will address and resolve open questions regarding impulsive energy release at the Sun. These questions include: What are the time scales of the processes that accelerate electrons? How do flare-accelerated electrons escape into the heliosphere? What is the energy input of accelerated electrons into the chromosphere, and how is super-heated coronal plasma produced?

40 CFR Table I-2 to Subpart I - Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics Industry

Code of Federal Regulations, 2012 CFR

2012-07-01

... Fluorinated Heat Transfer Fluids Used by the Electronics Industry I Table I-2 to Subpart I Protection of... REPORTING Electronics Manufacturing Pt. 98, Subpt. I, Table I-2 Table I-2 to Subpart I—Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics Industry Product type...

Mixed convection of nanofluids in a lid-driven rough cavity

NASA Astrophysics Data System (ADS)

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

2017-06-01

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

Electron energetics in the inner coma of Comet Halley

NASA Astrophysics Data System (ADS)

Gan, L.; Cravens, T. E.

1990-05-01

A quasi-two-dimensional model of the spatial and energy distribution of electrons in the inner coma of Comet Halley has been constructed from a spherically symmetric ion density profile based on Giotto measurements, using the two-stream electron transport method and the time-dependent electron energy equation. A sharp jump in the electron temperature was found to be present at a cometocentric distance of about 15,000 km. This thermal boundary separates an inner region where cooling processes are dominant from an outer region where heat transport is more important. Both thermal and suprathermal electron populations exist inside the thermal boundary with comparable kinetic pressures. Outside the thermal boundary, a cloud electron population does not exist, and the electrons are almost isothermal along the magnetic field lines.

Microwave sintering of Ag-nanoparticle thin films on a polyimide substrate

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

Fujii, S., E-mail: fujii.s.ap@m.titech.ac.jp; Department of Information and Communication System Engineering, National Institute of Technology, Okinawa College, Nago, Okinawa 905-2192; Kawamura, S.

2015-12-15

Ag-nanoparticle thin films on a polyimide substrate were subjected to microwave sintering by use of a single-mode waveguide applicator. A two-step sintering process was employed. First, at low conductivities of the film, the film sample was placed at the site of the maximum electric field and subjected to microwave irradiation. Second, when the conductivity of the film increased, the film sample was placed at the site of the maximum magnetic field and again subjected to microwave irradiation. The microwave sintering process was completed within 1.5 min, which is significantly lower than the time required for the oven heating process. Themore » resulting conductivity of the film, albeit only 30% of that of the bulk material, was seven times that of a film annealed at the same temperature in a furnace. Scanning electron microscopy images revealed that the nanoparticles underwent both grain necking and grain growth during microwave sintering. In addition, this sintering process was equivalent to the oven heating process performed at a 50 °C higher annealing temperature. An electromagnetic wave simulation and a heat transfer simulation of the microwave sintering process were performed to gain a thorough understanding of the process.« less

Multistep Ionization of Argon Clusters in Intense Femtosecond Extreme Ultraviolet Pulses

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

Bostedt, C.; Thomas, H.; Hoener, M.

The interaction of intense extreme ultraviolet femtosecond laser pulses ({lambda}=32.8 nm) from the FLASH free electron laser (FEL) with clusters has been investigated by means of photoelectron spectroscopy and modeled by Monte Carlo simulations. For laser intensities up to 5x10{sup 13} W/cm{sup 2}, we find that the cluster ionization process is a sequence of direct electron emission events in a developing Coulomb field. A nanoplasma is formed only at the highest investigated power densities where ionization is frustrated due to the deep cluster potential. In contrast with earlier studies in the IR and vacuum ultraviolet spectral regime, we find nomore » evidence for electron emission from plasma heating processes.« less

Stimulated electronic transition concept for an erasable optical memory

NASA Technical Reports Server (NTRS)

Albin, Sacharia; Satira, James D.; Livingston, David L.; Shull, Thomas A.

1992-01-01

A new concept for an erasable optical memory is demonstrated using stimulated electronic transition (SET). Large bandgap semiconductors are suitable materials for the SET medium. The properties of MgS:Eu,Sm and SrS:Eu,Sm as possible media for the SET process are investigated. Quantum storage is achieved in the form of charges in deep levels in the medium and stimulated radiative recombination is used as the reading process. Unlike magneto-optic (M-O) and phase change (PC) processes, optical writing, reading and erasing are achieved without localized heating. The SET process will have an inherently faster data transfer rate and a higher storage density, and the medium will be more durable than the M-O and PC media. A possible application of the SET process in neural networks is also discussed.

Shock wave as a probe of flux-dimited thermal transport in laser-heated solids

NASA Astrophysics Data System (ADS)

Smith, K.; Forsman, A.; Chiu, G.

1996-11-01

Laser-generated shock waves in solids result from the ablation of the target material. Where radiation transport is negligible, the ablation process is dominated by electron thermal conduction. This offers an opportunity to probe the degree of transport inhibition (compared with classical heat flow) for steep temperature gradients in a dense plasma. Using a 1-dimensional hydrodynamic code, we have examined the effect of flux-limited thermal conduction on the amplitude of the resulting shock wave.

Preliminary Results on Thermal Shock Behavior of CuZnAl Shape Memory Alloy Using a Solar Concentrator as Heating Source

NASA Astrophysics Data System (ADS)

Tudora, C.; Abrudeanu, M.; Stanciu, S.; Anghel, D.; Plaiaşu, G. A.; Rizea, V.; Ştirbu, I.; Cimpoeşu, N.

2018-06-01

It is highly accepted that martensitic transformation can be induced by temperature variation and by stress solicitation. Using a solar concentrator, we manage to increase the material surface temperature (till 573 respectively 873 K) in very short periods of time in order to analyze the material behavior under thermal shocks. The heating/cooling process was registered and analyzed during the experiments. Material surface was analyzed before and after thermal shocks by microstructure point of view using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The experiments follow the material behavior during fast heating and propose the possibility of activating smart materials using the sun heat for aerospace applications.

A Two-Temperature Model of the Intracluster Medium

NASA Astrophysics Data System (ADS)

Takizawa, Motokazu

1998-12-01

We investigate evolution of the intracluster medium (ICM), considering the relaxation process between the ions and electrons. According to the standard scenario of structure formation, the ICM is heated by the shock in the accretion flow to the gravitational potential well of the dark halo. The shock primarily heats the ions because the kinetic energy of an ion entering the shock is larger than that of an electron by the ratio of masses. Then the electrons and ions exchange the energy through Coulomb collisions and reach equilibrium. From simple order estimation we find that the region where the electron temperature is considerably lower than the ion temperature spreads out on a megaparsec scale. We then calculate the ion and electron temperature profiles by combining the adiabatic model of a two-temperature plasma by Fox & Loeb with spherically symmetric N-body and hydrodynamic simulations based on three different cosmological models. It is found that the electron temperature is about half the mean temperature at radii ~1 Mpc. This could lead to about a 50% underestimation in the total mass contained within ~1 Mpc when the electron temperature profiles are used. The polytropic indices of the electron temperature profiles are ~=1.5, whereas those of mean temperature are ~=1.3 for r >= 1 Mpc. This result is consistent both with the X-ray observations on electron temperature profiles and with some theoretical and numerical predictions about mean temperature profiles.

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

Zhang, Jiali, E-mail: j.zhang@mpie.de; Morsdorf, Lutz, E-mail: l.morsdorf@mpie.de; Tasan, Cemal Cem, E-mail: c.tasan@mpie.de

In-situ scanning electron microscopy observations of the microstructure evolution during heat treatments are increasingly demanded due to the growing number of alloys with complex microstructures. Post-mortem characterization of the as-processed microstructures rarely provides sufficient insight on the exact route of the microstructure formation. On the other hand, in-situ SEM approaches are often limited due to the arising challenges upon using an in-situ heating setup, e.g. in (i) employing different detectors, (ii) preventing specimen surface degradation, or (iii) controlling and measuring the temperature precisely. Here, we explore and expand the capabilities of the “mid-way” solution by step-wise microstructure tracking, ex-situ, atmore » selected steps of heat treatment. This approach circumvents the limitations above, as it involves an atmosphere and temperature well-controlled dilatometer, and high resolution microstructure characterization (using electron channeling contrast imaging, electron backscatter diffraction, atom probe tomography, etc.). We demonstrate the capabilities of this approach by focusing on three cases: (i) nano-scale carbide precipitation during low-temperature tempering of martensitic steels, (ii) formation of transformation-induced geometrically necessary dislocations in a dual-phase steel during intercritical annealing, and (iii) the partial recrystallization of a metastable β-Ti alloy. - Highlights: • A multi-probe method to track microstructures during heat treatment is developed. • It enables the analysis of various complex phenomena, even those at atomistic scale. • It circumvents some of the free surface effects of classical in-situ experiments.« less

Research on low-temperature anodic bonding using induction heating

NASA Astrophysics Data System (ADS)

Chen, Mingxiang; Yi, Xinjian; Yuan, Liulin; Liu, Sheng

2006-04-01

This paper presents a new low temperature silicon-glass anodic bonding process using induction heating. Anodic bonding between silicon and glass (Pyrex 7740) has been achieved at temperature below 300 °C and almost bubble-free interfaces have been obtained. A 1KW 400KHz power supply is used to induce heat in graphite susceptors (simultaneously as the high-voltage electrodes of anodic bonding), which conduct heat to the bonding pair and permanently join the pair in 5 minutes. The results of pull tests indicate a bonding strength of above 5.0MPa for induction heating, which is greater than the strength for resistive heating at the same temperature. The fracture mainly occurs across the interface or inside the glass other than in the interface when the bonding temperature is over 200 °C Finally, the interfaces are examined and analyzed by scanning electron microscopy (SEM) and the bonding mechanisms are discussed.

Influence of storage and heating on protein glycation levels of processed lactose-free and regular bovine milk products.

PubMed

Milkovska-Stamenova, Sanja; Hoffmann, Ralf

2017-04-15

Thermal treatment preserves the microbiological safety of milk, but also induces Maillard reactions modifying for example proteins. The purpose of this study was evaluating the influence of consumer behaviors (storage and heating) on protein glycation degrees in bovine milk products. Lactosylation and hexosylation sites were identified in ultra-high temperature (UHT), lactose-free pasteurized, and lactose-free UHT milk (ULF) and infant formula (IF) using tandem mass spectrometry (electron transfer dissociation). Overall, 303 lactosylated and 199 hexosylated peptides were identified corresponding to 170 lactosylation (31 proteins) and 117 hexosylation sites (25 proteins). In quantitative terms, storage increased lactosylation up to fourfold in UHT and IF and hexosylation up to elevenfold in ULF and threefold in IF. These levels increased additionally twofold when the stored samples were heated (40°C). In conclusion, storage and heating appear to influence protein glycation levels in milk at similar or even higher degrees than industrial processing. Copyright © 2016 Elsevier Ltd. All rights reserved.

Heat engine by exorcism of Maxwell Demon using spin angular momentum reservoir

NASA Astrophysics Data System (ADS)

Bedkihal, Salil; Wright, Jackson; Vaccaro, Joan; Gould, Tim

Landauer's erasure principle is a hallmark in thermodynamics and information theory. According to this principle, erasing one bit of information incurs a minimum energy cost. Recently, Vaccaro and Barnett (VB) have explored the role of multiple conserved quantities in memory erasure. They further illustrated that for the energy degenerate spin reservoirs, the cost of erasure can be solely in terms of spin angular momentum and no energy. Motivated by the VB erasure, in this work we propose a novel optical heat engine that operates under a single thermal reservoir and a spin angular momentum reservoir. The novel heat engine exploits ultrafast processes of phonon absorption to convert thermal phonon energy to coherent light. The entropy generated in this process then corresponds to a mixture of spin up and spin down populations of energy degenerate electronic ground states which acts as demon's memory. This information is then erased using a polarised spin reservoir that acts as an entropy sink. The proposed heat engines goes beyond the traditional Carnot engine.

Computational study of hot electron generation and energy transport in intense laser produced hot dense matter

NASA Astrophysics Data System (ADS)

Mishra, Rohini

Present ultra high power lasers are capable of producing high energy density (HED) plasmas, in controlled way, with a density greater than solid density and at a high temperature of keV (1 keV ˜ 11,000,000° K). Matter in such extreme states is particularly interesting for (HED) physics such as laboratory studies of planetary and stellar astrophysics, laser fusion research, pulsed neutron source etc. To date however, the physics in HED plasma, especially, the energy transport, which is crucial to realize applications, has not been understood well. Intense laser produced plasmas are complex systems involving two widely distinct temperature distributions and are difficult to model by a single approach. Both kinetic and collisional process are equally important to understand an entire process of laser-solid interaction. By implementing atomic physics models, such as collision, ionization, and radiation damping, self consistently, in state-of-the-art particle-in-cell code (PICLS) has enabled to explore the physics involved in the HED plasmas. Laser absorption, hot electron transport, and isochoric heating physics in laser produced hot dense plasmas are studied with a help of PICLS simulations. In particular, a novel mode of electron acceleration, namely DC-ponderomotive acceleration, is identified in the super intense laser regime which plays an important role in the coupling of laser energy to a dense plasma. Geometric effects on hot electron transport and target heating processes are examined in the reduced mass target experiments. Further, pertinent to fast ignition, laser accelerated fast electron divergence and transport in the experiments using warm dense matter (low temperature plasma) is characterized and explained.

Analysis of performance degradation in an electron heating dominant H-mode plasma after ECRH termination in EAST

NASA Astrophysics Data System (ADS)

Du, Hongfei; Ding, Siye; Chen, Jiale; Wang, Yifeng; Lian, Hui; Xu, Guosheng; Zhai, Xuemei; Liu, Haiqing; Zang, Qing; Lyu, Bo; Duan, Yanmin; Qian, Jinping; Gong, Xianzu

2018-06-01

In recent EAST experiments, significant performance degradation accompanied by a decrease of internal inductance is observed in an electron heating dominant H-mode plasma after the electron cyclotron resonance heating termination. The lower hybrid wave (LHW) deposition and effective electron heat diffusivity are calculated to explain this phenomenon. Analysis shows that the changes of LHW heating deposition rather than the increase of transport are responsible for the significant decrease in energy confinement (). The reason why the confinement degradation occurred on a long time scale could be attributed to both good local energy confinement in the core and also the dependence of LHW deposition on the magnetic shear. The electron temperature profile shows weaker stiffness in near axis region where electron heating is dominant, compared to that in large radius region. Unstable electron modes from low to high k in the core plasma have been calculated in the linear GYRO simulations, which qualitatively agree with the experimental observation. This understanding of the plasma performance degradation mechanism will help to find ways of improving the global confinement in the radio-frequency dominant scenario in EAST.

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

NASA Astrophysics Data System (ADS)

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

2016-10-01

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

Chaotic Motion of Relativistic Electrons Driven by Whistler Waves

NASA Technical Reports Server (NTRS)

Khazanov, G. V.; Telnikhin, A. A.; Kronberg, Tatiana K.

2007-01-01

Canonical equations governing an electron motion in electromagnetic field of the whistler mode waves propagating along the direction of an ambient magnetic field are derived. The physical processes on which the equations of motion are based .are identified. It is shown that relativistic electrons interacting with these fields demonstrate chaotic motion, which is accompanied by the particle stochastic heating and significant pitch angle diffusion. Evolution of distribution functions is described by the Fokker-Planck-Kolmogorov equations. It is shown that the whistler mode waves could provide a viable mechanism for stochastic energization of electrons with energies up to 50 MeV in the Jovian magnetosphere.

40 CFR Table I-2 to Subpart I of... - Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics Industry

Code of Federal Regulations, 2013 CFR

2013-07-01

... Fluorinated Heat Transfer Fluids Used by the Electronics Industry I Table I-2 to Subpart I of Part 98... GREENHOUSE GAS REPORTING Electronics Manufacturing Pt. 98, Subpt. I, Table I-2 Table I-2 to Subpart I of Part 98—Examples of Fluorinated GHGs and Fluorinated Heat Transfer Fluids Used by the Electronics Industry...

Reversing the Landauer's erasure: Single-electron Maxwell's demon operating at the limit of thermodynamic efficiency

NASA Astrophysics Data System (ADS)

Averin, Dmitri V.; Pekola, Jukka P.

2017-03-01

According to Landauer's principle, erasure of information is the only part of a computation process that unavoidably involves energy dissipation. If done reversibly, such an erasure generates the minimal heat of $k_BT\\ln 2$ per erased bit of information. The goal of this work is to discuss the actual reversal of the optimal erasure which can serve as the basis for the Maxwell's demon operating with ultimate thermodynamic efficiency as dictated by the second law of thermodynamics. The demon extracts $k_BT\\ln 2$ of heat from an equilibrium reservoir at temperature $T$ per one bit of information obtained about the measured system used by the demon. We have analyzed this Maxwell's demon in the situation when it uses a general quantum system with a discrete spectrum of energy levels as its working body. In the case of the effectively two-level system, which has been realized experimentally based on tunneling of individual electron in a single-electron box [J.V. Koski et al., PNAS 111, 13786 (2014)], we also studied and minimized corrections to the ideal reversible operation of the demon. These corrections include, in particular, the non-adiabatic terms which are described by a version of the classical fluctuation-dissipation theorem. The overall reversibility of the Maxwell's demon requires, beside the reversibility of the intrinsic working body dynamics, the reversibility of the measurement and feedback processes. The single-electron demon can, in principle, be made fully reversible by developing a thermodynamically reversible single-electron charge detector for measurements of the individual charge states of the single-electron box.

Collisionless electron heating in inductively coupled discharges

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

Shaing, K.C.; Aydemir, A.Y.

1996-07-01

A kinetic theory of collisionless electron heating is developed for inductively coupled discharges with a finite height L. The novel effect associated with the finite-length system is the resonance between the bounce motion of the electrons and the wave frequency, leading to enhanced heating. The theory is in agreement with results of particle simulations.

Enhanced noise at high bias in atomic-scale Au break junctions

PubMed Central

Chen, Ruoyu; Wheeler, Patrick J.; Di Ventra, M.; Natelson, D.

2014-01-01

Heating in nanoscale systems driven out of equilibrium is of fundamental importance, has ramifications for technological applications, and is a challenge to characterize experimentally. Prior experiments using nanoscale junctions have largely focused on heating of ionic degrees of freedom, while heating of the electrons has been mostly neglected. We report measurements in atomic-scale Au break junctions, in which the bias-driven component of the current noise is used as a probe of the electronic distribution. At low biases (<150 mV) the noise is consistent with expectations of shot noise at a fixed electronic temperature. At higher biases, a nonlinear dependence of the noise power is observed. We consider candidate mechanisms for this increase, including flicker noise (due to ionic motion), heating of the bulk electrodes, nonequilibrium electron-phonon effects, and local heating of the electronic distribution impinging on the ballistic junction. We find that flicker noise and bulk heating are quantitatively unlikely to explain the observations. We discuss the implications of these observations for other nanoscale systems, and experimental tests to distinguish vibrational and electron interaction mechanisms for the enhanced noise. PMID:24573177

Remote Joule heating by a carbon nanotube.

PubMed

Baloch, Kamal H; Voskanian, Norvik; Bronsgeest, Merijntje; Cumings, John

2012-04-08

Minimizing Joule heating remains an important goal in the design of electronic devices. The prevailing model of Joule heating relies on a simple semiclassical picture in which electrons collide with the atoms of a conductor, generating heat locally and only in regions of non-zero current density, and this model has been supported by most experiments. Recently, however, it has been predicted that electric currents in graphene and carbon nanotubes can couple to the vibrational modes of a neighbouring material, heating it remotely. Here, we use in situ electron thermal microscopy to detect the remote Joule heating of a silicon nitride substrate by a single multiwalled carbon nanotube. At least 84% of the electrical power supplied to the nanotube is dissipated directly into the substrate, rather than in the nanotube itself. Although it has different physical origins, this phenomenon is reminiscent of induction heating or microwave dielectric heating. Such an ability to dissipate waste energy remotely could lead to improved thermal management in electronic devices.

Remote Joule heating by a carbon nanotube

NASA Astrophysics Data System (ADS)

Baloch, Kamal H.; Voskanian, Norvik; Bronsgeest, Merijntje; Cumings, John

2012-05-01

Minimizing Joule heating remains an important goal in the design of electronic devices. The prevailing model of Joule heating relies on a simple semiclassical picture in which electrons collide with the atoms of a conductor, generating heat locally and only in regions of non-zero current density, and this model has been supported by most experiments. Recently, however, it has been predicted that electric currents in graphene and carbon nanotubes can couple to the vibrational modes of a neighbouring material, heating it remotely. Here, we use in situ electron thermal microscopy to detect the remote Joule heating of a silicon nitride substrate by a single multiwalled carbon nanotube. At least 84% of the electrical power supplied to the nanotube is dissipated directly into the substrate, rather than in the nanotube itself. Although it has different physical origins, this phenomenon is reminiscent of induction heating or microwave dielectric heating. Such an ability to dissipate waste energy remotely could lead to improved thermal management in electronic devices.

N and Cr ion implantation of natural ruby surfaces and their characterization

NASA Astrophysics Data System (ADS)

Rao, K. Sudheendra; Sahoo, Rakesh K.; Dash, Tapan; Magudapathy, P.; Panigrahi, B. K.; Nayak, B. B.; Mishra, B. K.

2016-04-01

Energetic ions of N and Cr were used to implant the surfaces of natural rubies (low aesthetic quality). Surface colours of the specimens were found to change after ion implantation. The samples without and with ion implantation were characterized by diffuse reflectance spectra in ultra violet and visible region (DRS-UV-Vis), field emission scanning electron microscopy (FESEM), selected area electron diffraction (SAED) and nano-indentation. While the Cr-ion implantation produced deep red surface colour (pigeon eye red) in polished raw sample (without heat treatment), the N-ion implantation produced a mixed tone of dark blue, greenish blue and violet surface colour in the heat treated sample. In the case of heat treated sample at 3 × 1017 N-ions/cm2 fluence, formation of colour centres (F+, F2, F2+ and F22+) by ion implantation process is attributed to explain the development of the modified surface colours. Certain degree of surface amorphization was observed to be associated with the above N-ion implantation.

Improved Stress Corrosion Cracking Resistance and Strength of a Two-Step Aged Al-Zn-Mg-Cu Alloy Using Taguchi Method

NASA Astrophysics Data System (ADS)

Lin, Lianghua; Liu, Zhiyi; Ying, Puyou; Liu, Meng

2015-12-01

Multi-step heat treatment effectively enhances the stress corrosion cracking (SCC) resistance but usually degrades the mechanical properties of Al-Zn-Mg-Cu alloys. With the aim to enhance SCC resistance as well as strength of Al-Zn-Mg-Cu alloys, we have optimized the process parameters during two-step aging of Al-6.1Zn-2.8Mg-1.9Cu alloy by Taguchi's L9 orthogonal array. In this work, analysis of variance (ANOVA) was performed to find out the significant heat treatment parameters. The slow strain rate testing combined with scanning electron microscope and transmission electron microscope was employed to study the SCC behaviors of Al-Zn-Mg-Cu alloy. Results showed that the contour map produced by ANOVA offered a reliable reference for selection of optimum heat treatment parameters. By using this method, a desired combination of mechanical performances and SCC resistance was obtained.

Continuum-atomistic simulation of picosecond laser heating of copper with electron heat capacity from ab initio calculation

NASA Astrophysics Data System (ADS)

Ji, Pengfei; Zhang, Yuwen

2016-03-01

On the basis of ab initio quantum mechanics (QM) calculation, the obtained electron heat capacity is implemented into energy equation of electron subsystem in two temperature model (TTM). Upon laser irradiation on the copper film, energy transfer from the electron subsystem to the lattice subsystem is modeled by including the electron-phonon coupling factor in molecular dynamics (MD) and TTM coupled simulation. The results show temperature and thermal melting difference between the QM-MD-TTM integrated simulation and pure MD-TTM coupled simulation. The successful construction of the QM-MD-TTM integrated simulation provides a general way that is accessible to other metals in laser heating.

Influence of heat-pretreatments on the microstructural and mechanical properties of galfan-coated metal bonds

NASA Astrophysics Data System (ADS)

Hordych, Illia; Rodman, Dmytro; Nürnberger, Florian; Schmidt, Hans Christian; Orive, Alejandro Gonzalez; Homberg, Werner; Grundmeier, Guido; Maier, Hans Jürgen

2018-05-01

In the present study, heat-treatment assisted bonding of galfan-coated low-carbon steel sheets was investigated. Steel sheets were bonded by cold rolling subsequently to a heat treatment in the temperature range from 400 °C to 550°C. The reduction ratio during cold rolling was varied in the range from 50% to 80%. Such high reduction ratios were achieved by splitting the bonding process into three stages. By employing heat-treatments, the mechanical properties of the bonds were improved. The heat-pretreatment allowed the formation of brittle intermetallic phases that were easily fractured in the rolling gap during the bonding process. Thus, juvenile non-oxidized surfaces were formed, which facilitated the bonding between the steel layers, and thus increased the bond strength. The intermetallic phases were actively formed at temperatures of 450 °C and above; however increasing temperatures resulted in decreasing mechanical properties due to oxidation processes. The local microstructure was analyzed by scanning electron microscopy in order to characterize the contact zone on the micro level with a focus on the formation of intermetallic phases. The mechanical properties were determined in tensile shear tests. Interestingly, it was found that the galfan coating allowed for bonding at room temperature, and the aluminum fraction was primarily responsible for the enhanced oxide formation during the heat-pretreatment.

An Investigation into the Comparative Costs of Additive Manufacture vs. Machine from Solid for Aero Engine Parts

DTIC Science & Technology

2006-05-01

welding power sources are not totally efficient at converting power drawn from the wall into heat energy used for the welding process . TIG sources are...Powder bed + Laser • Wire + Laser • Wire + Electron Beam • Wire + TIG Each system has its own unique attributes in terms of process variables...relative economics of producing a near net shape by Additive Manufacturing (AM) processes compared with traditional machine from solid processes (MFS

Dynamics of streamer-to-leader transition at reduced air densities and its implications for propagation of lightning leaders and gigantic jets

NASA Astrophysics Data System (ADS)

da Silva, Caitano L.; Pasko, Victor P.

2013-12-01

In this paper we present modeling studies of air heating by electrical discharges in a wide range of pressures. The developed model is capable of quantifying the different contributions for heating of air at the particle level and rigorously accounts for the vibration-dissociation-vibration coupling. The model is validated by calculating the breakdown times of short air gaps and comparing to available experimental data. Detailed discussion on the role of electron detachment in the development of the thermal-ionizational instability that triggers the spark development in short air gaps is presented. The dynamics of fast heating by quenching of excited electronic states is discussed and the scaling of its main channels with ambient air density is quantified. The developed model is employed to study the streamer-to-leader transition process and to obtain its scaling with ambient air density. Streamer-to-leader transition is the name given to a sequence of events occurring in a thin plasma channel through which a relatively strong current is forced through, culminating in heating of ambient gas and increase of the electrical conductivity of the channel. This process occurs during the inception of leaders (from sharp metallic structures, from hydrometeors inside the thundercloud, or in virgin air) and during their propagation (at the leader head or during the growth of a space leader). The development of a thermal-ionizational instability that culminates in the leader formation and propagation is characterized by a change in air ionization mechanism from electron impact to associative ionization and by contraction of the plasma channel. The introduced methodology for estimation of leader speeds shows that the propagation of a leader is limited by the air heating of every newly formed leader section. It is demonstrated that the streamer-to-leader transition time has an inverse-squared dependence on the ambient air density at near-ground pressures, in agreement with similarity laws for Joule heating in a streamer channel. Model results indicate that a deviation from this similarity scaling occurs at very low air densities, where the rate of electronic power deposition is balanced by the channel expansion, and air heating from quenching of excited electronic states is very inefficient. These findings place a limit on the maximum altitude at which a hot and highly conducting lightning leader channel can be formed in the Earth's atmosphere, result which is important for understating of the gigantic jet (GJ) discharges between thundercloud tops and the lower ionosphere. Simulations of leader speeds at GJ altitudes demonstrate that initial speeds of GJs are consistent with the leader propagation mechanism. The simulation of a GJ, escaping upward from a thundercloud top, shows that the lengthening of the leader streamer zone, in a medium of exponentially decreasing air density, determines the existence of an altitude at which the streamer zones of GJs become so long that they dynamically extend (jump) all the way to the ionosphere.

Thermionic Properties of Carbon Based Nanomaterials Produced by Microhollow Cathode PECVD

NASA Technical Reports Server (NTRS)

Haase, John R.; Wolinksy, Jason J.; Bailey, Paul S.; George, Jeffrey A.; Go, David B.

2015-01-01

Thermionic emission is the process in which materials at sufficiently high temperature spontaneously emit electrons. This process occurs when electrons in a material gain sufficient thermal energy from heating to overcome the material's potential barrier, referred to as the work function. For most bulk materials very high temperatures (greater than 1500 K) are needed to produce appreciable emission. Carbon-based nanomaterials have shown significant promise as emission materials because of their low work functions, nanoscale geometry, and negative electron affinity. One method of producing these materials is through the process known as microhollow cathode PECVD. In a microhollow cathode plasma, high energy electrons oscillate at very high energies through the Pendel effect. These high energy electrons create numerous radical species and the technique has been shown to be an effective method of growing carbon based nanomaterials. In this work, we explore the thermionic emission properties of carbon based nanomaterials produced by microhollow cathode PECVD under a variety of synthesis conditions. Initial studies demonstrate measureable current at low temperatures (approximately 800 K) and work functions (approximately 3.3 eV) for these materials.

Electronic Nose Characterization of the Quality Parameters of Freeze-Dried Bacteria

NASA Astrophysics Data System (ADS)

Capuano, R.; Santonico, M.; Martinelli, E.; Paolesse, R.; Passot, S.; Fonseca, F.; Cenard, S.; Trelea, C.; Di Natale, C.

2011-09-01

Freeze-drying is the method of choice for preserving heat sensitive biological products such as microorganisms. The development of a fast analytical method for evaluating the properties of the dehydrated bacteria is then necessary for a proper utilization of the product in several food processes. In this paper, dried bacteria headspace is analyzed by a GC-MS and an electronic nose. Results indicate that headspace contains enough information to assess the products quality.

The nucleation and growth mechanism of Ni-Sn eutectic in a single crystal superalloy

NASA Astrophysics Data System (ADS)

Jiang, Weiguo; Wang, Li; Li, Xiangwei; Lou, Langhong

2017-12-01

The microstructure of single crystal superalloy with and without tin layer on the surface of as-cast and heat-treatment state was investigated by optical microscope (OM) and scanning electron microscopy (SEM). The composition of different regions on the surface was tested by energy dispersive X-ray (EDS). The reaction intermetallic compound (IMC) formed in the heat treatment process was confirmed by X-ray diffraction (XRD). The orientations of different microstructure in samples as heat treatment state were determined by electron back-scattering diffraction (EBSD) method. The porosity location in the interdendritic region was observed by X-ray computed tomography (XCT). The experiment results showed that the remained Sn on the surface of the superalloy reacted with Ni, and then formed Ni3Sn4 in the as-cast state. Sn enriched by diffusion along the porosity located in the interdendritic region and γ + γ‧ (contain a little of Sn) eutectic and Ni3Sn2 formed in single crystal superalloy during heat treatment, and the recalescence behaviors were found. Ni3Sn2 nucleated independently in the cooled liquid at the front of (γ + γ‧) (Sn) eutectic. The nucleation and growth mechanism of the eutectic and Ni3Sn2 IMC during heat treatment was discussed in the present paper.

Thermoelectric-enhanced, liquid-based cooling of a multi-component electronic system

DOEpatents

Chainer, Timothy J; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Schmidt, Roger R; Steinke, Mark E

2015-11-10

Methods are provided for facilitating cooling of an electronic component. The methods include providing: a liquid-cooled structure, a thermal conduction path coupling the electronic component and the liquid-cooled structure, a coolant loop in fluid communication with a coolant-carrying channel of the liquid-cooled structure, and an outdoor-air-cooled heat exchange unit coupled to facilitate heat transfer from the liquid-cooled structure via, at least in part, the coolant loop. The thermoelectric array facilitates transfer of heat from the electronic component to the liquid-cooled structure, and the heat exchange unit cools coolant passing through the coolant loop by dissipating heat from the coolant to outdoor ambient air. In one implementation, temperature of coolant entering the liquid-cooled structure is greater than temperature of the outdoor ambient air to which heat is dissipated.

Thermoelectric-enhanced, liquid-based cooling of a multi-component electronic system

DOEpatents

Chainer, Timothy J; Graybill, David P; Iyengar, Madhusudan K; Kamath, Vinod; Kochuparambil, Bejoy J; Schmidt, Roger R; Steinke, Mark E

2015-05-12

Apparatus and method are provided for facilitating cooling of an electronic component. The apparatus includes a liquid-cooled structure, a thermal conduction path coupling the electronic component and the liquid-cooled structure, a coolant loop in fluid communication with a coolant-carrying channel of the liquid-cooled structure, and an outdoor-air-cooled heat exchange unit coupled to facilitate heat transfer from the liquid-cooled structure via, at least in part, the coolant loop. The thermoelectric array facilitates transfer of heat from the electronic component to the liquid-cooled structure, and the heat exchange unit cools coolant passing through the coolant loop by dissipating heat from the coolant to outdoor ambient air. In one implementation, temperature of coolant entering the liquid-cooled structure is greater than temperature of the outdoor ambient air to which heat is dissipated.

Occurrence of ion upflow associated with ion/electron heating in the polar cap and cusp regions

NASA Astrophysics Data System (ADS)

Ji, E. Y.; Jee, G.; Kwak, Y. S.

2017-12-01

We investigate the occurrence frequency of ion upflow in association with ion/electron heating in the polar cap and cusp regions, using the data obtained from the European Incoherent Scatter Svalbard radar (ESR) during the period of 2000 to 2010. We classify the upflow events by four cases: driven by ion heating (case 1), electron heating (case 2), both ion and electron heatings (case 3), and without any heating (case 4). The statistical analysis of the data shows that the upflow normaly starts at around 350 km altitude and the occurrence seems to peak at 11 MLT. Among the four cases, the occurrence frequency of the upflow is maximized for the case 3 and then followed by case 2, case 1 and case 3, which indicates that both ion and electron heatings are associated with ion upflow. At around 500 km altitude, however, the occurrence frequency is maximized when there is no heating (case 4). We also investigate the dependence of the occurrence frequency of the upflow on Kp and F10.7 indices. The maximum occurrence frequency seems to occur at moderate geomagnetic condition (2 ≤ Kp < 5). As for the solar activity, the occurrence frequency is higher for low solar activity than for high solar activity. The results of this study suggest that the ion upflow occurring in the polar cap/cusp region is mostly driven by both ion and electron heatings.

The Multi-species Farley-Buneman Instability in the Solar Chromosphere

NASA Astrophysics Data System (ADS)

Madsen, Chad A.; Dimant, Yakov S.; Oppenheim, Meers M.; Fontenla, Juan M.

2014-03-01

Empirical models of the solar chromosphere show intense electron heating immediately above its temperature minimum. Mechanisms such as resistive dissipation and shock waves appear insufficient to account for the persistence and uniformity of this heating as inferred from both UV lines and continuum measurements. This paper further develops the theory of the Farley-Buneman instability (FBI) which could contribute substantially to this heating. It expands upon the single-ion theory presented by Fontenla by developing a multiple-ion-species approach that better models the diverse, metal-dominated ion plasma of the solar chromosphere. This analysis generates a linear dispersion relationship that predicts the critical electron drift velocity needed to trigger the instability. Using careful estimates of collision frequencies and a one-dimensional, semi-empirical model of the chromosphere, this new theory predicts that the instability may be triggered by velocities as low as 4 km s-1, well below the neutral acoustic speed. In the Earth's ionosphere, the FBI occurs frequently in situations where the instability trigger speed significantly exceeds the neutral acoustic speed. From this, we expect neutral flows rising from the photosphere to have enough energy to easily create electric fields and electron Hall drifts with sufficient amplitude to make the FBI common in the chromosphere. If so, this process will provide a mechanism to convert neutral flow and turbulence energy into electron thermal energy in the quiet Sun.

Radiolytic Impacts of Energetic Electron Irradiation on Enceladus and Mimas

NASA Technical Reports Server (NTRS)

Cooper, J. F.; Sittler, E. C.; Sturner, S. J.

2011-01-01

Episodic overturn of the south polar terrain on Enceladus would convey radio lytic oxidants from surface irradiation by Saturn's inner magnetospheric electrons to the putative underlying polar sea and contribute to CO2 and other gas production driving the visibly active cryovolcanism. Low duty cycle of active episodes below 1 - 10 percent would raise the relative importance of the continuous radiolytic chemical energy input for mass and heat outflow, e.g. as compared to heating by gravitational tides. The "Pac-Man" thermal anomaly on Mimas most likely arises from leading-trailing asymmetry of electron irradiation and resultant radio lytic processing of the moon ice to a few centimeters of depth. The Mimas thermal anomaly distribution suggests a relatively stable surface unmodified by Enceladus-like geologic overturn or cryovolcanic activity. In both cases, the heavily irradiated skin depth corresponds to the sensible thermal layer probed by Cassini infrared measurements. Neutral gas and dust emissions from Enceladus limit energetic ion and plasma electron fluxes in the inner magnetosphere, thereby governing the irradiation of Mimas and other Saturn moons.

Quantum Noise of Electron-Phonon Heat Current

NASA Astrophysics Data System (ADS)

Pekola, Jukka P.; Karimi, Bayan

2018-06-01

We analyze heat current fluctuations between electrons and phonons in a metal. In equilibrium we recover the standard result consistent with the fluctuation-dissipation theorem. Here we show that heat current noise at finite frequencies remains non-vanishing down to zero temperature. From the experimental point of view, it is a small effect and up to now elusive. We briefly discuss the impact of electron-phonon heat current fluctuations on calorimetry, particularly in the regime of single microwave-photon detection.

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

Liu, Chang; Fox, William; Bhattacharjee, Amitava

Recent theory has demonstrated a novel physics regime for magnetic reconnection in high-energy-density plasmas where the magnetic field is advected by heat flux via the Nernst effect. In this paper, we elucidate the physics of the electron dissipation layer in this regime. Through fully kinetic simulation and a generalized Ohm's law derived from first principles, we show that momentum transport due to a nonlocal effect, the heat-flux-viscosity, provides the dissipation mechanism for magnetic reconnection. Scaling analysis, and simulations show that the reconnection process comprises a magnetic field compression stage and quasisteady reconnection stage, and the characteristic width of the currentmore » sheet in this regime is several electron mean-free paths. Finally, these results show the important interplay between nonlocal transport effects and generation of anisotropic components to the distribution function.« less

A mechanism for deep chromospheric heating during solar flares

NASA Technical Reports Server (NTRS)

Machado, M. E.; Emslie, A. G.; Mauas, P. J.

1986-01-01

The role of the negative hydrogen ion, H(-), in the energy balance of the deep solar chromosphere is reexamined and it is found, in contrast with earlier authors, that H(-) is a source of heating at these levels. The response of this region to an ionizing flux of flare-associated UV radiation (1500 to 1900 A) is then addressed: it is found that the excess ionization of Si to Si(+) increases the local electron number density considerably, since most species are largely neutral at deep chromospheric levels. This in turn increases the electron-hydrogen atom association rate, the H(-) abundance, and the rate of absorption of photospheric radiation by this ion. It is found that the excess absorption by this process may lead to a substantial temperature enhancement at temperature minimum levels during flares.

Low-Noise Wide Bandwith, Hot Electron Bolometer Mixers for Submillimeter Wavelengths

NASA Technical Reports Server (NTRS)

McGrath, W. R.

1995-01-01

Recently a novel superconductive hot-electron micro-bolometer has been proposed which is both fast and sensitive (D. E. Prober, Appl. Phys. Lett. 62, 2119, 1993). This device has several important properties which make it useful as a heterodyne sensor for radioastronomy applications at frequencies above 1 THz. The thermal response time of the device is fast enough, several 10's of picoseconds, to allow for IF's of several GHz. This bolometer mixer should operate well up to at least 10 THz. There is no energy gap limitation as in an SIS mixer, since the mixing process relies on heating of the electron gas. In fact, rf power is absorbed more uniformly above the gap frequency. The mixer noise should be near quantum-limited, and the local oscillator (LO) power requirement is very low: / 10 nW for a Nb device. One of the unique features of this device is that it employs rapid electron diffusion into a normal metal, rather than phonon emission, as the thermal conductance that cools the heated electrons. In order for diffusion to dominate over phonon emission, the device must be short, less than 0.5.

Implications of electron heating and non-uniformities in a VHF-CCP for sterilization of medical instruments

NASA Astrophysics Data System (ADS)

Stapelmann, Katharina; Fiebrandt, Marcel; Styrnoll, Tim; Baldus, Sabrina; Bibinov, Nikita; Awakowicz, Peter

2015-06-01

A capacitively coupled plasma driven at a frequency of 81.36 MHz from the VHF-band is investigated by means of optical emission spectroscopy (OES) and multipole resonance probe (MRP). The discharge is operated with hydrogen, yielding an electropositive discharge, as well as oxygen, yielding an electronegative discharge, and mixtures of both. Pressure is varied from p=5 Pa to p=25 Pa. Homogeneity of the discharge is investigated by CCD camera recordings as well as spatially resolved multipole resonance probe measurements. The results indicate the presence of electromagnetic edge effects as well as standing wave effects. Furthermore, a largely homogeneous discharge can be achieved with hydrogen as process gas at a pressure of p=5 -10 Pa. With increasing pressure as well as with increasing oxygen content, the discharge appears less homogeneously. The transition from an electropositive to an electronegative discharge leads to a change in electron heating mechanisms, with pronounced local maxima of electron density at the sheath edges. A comparison of OES and MRP results reveal a significant difference in electron density, which can be explained by a non-Maxwellian distribution function of electrons.

Scaling of Electron Heating During Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Ohia, O.; Le, A.; Daughton, W. S.; Egedal, J.

2016-12-01

While magnetic reconnection plays a major role in accelerating and heating magnetospheric plasma, it remains poorly understood how the level of particle energization depends on the plasma conditions. Meanwhile, a recent survey of THEMIS magnetopause reconnection observations [Phan et al. GRL 2013] and a numerical study [Shay et al. PoP 2014] found empirically that the electron heating scales with the square of the upstream Alfven speed. Equivalently for weak guide fields, the fractional electron temperature increase is inversely proportional to the upstream electron beta (ratio of electron to magnetic pressure). We present models for symmetric reconnection with moderate [Ohia et al., GRL 2015] or zero guide field that predict the electron bulk heating. In the models, adiabatically trapped electrons gain energy from parallel electric fields in the inflowing region. For purely anti-parallel reconnection, meandering electrons receive additional energy from the reconnection electric field. The predicted scalings are in quantitative agreement with fluid and kinetic simulations, as well as spacecraft observations. Using kinetic simulations, we extend this work to explore how the layer dynamics and electron bulk heating vary as functions of the magnetic shear and plasma and magnetic pressure asymmetry across the reconnection layer. These results are pertinent to recent Magnetospheric Multiscale (MMS) Mission measurements of electron dynamics during dayside magnetopause reconnection.

Studying the issues in the additive manufacturing of dental implants by Electron Beam MeltingRTM (EBM)

NASA Astrophysics Data System (ADS)

Jamshidinia, Mahdi

The ability of additive manufacturing (AM) processes to produce complex geometries is resulting in their rapid acceptance by a number of industries. This unique capability could be used for the optimization of the design of functional components that could find an application in different industries such as aerospace, automotive, energy, medical, and implants. However, there are still some challenges confronting this technology such as surface finish, residual stress, dimensional tolerance, processing speed, and anisotropy in microstructure and mechanical properties. Any of the mentioned issues could be influenced by the thermal history of a 3D printed component during the layer-by-layer manufacturing. Therefore, an understanding of the thermal cycling during the AM process is essential. In recent years, significant advances have been achieved in the design, manufacturing, and materials used for dental implants. However, there are still some differences between the natural tooth and a dental implant that might decrease patient satisfaction. One of the differences between the natural tooth and a dental implant is in its modulus of elasticity, which could result in an issue known as bone atrophy. The second important difference between a dental implant and a natural tooth is the fact that a natural tooth is surrounded by a periodontal ligament that allows the tooth to move in three directions. However, the periodontal ligament is destroyed during the extraction of a natural tooth. In the absence of the periodontal ligament, the biting force is directly transferred to the jawbone, resulting in discomfort for the patient. Also, the implant cannot be incorporated with the surrounding natural tooth and form a bridge. In this study, the application of a lattice structure for the manufacturing of a biocompatible dental implant is investigated. Three different lattice structures with different unit cell sizes were experimentally and numerically analyzed. The mechanical properties of lattice abutments in response to a static compression load were analyzed. However, the mechanical behavior of a structure could be considerably different under cyclic loads where fatigue failure could occur at stresses far below the static failure stress. Therefore, experimental and numerical analyses were performed in order to investigate the fatigue properties of the lattice dental abutment. Beside the design of a structure, some numerical models were developed to investigate the effects of Electron Beam MeltingRTM (EBM) process parameters on the heat distribution and the mentioned issues such as surface roughness and residual stress. A moving electron beam heat source and the temperature dependent properties of Ti-6Al- 4V were used in order to provide a 3D thermal-fluid flow model of EBMRTM, where the influence of process parameters as well as fluid convection on heat distribution were studied. Also, a coupled Computational Fluid Dynamic (CFD) - Finite Element Method (FEM) model was developed for studying the heat and thermal stress distribution in EBMRTM. The coupled CFD-FEM model combines the ability of CFD in considering the effects of fluid convection with the ability of FEM in calculating the thermal stress. The influences of the spacing distance between the Ti-6Al-4V plates produced by EBMRTM on the heat accumulation and the resultant surface roughness were investigated numerically and experimentally. An equation was derived from experimental data to predict the values of surface roughness as a function of the spacing distance. Finally, the influence of a novel design of heat sinks on the minimization of anisotropy was investigated, where the heat sinks were built in-situ during the EBMRTM process. Three sets of coupons with different numbers of heat sinks were designed and produced by EBMRTM. Another set of coupons was produced without a heat sink for comparison purposes. The results of the study could be used as the supportive experimental information required for the optimization of the support generation software in the powder-bed AM processes, such as the MagicsRTM used in EBMRTM .

Electron Heating and Acceleration in a Reconnecting Magnetotail

NASA Astrophysics Data System (ADS)

El-Alaoui, M.; Zhou, M.; Lapenta, G.; Berchem, J.; Richard, R. L.; Schriver, D.; Walker, R. J.

2017-12-01

Electron heating and acceleration in the magnetotail have been investigated intensively. A major site for this process is the reconnection region. However, where and how the electrons are accelerated in a realistic three-dimensional X-line geometry is not fully understood. In this study, we employed a three-dimensional implicit particle-in-cell (iPIC3D) simulation and large-scale kinetic (LSK) simulation to address these problems. We modeled a magnetotail reconnection event observed by THEMIS in an iPIC3D simulation with initial and boundary conditions given by a global magnetohydrodynamic (MHD) simulation of Earth's magnetosphere. The iPIC3D simulation system includes the region of fast outflow emanating from the reconnection site that drives dipolarization fronts. We found that current sheet electrons exhibit elongated (cigar-shaped) velocity distributions with a higher parallel temperature. Using LSK we then followed millions of test electrons using the electromagnetic fields from iPIC3D. We found that magnetotail reconnection can generate power law spectra around the near-Earth X-line. A significant number of electrons with energies higher than 50 keV are produced. We identified several acceleration mechanisms at different locations that were responsible for energizing these electrons: non-adiabatic cross-tail drift, betatron and Fermi acceleration. Relative contributions to the energy gain of these high energy electrons from the different mechanisms will be discussed.

Molecular dynamics study of solid-liquid heat transfer and passive liquid flow

NASA Astrophysics Data System (ADS)

Yesudasan Daisy, Sumith

High heat flux removal is a challenging problem in boilers, electronics cooling, concentrated photovoltaic and other power conversion devices. Heat transfer by phase change is one of the most efficient mechanisms for removing heat from a solid surface. Futuristic electronic devices are expected to generate more than 1000 W/cm2 of heat. Despite the advancements in microscale and nanoscale manufacturing, the maximum passive heat flux removal has been 300 W/cm2 in pool boiling. Such limitations can be overcome by developing nanoscale thin-film evaporation based devices, which however require a better understanding of surface interactions and liquid vapor phase change process. Evaporation based passive flow is an inspiration from the transpiration process that happens in trees. If we can mimic this process and develop heat removal devices, then we can develop efficient cooling devices. The existing passive flow based cooling devices still needs improvement to meet the future demands. To improve the efficiency and capacity of these devices, we need to explore and quantify the passive flow happening at nanoscales. Experimental techniques have not advanced enough to study these fundamental phenomena at the nanoscale, an alternative method is to perform theoretical study at nanoscales. Molecular dynamics (MD) simulation is a widely accepted powerful tool for studying a range of fundamental and engineering problems. MD simulations can be utilized to study the passive flow mechanism and heat transfer due to it. To study passive flow using MD, apart from the conventional methods available in MD, we need to have methods to simulate the heat transfer between solid and liquid, local pressure, surface tension, density, temperature calculation methods, realistic boundary conditions, etc. Heat transfer between solid and fluids has been a challenging area in MD simulations, and has only been minimally explored (especially for a practical fluid like water). Conventionally, an equilibrium canonical ensemble (NVT) is simulated using thermostat algorithms. For research in heat transfer involving solid liquid interaction, we need to perform non equilibrium MD (NEMD) simulations. In such NEMD simulations, the methods used for simulating heating from a surface is very important and must capture proper physics and thermodynamic properties. Development of MD simulation techniques to simulate solid-liquid heating and the study of fundamental mechanism of passive flow is the main focus of this thesis. An accurate surface-heating algorithm was developed for water which can now allow the study of a whole new set of fundamental heat transfer problems at the nanoscale like surface heating/cooling of droplets, thin-films, etc. The developed algorithm is implemented in the in-house developed C++ MD code. A direct two dimensional local pressure estimation algorithm is also formulated and implemented in the code. With this algorithm, local pressure of argon and platinum interaction is studied. Also, the surface tension of platinum-argon (solid-liquid) was estimated directly from the MD simulations for the first time. Contact angle estimation studies of water on platinum, and argon on platinum were also performed. A thin film of argon is kept above platinum plate and heated in the middle region, leading to the evaporation and pressure reduction thus creating a strong passive flow in the near surface region. This observed passive liquid flow is characterized by estimating the pressure, density, velocity and surface tension using Eulerian mapping method. Using these simulation, we have demonstrated the fundamental nature and origin of surface-driven passive flow. Heat flux removed from the surface is also estimated from the results, which shows a significant improvement can be achieved in thermal management of electronic devices by taking advantage of surface-driven strong passive liquid flow. Further, the local pressure of water on silicon di-oxide surface is estimated using the LAMMPS atomic to continuum (ATC) package towards the goal of simulating the passive flow in water.

Anomalous electronic heat capacity of copper nanowires at sub-Kelvin temperatures

NASA Astrophysics Data System (ADS)

Viisanen, K. L.; Pekola, J. P.

2018-03-01

We have measured the electronic heat capacity of thin film nanowires of copper and silver at temperatures 0.1-0.3 K; the films were deposited by standard electron-beam evaporation. The specific heat of the Ag films of sub-100-nm thickness agrees with the bulk value and the free-electron estimate, whereas that of similar Cu films exceeds the corresponding reference values by one order of magnitude. The origin of the anomalously high heat capacity of copper films remains unknown for the moment. Based on the small heat capacity at low temperatures and the possibility to devise a tunnel probe thermometer on it, metal films form a promising absorber material, e.g., for microwave photon calorimetry.

Selective Laser Melting Produced Ti-6Al-4V: Post-Process Heat Treatments to Achieve Superior Tensile Properties

PubMed Central

Becker, Thorsten H.

2018-01-01

Current post-process heat treatments applied to selective laser melting produced Ti-6Al-4V do not achieve the same microstructure and therefore superior tensile behaviour of thermomechanical processed wrought Ti-6Al-4V. Due to the growing demand for selective laser melting produced parts in industry, research and development towards improved mechanical properties is ongoing. This study is aimed at developing post-process annealing strategies to improve tensile behaviour of selective laser melting produced Ti-6Al-4V parts. Optical and electron microscopy was used to study α grain morphology as a function of annealing temperature, hold time and cooling rate. Quasi-static uniaxial tensile tests were used to measure tensile behaviour of different annealed parts. It was found that elongated α’/α grains can be fragmented into equiaxial grains through applying a high temperature annealing strategy. It is shown that bi-modal microstructures achieve a superior tensile ductility to current heat treated selective laser melting produced Ti-6Al-4V samples. PMID:29342079

Design analysis of levitation facility for space processing applications. [Skylab program, space shuttles

NASA Technical Reports Server (NTRS)

Frost, R. T.; Kornrumpf, W. P.; Napaluch, L. J.; Harden, J. D., Jr.; Walden, J. P.; Stockhoff, E. H.; Wouch, G.; Walker, L. H.

1974-01-01

Containerless processing facilities for the space laboratory and space shuttle are defined. Materials process examples representative of the most severe requirements for the facility in terms of electrical power, radio frequency equipment, and the use of an auxiliary electron beam heater were used to discuss matters having the greatest effect upon the space shuttle pallet payload interfaces and envelopes. Improved weight, volume, and efficiency estimates for the RF generating equipment were derived. Results are particularly significant because of the reduced requirements for heat rejection from electrical equipment, one of the principal envelope problems for shuttle pallet payloads. It is shown that although experiments on containerless melting of high temperature refractory materials make it desirable to consider the highest peak powers which can be made available on the pallet, total energy requirements are kept relatively low by the very fast processing times typical of containerless experiments and allows consideration of heat rejection capabilities lower than peak power demand if energy storage in system heat capacitances is considered. Batteries are considered to avoid a requirement for fuel cells capable of furnishing this brief peak power demand.

Experimental, theoretical, and device application development of nanoscale focused electron-beam-induced deposition

NASA Astrophysics Data System (ADS)

Randolph, Steven Jeffrey

Electron-beam-induced deposition (EBID) is a highly versatile nanofabrication technique that allows for growth of a variety of materials with nanoscale precision and resolution. While several applications and studies of EBID have been reported and published, there is still a significant lack of understanding of the complex mechanisms involved in the process. Consequently, EBID process control is, in general, limited and certain common experimental results regarding nanofiber growth have yet to be fully explained. Such anomalous results have been addressed in this work both experimentally and by computer simulation. Specifically, a correlation between SiOx nanofiber deposition observations and the phenomenon of electron beam heating (EBH) was shown by comparison of thermal computer models and experimental results. Depending on the beam energy, beam current, and nanostructure geometry, the heat generated can be substantial and may influence the deposition rate. Temperature dependent EBID growth experiments qualitatively verified the results of the EBH model. Additionally, EBID was used to produce surface image layers for maskless, direct-write lithography (MDL). A single layer process used directly written SiOx features as a masking layer for amorphous silicon thin films. A bilayer process implemented a secondary masking layer consisting of standard photoresist into which a pattern---directly written by EBID tungsten---was transferred. The single layer process was found to be extremely sensitive to the etch selectivity of the plasma etch. In the bilayer process, EBID tungsten was written onto photoresist and the pattern transferred by means of oxygen plasma dry development following a brief refractory descum. Conditions were developed to reduce the spatial spread of electrons in the photoresist layer and obtain ˜ 35 nm lines. Finally, an EBID-based technique for field emitter repair was applied to the Digital Electrostatically focused e-beam Array Lithography (DEAL) parallel electron beam lithography configuration to repair damaged or missing carbon nanofiber cathodes. The I-V response and lithography results from EBID tungsten-based devices were comparable to CNF-based DEAL devices indicating a successful repair technique.

Surface cleaning for negative electron affinity GaN photocathode

NASA Astrophysics Data System (ADS)

Qiao, Jianliang; Yin, Yingpeng; Gao, Youtang; Niu, Jun; Qian, Yunsheng; Chang, Benkang

2012-10-01

In the preparation process for negative electron affinity (NEA) GaN photocathode, the surface cleanness is very important to activation, it influences the sensitivity and stability of NEA GaN photocathode. The traditional corrosion methods based on oxidizing and dissolving can't remove oxygen (O) and carbon (C) on GaN surface effectively. How to get an ideal atom clean surface is still an important question at present. The cleaning techniques for GaN photocathode was studied by using NEA photocathode activation system and XPS surface analysis system. The experiment sample is p-type GaN doped with Mg, doped concentration is 1.37×1017 cm-3, the transfer rate is 3.08 cm2/V-S, and the thickness of activation layer is 0.51 μm, the substrate is 300 μm thick sapphire. The sample was dealed with chemical cleaning depuration at first. And to get the atom clean surface, the vacuum heat cleaning process was needed. The methods of chemical cleaning and the vacuum heating cleaning were given in detail. According to the X-ray photoelectron spectroscopy of GaN surface after chemical cleaning and the vacuum degree curve of the activation chamber during the heat cleaning, the cleaning effect and the cleaning mechanism were discussed. After the effective chemical cleaning and the heating of 700 Centigrade degree about 20 minutes in ultrahigh vacuum system, the oxides and carbon contaminants on cathode surface can be removed effectively, and the ideal atom clean surface can be obtained. The purpose of heating depuration process is that not only to get the atom clean GaN surface, but also to guarantee the contents of Ga, N on GaN surface stabilize and to keep the system ultra-high vacuum degree. Because of the volatilization of oxide and carbon impurity on the cathode surface, the vacuum degree curve drops with the rising of temperature on the whole.

Ultrafast demagnetization by hot electrons: Diffusion or super-diffusion?

PubMed

Salvatella, G; Gort, R; Bühlmann, K; Däster, S; Vaterlaus, A; Acremann, Y

2016-09-01

Ultrafast demagnetization of ferromagnetic metals can be achieved by a heat pulse propagating in the electron gas of a non-magnetic metal layer, which absorbs a pump laser pulse. Demagnetization by electronic heating is investigated on samples with different thicknesses of the absorber layer on nickel. This allows us to separate the contribution of thermalized hot electrons compared to non-thermal electrons. An analytical model describes the demagnetization amplitude as a function of the absorber thickness. The observed change of demagnetization time can be reproduced by diffusive heat transport through the absorber layer.

High power heating of magnetic reconnection in merging tokamak experiments

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

Ono, Y.; Tanabe, H.; Gi, K.

2015-05-15

Significant ion/electron heating of magnetic reconnection up to 1.2 keV was documented in two spherical tokamak plasma merging experiment on MAST with the significantly large Reynolds number R∼10{sup 5}. Measured 1D/2D contours of ion and electron temperatures reveal clearly energy-conversion mechanisms of magnetic reconnection: huge outflow heating of ions in the downstream and localized heating of electrons at the X-point. Ions are accelerated up to the order of poloidal Alfven speed in the reconnection outflow region and are thermalized by fast shock-like density pileups formed in the downstreams, in agreement with recent solar satellite observations and PIC simulation results. The magneticmore » reconnection efficiently converts the reconnecting (poloidal) magnetic energy mostly into ion thermal energy through the outflow, causing the reconnection heating energy proportional to square of the reconnecting (poloidal) magnetic field B{sub rec}{sup 2}  ∼  B{sub p}{sup 2}. The guide toroidal field B{sub t} does not affect the bulk heating of ions and electrons, probably because the reconnection/outflow speeds are determined mostly by the external driven inflow by the help of another fast reconnection mechanism: intermittent sheet ejection. The localized electron heating at the X-point increases sharply with the guide toroidal field B{sub t}, probably because the toroidal field increases electron confinement and acceleration length along the X-line. 2D measurements of magnetic field and temperatures in the TS-3 tokamak merging experiment also reveal the detailed reconnection heating mechanisms mentioned above. The high-power heating of tokamak merging is useful not only for laboratory study of reconnection but also for economical startup and heating of tokamak plasmas. The MAST/TS-3 tokamak merging with B{sub p} > 0.4 T will enables us to heat the plasma to the alpha heating regime: T{sub i} > 5 keV without using any additional heating facility.« less

Enhancement of Natural Convection by Carbon Nanotube Films Covered Microchannel-Surface for Passive Electronic Cooling Devices.

PubMed

Zhang, Guang; Jiang, Shaohui; Yao, Wei; Liu, Changhong

2016-11-16

Owing to the outstanding properties of thermal conduction, lightweight, and chemical durability, carbon nanotubes (CNTs) have revealed promising applications in thermal management materials. Meanwhile, the increasingly popular portable electronics and the rapid development of space technology need lighter weight, smaller size, and more effective thermal management devices. Here, a novel kind of heat dissipation devices based on the superaligned CNT films and underlying microchannels is proposed, and the heat dissipation properties are measured at the natural condition. Distinctive from previous studies, by combining the advantages of microchannels and CNTs, such a novel heat dissipation device enables superior natural convection heat transfer properties. Our findings prove that the novel CNT-based devices could show an 86.6% larger total natural heat dissipation properties than bare copper plate. Further calculations of the radiation and natural convection heat transfer properties demonstrate that the excellent passive cooling properties of these CNT-based devices are primarily caused by the reinforcement of the natural convection heat transfer properties. Furthermore, the heat dissipation mechanisms are briefly discussed, and we propose that the very high heat transfer coefficients and the porous structures of superaligned CNT films play critical roles in reinforcing the natural convection. The novel CNT-based heat dissipation devices also have advantages of energy-saving, free-noise, and without additional accessories. So we believe that the CNT-based heat dissipation devices would replace the traditional metal-finned heat dissipation devices and have promising applications in electronic devices, such as photovoltaic devices, portable electronic devices, and electronic displays.

Synergistic cross-scale coupling of turbulence in a tokamak plasma

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

Howard, N. T., E-mail: nthoward@psfc.mit.edu; Holland, C.; White, A. E.

2014-11-15

For the first time, nonlinear gyrokinetic simulations spanning both the ion and electron spatio-temporal scales have been performed with realistic electron mass ratio ((m{sub D}∕m{sub e}){sup 1∕2 }= 60.0), realistic geometry, and all experimental inputs, demonstrating the coexistence and synergy of ion (k{sub θ}ρ{sub s}∼O(1.0)) and electron-scale (k{sub θ}ρ{sub e}∼O(1.0)) turbulence in the core of a tokamak plasma. All multi-scale simulations utilized the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] to study the coupling of ion and electron-scale turbulence in the core (r/a = 0.6) of an Alcator C-Mod L-mode discharge shown previously to exhibit an under-predictionmore » of the electron heat flux when using simulations only including ion-scale turbulence. Electron-scale turbulence is found to play a dominant role in setting the electron heat flux level and radially elongated (k{sub r} ≪ k{sub θ}) “streamers” are found to coexist with ion-scale eddies in experimental plasma conditions. Inclusion of electron-scale turbulence in these simulations is found to increase both ion and electron heat flux levels by enhancing the transport at the ion-scale while also driving electron heat flux at sub-ρ{sub i} scales. The combined increases in the low and high-k driven electron heat flux may explain previously observed discrepancies between simulated and experimental electron heat fluxes and indicates a complex interaction of short and long wavelength turbulence.« less

Transient Nonlinear Optical Properties of Thin Film Titanium Nitride

DTIC Science & Technology

2017-03-23

representative of a semiconductor, and their total effect. The effect of carrier heating is shown in light purple. The effect of number of electrons in the...small amount of the excited electrons are heated to a very high temperature. [7] One model for how these hot electrons dissipate energy is called the...two temperature model”. The two temperatures are the temperature of the electron and the temperature of the lattice (or phonon). When heated by an

Electron heating in a Monte Carlo model of a high Mach number, supercritical, collisionless shock

NASA Technical Reports Server (NTRS)

Ellison, Donald C.; Jones, Frank C.

1987-01-01

Preliminary work in the investigation of electron injection and acceleration at parallel shocks is presented. A simple model of electron heating that is derived from a unified shock model which includes the effects of an electrostatic potential jump is described. The unified shock model provides a kinetic description of the injection and acceleration of ions and a fluid description of electron heating at high Mach number, supercritical, and parallel shocks.

Electron-bombarded 〈110〉-oriented tungsten tips for stable tunneling electron emission

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

Yamada, T. K.; Abe, T.; Nazriq, N. M. K.

A clean tungsten (W) tip apex with a robust atomic plane is required for producing a stable tunneling electron emission under strong electric fields. Because a tip apex fabricated from a wire by aqueous chemical etching is covered by impurity layers, heating treatment in ultra-high vacuum is experimentally known to be necessary. However, strong heating frequently melts the tip apex and causes unstable electron emissions. We investigated quantitatively the tip apex and found a useful method to prepare a tip with stable tunneling electron emissions by controlling electron-bombardment heating power. Careful characterizations of the tip structures were performed with combinationsmore » of using field emission I–V curves, scanning electron microscopy, X-ray diffraction (transmitted Debye-Scherrer and Laue) with micro-parabola capillary, field ion microscopy, and field emission microscopy. Tips were chemically etched from (1) polycrystalline W wires (grain size ∼1000 nm) and (2) long-time heated W wires (grain size larger than 1 mm). Heating by 10-40 W (10 s) was found to be good enough to remove oxide layers and produced stable electron emission; however, around 60 W (10 s) heating was threshold power to increase the tip radius, typically +10 ± 5 nm (onset of melting). Further, the grain size of ∼1000 nm was necessary to obtain a conical shape tip apex.« less

Accelerator Generation and Thermal Separation (AGATS) of Technetium-99m

ScienceCinema

Grover, Blaine

2018-05-01

Accelerator Generation and Thermal Separation (AGATS) of Technetium-99m is a linear electron accelerator-based technology for producing medical imaging radioisotopes from a separation process that heats, vaporizes and condenses the desired radioisotope. You can learn more about INL's education programs at http://www.facebook.com/idahonationallaboratory.

NASA Tech Briefs, August 2007

NASA Technical Reports Server (NTRS)

2007-01-01

Topics include: Program Merges SAR Data on Terrain and Vegetation Heights; Using G(exp 4)FETs as a Data Router for In-Plane Crossing of Signal Paths; Two Algorithms for Processing Electronic Nose Data; Radiation-Tolerant Dual Data Bus; General-Purpose Front End for Real-Time Data Processing; Nanocomposite Photoelectrochemical Cells; Ultracapacitor-Powered Cordless Drill, Cumulative Timers for Microprocessors; Photocatalytic/Magnetic Composite Particles; Separation and Sealing of a Sample Container Using Brazing; Automated Aerial Refueling Hitches a Ride on AFF; Cobra Probes Containing Replaceable Thermocouples; High-Speed Noninvasive Eye-Tracking System; Detergent-Specific Membrane Protein Crystallization Screens; Evaporation-Cooled Protective Suits for Firefighters; Plasmonic Antenna Coupling for QWIPs; Electronic Tongue Containing Redox and Conductivity Sensors; Improved Heat-Stress Algorithm; A Method of Partly Automated Testing of Software; Rover Wheel-Actuated Tool Interface; and Second-Generation Electronic Nose.

Brazing copper to dispersion-strengthened copper

NASA Astrophysics Data System (ADS)

Ryding, David G.; Allen, Douglas; Lee, Richard H.

1996-11-01

The advanced photon source is a state-of-the-art synchrotron light source that will produce intense x-ray beams, which will allow the study of smaller samples and faster reactions and processes at a greater level of detail than has ben possible to date. The beam is produced by using third- generation insertion devices in a 7-GeV electron/positron storage ring that is 1,104 meters in circumference. The heat load from these intense high-power devices is very high, and certain components must sustain total heat loads of 3 to 15 kW and heat fluxes of 30 W/mm$_2). Because the beams will cycle on and off many times, thermal shock and fatigue will be a problem. High heat flux impinging on a small area causes a large thermal gradient that results in high stress. GlidCop, a dispersion-strengthened copper, is the desired design material because of its high thermal conductivity and superior mechanical properties as compared to copper and its alloys. GlidCop is not amenable to joining by fusion welding, and brazing requires diligence because of high diffusivity. Brazing procedures were developed using optical and scanning electron microscopy.

Effect of Plasma Surface Finish on Wettability and Mechanical Properties of SAC305 Solder Joints

NASA Astrophysics Data System (ADS)

Kim, Kyoung-Ho; Koike, Junichi; Yoon, Jeong-Won; Yoo, Sehoon

2016-12-01

The wetting behavior, interfacial reactions, and mechanical reliability of Sn-Ag-Cu solder on a plasma-coated printed circuit board (PCB) substrate were evaluated under multiple heat-treatments. Conventional organic solderability preservative (OSP) finished PCBs were used as a reference. The plasma process created a dense and highly cross-linked polymer coating on the Cu substrates. The plasma finished samples had higher wetting forces and shorter zero-cross times than those with OSP surface finish. The OSP sample was degraded after sequential multiple heat treatments and reflow processes, whereas the solderability of the plasma finished sample was retained after multiple heat treatments. After the soldering process, similar microstructures were observed at the interfaces of the two solder joints, where the development of intermetallic compounds was observed. From ball shear tests, it was found that the shear force for the plasma substrate was consistently higher than that for the OSP substrate. Deterioration of the OSP surface finish was observed after multiple heat treatments. Overall, the plasma surface finish was superior to the conventional OSP finish with respect to wettability and joint reliability, indicating that it is a suitable material for the fabrication of complex electronic devices.

A BRDF study on the visual appearance properties of titanium in the heating process

NASA Astrophysics Data System (ADS)

Liu, Yanlei; Yu, Kun; Li, Longfei; Zhao, Yuejin; Liu, Zilong; Liu, Yufang

2018-04-01

Bidirectional reflectance distribution function (BRDF) offers complete description of the spectral and spatial characteristics of opaque materials, i.e. the visual appearance properties of materials. In this letter, the visual appearance properties of titanium in the heating process are investigated by BRDF. The reliability of our results is verified by comparing the experimental data of polytetrafluoroethylene with the reference data. The in-plane spectral BRDF in visible region of heated commercial pure Ti at different incident and reflected zenith angles are measured. The experimental result indicates that the change tendency of BRDF vs. wavelength is not influenced by incident and reflected zenith angle, which implying that the colours of Ti may be pigment colouration rather than the structural colouration. Scanning electron microscopy (SEM) and the X-ray diffraction (XRD) testing are performed, and no titanium oxides are detected. The testing results imply that the colours may be generated by intermediate products during heated process. The powder samples are prepared, and the same colours as that of flake samples indirectly prove the validity of our conclusion. In addition, the spectral BRDF of optically smooth samples are measured, the results verify the reliability of our conclusion.

Effect of heat bed temperature of 3D bioprinter to hardness and compressive strength of scaffold bovine hydroxyapatite

NASA Astrophysics Data System (ADS)

Triyono, Joko; Pratama, Aditya; Sukanto, Heru; Nugroho, Yohanes; Wijayanta, Agung Tri

2018-02-01

This study aimed to investigate the effect of heat bed temperature of 3D bioprinter toward compressive strength and hardness bovine bone hydroxyapatite scaffold for bone filler applications. BHA-glycerin mixed with a ratio of 1:1, and keep it for 24 hours. After the homogenization process acquired, bio-Ink with shaped slurry will be used as a material for a 3D printer. The printing process with a temperature variation have performed by setting up heat bed temperature. After printing process was completed, the 3D scaffold was detained on the heat bed for 10 minutes before being picked up. The test results in this study had the lowest hardness value of 9.82±0.62 VHN and the highest number of 24.32±0.99 VHN. The compressive strength testing had the lowest value of 1.62±0.16 MPa with the highest number of 5.67±0.39 MPa. Pore observation using a scanning electron microscope. The result shows that the size of the pores were not much different, that was ±100-200 µm. This observation also indicated that the pore form was square pores.

The effect of electron cyclotron heating on density fluctuations at ion and electron scales in ITER baseline scenario discharges on the DIII-D tokamak

NASA Astrophysics Data System (ADS)

Marinoni, A.; Pinsker, R. I.; Porkolab, M.; Rost, J. C.; Davis, E. M.; Burrell, K. H.; Candy, J.; Staebler, G. M.; Grierson, B. A.; McKee, G. R.; Rhodes, T. L.; The DIII-D Team

2017-12-01

Experiments simulating the ITER baseline scenario on the DIII-D tokamak show that torque-free pure electron heating, when coupled to plasmas subject to a net co-current beam torque, affects density fluctuations at electron scales on a sub-confinement time scale, whereas fluctuations at ion scales change only after profiles have evolved to a new stationary state. Modifications to the density fluctuations measured by the phase contrast imaging diagnostic (PCI) are assessed by analyzing the time evolution following the switch-off of electron cyclotron heating (ECH), thus going from mixed beam/ECH to pure neutral beam heating at fixed βN . Within 20 ms after turning off ECH, the intensity of fluctuations is observed to increase at frequencies higher than 200 kHz in contrast, fluctuations at lower frequency are seen to decrease in intensity on a longer time scale, after other equilibrium quantities have evolved. Non-linear gyro-kinetic modeling at ion and electron scales scales suggest that, while the low frequency response of the diagnostic is consistent with the dominant ITG modes being weakened by the slow-time increase in flow shear, the high frequency response is due to prompt changes to the electron temperature profile that enhance electron modes and generate a larger heat flux and an inward particle pinch. These results suggest that electron heated regimes in ITER will feature multi-scale fluctuations that might affect fusion performance via modifications to profiles.

The space shuttle payload planning working groups: Volume 9: Materials processing and space manufacturing

NASA Technical Reports Server (NTRS)

1973-01-01

The findings and recommendations of the Materials Processing and Space Manufacturing group of the space shuttle payload planning activity are presented. The effects of weightlessness on the levitation processes, mixture stability, and control over heat and mass transport in fluids are considered for investigation. The research and development projects include: (1) metallurgical processes, (2) electronic materials, (3) biological applications, and (4)nonmetallic materials and processes. Additional recommendations are provided concerning the allocation of payload space, acceptance of experiments for flight, flight qualification, and private use of the space shuttle.

Heat-load simulator for heat sink design

NASA Technical Reports Server (NTRS)

Dunleavy, A. M.; Vaughn, T. J.

1968-01-01

Heat-load simulator is fabricated from 1/4-inch aluminum plate with a contact surface equal in dimensions and configuration to those of the electronic installation. The method controls thermal output to simulate actual electronic component thermal output.

Role of intensive milling in the processing of barium ferrite/magnetite/iron hybrid magnetic nano-composites via partial reduction of barium ferrite

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

Molaei, M.J., E-mail: mj.molaee@merc.ac.ir; Delft Chem Tech, Faculty of Applied Sciences, Delft University of Technology, Julianalaan 136, 2628 BL Delft; Ataie, A.

2015-03-15

In this research a mixture of barium ferrite and graphite was milled for different periods of time and then heat treated at different temperatures. The effects of milling time and heat treatment temperature on the phase composition, thermal behavior, morphology and magnetic properties of the samples have been investigated using X-ray diffraction, differential thermal analysis, high resolution transmission electron microscopy and vibrating sample magnetometer techniques, respectively. X-ray diffraction results revealed that BaFe{sub 12}O{sub 19}/Fe{sub 3}O{sub 4} nanocomposites form after a 20 h milling due to the partial reduction of BaFe{sub 12}O{sub 19}. High resolution transmission electron microscope images of amore » 40 h milled sample showed agglomerated structure consisting of nanoparticles with a mean particle size of 30 nm. Thermal analysis of the samples via differential thermal analysis indicated that for un-milled samples, heat treatment up to 900 °C did not result in α-Fe formation, while for a 20 h milled sample heat treatment at 700 °C resulted in reduction process progress to the formation of α-Fe. Wustite was disappeared in an X-ray diffraction pattern of a heat treated sample at 850 °C, by increasing the milling time from 20 to 40 h. By increasing the milling time, the structure of heat treated samples becomes magnetically softer due to an increase in saturation magnetization and a decrease in coercivity. Saturation magnetization and coercivity of a sample milled for 20 h and heat treated at 850 °C were 126.3 emu/g and 149.5 Oe which by increasing the milling time to 40 h, alter to 169.1 emu/g and 24.3 Oe, respectively. High coercivity values of milled and heat treated samples were attributed to the nano-scale formed iron particles. - Graphical abstract: Display Omitted - Highlights: • Barium ferrite and graphite were treated mechano-thermally. • Increasing milling time increases reduction progress after heat treatment. • Composites including iron nano-crystals forms by milling and heat treatment. • Shorter milling time results in higher H{sub C} of the milled and heat treated samples.« less

Electron Heating at Kinetic Scales in Magnetosheath Turbulence

NASA Technical Reports Server (NTRS)

Chasapis, Alexandros; Matthaeus, W. H.; Parashar, T. N.; Lecontel, O.; Retino, A.; Breuillard, H.; Khotyaintsev, Y.; Vaivads, A.; Lavraud, B.; Eriksson, E.;

Understanding the bursty electron cyclotron emission during a sawtooth crash in the HT-7 tokamak

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

Li, Erzhong, E-mail: rzhonglee@ipp.ac.cn; Hu, Liqun; Chen, Kaiyun

2014-01-15

Bursts in electron cyclotron emission (ECE) were observed during sawtooth crashes in HT-7 in discharges with ion cyclotron resonance heating injected near the q = 1 rational surface (q is the safety factor). The local ECE measurement indicated that the bursty radiation is only observed on channels near but a little away outward from the q = 1 magnetic surface. In conjunction with the soft x-ray tomography analysis, it was determined that, for the first time, only a compression process survives in the later stage of fast magnetic reconnection but before prompt heat transport. The compression enhanced the electron radiation temperature, the increased amplitudemore » of which agreed well with the estimation according to a kinetic compression theory model [R. J. Hastie and T. C. Hender, Nucl. Fusion 28, 585 (1988)]. This paper presents the experimental evidence that there indeed exists a transient compression phase which results in the bursty ECE radiation during a sawtooth crash.« less

Strong Turbulence in Alkali Halide Negative Ion Plasmas

NASA Astrophysics Data System (ADS)

Sheehan, Daniel

1999-11-01

Negative ion plasmas (NIPs) are charge-neutral plasmas in which the negative charge is dominated by negative ions rather than electrons. They are found in laser discharges, combustion products, semiconductor manufacturing processes, stellar atmospheres, pulsar magnetospheres, and the Earth's ionosphere, both naturally and man-made. They often display signatures of strong turbulence^1. Development of a novel, compact, unmagnetized alkali halide (MX) NIP source will be discussed, it incorporating a ohmically-heated incandescent (2500K) tantulum solenoid (3cm dia, 15 cm long) with heat shields. The solenoid ionizes the MX vapor and confines contaminant electrons, allowing a very dry (electron-free) source. Plasma densities of 10^10 cm-3 and positive to negative ion mass ratios of 1 <= fracm_+m- <= 20 are achievable. The source will allow tests of strong turbulence theory^2. 1 Sheehan, D.P., et al., Phys. Fluids B5, 1593 (1993). 2 Tsytovich, V. and Wharton, C.W., Comm. Plasma Phys. Cont. Fusion 4, 91 (1978).

Energetics and dynamics of resonant and nonresonant scattering in strong magnetic fields

NASA Technical Reports Server (NTRS)

Lamb, Don Q.; Wang, John C. L.; Wasserman, Ira M.

1990-01-01

The energetics and the dynamics resulting from electron-photon resonant and nonresonant scattering in a plasma with magnetic field about 10 to the 12th G are studied in detail. Precise analytic results are obtained in the optically thin limit, and numerical results are presented for the optically thick case. For the latter, it is found that when the equilibrium temperature T(C) is determined by the cooling/heating balance due solely to cyclotron resonant scattering, the ratio of T(C) to the superstrong field B remains fairly constant for N(e) up to about 6 x 10 to the 21st electrons/sq cm. This line-dominated region comes to an end when the extra heating from the hard continuum photons becomes competitive with the line processes and drives T(C) well above the pure line value. For parameters characteristic of GB 880205, the thickness of the line-dominated region is determined to be between 10 to the 21st and 10 to the 22nd electrons/sq cm.

Real-time monitoring of laser hot-wire cladding of Inconel 625

NASA Astrophysics Data System (ADS)

Liu, Shuang; Liu, Wei; Harooni, Masoud; Ma, Junjie; Kovacevic, Radovan

2014-10-01

Laser hot-wire cladding (LHWC), characterized by resistance heating of the wire, largely increases the productivity and saves the laser energy. However, the main issue of applying this method is the occurrence of arcing which causes spatters and affects the stability of the process. In this study, an optical spectrometer was used for real-time monitoring of the LHWC process. The corresponding plasma intensity was analyzed under various operating conditions. The electron temperature of the plasma was calculated for elements of nickel and chromium that mainly comprised the plasma plume. There was a correlation between the electron temperature and the stability of the process. The characteristics of the resulted clad were also investigated by measuring the dilution, hardness and microstructure.

Particle Morphology From Wood-Burning Cook Stoves Emissions

NASA Astrophysics Data System (ADS)

Peralta, O.; Carabali, G.; Castro, T.; Torres, R.; Ruiz, L. G.; Molina, L. T.; Saavedra, I.

2013-12-01

Emissions from three wood-burning cook stoves were sampled to collect particles. Transmission electron microscope (TEM) copper grids were placed on the last two stages of an 8-stage MOUDI cascade impactor (d50= 0.32, and 0.18 μm). Samples were obtained on two heating stages of cooking, the first is a quick heating process to boil 1 liter of water, and the second is to keep the water at 90 C. Absorption coefficient, scattering coefficients, and particles concentration (0.01 - 2.5 μm aerodynamic diameter) were measured simultaneously using an absorption photometer (operated at 550 nm), a portable integrating nephelometer (at 530 nm), and a condensation particle counter connected to a chamber to dilute the wood stoves emissions. Transmission electron micrographic images of soot particles were acquired at different magnifications using a High Resolution Transmission Electron Microscope (HRTEM) JEOL HRTEM 4000EX operating at 200 kV, equipped with a GATAN digital micrograph system for image acquisition. The morphology of soot particles was analyzed calculating the border-based fractal dimension (Df). Particles sampled on the first heating stage exhibit complex shapes with high values of Df, which are present as aggregates formed by carbon ceno-spheres. The presence of high numbers of carbon ceno-spheres can be attributed to pyrolysis, thermal degradation, and others processes prior to combustion. Energy dispersive X-ray spectroscopy (EDS) was used to determine the elemental composition of particles. EDS analysis in particles with d50= 0.18 μm showed a higher content of carbonaceous material and relevant amounts of Si, S and K.

Numerical investigation of thermal performance of a water-cooled mini-channel heat sink for different chip arrangement

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

Tikadar, Amitav, E-mail: amitav453@gmail.com; Hossain, Md. Mahamudul; Morshed, A. K. M. M.

Heat transfer from electronic chip is always challenging and very crucial for electronic industry. Electronic chips are assembled in various manners according to the design conditions and limitationsand thus the influence of chip assembly on the overall thermal performance needs to be understand for the efficient design of electronic cooling system. Due to shrinkage of the dimension of channel and continuous increment of thermal load, conventional heat extraction techniques sometimes become inadequate. Due to high surface area to volume ratio, mini-channel have the natural advantage to enhance convective heat transfer and thus to play a vital role in the advancedmore » heat transfer devices with limited surface area and high heat flux. In this paper, a water cooled mini-channel heat sink was considered for electronic chip cooling and five different chip arrangements were designed and studied, namely: the diagonal arrangement, parallel arrangement, stacked arrangement, longitudinal arrangement and sandwiched arrangement. Temperature distribution on the chip surfaces was presented and the thermal performance of the heat sink in terms of overall thermal resistance was also compared. It is found that the sandwiched arrangement of chip provides better thermal performance compared to conventional in line chip arrangement.« less

Solar heating for an electronics manufacturing plant--Blue Earth, Minnesota

NASA Technical Reports Server (NTRS)

1981-01-01

Partial space heating for 97,000 square foot plant is supplied by 360 flat plate solar collectors; energy is sorted as heat in indoor 20,000 gallon water tank. System includes all necessary control electronics for year round operation. During December 1978, solar energy supplied 24.4 percent of building's space heating load.

The effect of cyclic heat treatment on the physicochemical properties of bio hydroxyapatite from bovine bone.

PubMed

Londoño-Restrepo, S M; Jeronimo-Cruz, R; Rubio-Rosas, E; Rodriguez-García, M E

2018-05-02

This paper focus on physicochemical changes in bio-hydroxyapatite (BIO-HAp) from bovine femur obtained by calcination at high temperatures: 520-620 (each 20 °C) at 7.4 °C/min and from 700 to 1100 °C (each 100 °C) at three heating rates: 7.4, 9.9, and 11.1 °C/min. BIO-HAp samples were obtained using a multi-step process: cleaning, milling, hydrothermal process, calcination in an air atmosphere, and cooling in furnace air. Inductively Couple Plasma (ICP) showed that the presence of Mg, K, S, Ba, Zn, and Na, is not affected by the annealing temperature and heating rate. While Scanning Electron Microscopy (SEM) images showed the continuous growth of the HAp crystals during the calcination process due to the coalescence phenomenon, and the Full Width at the Half Maximum for the X-ray patterns for temperatures up to 700 is affected by the annealing temperature and the heating rate. Through X-ray diffraction, thermal, and calorimetric analysis (TGA-DSC), a partial dehydroxylation of hydroxyapatite was found in samples calcined up to 900 °C for the three heating rates. Also, Ca/P molar ratio decreased for samples calcined up to 900 °C as a result of the dehydroxylation process. NaCaPO 4 , CaCO 3 , Ca 3 (PO 4 ) 2 , MgO, and Ca(H 2 PO 4 ) 2 are some phases identified by X-ray diffraction; some of them are part of the bone and others were formed during the calcination process as a function of annealing temperature and heating rate, as it is the case for MgO.

Studies on A-TIG welding of Low Activation Ferritic/Martensitic (LAFM) steel

NASA Astrophysics Data System (ADS)

Vasantharaja, P.; Vasudevan, M.

2012-02-01

Low Activation Ferritic-Martensitic steels (LAFM) are chosen as the candidate material for structural components in fusion reactors. The structural components are generally fabricated by welding processes. Activated Tungsten Inert Gas (A-TIG) welding is an emerging process for welding of thicker components. In the present work, attempt was made to develop A-TIG welding technology for LAFM steel plates of 10 mm thick. Activated flux was developed for LAFM steel by carrying out various bead-on-plate TIG welds without flux and with flux. The optimum flux was identified as one which gave maximum depth of penetration at minimum heat input values. With the optimized flux composition, LAFM steel plate of 10 mm thickness was welded in square butt weld joint configuration using double side welding technique. Optical and Scanning Electron Microscopy was used for characterizing the microstructures. Microhardness measurements were made across the weld cross section for as welded and post weld heat treated samples. Tensile and impact toughness properties were determined. The mechanical properties values obtained in A-TIG weld joint were comparable to that obtained in weld joints of LAFM steel made by Electron beam welding process.

On the existence of and mechanism for microwave-specific reaction rate enhancement† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c4sc03372h Click here for additional data file.

PubMed Central

Dudley, Gregory B.; Richert, Ranko

2015-01-01

The use of microwave radiation to drive chemical reactions has become ubiquitous in almost all fields of chemistry. In all of these areas it is principally due to rapid and convenient heating resulting in significantly higher rates of reaction, with other advantages including enhanced product selectivity and control of materials properties. Although microwave heating continues to grow as an enabling technology, fundamental research into the nature of microwave heating has not grown at the same rate. In the case of chemical reactions run in homogeneous solution, particularly synthetic organic reactions, there is considerable controversy over the origins of rate enhancement, with a fundamental question being whether there exist microwave-specific effects, distinct from what can be attained under conventional convective heating, that can accelerate a reaction rate. In this Perspective, we discuss unique aspects of microwave heating of molecules in solution and discuss the origin and nature of microwave-specific effects arising from the process of “selective heating” of reactants in solution. Integral to this discussion is work from the field of dielectric relaxation spectroscopy, which provides a model for selective heating by Debye relaxation processes. The Perspective also includes a critical discussion of hypotheses of non-thermal effects (alternatively classified here as resonant processes) and an outline of specific reaction parameters for chemical systems in which microwave-specific Debye relaxation processes can result in observable reaction rate enhancement. PMID:29308138

Enhancement of ohmic and stochastic heating by resonance effects in capacitive radio frequency discharges: a theoretical approach.

PubMed

Mussenbrock, T; Brinkmann, R P; Lieberman, M A; Lichtenberg, A J; Kawamura, E

2008-08-22

In low-pressure capacitive radio frequency discharges, two mechanisms of electron heating are dominant: (i) Ohmic heating due to collisions of electrons with neutrals of the background gas and (ii) stochastic heating due to momentum transfer from the oscillating boundary sheath. In this work we show by means of a nonlinear global model that the self-excitation of the plasma series resonance which arises in asymmetric capacitive discharges due to nonlinear interaction of plasma bulk and sheath significantly affects both Ohmic heating and stochastic heating. We observe that the series resonance effect increases the dissipation by factors of 2-5. We conclude that the nonlinear plasma dynamics should be taken into account in order to describe quantitatively correct electron heating in asymmetric capacitive radio frequency discharges.

Submammary Granular Parakeratosis Treated With Mastopexy.

PubMed

Nelson, Garrett; Lien, Mary H; Messina, Jane L; Ranjit, Sonali; Fenske, Neil Alan

2017-08-01

Granular parakeratosis, originally named axillary granular parakeratosis, is an uncommon disease with an unclear etiology. It is thought to result from defective processing of profillagrin to fillagrin, causing retention of keratohyaline granules in the epidermis. A myriad of causative factors has been proposed, including friction, moisture, heat, and contact irritants such as deodorants. We present a case in the inframammary area that resolved with mastopexy, further supporting the role of friction, moisture, and heat. Furthermore, we present electron microscopic evidence demonstrating non-degraded keratohyaline granules upon epidermal maturation. This entity, we believe, is reactive and represents a protective response of the body to moisture and heat.

J Drugs Dermatol. 2017;16(8):810-812.

4D multiple-cathode ultrafast electron microscopy

PubMed Central

Baskin, John Spencer; Liu, Haihua; Zewail, Ahmed H.

2014-01-01

Four-dimensional multiple-cathode ultrafast electron microscopy is developed to enable the capture of multiple images at ultrashort time intervals for a single microscopic dynamic process. The dynamic process is initiated in the specimen by one femtosecond light pulse and probed by multiple packets of electrons generated by one UV laser pulse impinging on multiple, spatially distinct, cathode surfaces. Each packet is distinctly recorded, with timing and detector location controlled by the cathode configuration. In the first demonstration, two packets of electrons on each image frame (of the CCD) probe different times, separated by 19 picoseconds, in the evolution of the diffraction of a gold film following femtosecond heating. Future elaborations of this concept to extend its capabilities and expand the range of applications of 4D ultrafast electron microscopy are discussed. The proof-of-principle demonstration reported here provides a path toward the imaging of irreversible ultrafast phenomena of materials, and opens the door to studies involving the single-frame capture of ultrafast dynamics using single-pump/multiple-probe, embedded stroboscopic imaging. PMID:25006261

4D multiple-cathode ultrafast electron microscopy.

PubMed

Baskin, John Spencer; Liu, Haihua; Zewail, Ahmed H

2014-07-22

Four-dimensional multiple-cathode ultrafast electron microscopy is developed to enable the capture of multiple images at ultrashort time intervals for a single microscopic dynamic process. The dynamic process is initiated in the specimen by one femtosecond light pulse and probed by multiple packets of electrons generated by one UV laser pulse impinging on multiple, spatially distinct, cathode surfaces. Each packet is distinctly recorded, with timing and detector location controlled by the cathode configuration. In the first demonstration, two packets of electrons on each image frame (of the CCD) probe different times, separated by 19 picoseconds, in the evolution of the diffraction of a gold film following femtosecond heating. Future elaborations of this concept to extend its capabilities and expand the range of applications of 4D ultrafast electron microscopy are discussed. The proof-of-principle demonstration reported here provides a path toward the imaging of irreversible ultrafast phenomena of materials, and opens the door to studies involving the single-frame capture of ultrafast dynamics using single-pump/multiple-probe, embedded stroboscopic imaging.

Optimization and stabilization of gold nanoparticles by using herbal plant extract with microwave heating

NASA Astrophysics Data System (ADS)

Yasmin, Akbar; Ramesh, Kumaraswamy; Rajeshkumar, Shanmugam

2014-04-01

In this study, we have synthesized the gold nanoparticles by using Hibiscus rosa-sinensis, a medicinal plant. The gold nanoparticles were synthesized rapidly by the involvement of microwave heating. By changing of plant extract concentration, gold solution concentration, microwave heating time and power of microwave heating the optimized condition was identified. The surface Plasmon resonance found at 520 nm confirmed the gold nanoparticles synthesis. The spherical sized nanoparticles in the size range of 16-30 nm were confirmed by Transmission Electron Microscope (TEM). The stability of the nanoparticles is very well proved in the invitro stability tests. The biochemical like alkaloids and flavonoids play a vital role in the nanoparticles synthesis was identified using the Fourier Transform Infrared Spectroscopy (FTIR). Combining the phytochemical and microwave heating, the rapid synthesis of gold nanoparticles is the novel process for the medically applicable gold nanoparticles production.

Experimental metrology to obtain thermal phonon transmission coefficients at solid interfaces

DOE PAGES

Hua, Chengyun; Chen, Xiangwen; Ravichandran, Navaneetha K.; ...

2017-05-17

Interfaces play an essential role in phonon-mediated heat conduction in solids, impacting applications ranging from thermoelectric waste heat recovery to heat dissipation in electronics. From the microscopic perspective, interfacial phonon transport is described by transmission coefficients that link vibrational modes in the materials composing the interface. But, direct experimental determination of these coefficients is challenging because most experiments provide a mode-averaged interface conductance that obscures the microscopic detail. Here, we report a metrology to extract thermal phonon transmission coefficients at solid interfaces using ab initio phonon transport modeling and a thermal characterization technique, time-domain thermoreflectance. In combination with transmission electronmore » microscopy characterization of the interface, our approach allows us to link the atomic structure of an interface to the spectral content of the heat crossing it. This work provides a useful perspective on the microscopic processes governing interfacial heat conduction.« less

Thermionic Power Cell To Harness Heat Energies for Geothermal Applications

NASA Technical Reports Server (NTRS)

Manohara, Harish; Mojarradi, Mohammad; Greer, Harold F.

2011-01-01

A unit thermionic power cell (TPC) concept has been developed that converts natural heat found in high-temperature environments (460 to 700 C) into electrical power for in situ instruments and electronics. Thermionic emission of electrons occurs when an emitter filament is heated to gwhite hot h temperatures (>1,000 C) allowing electrons to overcome the potential barrier and emit into the vacuum. These electrons are then collected by an anode, and transported to the external circuit for energy storage.

Fabrication of compact electron gun for 6 MeV X-ray source

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

Ghodke, S.R.; Barnwal, Rajesh; Kumar, Mahendra, E-mail: ghodke_barc@yahoo.co.in

The 6 MeV X-Ray source for container cargo scanning application has been designed and developed by the Accelerator and Pulse Power Division, BARC, Mumbai. This compact linac has been designed as a mobile system, to be mounted on a moving container. In linac-based cargo-scanning system, to work electron gun on a movable container, it has to be robust. Electron gun is to work at 10{sup -7} mbar vacuum and 2000 degree Celsius temperature. An effort is made to engineer the gun assembly to make it more robust and aligned. The linac acts as the source of X-rays, which fall onmore » the cargo and are then detected by the detector system. Many components are indigenously developed like grid, insulating ring, Tungsten filament and filament guide, which are made from alumina ceramic and Tantalum which is to work at 1500 degree Celsius. Filament connector is made from Invar to reduce heat loss and to make rigid connection. It was CNC machined and wire cut by EDM. Invar and Copper electrode feed through is shrink fitted with the help of liquid Nitrogen. Shrink fit tolerances of 15 micrometer are achieved by jig boring machining processes. Tantalum cup for LaB6 cathode and heat shield are made from die and punch mechanism. For alignment of electron emitter with beam axis this Tantalum cup is a crucial component. Electron gun is assembled and aligned its components with the help of precision jigs. The whole assembly was Helium leak tested by MSLD up to 4 x 10{sup -10} mbar.l/s vacuum, no leak was found. This paper will describe the machining, Tantalum cup forming, ceramic components development, heat shields, ceramic feed through etc of electron gun. (author)« less

Electron Beam Welding of IN792 DS: Effects of Pass Speed and PWHT on Microstructure and Hardness.

PubMed

Angella, Giuliano; Barbieri, Giuseppe; Donnini, Riccardo; Montanari, Roberto; Richetta, Maria; Varone, Alessandra

2017-09-05

Electron Beam (EB) welding has been used to realize seams on 2 mm-thick plates of directionally solidified (DS) IN792 superalloy. The first part of this work evidenced the importance of pre-heating the workpiece to avoid the formation of long cracks in the seam. The comparison of different pre-heating temperatures (PHT) and pass speeds ( v ) allowed the identification of optimal process parameters, namely PHT = 300 °C and v = 2.5 m/min. The microstructural features of the melted zone (MZ); the heat affected zone (HAZ), and base material (BM) were investigated by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), electron back-scattered diffraction (EBSD), X-ray diffraction (XRD), and micro-hardness tests. In the as-welded condition; the structure of directionally oriented grains was completely lost in MZ. The γ' phase in MZ consisted of small (20-40 nm) round shaped particles and its total amount depended on both PHT and welding pass speed, whereas in HAZ, it was the same BM. Even if the amount of γ' phase in MZ was lower than that of the as-received material, the nanometric size of the particles induced an increase in hardness. EDS examinations did not show relevant composition changes in the γ' and γ phases. Post-welding heat treatments (PWHT) at 700 and 750 °C for two hours were performed on the best samples. After PWHTs, the amount of the ordered phase increased, and the effect was more pronounced at 750 °C, while the size of γ' particles in MZ remained almost the same. The hardness profiles measured across the joints showed an upward shift, but peak-valley height was a little lower, indicating more homogeneous features in the different zones.

Oscillating two-stream instability in a magnetized electron-positron-ion plasma

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

Tinakiche, Nouara; Faculty of Physics, U.S.T.H.B, Algiers 16111; Annou, R.

2015-04-15

Oscillating two-stream instability (OTSI) in a magnetized electron-ion plasma has been thoroughly studied, e.g., in ionospheric heating experiments [C. S. Liu and V. K. Tripathi, Interaction of Electromagnetic Waves With Electron Beams and Plasmas (World Scientific, 1994); V. K. Tripathi and P. V. Siva Rama Prasad, J. Plasma Phys. 41, 13 (1989); K. Ramachandran and V. K. Tripathi, IEEE Trans. Plasma Sci. 25, 423 (1997)]. In this paper, OTSI is investigated in a magnetized electron-positron-ion plasma. The dispersion relation of the process is established. The pump field threshold, along with the maximum growth rate of the instability is assessed usingmore » the Arecibo and HAARP parameters.« less

Oscillating two-stream instability in a magnetized electron-positron-ion plasma

NASA Astrophysics Data System (ADS)

Tinakiche, Nouara; Annou, R.

2015-04-01

Oscillating two-stream instability (OTSI) in a magnetized electron-ion plasma has been thoroughly studied, e.g., in ionospheric heating experiments [C. S. Liu and V. K. Tripathi, Interaction of Electromagnetic Waves With Electron Beams and Plasmas (World Scientific, 1994); V. K. Tripathi and P. V. Siva Rama Prasad, J. Plasma Phys. 41, 13 (1989); K. Ramachandran and V. K. Tripathi, IEEE Trans. Plasma Sci. 25, 423 (1997)]. In this paper, OTSI is investigated in a magnetized electron-positron-ion plasma. The dispersion relation of the process is established. The pump field threshold, along with the maximum growth rate of the instability is assessed using the Arecibo and HAARP parameters.

Verification and validation of a rapid heat transfer calculation methodology for transient melt pool solidification conditions in powder bed metal additive manufacturing

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

Plotkowski, A.; Kirka, M. M.; Babu, S. S.

A fundamental understanding of spatial and temporal thermal distributions is crucial for predicting solidification and solid-state microstructural development in parts made by additive manufacturing. While sophisticated numerical techniques that are based on finite element or finite volume methods are useful for gaining insight into these phenomena at the length scale of the melt pool (100 - 500 µm), they are ill-suited for predicting engineering trends over full part cross-sections (> 10 x 10 cm) or many layers over long process times (> many days) due to the necessity of fully resolving the heat source characteristics. On the other hand, itmore » is extremely difficult to resolve the highly dynamic nature of the process using purely in-situ characterization techniques. This article proposes a pragmatic alternative based on a semi-analytical approach to predicting the transient heat conduction during powder bed metal additive manufacturing process. The model calculations were theoretically verified for selective laser melting of AlSi10Mg and electron beam melting of IN718 powders for simple cross-sectional geometries and the transient results are compared to steady state predictions from the Rosenthal equation. It is shown that the transient effects of the scan strategy create significant variations in the melt pool geometry and solid-liquid interface velocity, especially as the thermal diffusivity of the material decreases and the pre-heat of the process increases. With positive verification of the strategy, the model was then experimentally validated to simulate two point-melt scan strategies during electron beam melting of IN718, one intended to produce a columnar and one an equiaxed grain structure. Lastly, through comparison of the solidification conditions (i.e. transient and spatial variations of thermal gradient and liquid-solid interface velocity) predicted by the model to phenomenological CET theory, the model accurately predicted the experimental grain structures.« less

Verification and validation of a rapid heat transfer calculation methodology for transient melt pool solidification conditions in powder bed metal additive manufacturing

DOE PAGES

Plotkowski, A.; Kirka, M. M.; Babu, S. S.

2017-10-16

A fundamental understanding of spatial and temporal thermal distributions is crucial for predicting solidification and solid-state microstructural development in parts made by additive manufacturing. While sophisticated numerical techniques that are based on finite element or finite volume methods are useful for gaining insight into these phenomena at the length scale of the melt pool (100 - 500 µm), they are ill-suited for predicting engineering trends over full part cross-sections (> 10 x 10 cm) or many layers over long process times (> many days) due to the necessity of fully resolving the heat source characteristics. On the other hand, itmore » is extremely difficult to resolve the highly dynamic nature of the process using purely in-situ characterization techniques. This article proposes a pragmatic alternative based on a semi-analytical approach to predicting the transient heat conduction during powder bed metal additive manufacturing process. The model calculations were theoretically verified for selective laser melting of AlSi10Mg and electron beam melting of IN718 powders for simple cross-sectional geometries and the transient results are compared to steady state predictions from the Rosenthal equation. It is shown that the transient effects of the scan strategy create significant variations in the melt pool geometry and solid-liquid interface velocity, especially as the thermal diffusivity of the material decreases and the pre-heat of the process increases. With positive verification of the strategy, the model was then experimentally validated to simulate two point-melt scan strategies during electron beam melting of IN718, one intended to produce a columnar and one an equiaxed grain structure. Lastly, through comparison of the solidification conditions (i.e. transient and spatial variations of thermal gradient and liquid-solid interface velocity) predicted by the model to phenomenological CET theory, the model accurately predicted the experimental grain structures.« less

Advanced electron cyclotron heating and current drive experiments on the stellarator Wendelstein 7-X

NASA Astrophysics Data System (ADS)

Stange, Torsten; Laqua, Heinrich Peter; Beurskens, Marc; Bosch, Hans-Stephan; Bozhenkov, Sergey; Brakel, Rudolf; Braune, Harald; Brunner, Kai Jakob; Cappa, Alvaro; Dinklage, Andreas; Erckmann, Volker; Fuchert, Golo; Gantenbein, Gerd; Gellert, Florian; Grulke, Olaf; Hartmann, Dirk; Hirsch, Matthias; Höfel, Udo; Kasparek, Walter; Knauer, Jens; Langenberg, Andreas; Marsen, Stefan; Marushchenko, Nikolai; Moseev, Dmitry; Pablant, Novomir; Pasch, Ekkehard; Rahbarnia, Kian; Mora, Humberto Trimino; Tsujimura, Toru; Turkin, Yuriy; Wauters, Tom; Wolf, Robert

2017-10-01

During the first operational phase (OP 1.1) of Wendelstein 7-X (W7-X) electron cyclotron resonance heating (ECRH) was the exclusive heating method and provided plasma start-up, wall conditioning, heating and current drive. Six gyrotrons were commissioned for OP1.1 and used in parallel for plasma operation with a power of up to 4.3 MW. During standard X2-heating the spatially localized power deposition with high power density allowed controlling the radial profiles of the electron temperature and the rotational transform. Even though W7-X was not fully equipped with first wall tiles and operated with a graphite limiter instead of a divertor, electron densities of n e > 3·1019 m-3 could be achieved at electron temperatures of several keV and ion temperatures above 2 keV. These plasma parameters allowed the first demonstration of a multipath O2-heating scenario, which is envisaged for safe operation near the X-cutoff-density of 1.2·1020 m-3 after full commissioning of the ECRH system in the next operation phase OP1.2.

Synthesis of Al₂Ca Dispersoids by Powder Metallurgy Using a Mg-Al Alloy and CaO Particles.

PubMed

Fujita, Junji; Umeda, Junko; Kondoh, Katsuyoshi

2017-06-28

The elemental mixture of Mg-6 wt %Al-1 wt %Zn-0.3 wt %Mn (AZ61B) alloy powder and CaO particles was consolidated by an equal-channel angular bulk mechanical alloying (ECABMA) process to form a composite precursor. Subsequently, the precursor was subjected to a heat treatment to synthesize fine Al₂Ca particles via a solid-state reaction between the Mg-Al matrix and CaO additives. Scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) and electron probe micro-analysis on the precursor indicated that 4.7-at % Al atoms formed a supersaturated solid solution in the α-Mg matrix. Transmission electron microscopy-EDS and X-ray diffraction analyses on the AZ61B composite precursor with 10-vol % CaO particles obtained by heat treatment confirmed that CaO additives were thermally decomposed in the Mg-Al alloy, and the solid-soluted Ca atoms diffused along the α-Mg grain boundaries. Al atoms also diffused to the grain boundaries because of attraction to the Ca atoms resulting from a strong reactivity between Al and Ca. As a result, needle-like (Mg,Al)₂Ca intermetallics were formed as intermediate precipitates in the initial reaction stage during the heat treatment. Finally, the precipitates were transformed into spherical Al₂Ca particles by the substitution of Al atoms for Mg atoms in (Mg,Al)₂Ca after a long heat treatment.

Electronic and Solid State Sciences Program Summary, FY 1979.

DTIC Science & Technology

1979-01-01

studies of the interaction of the electromagnetic field with heat conducting and electrically non-conducting and conducting polarizable and mag- netizable...Physical Review Letters, 42, 401-404 (1979). 9. "The low temperature electronic specific heat of disordered one dimensional chains", by P. S...technique exploits parallel photoheating and dc electrical- heating experiments. The CO laser hot electron studies have provided information on the

Electromagnetic containerless processing requirements and recommended facility concept and capabilities for space lab

NASA Technical Reports Server (NTRS)

Frost, R. T.; Bloom, H. L.; Napaluch, L. J.; Stockhoff, E. H.; Wouch, G.

1974-01-01

Containerless melting, reaction, and solidification experiments and processes which potentially can lead to new understanding of material science and production of new or improved materials in the weightless space environment are reviewed in terms of planning for spacelab. Most of the experiments and processes discussed are amenable to the employment of electromagnetic position control and electromagnetic induction or electron beam heating and melting. The spectrum of relevant properties of materials, which determine requirements for a space laboratory electromagnetic containerless processing facility are reviewed. Appropriate distributions and associated coil structures are analyzed and compared on the basis of efficiency, for providing the functions of position sensing, control, and induction heating. Several coil systems are found capable of providing these functions. Exchangeable modular coils in appropriate sizes are recommended to achieve the maximum power efficiencies, for a wide range of specimen sizes and resistivities, in order to conserve total facility power.

Enhanced emission of encaged-OH--free Ca12(1-x)Sr12xAl14O33:0.1%Gd3+ conductive phosphors via tuning the encaged-electron concentration for low-voltage FEDs.

PubMed

Zhang, Meng; Liu, Yuxue; Yang, Jian; Zhu, Hancheng; Yan, Duanting; Zhang, Xinyang; Liu, Chunguang; Xu, Changshan; Zhang, Hong

2017-05-24

Encaged-OH - -free Ca 12(1-x) Sr 12x Al 14 O 33 :0.1%Gd 3+ conductive phosphors were prepared through a melt-solidification process in combination with a subsequent heat treatment. Absorption spectra showed that the maximum encaged-electron concentration was increased to 1.08 × 10 21 cm -3 through optimizing the doping amount of Sr 2+ (x = 0.005). Meanwhile, FTIR and Raman spectra indicated that pure Ca 11.94 Sr 0.06 Al 14 O 33 :0.1%Gd 3+ conductive phosphor without encaged OH - and C 2 2- anions was acquired. For the conductive powders heat-treated in air for different times, the encaged-electron concentrations were tuned from 1.02 × 10 21 to 8.3 × 10 20 cm -3 . ESR, photoluminescence, and luminescence kinetics analyses indicated that the emission at 312 nm mainly originated from Gd 3+ ions surrounded by encaged O 2- anions, while Gd 3+ ions surrounded by encaged electrons had a negative contribution to the UV emission due to the existence of an energy transfer process. Under low-voltage electron-beam excitation (3 kV), enhanced cathodoluminescence (CL) of the conductive phosphors could be achieved by tuning the encaged-electron concentrations. In particular, for the encaged-OH - -free conductive phosphor, the emission intensity of the CL was about one order of magnitude higher than that of the conductive phosphor containing encaged OH - anions. Our results suggested that the encaged-OH - -free conductive phosphors have potential application in low-voltage FEDs.

Boiling Heat Transfer Mechanisms in Earth and Low Gravity: Boundary Condition and Heater Aspect Ratio Effects

NASA Technical Reports Server (NTRS)

Kim, Jungho

2004-01-01

Boiling is a complex phenomenon where hydrodynamics, heat transfer, mass transfer, and interfacial phenomena are tightly interwoven. An understanding of boiling and critical heat flux in microgravity environments is of importance to space based hardware and processes such as heat exchange, cryogenic fuel storage and transportation, electronic cooling, and material processing due to the large amounts of heat that can be removed with relatively little increase in temperature. Although research in this area has been performed in the past four decades, the mechanisms by which heat is removed from surfaces in microgravity are still unclear. Recently, time and space resolved heat transfer data were obtained in both earth and low gravity environments using an array of microheaters varying in size between 100 microns to 700 microns. These heaters were operated in both constant temperature as well as constant heat flux mode. Heat transfer under nucleating bubbles in earth gravity were directly measured using a microheater array with 100 m resolution operated in constant temperature mode with low and high subcooled bulk liquid along with images from below and from the side. The individual bubble departure diameter and energy transfer were larger with low subcooling but the departure frequency increased at high subcooling, resulting in higher overall heat transfer. The bubble growth for both subcoolings was primarily due to energy transfer from the superheated liquid layer relatively little was due to wall heat transfer during the bubble growth process. Oscillating bubbles and sliding bubbles were also observed in highly subcooled boiling. Transient conduction and/or microconvection was the dominant heat transfer mechanism in the above cases. A transient conduction model was developed and compared with the experimental data with good agreement. Data was also obtained with the heater array operated in a constant heat flux mode and measuring the temperature distribution across the array during boiling. The instantaneous heat transfer into the substrate was numerically determined and subtracted from the supplied heat to obtain the wall to liquid heat flux.

77 FR 10373 - Greenhouse Gas Reporting Program: Electronics Manufacturing: Revisions to Heat Transfer Fluid...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-02-22

... Greenhouse Gas Reporting Program: Electronics Manufacturing: Revisions to Heat Transfer Fluid Provisions... technical revisions to the electronics manufacturing source category of the Greenhouse Gas Reporting Rule... related to the electronics manufacturing source category. DATES: This rule will be effective on March 23...

Laser ablation under different electron heat conduction models in inertial confinement fusion

NASA Astrophysics Data System (ADS)

Li, Shuanggui; Ren, Guoli; Huo, Wen Yi

2018-06-01

In this paper, we study the influence of three different electron heat conduction models on the laser ablation of gold plane target. Different from previous studies, we concentrate on the plasma conditions, the conversion efficiency from laser into soft x rays and the scaling relation of mass ablation, which are relevant to hohlraum physics study in indirect drive inertial confinement fusion. We find that the simulated electron temperature in corona region is sensitive to the electron heat conduction models. For different electron heat conduction models, there are obvious differences in magnitude and spatial profile of electron temperature. For the flux limit model, the calculated conversion efficiency is sensitive to flux limiters. In the laser ablation of gold, most of the laser energies are converted into x rays. So the scaling relation of mass ablation rate is quite different from that of low Z materials.

X-ray analysis of electron Bernstein wave heating in MST

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

Seltzman, A. H., E-mail: seltzman@wisc.edu; Anderson, J. K.; DuBois, A. M.

2016-11-15

A pulse height analyzing x-ray tomography system has been developed to detect x-rays from electron Bernstein wave heated electrons in the Madison symmetric torus reversed field pinch (RFP). Cadmium zinc telluride detectors are arranged in a parallel beam array with two orthogonal multi-chord detectors that may be used for tomography. In addition a repositionable 16 channel fan beam camera with a 55° field of view is used to augment data collected with the Hard X-ray array. The chord integrated signals identify target emission from RF heated electrons striking a limiter located 12° toroidally away from the RF injection port. Thismore » provides information on heated electron spectrum, transport, and diffusion. RF induced x-ray emission from absorption on harmonic electron cyclotron resonances in low current (<250 kA) RFP discharges has been observed.« less

Fast plasmonic laser nanowelding for a Cu-nanowire percolation network for flexible transparent conductors and stretchable electronics.

PubMed

Han, Seungyong; Hong, Sukjoon; Ham, Jooyeun; Yeo, Junyeob; Lee, Jinhwan; Kang, Bongchul; Lee, Phillip; Kwon, Jinhyeong; Lee, Seung S; Yang, Min-Yang; Ko, Seung Hwan

2014-09-03

A facile fast laser nanoscale welding process uses the plasmonic effect at a nanowire (NW) junction to suppress oxidation and successfully fabricate a Cu-NW-based percolation-network conductor. The "nanowelding" process does not require an inert or vacuum environment. Due to the low-temperature and fast-process nature, plasmonic laser nanowelding may form Cu-nanowire networks on heat-sensitive, flexible or even stretchable substrates. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electron Heating in Low-Mach-number Perpendicular Shocks. I. Heating Mechanism

NASA Astrophysics Data System (ADS)

Guo, Xinyi; Sironi, Lorenzo; Narayan, Ramesh

2017-12-01

Recent X-ray observations of merger shocks in galaxy clusters have shown that the postshock plasma has two temperatures, with the protons hotter than the electrons. By means of two-dimensional particle-in-cell simulations, we study the physics of electron irreversible heating in low-Mach-number perpendicular shocks, for a representative case with sonic Mach number of 3 and plasma beta of 16. We find that two basic ingredients are needed for electron entropy production: (1) an electron temperature anisotropy, induced by field amplification coupled to adiabatic invariance; and (2) a mechanism to break the electron adiabatic invariance itself. In shocks, field amplification occurs at two major sites: at the shock ramp, where density compression leads to an increase of the frozen-in field; and farther downstream, where the shock-driven proton temperature anisotropy generates strong proton cyclotron and mirror modes. The electron temperature anisotropy induced by field amplification exceeds the threshold of the electron whistler instability. The growth of whistler waves breaks the electron adiabatic invariance and allows for efficient entropy production. For our reference run, the postshock electron temperature exceeds the adiabatic expectation by ≃ 15 % , resulting in an electron-to-proton temperature ratio of ≃ 0.45. We find that the electron heating efficiency displays only a weak dependence on mass ratio (less than ≃ 30 % drop, as we increase the mass ratio from {m}i/{m}e=49 up to {m}i/{m}e=1600). We develop an analytical model of electron irreversible heating and show that it is in excellent agreement with our simulation results.

Heating a plasma by a broadband stream of fast electrons: Fast ignition, shock ignition, and Gbar shock wave applications

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

Gus’kov, S. Yu., E-mail: guskov@sci.lebedev.ru; Nicolai, Ph.; Ribeyre, X.

2015-09-15

An exact analytic solution is found for the steady-state distribution function of fast electrons with an arbitrary initial spectrum irradiating a planar low-Z plasma with an arbitrary density distribution. The solution is applied to study the heating of a material by fast electrons of different spectra such as a monoenergetic spectrum, a step-like distribution in a given energy range, and a Maxwellian spectrum, which is inherent in laser-produced fast electrons. The heating of shock- and fast-ignited precompressed inertial confinement fusion (ICF) targets as well as the heating of a target designed to generate a Gbar shock wave for equation ofmore » state (EOS) experiments by laser-produced fast electrons with a Maxwellian spectrum is investigated. A relation is established between the energies of two groups of Maxwellian fast electrons, which are responsible for generation of a shock wave and heating the upstream material (preheating). The minimum energy of the fast and shock igniting beams as well as of the beam for a Gbar shock wave generation increases with the spectral width of the electron distribution.« less

Time Dependent Predictive Modeling of DIII-D ITER Baseline Scenario using Predictive TRANSP

NASA Astrophysics Data System (ADS)

Grierson, B. A.; Andre, R. G.; Budny, R. V.; Solomon, W. M.; Yuan, X.; Candy, J.; Pinsker, R. I.; Staebler, G. M.; Holland, C.; Rafiq, T.

2015-11-01

ITER baseline scenario discharges on DIII-D are modeled with TGLF and MMM transitioning from combined ECH (3.3MW) +NBI(2.8MW) heating to NBI only (3.0 MW) heating maintaining βN = 2.0 on DIII-D predicting temperature, density and rotation for comparison to experimental measurements. These models capture the reduction of confinement associated with direct electron heating H98y2 = 0.89 vs. 1.0) consistent with stiff electron transport. Reasonable agreement between experimental and modeled temperature profiles is achieved for both heating methods, whereas density and momentum predictions differ significantly. Transport fluxes from TGLF indicate that on DIII-D the electron energy flux has reached a transition from low-k to high-k turbulence with more stiff high-k transport that inhibits an increase in core electron stored energy with additional electron heating. Projections to ITER also indicate high electron stiffness. Supported by US DOE DE-AC02-09CH11466, DE-FC02-04ER54698, DE-FG02-07ER54917, DE-FG02-92-ER54141.

Manufacturing development for the SAFE 100 kW core

NASA Astrophysics Data System (ADS)

Carter, Robert; Roman, Jose; Salvail, Pat

2002-01-01

In stark contrast to what is sometimes considered the norm in traditional manufacturing processes, engineers at the Marshall Space Flight Center (MSFC) arc in the practice of altering the standard in an effort to realize other potential methods in core manufacturing. While remaining within the bounds of the materials database, we are researching into core manufacturing techniques that may have been overlooked in the past due to funding and/or time constraints. To augment proven core fabrication capabilities we are pursuing plating processes as another possible method for core build-up and assembly. Although brazing and a proprietary HIP cycle are used for module assembly (proven track record for stability and endurance), it is prudent to pursue secondary or backup methods of module and core assembly. For this reason heat tube manufacture and module assembly by means of plating is being investigated. Potentially, the plating processes will give engineers the ability to manufacture replacement modules for any module that might fail to perform nominally, and to assemble/disassemble a complete core in much less time than would be required for the conventional Braze-HIP process. Another area of improvement in core manufacturing capabilities is the installation of a sodium and lithium liquid metal heat pipe fill machine. This, along with the ability to Electron Beam Weld heat pipe seals and wet-in the pipes in the necessary vacuum atmosphere, will eliminate the need to ship potentially hazardous components outside for processing. In addition to developing core manufacturing techniques, the SAFE manufacturing team has been evaluating the thermal heat transfer characteristics, and manufacturability of several heat exchanger design concepts. .

Non-Equilibrium Phenomena in High Power Beam Materials Processing

NASA Astrophysics Data System (ADS)

Tosto, Sebastiano

2004-03-01

The paper concerns some aspects of non-equilibrium materials processing with high power beams. Three examples show that the formation of metastable phases plays a crucial role to understand the effects of beam-matter interaction: (i) modeling of pulsed laser induced thermal sputtering; (ii) formation of metastable phases during solidification of the melt pool; (i) possibility of carrying out heat treatments by low power irradiation ``in situ''. The case (i) deals with surface evaporation and boiling processes in presence of superheating. A computer simulation model of thermal sputtering by vapor bubble nucleation in molten phase shows that non-equilibrium processing enables the rise of large surface temperature gradients in the boiling layer and the possibility of sub-surface temperature maximum. The case (ii) concerns the heterogeneous welding of Cu and AISI 304L stainless steel plates by electron beam irradiation. Microstructural investigation of the molten zone has shown that dwell times of the order of 10-1-10-3 s, consistent with moderate cooling rates in the range 10^3-10^5 K/s, entail the formation of metastable Cu-Fe phases. The case (iii) concerns electron beam welding and post-welding treatments of 2219 Al base alloy. Electron microscopy and positron annihilation have explained why post-weld heat transients induced by low power irradiation of specimens in the as welded condition enable ageing effects usually expected after some hours of treatment in furnace. The problem of microstructural instability is particularly significant for a correct design of components manufactured with high power beam technologies and subjected to severe acceptance standards to ensure advanced performances during service life.

Susceptor heating device for electron beam brazing

DOEpatents

Antieau, Susan M.; Johnson, Robert G. R.

1999-01-01

A brazing device and method are provided which locally apply a controlled amount of heat to a selected area, within a vacuum. The device brazes two components together with a brazing metal. A susceptor plate is placed in thermal contact with one of the components. A serrated pedestal supports the susceptor plate. When the pedestal and susceptor plate are in place, an electron gun irradiates an electron beam at the susceptor plate such that the susceptor plate is sufficiently heated to transfer heat through the one component and melt the brazing metal.

Electron heat flux dropouts in the solar wind - Evidence for interplanetary magnetic field reconnection?

NASA Technical Reports Server (NTRS)

Mccomas, D. J.; Gosling, J. T.; Phillips, J. L.; Bame, S. J.; Luhmann, J. G.; Smith, E. J.

1989-01-01

An examination of ISEE-3 data from 1978 reveal 25 electron heat flux dropout events ranging in duration from 20 min to over 11 hours. The heat flux dropouts are found to occur in association with high plasma densities, low plasma velocities, low ion and electron temperatures, and low magnetic field magnitudes. It is suggested that the heat flux dropout intervals may indicate that the spacecraft is sampling plasma regimes which are magnetically disconnected from the sun and instead are connected to the outer heliosphere at both ends.

Kinetic limit of heterogeneous melting in metals.

PubMed

Ivanov, Dmitriy S; Zhigilei, Leonid V

2007-05-11

The velocity and nanoscale shape of the melting front are investigated in a model that combines the molecular dynamics method with a continuum description of the electron heat conduction and electron-phonon coupling. The velocity of the melting front is strongly affected by the local drop of the lattice temperature, defined by the kinetic balance between the transfer of thermal energy to the latent heat of melting, the electron heat conduction from the overheated solid, and the electron-phonon coupling. The maximum velocity of the melting front is found to be below 3% of the room temperature speed of sound in the crystal, suggesting a limited contribution of heterogeneous melting under conditions of fast heating.

Electron Heating at Kinetic Scales in Magnetosheath Turbulence

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

Chasapis, Alexandros; Matthaeus, W. H.; Parashar, T. N.

2017-02-20

We present a statistical study of coherent structures at kinetic scales, using data from the Magnetospheric Multiscale mission in the Earth’s magnetosheath. We implemented the multi-spacecraft partial variance of increments (PVI) technique to detect these structures, which are associated with intermittency at kinetic scales. We examine the properties of the electron heating occurring within such structures. We find that, statistically, structures with a high PVI index are regions of significant electron heating. We also focus on one such structure, a current sheet, which shows some signatures consistent with magnetic reconnection. Strong parallel electron heating coincides with whistler emissions at themore » edges of the current sheet.« less

Empirical Constraints on Proton and Electron Heating in the Fast Solar Wind

NASA Technical Reports Server (NTRS)

Cranmer, Steven R.; Matthaeus, William H.; Breech, Benjamin A.; Kasper, Justin C.

2009-01-01

This paper presents analyses of measured proton and electron temperatures in the high-speed solar wind that are used to calculate the separate rates of heat deposition for protons and electrons. It was found that the protons receive about 60% of the total plasma heating in the inner heliosphere, and that this fraction increases to approximately 80% by the orbit of Jupiter. The empirically derived partitioning of heat between protons and electrons is in rough agreement with theoretical predictions from a model of linear Vlasov wave damping. For a modeled power spectrum consisting only of Alfvenic fluctuations, the best agreement was found for a distribution of wavenumber vectors that evolves toward isotropy as distance increases.

Anomalous transport theory for the reversed field pinch

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

Terry, P.W.; Hegna, C.C; Sovinec, C.R.

1996-09-01

Physically motivated transport models with predictive capabilities and significance beyond the reversed field pinch (RFP) are presented. It is shown that the ambipolar constrained electron heat loss observed in MST can be quantitatively modeled by taking account of the clumping in parallel streaming electrons and the resultant self-consistent interaction with collective modes; that the discrete dynamo process is a relaxation oscillation whose dependence on the tearing instability and profile relaxation physics leads to amplitude and period scaling predictions consistent with experiment; that the Lundquist number scaling in relaxed plasmas driven by magnetic turbulence has a weak S{sup {minus}1/4} scaling; andmore » that radial E{times}B shear flow can lead to large reductions in the edge particle flux with little change in the heat flux, as observed in the RFP and tokamak. 24 refs.« less

The effect of Electron Cyclotron Heating on density fluctuations at ion and electron scales in ITER Baseline Scenario discharges on the DIII-D tokamak

DOE PAGES

Marinoni, Alessandro; Pinsker, Robert I.; Porkolab, Miklos; ...

2017-08-01

Experiments simulating the ITER Baseline Scenario on the DIII-D tokamak show that torque-free pure electron heating, when coupled to plasmas subject to a net co-current beam torque, affects density fluctuations at electron scales on a sub-confinement time scale, whereas fluctuations at ion scales change only after profiles have evolved to a new stationary state. Modifications to the density fluctuations measured by the Phase Contrast Imaging diagnostic (PCI) are assessed by analyzing the time evolution following the switch-off of Electron Cyclotron Heating (ECH), thus going from mixed beam/ECH to pure neutral beam heating at fixed β N . Within 20 msmore » after turning off ECH, the intensity of fluctuations is observed to increase at frequencies higher than 200 kHz; in contrast, fluctuations at lower frequency are seen to decrease in intensity on a longer time scale, after other equilibrium quantities have evolved. Non-linear gyro-kinetic modeling at ion and electron scales scales suggest that, while the low frequency response of the diagnostic is consistent with the dominant ITG modes being weakened by the slow-time increase in flow shear, the high frequency response is due to prompt changes to the electron temperature profile that enhance electron modes and generate a larger heat flux and an inward particle pinch. Furthermore, these results suggest that electron heated regimes in ITER will feature multi-scale fluctuations that might affect fusion performance via modifications to profiles.« less

Validation of nonlinear gyrokinetic simulations of L- and I-mode plasmas on Alcator C-Mod

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

Creely, A. J.; Howard, N. T.; Rodriguez-Fernandez, P.

New validation of global, nonlinear, ion-scale gyrokinetic simulations (GYRO) is carried out for L- and I-mode plasmas on Alcator C-Mod, utilizing heat fluxes, profile stiffness, and temperature fluctuations. Previous work at C-Mod found that ITG/TEM-scale GYRO simulations can match both electron and ion heat fluxes within error bars in I-mode [White PoP 2015], suggesting that multi-scale (cross-scale coupling) effects [Howard PoP 2016] may be less important in I-mode than in L-mode. New results presented here, however, show that global, nonlinear, ion-scale GYRO simulations are able to match the experimental ion heat flux, but underpredict electron heat flux (at most radii),more » electron temperature fluctuations, and perturbative thermal diffusivity in both L- and I-mode. Linear addition of electron heat flux from electron scale runs does not resolve this discrepancy. These results indicate that single-scale simulations do not sufficiently describe the I-mode core transport, and that multi-scale (coupled electron- and ion-scale) transport models are needed. In conclusion a preliminary investigation with multi-scale TGLF, however, was unable to resolve the discrepancy between ion-scale GYRO and experimental electron heat fluxes and perturbative diffusivity, motivating further work with multi-scale GYRO simulations and a more comprehensive study with multi-scale TGLF.« less

Validation of nonlinear gyrokinetic simulations of L- and I-mode plasmas on Alcator C-Mod

DOE PAGES

Creely, A. J.; Howard, N. T.; Rodriguez-Fernandez, P.; ...

2017-03-02

New validation of global, nonlinear, ion-scale gyrokinetic simulations (GYRO) is carried out for L- and I-mode plasmas on Alcator C-Mod, utilizing heat fluxes, profile stiffness, and temperature fluctuations. Previous work at C-Mod found that ITG/TEM-scale GYRO simulations can match both electron and ion heat fluxes within error bars in I-mode [White PoP 2015], suggesting that multi-scale (cross-scale coupling) effects [Howard PoP 2016] may be less important in I-mode than in L-mode. New results presented here, however, show that global, nonlinear, ion-scale GYRO simulations are able to match the experimental ion heat flux, but underpredict electron heat flux (at most radii),more » electron temperature fluctuations, and perturbative thermal diffusivity in both L- and I-mode. Linear addition of electron heat flux from electron scale runs does not resolve this discrepancy. These results indicate that single-scale simulations do not sufficiently describe the I-mode core transport, and that multi-scale (coupled electron- and ion-scale) transport models are needed. In conclusion a preliminary investigation with multi-scale TGLF, however, was unable to resolve the discrepancy between ion-scale GYRO and experimental electron heat fluxes and perturbative diffusivity, motivating further work with multi-scale GYRO simulations and a more comprehensive study with multi-scale TGLF.« less

The Use of Liquid Isopropyl Alcohol and Hydrogen Peroxide Gas Plasma to Biologically Decontaminate Spacecraft Electronics

NASA Technical Reports Server (NTRS)

Bonner, J. K.; Tudryn, Carissa D.; Choi, Sun J.; Eulogio, Sebastian E.; Roberts, Timothy J.; Tudryn, Carissa D.

2006-01-01

Legitimate concern exists regarding sending spacecraft and their associated hardware to solar system bodies where they could possibly contaminate the body's surface with terrestrial microorganisms. The NASA approved guidelines for sterilization as set forth in NPG 8020.12C, which is consistent with the biological contamination control objectives of the Committee on Space Research (COSPAR), recommends subjecting the spacecraft and its associated hardware to dry heat-a dry heat regimen that could potentially employ a temperature of 110(deg)C for up to 200 hours. Such a temperature exposure could prove detrimental to the spacecraft electronics. The stimulated growth of intermetallic compounds (IMCs) in metallic interconnects and/or thermal degradation of organic materials composing much of the hardware could take place over a prolonged temperature regimen. Such detrimental phenomena would almost certainly compromise the integrity and reliability of the electronics. Investigation of sterilization procedures in the medical field suggests that hydrogen peroxide (H202) gas plasma (HPGP) technology can effectively function as an alternative to heat sterilization, especially for heat-sensitive items. Treatment with isopropyl alcohol (IPA) in liquid form prior to exposure of the hardware to HPGP should also prove beneficial. Although IPA is not a sterilant, it is frequently used as a disinfectant because of its bactericidal properties. The use of IPA in electronics cleaning is widely recognized and has been utilized for many years with no adverse affects reported. In addition, IPA is the principal ingredient of the test fluid used in ionic contamination testers to assess the amount of ionic contamination found on the surfaces of printed wiring assemblies. This paper will set forth experimental data confirming the feasibility of the IPA/H202 approach to reach acceptable microbial reduction (MR) levels of spacecraft electronic hardware. In addition, a proposed process flow in which both IPA liquid and HPGP are utilized will be presented in Section 7.0.

Electron-impact excitation heating rates in the atmosphere of Titan

NASA Astrophysics Data System (ADS)

Campbell, L.; Kato, H.; Brunger, M. J.; Bradshaw, M. D.

2010-09-01

A previous study of various heating rates in the atmosphere of Titan included electron-impact excitation of molecular nitrogen as one component. This work examines this component in more detail, using a statistical equilibrium calculation to avoid approximations made in the earlier work. The sensitivity of the results to different cross-section sets is investigated. It is found that using recent and more physical cross sections for vibrational excitation produces a significant increase in the heating rate. On the other hand, using more accurate cross sections for the electronic states had little apparent effect on the heating rates when used within the approximations made in the previous model. However, the inclusion of more transitions in this study produces a significant increase in the electronic state heating rates, as states that were originally neglected are now accounted for here.

Surfaces for high heat dissipation with no Leidenfrost limit

NASA Astrophysics Data System (ADS)

Sajadi, Seyed Mohammad; Irajizad, Peyman; Kashyap, Varun; Farokhnia, Nazanin; Ghasemi, Hadi

2017-07-01

Heat dissipation from hot surfaces through cooling droplets is limited by the Leidenfrost point (LFP), in which an insulating vapor film prevents direct contact between the cooling droplet and the hot surface. A range of approaches have been developed to raise this limit to higher temperatures, but the limit still exists. Recently, a surface architecture, decoupled hierarchical structure, was developed that allows the suppression of LFP completely. However, heat dissipation by the structure in the low superheat region was inferior to other surfaces and the structure required an extensive micro/nano fabrication procedure. Here, we present a metallic surface structure with no LFP and high heat dissipation capacity in all temperature ranges. The surface features the nucleate boiling phenomenon independent of the temperature with an approximate heat transfer coefficient of 20 kW m-2 K-1. This surface is developed in a one-step process with no micro/nano fabrication. We envision that this metallic surface provides a unique platform for high heat dissipation in power generation, photonics/electronics, and aviation systems.

Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin

NASA Astrophysics Data System (ADS)

Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno; Das, Prodip K.

2016-07-01

Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid's thermo-physical properties as well as due to the complex interactions among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.

Mixed convection flow of nanofluid in a square enclosure with an intruded rectangular fin

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

Cong, Ran; Zhou, Xuanyu; De Souza Machado, Bruno

Mixed convection flow in enclosures has been a subject of interest for many years due to their ever increasing applications in solar collectors, electronic cooling, lubrication technologies, food processing, and nuclear reactors. In comparison, little effort has been given to the problem of mixed convection in enclosures filled with nanofluids, while the addition of nanoparticles in a fluid base to alter specific material properties is considered a feasible solution for many heat transfer problems. Mixed convection of nanofluids is a challenging problem as the addition of nanoparticles changes the fluid’s thermo-physical properties as well as due to the complex interactionsmore » among inertia, viscous, and buoyancy forces. In this study, a two-dimensional steady-state numerical model has been developed to investigate mixed convection flow of nanofluids in a square enclosure with an intruded rectangular fin and to optimize the fin geometry for maximizing the heat transfer using the Constructal design. The model has been developed using ANSYS-FLUENT for various fin geometries. Flow fields, temperature fields, and heat transfer rates are examined for different values of Rayleigh and Reynolds numbers for several geometries of the fin with the aim of maximizing the heat transfer from the fin to the surrounding flow. Outcome of this study provides important insight into the heat transfer behavior of nanofluids, which will help in developing novel geometries with enhanced and controlled heat transfer for solar collectors and electronic devices.« less

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

Ling, Meng-Chieh

Graphene, a two-dimensional (2D) honeycomb structure allotrope of carbon atoms, has a long history since the invention of the pencil [Petroski (1989)] and the linear dispersion band structure proposed by Wallace [Wal]; however, only after Novoselov et al. successively isolated graphene from graphite [Novoselov et al. (2004)], it has been studied intensively during the recent years. It draws so much attentions not only because of its potential application in future electronic devices but also because of its fundamental properties: its quasiparticles are governed by the two-dimensional Dirac equation, and exhibit a variety of phenomena such as the anomalous integer quantummore » Hall effect (IQHE) [Novoselov et al. (2005)] measured experimentally, a minimal conductivity at vanishing carrier concentration [Neto et al. (2009)], Kondo effect with magnetic element doping [Hentschel and Guinea (2007)], Klein tunneling in p-n junctions [Cheianov and Fal’ko (2006), Beenakker (2008)], Zitterbewegung [Katsnelson (2006)], and Schwinger pair production [Schwinger (1951); Dora and Moessner (2010)]. Although both electron-phonon coupling and photoconductivity in graphene also draws great attention [Yan et al. (2007); Satou et al. (2008); Hwang and Sarma (2008); Vasko and Ryzhii (2008); Mishchenko (2009)], the nonequilibrium behavior based on the combination of electronphonon coupling and Schwinger pair production is an intrinsic graphene property that has not been investigated. Our motivation for studying clean graphene at low temperature is based on the following effect: for a fixed electric field, below a sufficiently low temperature linear eletric transport breaks down and nonlinear transport dominates. The criteria of the strength of this field [Fritz et al. (2008)] is eE = T2/~vF (1.1) For T >√eE~vF the system is in linear transport regime while for T <√eE~vF the system is in nonlinear transport regime. From the scaling’s point of view, at the nonlinear transport regime the temperature T and electric field E are also related. In this thesis we show that the nontrivial electron distribution function can be associated with an effective temperature T which exhibits a dependence on electric field E and electron-phonon coupling g: T ∝ E1/4g(1.2) The anamolous exponent 1/4 may obtained from scaling. Meanwhile, yet we cannot obtain the distribution function, however, argument based on scaling gives us the current dependence on electric field: J ∝√Eg2 (1.3) which is a very different result compared with the results in which electrons do not experience scattering. This result provides us with important insighht into the correct nonequilibrium distribution function because now we know what the electric field dependence of current must be. Due to the applied field, the electronic system produces heat which prevents us from reaching a steady state. In order to remove Joule heat, we imagine that we have a graphene flake attached to a semiconductor substrate. Joule heat either transport to its environment or to the substrate as shown in 1.1. The red lines represent heat current flowing from high temperature sample to the low temperature reservoir. However, for a very large system, the temperature gradient is 0 in the plane so heat cannot be conducted outside in the horizontal direction, while the energy gap in semiconductor also forbids electron current from flowing into the substrate. But for phonon thermal current, the temperature gradient is large in the vertical direction, so heat can be transported into the substrate via phonons. There are two possible channels of phonon degrees of freedom, acoustic phonon and optical phonon. As we can see from Fig. 1.2 [Kusminskiy et al. (2009)], since the optical phonon excitation energy is too large for a low temperature system, it is note likely to be excited by the nonlinear electric field, so the possible way left is by electron-acoustic phonon scattering. Here acoustic phonon acts as a heat bath to absorb the Joule heat created by pair production process. Hence the scattering process is determined by electron-acoustic phonon interaction which will be introduced in section 3.3.« less

Electron and ion heating by whistler turbulence: Three-dimensional particle-in-cell simulations

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

Hughes, R. Scott; Gary, S. Peter; Wang, Joseph

2014-12-17

Three-dimensional particle-in-cell simulations of decaying whistler turbulence are carried out on a collisionless, homogeneous, magnetized, electron-ion plasma model. In addition, the simulations use an initial ensemble of relatively long wavelength whistler modes with a broad range of initial propagation directions with an initial electron beta β e = 0.05. The computations follow the temporal evolution of the fluctuations as they cascade into broadband turbulent spectra at shorter wavelengths. Three simulations correspond to successively larger simulation boxes and successively longer wavelengths of the initial fluctuations. The computations confirm previous results showing electron heating is preferentially parallel to the background magnetic fieldmore » B o, and ion heating is preferentially perpendicular to B o. The new results here are that larger simulation boxes and longer initial whistler wavelengths yield weaker overall dissipation, consistent with linear dispersion theory predictions of decreased damping, stronger ion heating, consistent with a stronger ion Landau resonance, and weaker electron heating.« less

Ion Thermalization and Electron Heating across Quasi-Perpendicular Shocks Observed by the MMS Mission

NASA Astrophysics Data System (ADS)

Chen, L.-J.; Wilson, L. B., III; Wang, S.; Bessho, N.; Viñas, A. F.-; Lai, H.; Russell, C. T.; Schwartz, S. J.; Hesse, M.; Moore, T. E.; Burch, J. L.; Gershman, D. J.; Giles, B. L.; Torbert, R. B.; Ergun, R. E.; Dorelli, J.; Strangeway, R. J.; Paterson, W. R.; Lavraud, B.; Khotyaintsev, Yu. V.

2017-12-01

Collisionless shocks often involve intense plasma heating in space and astrophysical systems. Despite decades of research, a number of key questions concerning electron and ion heating across collisionless shocks remain unanswered. We 'image' 20 supercritical quasi-perpendicular bow shocks encountered by the Magnetospheric Multiscale (MMS) spacecraft with electron and ion distribution functions to address how ions are thermalized and how electrons are heated. The continuous burst measurements of 3D plasma distribution functions from MMS reveal that the primary thermalization phase of ions occurs concurrently with the main temperature increase of electrons as well as large-amplitude wave fluctuations. Approaching the shock from upstream, the ion temperature (Ti) increases due to the reflected ions joining the incoming solar wind population, as recognized by prior studies, and the increase of Ti precedes that of the electrons. Thermalization in the form of merging between the decelerated solar wind ions and the reflected component often results in a decrease in Ti. In most cases, the Ti decrease is followed by a gradual increase further downstream. Anisotropic, energy-dependent, and/or nongyrotropic electron energization are observed in association with large electric field fluctuations in the main electron temperature (Te) gradient, motivating a renewed scrutiny of the effects from the electrostatic cross-shock potential and wave fluctuations on electron heating. Particle-in-cell (PIC) simulations are carried out to assist interpretations of the MMS observations. We assess the roles of instabilities and the cross-shock potential in thermalizing ions and heating electrons based on the MMS measurements and PIC simulation results. Challenges will be posted for future computational studies and laboratory experiments on collisionless shocks.

Ion Thermalization and Electron Heating across Quasi-Perpendicular Shocks Observed by the MMS Mission

NASA Astrophysics Data System (ADS)

Chen, L. J.; Wilson, L. B., III; Wang, S.; Bessho, N.; Figueroa-Vinas, A.; Lai, H.; Russell, C. T.; Schwartz, S. J.; Hesse, M.; Moore, T. E.; Burch, J.; Gershman, D. J.; Giles, B. L.; Torbert, R. B.; Ergun, R.; Dorelli, J.; Strangeway, R. J.; Paterson, W. R.; Lavraud, B.; Khotyaintsev, Y. V.

2017-12-01

Collisionless shocks often involve intense plasma heating in space and astrophysical systems. Despite decades of research, a number of key questions concerning electron and ion heating across collisionless shocks remain unanswered. We `image' 20 supercritical quasi-perpendicular bow shocks encountered by the Magnetospheric Multiscale (MMS) spacecraft with electron and ion distribution functions to address how ions are thermalized and how electrons are heated. The continuous burst measurements of 3D plasma distribution functions from MMS reveal that the primary thermalization phase of ions occurs concurrently with the main temperature increase of electrons as well as large-amplitude wave fluctuations. Approaching the shock from upstream, the ion temperature (Ti) increases due to the reflected ions joining the incoming solar wind population, as recognized by prior studies, and the increase of Ti precedes that of the electrons. Thermalization in the form of merging between the decelerated solar wind ions and the reflected component often results in a decrease in Ti. In most cases, the Ti decrease is followed by a gradual increase further downstream. Anisotropic, energy-dependent, and/or nongyrotropic electron energization are observed in association with large electric field fluctuations in the main electron temperature (Te) gradient, motivating a renewed scrutiny of the effects from the electrostatic cross-shock potential and wave fluctuations on electron heating. Particle-in-cell (PIC) simulations are carried out to assist interpretations of the MMS observations. We assess the roles of instabilities and the cross-shock potential in thermalizing ions and heating electrons based on the MMS measurements and PIC simulation results. Challenges will be posted for future computational studies and laboratory experiments on collisionless shocks.

Light weight Heat-Sink, Based on Phase-Change-Material for a High powered - Time limited application

NASA Astrophysics Data System (ADS)

Leibovitz, Johnathan

2002-01-01

When designing components for an aerospace application, whether it is an aircraft, satellite, space station or a launcher - a major considered parameter is its weight . For a combat aircraft, an addition of such a lightweight Heat sink to a high power component, can extend significantly avionics performance at very high altitude - when cooling means are poor. When dealing with a satellite launcher, each pound saved from the launcher in favor of the satellite - may contribute, for instance, several months of satellite life. The solution presented in this paper deals with an electronic device producing high power, for limited time and requires relatively low temperature base plate. The requirements demand that a base plate temperature should not exceed 70°c while exposed to a heat- flux of about 1.5W/cm^2 from an electronic device, during approximately 14 minutes. The classical solution for this transient process requires an Aluminum block heat sink of about 1100 grams . The PCM based heat-sink gives the solution for this case with about 400 grams only with a compact package. It also includes an option for cooling the system by forced convection (and in principle by radiation), when those means of heat dissipation - are available. The work includes a thermal analysis for the Aluminum - PCM heat sink and a series of validation tests of a model. The paper presents results of the analysis and results of the tests, including comparison to the classical robust solution. A parametric performance envelope for customizing to other potential applications is presented as well.

Digital selective growth of a ZnO nanowire array by large scale laser decomposition of zinc acetate.

PubMed

Hong, Sukjoon; Yeo, Junyeob; Manorotkul, Wanit; Kang, Hyun Wook; Lee, Jinhwan; Han, Seungyong; Rho, Yoonsoo; Suh, Young Duk; Sung, Hyung Jin; Ko, Seung Hwan

2013-05-07

We develop a digital direct writing method for ZnO NW micro-patterned growth on a large scale by selective laser decomposition of zinc acetate. For ZnO NW growth, by replacing the bulk heating with the scanning focused laser as a fully digital local heat source, zinc acetate crystallites can be selectively activated as a ZnO seed pattern to grow ZnO nanowires locally on a larger area. Together with the selective laser sintering process of metal nanoparticles, more than 10,000 UV sensors have been demonstrated on a 4 cm × 4 cm glass substrate to develop all-solution processible, all-laser mask-less digital fabrication of electronic devices including active layer and metal electrodes without any conventional vacuum deposition, photolithographic process, premade mask, high temperature and vacuum environment.

Computer simulation of the Farley-Buneman instability and anomalous electron heating in the auroral ionosphere

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

Machida, S.; Goertz, C.K.

1988-09-01

We study the nonlinear saturation of the Farley-Buneman instability in a collisional plasma by a 2 1/2 dimensional electrostatic particle simulation which includes inelastic and elastic collisions of electrons and elastic collision of ions with neutrals. In our simulation, a uniform convection electric field is applied externally so that the relative velocity between the electrons and ions is greater than the ion sound speed and destabilizes the instability. We find a nonlinear frequency shift from higher to lower frequencies and diffusion of the wave spectrum in two dimensional wave number space. We are especially interested in finding whether the saturatedmore » wave turbulence can account for the anomalous heating rates observed in the polar ionosphere by Schlegel and St.-Maurice (1981). We find that the dominant mechanism for electron heating is due to an enhanced effective electron collision frequency and hence enhanced resistive heating as suggested by Primdahl (1986) and Robinson (1986) and not due to the heating of electrons by the electric field of the waves parallel to the magnetic field. For the ionospheric conditions discussed by Schlegel and St.-Maurice (1981) we find an anomalous heating rate of about 4 x 10/sup -7/ W/m/sup 3/. copyright American Geophysical Union 1988« less

Observation of Electron Bernstein Wave Heating in the RFP

NASA Astrophysics Data System (ADS)

Seltzman, Andrew; Anderson, Jay; Goetz, John; Forest, Cary

2017-10-01

The first observation of RF heating in a reversed field pinch (RFP) using the electron Bernstein wave (EBW) has been demonstrated on MST. Efficient mode conversion of an outboard-launched X mode wave at 5.5 GHz leads to Doppler-shifted resonant absorption (ωrf = nωce-k||v||) for a broad range (n =1-7) of harmonics. The dynamics of EBW-heated electrons are measured using a spatial distribution of solid targets with diametrically opposed x-ray detectors. EBW heating produces a clear supra-thermal electron tail in MST. Radial deposition of the EBW is controlled with |B|and is measured using the HXR flux emitted from an insertable probe. In the thick-shelled MST RFP, the radial accessibility of EBW is limited to r/a >0.8 ( 10cm) by magnetic field error induced by the porthole necessary for the antenna. Experimental measurements show EBW propagation inward through a stochastic magnetic field. EBW-heated test electrons are used as a direct probe of edge (r/a >0.9) radial transport, showing a modest transition from `standard' to reduced-tearing RFP operation. Electron loss is too fast for collisional effects and implies a large non-collisional radial diffusivity. EBW heating has been demonstrated in reduced magnetic stochasticity plasmas with β = 15-20%. Work supported by USDOE.

Improved silicon nitride for advanced heat engines

NASA Technical Reports Server (NTRS)

Yeh, Harry C.; Fang, Ho T.

1991-01-01

The results of a four year program to improve the strength and reliability of injection-molded silicon nitride are summarized. Statistically designed processing experiments were performed to identify and optimize critical processing parameters and compositions. Process improvements were monitored by strength testing at room and elevated temperatures, and microstructural characterization by optical, scanning electron microscopes, and scanning transmission electron microscope. Processing modifications resulted in a 20 percent strength and 72 percent Weibull slope improvement of the baseline material. Additional sintering aids screening and optimization experiments succeeded in developing a new composition (GN-10) capable of 581.2 MPa at 1399 C. A SiC whisker toughened composite using this material as a matrix achieved a room temperature toughness of 6.9 MPa m(exp .5) by the Chevron notched bar technique. Exploratory experiments were conducted on injection molding of turbocharger rotors.

Carbon activation process for increased surface accessibility in electrochemical capacitors

DOEpatents

Doughty, Daniel H.; Eisenmann, Erhard T.

2001-01-01

A process for making carbon film or powder suitable for double capacitor electrodes having a capacitance of up to about 300 F/cm.sup.3 is disclosed. This is accomplished by treating in aqueous nitric acid for a period of about 5 to 15 minutes thin carbon films obtained by carbonizing carbon-containing polymeric material having a high degree of molecular directionality, such as polyimide film, then heating the treated carbon film in a non-oxidizing atmosphere at a non-graphitizing temperature of at least 350.degree. C. for about 20 minutes, and repeating alternately the nitric acid step and the heating step from 7 to 10 times. Capacitors made with this carbon may find uses ranging from electronic devices to electric vehicle applications.

Rapid Cellulose-Mediated Microwave Sintering for High-Conductivity Ag Patterns on Paper.

PubMed

Jung, Sunshin; Chun, Su Jin; Shon, Chae-Hwa

2016-08-10

Cellulose-based paper is essential in everyday life, but it also has further potentials for use in low-cost, printable, disposable, and eco-friendly electronics. Here, a method is developed for the cellulose-mediated microwave sintering of Ag patterns on conventional paper, in which the paper plays a significant role both as a flexible insulating substrate for the conductive Ag pattern and as a lossy dielectric media for rapid microwave heating. The anisotropic dielectric properties of the cellulose fibers mean that a microwave electric field applied parallel to the paper substrate provides sufficient heating to produce Ag patterns with a conductivity 29-38% that of bulk Ag in a short period of time (∼1 s) at 250-300 °C. Significantly, there is little thermal degradation of the substrate during this process. The microwave-sintered Ag patterns exhibit good mechanical stability against 10 000 bending cycles and can be easily soldered with lead-free solder. Therefore, cellulose-mediated microwave sintering presents a promising means of achieving short processing times and high electrical performance in flexible paper electronics.

Precipitation phases at different processes and heat treat ments as well as their effects on the mechanical properties of super-austenitic stainless steel

NASA Astrophysics Data System (ADS)

Sun, Hunying; Zhou, Zhangjian; Wang, Man; Li, Shaofu; Zhang, Liwei; Zou, Lei

2013-03-01

A new type lCr30Ni30Mo2TiZr super-austenitic stainless steel has been developed. The microstructures, precipitation phases and mechanical properties of the steel under different deformation processes and heat treatment (solution, stabilized treatment) were investigated using X-ray Diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) as well as mechanical tests. The results indicate that coarse carbides such as Cr-rich M23C6, sigma (σ), and little chi (χ) phases were formed in the steel, and large α' -Cr phases were also detected at three joint grain boundaries, and they were promoted by large strain. The precipitate phases were dissolved or transformed to intermetallic phase even at higher elevated temperature, and influenced the mechanical property obviously. These intermetallic compounds seriously reduced elongation of the rolled steel at room temperature and 700 °C, but increased the forged one at 700 °C. Impact absorbed energies of the stabilized specimens were lower than half of that solution status.

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

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

At present, single-phase liquid, forced convection cooled heat sinks with fins are used to cool power electronics in hybrid electric vehicles (HEVs). Although use of fins in the cooling channels increases heat transfer rates considerably, a second low-temperature radiator and associated pumping system are still required in HEVs. This additional cooling system adds weight and cost while decreasing the efficiency of HEVs. With the objective of eliminating this additional low-temperature radiator and pumping system in HEVs, an alternative cooling technology, subcooled boiling in the cooling channels, was investigated in the present study. Numerical heat transfer simulations were performed using subcooledmore » boiling in the power electronics cooling channels with the coolant supplied from the existing main engine cooling system. Results show that this subcooled boiling system is capable of removing 25% more heat from the power electronics than the conventional forced convection cooling technology, or it can reduce the junction temperature of the power electronics at the current heat removal rate. With the 25% increased heat transfer option, high heat fluxes up to 250 W/cm(2) (typical for wideband-gap semiconductor applications) are possible by using the subcooled boiling system.« less

Photoemission, NMR, susceptibility and specific heat in V and A15 V 3Pt

NASA Astrophysics Data System (ADS)

Amamou, A.; Turek, P.; Kuentzler, R.

1982-08-01

We present a study on the electronic structure of V and V 3Pt, based on photoemission (XPS and UPS) measurements and on the examination of previous band calculations, specific heat, susceptibility and NMR results. Photoemission spectra on pure V, in particular the XPS one, show a good agreement with band calculations ; the He II spectrum exhibits a strong satellite which could be attributed to a simple Auger effect or to a resonant process. Photoemission on V 3Pt allows an evaluation of the partial densities of states (PDOS) ; the Vanadium PDOS is similar to that of pure element, at least for the upper part of the valence band ; meanwhile the Platinium partial EDOS is drastically modified. This can be understood in the framework of electronic structure of compounds involving early and late transition metals where the atomic structure seems to play an important role. An evaluation of the EDOS's at the Fermi level n(E F) can also be tempted and compared to those obtained from the other mentioned techniques. Therefore it is suggested that for Vanadium n(E F) is similar to that of pure element ; for Platinium n(E F) is strongly reduced. Finally the analysis of the electronic specific heat of V, Pt and V 3Pt indicates that the parameter of electron-phonon coupling determined by the Mc Millan's theory is likely underesti:ated, due to the occurence of an estimated coupling in V and V 3Pt.

Correlation between core ion energization, suprathermal electron bursts, and broadband ELF plasma waves

NASA Astrophysics Data System (ADS)

Knudsen, David J.; Clemmons, James H.; Wahlund, Jan-Erik

1998-03-01

Observations of the lowest energy or core ions provide a particularly sensitive measure of the early stages of auroral ion energization. Freja satellite observations of 0-20 eV core ions in the topside auroral ionosphere and cusp/cleft show signs of heating within both regions of VLF hiss and broadband ELF plasma waves. However, heating to several eV or more is associated predominantly with the ELF waves. A correlation analysis of wave and core ion data formed from orbital segments shows that, on average, correlations are highest for wave frequencies below several hundred Hz, and less at VLF hiss frequencies. A similar analysis shows a higher correlation between electron precipitation and ion heating for electron energies below several hundred eV (i.e., the energies associated with suprathermal electron bursts) and a lower correlation above the 1 keV energies associated with auroral inverted-V's. Signs of core ion heating begin to appear when wave power at the O+ gyrofrequency exceeds about 10-3(mVm-1)2/Hz, and when the integrated field-aligned electron flux exceeds a few times 107cm-2s-1sr-1. This electron energy flux threshold is at least an order of magnitude lower than previously inferred from earlier studies comparing suprathermal electron fluxes and energetic ions. Almost all observed heating events occur during enhanced or active geomagnetic conditions; i.e., Kp>=4. While the most intense core ion heating is correlated with broadband ELF waves, we also present one example of weak ion heating of a few eV in a region of VLF auroral hiss.

Whistler turbulence heating of electrons and ions: Three-dimensional particle-in-cell simuations

DOE PAGES

Gary, S. Peter; Hughes, R. Scott; Wang, Joseph

2016-01-14

In this study, the decay of whistler turbulence in a collisionless, homogeneous, magnetized plasma is studied using three-dimensional particle-in-cell simulations. The simulations are initialized with a narrowband, relatively isotropic distribution of long wavelength whistler modes. A first ensemble of simulations at electron betamore » $${\\beta }_{{\\rm{e}}}$$ = 0.25 and ion-to-electron mass ratio $${m}_{{\\rm{i}}}$$/$${m}_{{\\rm{e}}}$$ = 400 is carried out on a domain cube of dimension $$L{\\omega }_{\\mathrm{pi}}$$/c = 5.12 where $${\\omega }_{\\mathrm{pi}}$$ is the ion plasma frequency. The simulations begin with a range of dimensionless fluctuating field energy densities, $${\\epsilon }_{{\\rm{o}}}$$, and follow the fluctuations as they cascade to broadband, anisotropic turbulence which dissipates at shorter wavelengths, heating both electrons and ions. The electron heating is stronger and preferentially parallel/antiparallel to the background magnetic field $${{\\boldsymbol{B}}}_{{\\rm{o}}};$$ the ion energy gain is weaker and is preferentially in directions perpendicular to $${{\\boldsymbol{B}}}_{{\\rm{o}}}$$. The important new results here are that, over 0.01 < $${\\epsilon }_{{\\rm{o}}}$$ < 0.25, the maximum rate of electron heating scales approximately as $${\\epsilon }_{{\\rm{o}}}$$, and the maximum rate of ion heating scales approximately as $${\\epsilon }_{{\\rm{o}}}^{1.5}$$. A second ensemble of simulations at $${\\epsilon }_{{\\rm{o}}}$$ = 0.10 and $${\\beta }_{{\\rm{e}}}$$ = 0.25 shows that, over 25 < $${m}_{{\\rm{i}}}$$/$${m}_{{\\rm{e}}}\\;$$< 1836, the ratio of the maximum ion heating rate to the maximum electron heating rate scales approximately as $${m}_{{\\rm{e}}}$$/$${m}_{{\\rm{i}}}$$.« less

ECR ion source with electron gun

DOEpatents

Xie, Z.Q.; Lyneis, C.M.

1993-10-26

An Advanced Electron Cyclotron Resonance ion source having an electron gun for introducing electrons into the plasma chamber of the ion source is described. The ion source has a injection enclosure and a plasma chamber tank. The plasma chamber is defined by a plurality of longitudinal magnets. The electron gun injects electrons axially into the plasma chamber such that ionization within the plasma chamber occurs in the presence of the additional electrons produced by the electron gun. The electron gun has a cathode for emitting electrons therefrom which is heated by current supplied from an AC power supply while bias potential is provided by a bias power supply. A concentric inner conductor and outer conductor carry heating current to a carbon chuck and carbon pusher which hold the cathode in place and also heat the cathode. In the Advanced Electron Cyclotron Resonance ion source, the electron gun replaces the conventional first stage used in prior electron cyclotron resonance ion generators. 5 figures.

Changes in the Martian atmosphere induced by auroral electron precipitation

NASA Astrophysics Data System (ADS)

Shematovich, V. I.; Bisikalo, D. V.; Gérard, J.-C.; Hubert, B.

2017-09-01

Typical auroral events in the Martian atmosphere, such as discrete and diffuse auroral emissions detected by UV spectrometers onboard ESA Mars Express and NASA MAVEN, are investigated. Auroral electron kinetic energy distribution functions and energy spectra of the upward and downward electron fluxes are obtained by electron transport calculations using the kinetic Monte Carlo model. These characteristics of auroral electron fluxes make it possible to calculate both the precipitation-induced changes in the atmosphere and the observed manifestations of auroral events on Mars. In particular, intensities of discrete and diffuse auroral emissions in the UV and visible wavelength ranges (Soret et al., 2016; Bisikalo et al., 2017; Gérard et al., 2017). For these conditions of auroral events, the analysis is carried out, and the contribution of the fluxes of precipitating electrons to the heating and ionization of the Martian atmosphere is estimated. Numerical calculations show that in the case of discrete auroral events the effect of the residual crustal magnetic field leads to a significant increase in the upward fluxes of electrons, which causes a decrease in the rates of heating and ionization of the atmospheric gas in comparison with the calculations without taking into account the residual magnetic field. It is shown that all the above-mentioned impact factors of auroral electron precipitation processes should be taken into account both in the photochemical models of the Martian atmosphere and in the interpretation of observations of the chemical composition and its variations using the ACS instrument onboard ExoMars.

Evolving non-thermal electrons in simulations of black hole accretion

NASA Astrophysics Data System (ADS)

Chael, Andrew A.; Narayan, Ramesh; Saḑowski, Aleksander

2017-09-01

Current simulations of hot accretion flows around black holes assume either a single-temperature gas or, at best, a two-temperature gas with thermal ions and electrons. However, processes like magnetic reconnection and shocks can accelerate electrons into a non-thermal distribution, which will not quickly thermalize at the very low densities found in many systems. Such non-thermal electrons have been invoked to explain the infrared and X-ray spectra and strong variability of Sagittarius A* (Sgr A*), the black hole at the Galactic Center. We present a method for self-consistent evolution of a non-thermal electron population in the general relativistic magnetohydrodynamic code koral. The electron distribution is tracked across Lorentz factor space and is evolved in space and time, in parallel with thermal electrons, thermal ions and radiation. In this study, for simplicity, energy injection into the non-thermal distribution is taken as a fixed fraction of the local electron viscous heating rate. Numerical results are presented for a model with a low mass accretion rate similar to that of Sgr A*. We find that the presence of a non-thermal population of electrons has negligible effect on the overall dynamics of the system. Due to our simple uniform particle injection prescription, the radiative power in the non-thermal simulation is enhanced at large radii. The energy distribution of the non-thermal electrons shows a synchrotron cooling break, with the break Lorentz factor varying with location and time, reflecting the complex interplay between the local viscous heating rate, magnetic field strength and fluid velocity.

Novel Self-Heated Gas Sensors Using on-Chip Networked Nanowires with Ultralow Power Consumption.

PubMed

Tan, Ha Minh; Manh Hung, Chu; Ngoc, Trinh Minh; Nguyen, Hugo; Duc Hoa, Nguyen; Van Duy, Nguyen; Hieu, Nguyen Van

2017-02-22

The length of single crystalline nanowires (NWs) offers a perfect pathway for electron transfer, while the small diameter of the NWs hampers thermal losses to tje environment, substrate, and metal electrodes. Therefore, Joule self-heating effect is nearly ideal for operating NW gas sensors at ultralow power consumption, without additional heaters. The realization of the self-heated NW sensors using the "pick and place" approach is complex, hardly reproducible, low yield, and not applicable for mass production. Here, we present the sensing capability of the self-heated networked SnO 2 NWs effectively prepared by on-chip growth. Our developed self-heated sensors exhibit a good response of 25.6 to 2.5 ppm NO 2 gas, while the response to 500 ppm H 2 , 100 ppm NH 3 , 100 ppm H 2 S, and 500 ppm C 2 H 5 OH is very low, indicating the good selectivity of the sensors to NO 2 gas. Furthermore, the detection limit is very low, down to 82 parts-per-trillion. As-obtained sensing performance under self-heating mode is nearly identical to that under external heating mode. While the power consumption under self-heating mode is extremely low, around hundreds of microwatts, as scaled-down the size of the electrode is below 10 μm. The selectivity of the sensors can be controlled simply by tuning the loading power that enables simple detection of NO 2 in mixed gases. Remarkable performance together with a significantly facile fabrication process of the present sensors enhances the potential application of NW sensors in next generation technologies such as electronic noses, the Internet of Things, and smartphone sensing.

[Effect of heat treatment on the structure of a Cu-Zn-Al-Ni system dental alloy].

PubMed

Guastaldi, A C; Adorno, A T; Beatrice, C R; Mondelli, J; Ishikiriama, A; Lacefield, W

1990-01-01

This article characterizes the structural phases present in the copper-based metallic alloy system "Cu-Zn-Al-Ni" developed for dental use, and relates those phases to other properties. The characterization was obtained after casting (using the lost wax process), and after heat treatment. In order to obtain better corrosion resistance by changing the microstructure, the castings were submitted to 30, 45 and 60 minutes of heat treatment at the following temperatures: 750 degrees C, 800 degrees C, and 850 degrees C. The various phases were analyzed using X-ray diffraction and scanning electron microscopy (SEM). The results after heat treatment showed a phase (probably Cu3Al), that could be responsible for the improvement in the alloy's resistance to corrosion as compared to the as-cast structure.

Whistlers, Helicons, Lower Hybrid Waves: the Physics of RF Wave Absorption Without Cyclotron Resonances

NASA Astrophysics Data System (ADS)

Pinsker, R. I.

2014-10-01

In hot magnetized plasmas, two types of linear collisionless absorption processes are used to heat and drive noninductive current: absorption at ion or electron cyclotron resonances and their harmonics, and absorption by Landau damping and the transit-time-magnetic-pumping (TTMP) interactions. This tutorial discusses the latter process, i.e., parallel interactions between rf waves and electrons in which cyclotron resonance is not involved. Electron damping by the parallel interactions can be important in the ICRF, particularly in the higher harmonic region where competing ion cyclotron damping is weak, as well as in the Lower Hybrid Range of Frequencies (LHRF), which is in the neighborhood of the geometric mean of the ion and electron cyclotron frequencies. On the other hand, absorption by parallel processes is not significant in conventional ECRF schemes. Parallel interactions are especially important for the realization of high current drive efficiency with rf waves, and an application of particular recent interest is current drive with the whistler or helicon wave at high to very high (i.e., the LHRF) ion cyclotron harmonics. The scaling of absorption by parallel interactions with wave frequency is examined and the advantages and disadvantages of fast (helicons/whistlers) and slow (lower hybrid) waves in the LHRF in the context of reactor-grade tokamak plasmas are compared. In this frequency range, both wave modes can propagate in a significant fraction of the discharge volume; the ways in which the two waves can interact with each other are considered. The use of parallel interactions to heat and drive current in practice will be illustrated with examples from past experiments; also looking forward, this tutorial will provide an overview of potential applications in tokamak reactors. Supported by the US Department of Energy under DE-FC02-04ER54698.

Thermal performance of ethylene glycol based nanofluids in an electronic heat sink.

PubMed

Selvakumar, P; Suresh, S

2014-03-01

Heat transfer in electronic devices such as micro processors and power converters is much essential to keep these devices cool for the better functioning of the systems. Air cooled heat sinks are not able to remove the high heat flux produced by the today's electronic components. Liquids work better than air in removing heat. Thermal conductivity which is the most essential property of any heat transfer fluid can be enhanced by adding nano scale solid particles which possess higher thermal conductivity than the liquids. In this work the convective heat transfer and pressure drop characteristics of the water/ethylene glycol mixture based nanofluids consisting of Al2O3, CuO nanoparticles with a volume concentration of 0.1% are studied experimentally in a rectangular channel heat sink. The nano particles are characterized using Scanning Electron Microscope and the nannofluids are prepared by using an ultrasonic vibrator and Sodium Lauryl Salt surfactant. The experimental results showed that nanofluids of 0.1% volume concentration give higher convective heat transfer coefficient values than the plain water/ethylene glycol mixture which is prepared in the volume ratio of 70:30. There is no much penalty in the pressure drop values due to the inclusion of nano particles in the water/ethylene glycol mixture.

The structure of high-temperature solar flare plasma in non-thermal flare models

NASA Technical Reports Server (NTRS)

Emslie, A. G.

1985-01-01

Analytic differential emission measure distributions have been derived for coronal plasma in flare loops heated both by collisions of high-energy suprathermal electrons with background plasma, and by ohmic heating by the beam-normalizing return current. For low densities, reverse current heating predominates, while for higher densities collisional heating predominates. There is thus a minimum peak temperature in an electron-heated loop. In contrast to previous approximate analyses, it is found that a stable reverse current can dominate the heating rate in a flare loop, especially in the low corona. Two 'scaling laws' are found which relate the peak temperature in the loop to the suprathermal electron flux. These laws are testable observationally and constitute a new diagnostic procedure for examining modes of energy transport in flaring loops.

Understanding catalyst behavior during in situ heating through simultaneous secondary and transmitted electron imaging

DOE PAGES

Howe, Jane Y.; Allard, Jr., Lawrence Frederick; Demers, Hendrix; ...

2014-11-14

In situ heating study via a simultaneous secondary electron (SE) and transmitted electron (TE) microscopy is extremely insightful because information from the surface (SE) and bulk (TE) can be readily obtained. The leached Au/Fe 2O 3 catalyst has voids on the surface of Fe 2O 3. Upon heating to 500 °C, voids shrank and disappeared, while internal Au species diffused to the surface to form new nanoparticles. Heating in vacuum reduced Fe 2O 3 to Fe 3O 4. Heating at 700 °C caused coalescence and growth of Au particles and formation of faceted Fe 3O 4 surfaces. We achieved 1.1more » nm resolution in SE imaging during in situ heating.« less

Tracing Chromospheric Evaporation in Radio and Soft X-rays

NASA Technical Reports Server (NTRS)

Aschwanden, Markus J.

1997-01-01

There are three publications in refereed journals and several presentations at scientific conferences resulted from this work, over a period of 6 months during 1995/1996. In the first paper, the discovery of the chromospheric evaporation process at radio wavelengths is described. In the second paper, the radio detection is used to quantify electron densities in the upflowing heated plasma in flare loops, which is then compared with independent other density measurements from soft X-rays, or the plasma frequency of electron beams originating in the acceleration region. In the third paper, the diagnostic results of the chromospheric evaporation process are embedded into a broader picture of a standard flare scenario. Abstracts of these three papers are attached.

Amorphization and Directional Crystallization of Metals Confined in Carbon Nanotubes Investigated by in Situ Transmission Electron Microscopy.

PubMed

Tang, Dai-Ming; Ren, Cui-Lan; Lv, Ruitao; Yu, Wan-Jing; Hou, Peng-Xiang; Wang, Ming-Sheng; Wei, Xianlong; Xu, Zhi; Kawamoto, Naoyuki; Bando, Yoshio; Mitome, Masanori; Liu, Chang; Cheng, Hui-Ming; Golberg, Dmitri

2015-08-12

The hollow core of a carbon nanotube (CNT) provides a unique opportunity to explore the physics, chemistry, biology, and metallurgy of different materials confined in such nanospace. Here, we investigate the nonequilibrium metallurgical processes taking place inside CNTs by in situ transmission electron microscopy using CNTs as nanoscale resistively heated crucibles having encapsulated metal nanowires/crystals in their channels. Because of nanometer size of the system and intimate contact between the CNTs and confined metals, an efficient heat transfer and high cooling rates (∼10(13) K/s) were achieved as a result of a flash bias pulse followed by system natural quenching, leading to the formation of disordered amorphous-like structures in iron, cobalt, and gold. An intermediate state between crystalline and amorphous phases was discovered, revealing a memory effect of local short-to-medium range order during these phase transitions. Furthermore, subsequent directional crystallization of an amorphous iron nanowire formed by this method was realized under controlled Joule heating. High-density crystalline defects were generated during crystallization due to a confinement effect from the CNT and severe plastic deformation involved.

Evaluation of the AISI 904L Alloy Weld Overlays Obtained by GMAW and Electro-Slag Welding Processes

NASA Astrophysics Data System (ADS)

Jorge, Jorge C. F.; Meira, O. G.; Madalena, F. C. A.; de Souza, L. F. G.; Araujo, L. S.; Mendes, M. C.

2017-05-01

The use of superaustenitic stainless steels (SASS) as an overlay replacement for nickel-based alloys can be an interesting alternative for the oil and gas industries, due to its lower cost, when compared to superalloys. Usually, the deposition is made with several welding passes by using conventional arc welding processes, such as gas tungsten arc welding (GTAW) or gas metal arc welding (GMAW) processes. In this respect, electro-slag welding (ESW), which promotes high heat inputs and low dilution of the welds, can also be attractive for this application, as it provides a higher productivity, once only one layer is needed for the deposition of the minimum thickness required. The present work evaluates the behavior of an AISI 904L SASS weld overlay deposited on a carbon steel ASTM A516 Grade 70 by ESW and GMAW processes. Both as-welded and heat-treated conditions were evaluated and compared. A multipass welding by GMAW process with three layers and 48 passes was performed on 12.5 × 200 × 250 mm steel plates with average welding energy of 1.0 kJ/mm. For ESW process, only one layer was deposited on 50 × 400 × 400 mm steel plates with average welding energy of 11.7 kJ/mm. After welding, a post-weld heat treatment (PWHT) at 620 °C for 10 h was performed in half of the steel plate, in order to allow the comparison between this condition and the as-welded one. For both processes, the austenitic microstructure of the weld deposits was characterized by optical microscopy and scanning electron microscopy with electron backscatter diffraction. A low proportion of secondary phases were observed in all conditions, and the PWHT did not promote significant changes on the hardness profile. Martensite for GMAW process and bainite for ESW process were the microstructural constituents observed at the coarse grain heat-affected zone, due to the different cooling rates. For ESW process, no evidences of partially diluted zones were found. As a consequence of the microstructural findings, the hardness results for ESW were lower than those usually observed for other electric arc welding processes. In addition, specimens subject to bending tests performed in accordance with the current standards used for qualification of welding procedures were approved. These evidences allow the conclusion that the ESW process can provide deposits with high quality despite the high welding energy levels, in order to achieve the desired productivity, being an interesting alternative for AISI 904L weld overlays.

Electron emission from diamond films seeded using kitchen-wrap polyethylene

NASA Astrophysics Data System (ADS)

Varshney, D.; Makarov, V. I.; Saxena, P.; Guinel, M. J. F.; Kumar, A.; Scott, J. F.; Weiner, B. R.; Morell, G.

2011-03-01

Diamond has many potential electronic applications, but the diamond seeding methods are generally harsh on the substrates rendering them unsuitable for integration in electronics. We report a non-abrasive, scalable and economic process of diamond film seeding using kitchen-wrap polyethylene employing hot filament chemical vapour reaction of H2S/CH4/H2 gas mixtures on Cu substrates. The fabricated diamond films were characterized with scanning electron microscopy, transmission electron microscopy and Raman spectroscopy, which confirm that the deposited film consists of a microcrystalline diamond of size in the range 0.5-1.0 µm. The synthesized diamond films exhibit a turn-on field of about 8.5 V µm-1 and long-term stability. Diamond film synthesis using polyethylene will enable the integration of diamond heat sinks into high-power and high-temperature electronic devices.

Nitrogen-Doped Carbon Fiber Paper by Active Screen Plasma Nitriding and Its Microwave Heating Properties.

PubMed

Zhu, Naishu; Ma, Shining; Sun, Xiaofeng

2016-12-28

In this paper, active screen plasma nitriding (ASPN) treatment was performed on polyacrylonitrile carbon fiber papers. Electric resistivity and microwave loss factor of carbon fiber were described to establish the relationship between processing parameters and fiber's ability to absorb microwaves. The surface processing effect of carbon fiber could be characterized by dynamic thermal mechanical analyzer testing on composites made of carbon fiber. When the process temperature was at 175 °C, it was conducive to obtaining good performance of dynamical mechanical properties. The treatment provided a way to change microwave heating properties of carbon fiber paper by performing different treatment conditions, such as temperature and time parameters. Atomic force microscope, scanning electron microscope, and X-ray photoelectron spectroscopy analysis showed that, during the course of ASPN treatment on carbon fiber paper, nitrogen group was introduced and silicon group was removed. The treatment of nitrogen-doped carbon fiber paper represented an alternative promising candidate for microwave curing materials used in repairing and heating technology, furthermore, an efficient dielectric layer material for radar-absorbing structure composite in metamaterial technology.

Numerical modeling of materials processing applications of a pulsed cold cathode electron gun

NASA Astrophysics Data System (ADS)

Etcheverry, J. I.; Martínez, O. E.; Mingolo, N.

1998-04-01

A numerical study of the application of a pulsed cold cathode electron gun to materials processing is performed. A simple semiempirical model of the discharge is used, together with backscattering and energy deposition profiles obtained by a Monte Carlo technique, in order to evaluate the energy source term inside the material. The numerical computation of the heat equation with the calculated source term is performed in order to obtain useful information on melting and vaporization thresholds, melted radius and depth, and on the dependence of these variables on processing parameters such as operating pressure, initial voltage of the discharge and cathode-sample distance. Numerical results for stainless steel are presented, which demonstrate the need for several modifications of the experimental design in order to achieve a better efficiency.

Reversible electron heating vs. wave-particle interactions in quasi-perpendicular shocks

NASA Technical Reports Server (NTRS)

Veltri, P.; Mangeney, A.; Scudder, J. D.

1992-01-01

The energy necessary to explain the electron heating in quasi-perpendicular collisionless shocks can be derived either from the electron acceleration in the d.c. cross shock electric potential, or by the interactions between the electrons and the waves existing in the shock. A Monte Carlo simulation has been performed to study the electron distribution function evolution through the shock structure, with and without particle diffusion on waves. This simulation has allowed us to clarify the relative importance of the two possible energy sources; in particular it has been shown that the electron parallel temperature is determined by the d.c. electromagnetic field and not by any wave-particle-induced heating. Wave particle interactions are effective in smoothing out the large gradients in phase space produced by the 'reversible' motion of the electrons, thus producing a 'cooling' of the electrons.

Electron Energetics in the Martian Dayside Ionosphere: Model Comparisons with MAVEN Data

NASA Technical Reports Server (NTRS)

Sakai, Shotaro; Andersson, Laila; Cravens, Thomas E.; Mitchell, David L.; Mazelle, Christian; Rahmati, Ali; Fowler, Christopher M.; Bougher, Stephen W.; Thiemann, Edward M. B.; Epavier, Francis G.;

Aircraft skin cooling system for thermal management of onboard high power electronic equipment

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

Hashemi, A.; Dyson, E.

1996-12-31

Integration of high-power electronic devices into existing aircraft, while minimizing the impact of additional heat load on the environmental control system of the aircraft, requires innovative approaches. One such approach is to reject heat through the aircraft skin by use of internal skin ducts with enhanced surfaces. This approach requires a system level consideration of the effect of cooling ducts, inlets and outlets on the performance of the electronic equipment and effectiveness of the heat rejection system. This paper describes the development of a system-level model to evaluate the performance of electronic equipment in an aircraft cabin and heat rejectionmore » through the skin. In this model, the outer surface of the fuselage is treated as a heat exchanger. Hot air from an equipment exhaust plenum is drawn into a series of baffled ducts within the fuselage support structure, where the heat is rejected, and then recirculated into the cabin. The cooler air form the cabin is then drawn into the electronic equipment. The aircraft air conditioning unit is also modeled to provide chilled air directly into the cabin. In addition, this paper describes a series of tests which were performed to verify the model assumptions for heat dissipation from and air flow through the equipment. The tests were performed using the actual electronic equipment in a representative cabin configuration. Results indicate very good agreement between the analytical calculations for the design point and model predictions.« less

Heat capacity of free electrons at the degenerate-nondegenerate transition

NASA Astrophysics Data System (ADS)

Nimtz, G.; Stadler, J. P.

1985-04-01

In this Brief Report the heat capacity of an electron gas at the degenerate-nondegenerate transition is presented. The values are deduced from hot-carrier data of InSb with ~=1014 electrons/cm3 determined by Maneval, Zylberstejn, and Budd.

Anomalous electron heating effects on the E region ionosphere in TIEGCM

NASA Astrophysics Data System (ADS)

Liu, Jing; Wang, Wenbin; Oppenheim, Meers; Dimant, Yakov; Wiltberger, Michael; Merkin, Slava

2016-03-01

We have recently implemented a new module that includes both the anomalous electron heating and the electron-neutral cooling rate correction associated with the Farley-Buneman Instability (FBI) in the thermosphere-ionosphere electrodynamics global circulation model (TIEGCM). This implementation provides, for the first time, a modeling capability to describe macroscopic effects of the FBI on the ionosphere and thermosphere in the context of a first-principle, self-consistent model. The added heating sources primarily operate between 100 and 130 km altitude, and their magnitudes often exceed auroral precipitation heating in the TIEGCM. The induced changes in E region electron temperature in the auroral oval and polar cap by the FBI are remarkable with a maximum Te approaching 2200 K. This is about 4 times larger than the TIEGCM run without FBI heating. This investigation demonstrates how researchers can add the important effects of the FBI to magnetosphere-ionosphere-thermosphere models and simulators.

Residual stress prediction in a powder bed fusion manufactured Ti6Al4V hip stem

NASA Astrophysics Data System (ADS)

Barrett, Richard A.; Etienne, Titouan; Duddy, Cormac; Harrison, Noel M.

2017-10-01

Powder bed fusion (PBF) is a category of additive manufacturing (AM) that is particularly suitable for the production of 3D metallic components. In PBF, only material in the current build layer is at the required melt temperature, with the previously melted and solidified layers reducing in temperature, thus generating a significant thermal gradient within the metallic component, particularly for laser based PBF components. The internal thermal stresses are subsequently relieved in a post-processing heat-treatment step. Failure to adequately remove these stresses can result in cracking and component failure. A prototype hip stem was manufactured from Ti6Al4V via laser PBF but was found to have fractured during over-seas shipping. This study examines the evolution of thermal stresses during the laser PBF manufacturing and heat treatment processes of the hip stem in a 2D finite element analysis (FEA) and compares it to an electron beam PBF process. A custom written script for the automatic conversion of a gross geometry finite element model into a thin layer- by-layer finite element model was developed. The build process, heat treatment (for laser PBF) and the subsequent cooling were simulated at the component level. The results demonstrate the effectiveness of the heat treatment in reducing PBF induced thermal stresses, and the concentration of stresses in the region that fractured.

Thermal Enhancement of Silicon Carbide (SiC) Power Electronics and Laser Bars: Statistical Design Optimization of a Liquid-Cooled Power Electronic Heat Sink

DTIC Science & Technology

2015-08-01

Forced Convective Heat Transfer Across a Pin Fin Micro Heat Sink”, International Journal of Heat and Mass Transfer 48 (2005) 3615-3627. 3. Cao...from Pin Fins Situated in an Oncoming Longitudinal Flow Which Turns to Crossflow”, International Journal of Heat and Mass Transfer, Vol. 25 No. 5...Flow Forced Convection”, International Journal of Heat and Mass Transfer, Vol. 39, No. 2, pp. 311-317, 1996. 11. Khan, W., Culham, J., and Yovanovich

Surface modification of steels and magnesium alloy by high current pulsed electron beam

NASA Astrophysics Data System (ADS)

Hao, Shengzhi; Gao, Bo; Wu, Aimin; Zou, Jianxin; Qin, Ying; Dong, Chuang; An, Jian; Guan, Qingfeng

2005-11-01

High current pulsed electron beam (HCPEB) is now developing as a useful tool for surface modification of materials. When concentrated electron flux transferring its energy into a very thin surface layer within a short pulse time, superfast processes such as heating, melting, evaporation and consequent solidification, as well as dynamic stress induced may impart the surface layer with improved physico-chemical and mechanical properties. This paper presents our research work on surface modification of steels and magnesium alloy with HCPEB of working parameters as electron energy 27 keV, pulse duration ∼1 μs and energy density ∼2.2 J/cm2 per pulse. Investigations performed on carbon steel T8, mold steel D2 and magnesium alloy AZ91HP have shown that the most pronounced changes of phase-structure state and properties occurring in the near-surface layers, while the thickness of the modified layer with improved microhardness (several hundreds of micrometers) is significantly greater than that of the heat-affected zone. The formation mechanisms of surface cratering and non-stationary hardening effect in depth are discussed based on the elucidation of non-equilibrium temperature filed and different kinds of stresses formed during pulsed electron beam melting treatment. After the pulsed electron beam treatments, samples show significant improvements in measurements of wear and corrosion resistance.

Low Temperature Specific Heat in Lightly Mn-Substituted Electron-Doped SrTiO3

NASA Astrophysics Data System (ADS)

Okuda, Tetsuji; Hata, Hiroto; Eto, Takahiro; Sobaru, Shogo; Oda, Ryosuke; Noda, Masaaki; Kuwahara, Hideki

2017-08-01

We found large changes in the low-temperature specific heat (low-T C) in the lightly Mn-substituted electron-doped perovskites Sr0.95La0.05Ti1-yMnzO3 with y = 0.02 and 0.04 by applying magnetic fields up to 9 T. The changes in the low-T C are qualitatively well explained by the Schottky specific heat (CSch) of localized spins of the Mn 3d electrons in weak internal magnetic fields via itinerant electrons. However, the actual numbers of localized spins estimated from CSch are about 30% smaller than the expected values. Part of the localized spins of the Mn 3d electrons may disappear due to Kondo coupling with the itinerant electrons.

A Generalized Electron Heat Flow Relation and its Connection to the Thermal Force and the Solar Wind Parallel Electric Field

NASA Astrophysics Data System (ADS)

Scudder, J. D.

2017-12-01

Enroute to a new formulation of the heat law for the solar wind plasma the role of the invariably neglected, but omnipresent, thermal force for the multi-fluid physics of the corona and solar wind expansion will be discussed. This force (a) controls the size of the collisional ion electron energy exchange, favoring the thermal vs supra thermal electrons; (b) occurs whenever heat flux occurs; (c) remains after the electron and ion fluids come to a no slip, zero parallel current, equilibrium; (d) enhances the equilibrium parallel electric field; but (e) has a size that is theoretically independent of the electron collision frequency - allowing its importance to persist far up into the corona where collisions are invariably ignored in first approximation. The constituent parts of the thermal force allow the derivation of a new generalized electron heat flow relation that will be presented. It depends on the separate field aligned divergences of electron and ion pressures and the gradients of the ion gravitational potential and parallel flow energies and is based upon a multi-component electron distribution function. The new terms in this heat law explicitly incorporate the astrophysical context of gradients, acceleration and external forces that make demands on the parallel electric field and quasi-neutrality; essentially all of these effects are missing in traditional formulations.

Electronic modules easily separated from heat sink

NASA Technical Reports Server (NTRS)

1965-01-01

Metal heat sink and electronic modules bonded to a thermal bridge can be easily cleaved for removal of the modules for replacement or repair. A thin film of grease between a fluorocarbon polymer film on the metal heat sink and an adhesive film on the modules acts as the cleavage plane.

Evolution and Control of 2219 Aluminum Microstructural Features through Electron Beam Freeform Fabrication

NASA Technical Reports Server (NTRS)

Taminger, Karen M.; Hafley, Robert A.; Domack, Marcia S.

2006-01-01

Electron beam freeform fabrication (EBF3) is a new layer-additive process that has been developed for near-net shape fabrication of complex structures. EBF3 uses an electron beam to create a molten pool on the surface of a substrate. Wire is fed into the molten pool and the part translated with respect to the beam to build up a 3-dimensional structure one layer at a time. Unlike many other freeform fabrication processes, the energy coupling of the electron beam is extremely well suited to processing of aluminum alloys. The layer-additive nature of the EBF3 process results in a tortuous thermal path producing complex microstructures including: small homogeneous equiaxed grains; dendritic growth contained within larger grains; and/or pervasive dendritic formation in the interpass regions of the deposits. Several process control variables contribute to the formation of these different microstructures, including translation speed, wire feed rate, beam current and accelerating voltage. In electron beam processing, higher accelerating voltages embed the energy deeper below the surface of the substrate. Two EBF3 systems have been established at NASA Langley, one with a low-voltage (10-30kV) and the other a high-voltage (30-60 kV) electron beam gun. Aluminum alloy 2219 was processed over a range of different variables to explore the design space and correlate the resultant microstructures with the processing parameters. This report is specifically exploring the impact of accelerating voltage. Of particular interest is correlating energy to the resultant material characteristics to determine the potential of achieving microstructural control through precise management of the heat flux and cooling rates during deposition.

Electron-phonon mediated heat flow in disordered graphene

NASA Astrophysics Data System (ADS)

Chen, Wei; Clerk, Aashish A.

2012-09-01

We calculate the heat flux and electron-phonon thermal conductance in a disordered graphene sheet, going beyond a Fermi’s golden rule approach to fully account for the modification of the electron-phonon interaction by disorder. Using the Keldysh technique combined with standard impurity averaging methods in the regime kFl≫1 (where kF is the Fermi wave vector and l is the mean free path), we consider both scalar potential (i.e., deformation potential) and vector-potential couplings between electrons and phonons. We also consider the effects of electronic screening at the Thomas-Fermi level. We find that the temperature dependence of the heat flux and thermal conductance is sensitive to the presence of disorder and screening, and reflects the underlying chiral nature of electrons in graphene and the corresponding modification of their diffusive behavior. In the case of weak screening, disorder enhances the low-temperature heat flux over the clean system (changing the associated power law from T4 to T3), and the deformation potential dominates. For strong screening, both the deformation potential and vector-potential couplings make comparable contributions, and the low-temperature heat flux obeys a T5 power law.

The frequency dependence of the discharge properties in a capacitively coupled oxygen discharge

NASA Astrophysics Data System (ADS)

Gudmundsson, J. T.; Snorrason, D. I.; Hannesdottir, H.

2018-02-01

We use the one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 to explore the evolution of the charged particle density profiles, electron heating mechanism, the electron energy probability function (EEPF), and the ion energy distribution in a single frequency capacitively coupled oxygen discharge, with driving frequency in the range 12-100 MHz. At a low driving frequency and low pressure (5 and 10 mTorr), a combination of stochastic (α-mode) and drift ambipolar (DA) heating in the bulk plasma (the electronegative core) is observed and the DA-mode dominates the time averaged electron heating. As the driving frequency or pressure are increased, the heating mode transitions into a pure α-mode, where electron heating in the sheath region dominates. At low pressure (5 and 10 mTorr), this transition coincides with a sharp decrease in electronegativity. At low pressure and low driving frequency, the EEPF is concave. As the driving frequency is increased, the number of low energy electrons increases and the relative number of higher energy electrons (>10 eV) increases. At high driving frequency, the EEPF develops a convex shape or becomes bi-Maxwellian.

Radiative properties of advanced spacecraft heat shield materials

NASA Technical Reports Server (NTRS)

Cunnington, G. R.; Funai, A. I.; Mcnab, T. K.

1983-01-01

Experimental results are presented to show the effects of simulated reentry exposure by convective heating and by radiant heating on spectral and total emittance of statically oxidized Inconel 617 and Haynes HS188 superalloys to 1260 K and a silicide coatea (R512E) columbium 752 alloy to 1590 K. Convective heating exposures were conducted in a supersonic arc plasma wind tunnel using a wedge-shaped specimen configuration. Radiant tests were conducted at a pressure of .003 atmospheres of dry air at a flow velocity of several meters per second. Convective heating specimens were subjected to 8, 20, and 38 15-min heating cycles, and radiant heating specimens were tested for 10, 20, 50, and 100 30-min heating cycles. Changes in radiative properties are explained in terms of changes in composition resulting from simulated reentry tests. The methods used to evaluate morphological, compositional and crystallographic changes include: Auger electron spectroscopy; scanning electron microscopy; X-ray diffraction analysis; and electron microprobe analysis.

On electron heating in a low pressure capacitively coupled oxygen discharge

NASA Astrophysics Data System (ADS)

Gudmundsson, J. T.; Snorrason, D. I.

2017-11-01

We use the one-dimensional object-oriented particle-in-cell Monte Carlo collision code oopd1 to explore the charged particle densities, the electronegativity, the electron energy probability function, and the electron heating mechanism in a single frequency capacitively coupled oxygen discharge, when the applied voltage amplitude is varied. We explore discharges operated at 10 mTorr, where electron heating within the plasma bulk (the electronegative core) dominates, and at 50 mTorr, where sheath heating dominates. At 10 mTorr, the discharge is operated in a combined drift-ambipolar and α-mode, and at 50 mTorr, it is operated in the pure α-mode. At 10 mTorr, the effective electron temperature is high and increases with increased driving voltage amplitude, while at 50 mTorr, the effective electron temperature is much lower, in particular, within the electronegative core, where it is roughly 0.2-0.3 eV, and varies only a little with the voltage amplitude.

Applications for Gradient Metal Alloys Fabricated Using Additive Manufacturing

NASA Technical Reports Server (NTRS)

Hofmann, Douglas C.; Borgonia, John Paul C.; Dillon, Robert P.; Suh, Eric J.; Mulder, jerry L.; Gardner, Paul B.

2013-01-01

Recently, additive manufacturing (AM) techniques have been developed that may shift the paradigm of traditional metal production by allowing complex net-shaped hardware to be built up layer-by-layer, rather than being machined from a billet. The AM process is ubiquitous with polymers due to their low melting temperatures, fast curing, and controllable viscosity, and 3D printers are widely available as commercial or consumer products. 3D printing with metals is inherently more complicated than with polymers due to their higher melting temperatures and reactivity with air, particularly when heated or molten. The process generally requires a high-power laser or other focused heat source, like an electron beam, for precise melting and deposition. Several promising metal AM techniques have been developed, including laser deposition (also called laser engineered net shaping or LENS® and laser deposition technology (LDT)), direct metal laser sintering (DMLS), and electron beam free-form (EBF). These machines typically use powders or wire feedstock that are melted and deposited using a laser or electron beam. Complex net-shape parts have been widely demonstrated using these (and other) AM techniques and the process appears to be a promising alternative to machining in some cases. Rather than simply competing with traditional machining for cost and time savings, the true advantage of AM involves the fabrication of hardware that cannot be produced using other techniques. This could include parts with "blind" features (like foams or trusses), parts that are difficult to machine conventionally, or parts made from materials that do not exist in bulk forms. In this work, the inventors identify that several AM techniques can be used to develop metal parts that change composition from one location in the part to another, allowing for complete control over the mechanical or physical properties. This changes the paradigm for conventional metal fabrication, which relies on an assortment of "post-processing" methods to locally alter properties (such as coating, heat treating, work hardening, shot peening, etching, anodizing, among others). Building the final part in an additive process allows for the development of an entirely new class of metals, so-called "functionally graded metals" or "gradient alloys." By carefully blending feedstock materials with different properties in an AM process, hardware can be developed with properties that cannot be obtained using other techniques but with the added benefit of the net-shaped fabrication that AM allows.

Electron heating at interplanetary shocks

NASA Technical Reports Server (NTRS)

Feldman, W. C.; Asbridge, J. R.; Bame, S. J.; Gosling, J. T.; Zwickl, R. D.

1982-01-01

Data for 41 forward interplanetary shocks show that the ratio of downstream to upstream electron temperatures, T/sub e/(d/u) is variable in the range between 1.0 (isothermal) and 3.0. On average, (T/sub e/(d/u) = 1.5 with a standard deviation, sigma e = 0.5. This ratio is less than the average ratio of proton temperatures across the same shocks, (T/sub p/(d/u)) = 3.3 with sigma p = 2.5 as well as the average ratio of electron temperatures across the Earth's bow shock. Individual samples of T/sub e/(d/u) and T/sub p/(d/u) appear to be weakly correlated with the number density ratio. However the amounts of electron and proton heating are well correlated with each other as well as with the bulk velocity difference across each shock. The stronger shocks appear to heat the protons relatively more efficiently than they heat the electrons.

Intermittent electron density and temperature fluctuations and associated fluxes in the Alcator C-Mod scrape-off layer

NASA Astrophysics Data System (ADS)

Kube, R.; Garcia, O. E.; Theodorsen, A.; Brunner, D.; Kuang, A. Q.; LaBombard, B.; Terry, J. L.

2018-06-01

The Alcator C-Mod mirror Langmuir probe system has been used to sample data time series of fluctuating plasma parameters in the outboard mid-plane far scrape-off layer. We present a statistical analysis of one second long time series of electron density, temperature, radial electric drift velocity and the corresponding particle and electron heat fluxes. These are sampled during stationary plasma conditions in an ohmically heated, lower single null diverted discharge. The electron density and temperature are strongly correlated and feature fluctuation statistics similar to the ion saturation current. Both electron density and temperature time series are dominated by intermittent, large-amplitude burst with an exponential distribution of both burst amplitudes and waiting times between them. The characteristic time scale of the large-amplitude bursts is approximately 15 μ {{s}}. Large-amplitude velocity fluctuations feature a slightly faster characteristic time scale and appear at a faster rate than electron density and temperature fluctuations. Describing these time series as a superposition of uncorrelated exponential pulses, we find that probability distribution functions, power spectral densities as well as auto-correlation functions of the data time series agree well with predictions from the stochastic model. The electron particle and heat fluxes present large-amplitude fluctuations. For this low-density plasma, the radial electron heat flux is dominated by convection, that is, correlations of fluctuations in the electron density and radial velocity. Hot and dense blobs contribute only a minute fraction of the total fluctuation driven heat flux.

Kinetics of electron-beam dispersion of fullerite C60

NASA Astrophysics Data System (ADS)

Razanau, Ihar; Mieno, Tetsu; Kazachenko, Victor

2012-06-01

Electron-beam dispersion of pressed fullerite C60 targets in vacuum leads to the deposition of thin films containing polymeric forms of C60. The aim of the present report is to analyze physical-chemical processes in the fullerite target during its electron-beam dispersion through the analysis of the kinetics of the radiation temperature of the target surface, the coating growth rate and the density of negative current on the substrate. It was shown that the induction stage of the process is determined by the negative charging and radiation-induced modification and heating of the target. The transitional stage is characterized by nonstationary sublimation of the target material through the pores in the modified surface layer and release of the accumulated negative charge. Stabilization of the process parameters owing to the convection cooling of the target by the sublimation products and the decrease in the pressure inside the microcavities beneath the pores leads to a quasi-stationary stage of target sublimation and deposition of a coating containing polymeric forms of C60.

Reversible Quantum Brownian Heat Engines for Electrons

NASA Astrophysics Data System (ADS)

Humphrey, T. E.; Newbury, R.; Taylor, R. P.; Linke, H.

2002-08-01

Brownian heat engines use local temperature gradients in asymmetric potentials to move particles against an external force. The energy efficiency of such machines is generally limited by irreversible heat flow carried by particles that make contact with different heat baths. Here we show that, by using a suitably chosen energy filter, electrons can be transferred reversibly between reservoirs that have different temperatures and electrochemical potentials. We apply this result to propose heat engines based on mesoscopic semiconductor ratchets, which can quasistatically operate arbitrarily close to Carnot efficiency.

Reversible quantum heat engines for electrons

NASA Astrophysics Data System (ADS)

Linke, Heiner; Humphrey, Tammy E.; Newbury, Richard; Taylor, Richard P.

2002-03-01

Brownian heat engines use local temperature gradients in asymmetric potentials to move particles against an external force. The energy efficiency of such machines is generally limited by irreversible heat flow carried by particles that make contact with different heat baths. Here we show that, by using a suitably chosen energy filter, electrons can be transferred reversibly between reservoirs that have different temperatures and electrochemical potentials. We apply this result to propose heat engines based on quantum ratchets, which can quasistatically operate at Carnot efficiency.

The spatial distribution of VLF transmitters at topside ionosphere and the VLF-induced heating phenomena

NASA Astrophysics Data System (ADS)

Zhang, X.; Zhao, S.; Zhou, C.

2016-12-01

Based on the electric field observation at VLF frequency band onboard DEMETER satellite, the spatial distribution was studied about some VLF transmitters at different latitudes on ground, as while the maximal intensity, the attenuation rate and affected areas, including NWC and GBZ with high power, and some transmitters with low radiated power. As while the full wave propagation model is used to simulate the theoretical results at topside ionosphere. The results show that, (1) the intensity of electromagnetic waves at topside ionosphere with 1000kW radiated power is higher as one or two orders of magnitude than those with 500 kW power; (2) at same station, the amplitudes in electric field are larger with high frequency signals than those lower ones at the same station; (3) at same frequency points, the ionospheric background affected strongly the waves penetrating into the ionosphere, for the intensity of same frequency signals differed apparently at different transmitters. Due to the high energy of VLF transmitters, the heating phenomena were also observed extensively at DEMETER satellite. Here the VLF-induced ionospheric heating perturbations were selected and analyzed during the solar minimum years of 2008-2009. There are three main features in VLF heating, (1) the temperature of electron and ion increased, while the electron density and O+ density at topside ionosphere decreased; (2) the low hybrid waves were excited at 10-20kHz; (3) the plasma frequency was emitted at some points around 1.92MHz; (4) the VLF induced heating phenomena were associated closely with the radiated power of transmitters, while the transmitters with power <500kW are hard to cause the ionospheric disturbances directly. Considering the propagation and heating process of VLF electromagnetic wave, these features above were discussed and compared with HF heating processes. By learning for the man-made signals propagating from ground into ionosphere, it is helpful to further understand the coupling mechanism among different earth spheres. Acknowledgement: This paper is supported by the International Cooperation Project (2014DFR21280).

Quasi-exospheric heat flux of solar-wind electrons

NASA Technical Reports Server (NTRS)

Eviatar, A.; Schultz, M.

1975-01-01

Density, bulk-velocity, and heat-flow moments are calculated for truncated Maxwellian distributions representing the cool and hot populations of solar-wind electrons, as realized at the base of a hypothetical exosphere. The electrostatic potential is thus calculated by requiring charge quasi-neutrality and the absence of electrical current. Plasma-kinetic coupling of the cool-electron and proton bulk velocities leads to an increase in the electrostatic potential and a decrease in the heat-flow moment.

Hybrid modelling of a high-power X-ray attenuator plasma.

PubMed

Martín Ortega, Álvaro; Lacoste, Ana; Minea, Tiberiu

2018-05-01

X-ray gas attenuators act as stress-free high-pass filters for synchrotron and free-electron laser beamlines to reduce the heat load in downstream optical elements without affecting other properties of the X-ray beam. The absorption of the X-ray beam triggers a cascade of processes that ionize and heat up the gas locally, changing its density and therefore the X-ray absorption. Aiming to understand and predict the behaviour of the gas attenuator in terms of efficiency versus gas pressure, a hybrid model has been developed, combining three approaches: an analytical description of the X-ray absorption; Monte Carlo for the electron thermalization; and a fluid treatment for the electron diffusion, recombination and excited-states relaxation. The model was applied to an argon-filled attenuator prototype built and tested at the European Synchrotron Radiation Facility, at a pressure of 200 mbar and assuming stationary conditions. The results of the model showed that the electron population thermalizes within a few nanoseconds after the X-ray pulse arrival and it occurs just around the X-ray beam path, recombining in the bulk of the gas rather than diffusing to the attenuator walls. The gas temperature along the beam path reached 850 K for 770 W of incident power and 182 W m -1 of absorbed power. Around 70% of the absorbed power is released as visible and UV radiation rather than as heat to the gas. Comparison of the power absorption with the experiment showed an overall agreement both with the plasma radial profile and power absorption trend, the latter within an error smaller than 20%. This model can be used for the design and operation of synchrotron gas attenuators and as a base for a time-dependent model for free-electron laser attenuators.

Viscosity of the liquid Al-6Mg-1Mn-0.2Sc-0.1Zr alloy

NASA Astrophysics Data System (ADS)

Reznik, P. L.; Chikova, O. A.; Tsepelev, V. S.

2017-07-01

The microstructure and the phase composition of as-cast Al-Mg-Mn-Sc-Zr alloy samples are studied by electron microscopy and electron-probe microanalysis. The processes of solidification and melting of this alloy are described. The temperature dependence of the kinematic viscosity of the Al-Mg-Mn-Sc-Zr melts is studied during heating and subsequent cooling of the samples. The measurement results are used to determine the temperature at which inherited microheterogeneities in the melts are destroyed irreversibly.

Collisionless dissipation in quasi-perpendicular shocks. [in terresrial bow waves

NASA Technical Reports Server (NTRS)

Forslund, D. W.; Quest, K. B.; Brackbill, J. U.; Lee, K.

1984-01-01

Microscopic dissipation processes in quasi-perpendicular shocks are studied by two-dimensional plasma simulations in which electrons and ions are treated as particles moving in self-consistent electric and magnetic fields. Cross-field currents induce substantial turbulence at the shock front reducing the reflected ion fraction, increasing the bulk ion temperature behind the shock, doubling the average magnetic ramp thickness, and enhancing the upstream field aligned electron heat flow. The short scale length magnetic fluctuations observed in the bow shock are probably associated with this turbulence.

Vitrification of waste

DOEpatents

Wicks, G.G.

1999-04-06

A method is described for encapsulating and immobilizing waste for disposal. Waste, preferably, biologically, chemically and radioactively hazardous, and especially electronic wastes, such as circuit boards, are placed in a crucible and heated by microwaves to a temperature in the range of approximately 300 C to 800 C to incinerate organic materials, then heated further to a temperature in the range of approximately 1100 C to 1400 C at which temperature glass formers present in the waste will cause it to vitrify. Glass formers, such as borosilicate glass, quartz or fiberglass can be added at the start of the process to increase the silicate concentration sufficiently for vitrification.

Determination of crystal growth rates during rapid solidification of polycrystalline aluminum by nano-scale spatio-temporal resolution in situ transmission electron microscopy

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

Zweiacker, K.; McKeown, J. T.; Liu, C.

In situ investigations of rapid solidification in polycrystalline Al thin films were conducted using nano-scale spatio-temporal resolution dynamic transmission electron microscopy. Differences in crystal growth rates and asymmetries in melt pool development were observed as the heat extraction geometry was varied by controlling the proximity of the laser-pulse irradiation and the associated induced melt pools to the edge of the transmission electron microscopy support grid, which acts as a large heat sink. Experimental parameters have been established to maximize the reproducibility of the material response to the laser-pulse-related heating and to ensure that observations of the dynamical behavior of themore » metal are free from artifacts, leading to accurate interpretations and quantifiable measurements with improved precision. Interface migration rate measurements revealed solidification velocities that increased consistently from ~1.3 m s –1 to ~2.5 m s –1 during the rapid solidification process of the Al thin films. Under the influence of an additional large heat sink, increased crystal growth rates as high as 3.3 m s –1 have been measured. The in situ experiments also provided evidence for development of a partially melted, two-phase region prior to the onset of rapid solidification facilitated crystal growth. As a result, using the experimental observations and associated measurements as benchmarks, finite-element modeling based calculations of the melt pool evolution after pulsed laser irradiation have been performed to obtain estimates of the temperature evolution in the thin films.« less

Determination of crystal growth rates during rapid solidification of polycrystalline aluminum by nano-scale spatio-temporal resolution in situ transmission electron microscopy

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

Zweiacker, K., E-mail: Kai@zweiacker.org; Liu, C.; Wiezorek, J. M. K.

In situ investigations of rapid solidification in polycrystalline Al thin films were conducted using nano-scale spatio-temporal resolution dynamic transmission electron microscopy. Differences in crystal growth rates and asymmetries in melt pool development were observed as the heat extraction geometry was varied by controlling the proximity of the laser-pulse irradiation and the associated induced melt pools to the edge of the transmission electron microscopy support grid, which acts as a large heat sink. Experimental parameters have been established to maximize the reproducibility of the material response to the laser-pulse-related heating and to ensure that observations of the dynamical behavior of themore » metal are free from artifacts, leading to accurate interpretations and quantifiable measurements with improved precision. Interface migration rate measurements revealed solidification velocities that increased consistently from ∼1.3 m s{sup −1} to ∼2.5 m s{sup −1} during the rapid solidification process of the Al thin films. Under the influence of an additional large heat sink, increased crystal growth rates as high as 3.3 m s{sup −1} have been measured. The in situ experiments also provided evidence for development of a partially melted, two-phase region prior to the onset of rapid solidification facilitated crystal growth. Using the experimental observations and associated measurements as benchmarks, finite-element modeling based calculations of the melt pool evolution after pulsed laser irradiation have been performed to obtain estimates of the temperature evolution in the thin films.« less

Determination of crystal growth rates during rapid solidification of polycrystalline aluminum by nano-scale spatio-temporal resolution in situ transmission electron microscopy

DOE PAGES

Zweiacker, K.; McKeown, J. T.; Liu, C.; ...

2016-08-04

In situ investigations of rapid solidification in polycrystalline Al thin films were conducted using nano-scale spatio-temporal resolution dynamic transmission electron microscopy. Differences in crystal growth rates and asymmetries in melt pool development were observed as the heat extraction geometry was varied by controlling the proximity of the laser-pulse irradiation and the associated induced melt pools to the edge of the transmission electron microscopy support grid, which acts as a large heat sink. Experimental parameters have been established to maximize the reproducibility of the material response to the laser-pulse-related heating and to ensure that observations of the dynamical behavior of themore » metal are free from artifacts, leading to accurate interpretations and quantifiable measurements with improved precision. Interface migration rate measurements revealed solidification velocities that increased consistently from ~1.3 m s –1 to ~2.5 m s –1 during the rapid solidification process of the Al thin films. Under the influence of an additional large heat sink, increased crystal growth rates as high as 3.3 m s –1 have been measured. The in situ experiments also provided evidence for development of a partially melted, two-phase region prior to the onset of rapid solidification facilitated crystal growth. As a result, using the experimental observations and associated measurements as benchmarks, finite-element modeling based calculations of the melt pool evolution after pulsed laser irradiation have been performed to obtain estimates of the temperature evolution in the thin films.« less

Suprathermal electron energy distribution within the dayside Venus ionosphere

NASA Technical Reports Server (NTRS)

Knudsen, W. C.; Miller, K. L.; Spenner, K.; Novak, V.; Michelson, P. F.; Whitten, R. C.

1980-01-01

The suprathermal electron energy distribution for the dayside ionosphere has been derived from data returned by the Pioneer-Venus orbiter retarding potential analyzer. The shape and magnitude of the spectrum are consistent with the assumption that solar EUV radiation is the only significant source. The magnitude of the spectrum and its variation with altitude suggest that significant vertical transport occurs, with the electrons being lost through the ionopause. In turn, significant vertical transport suggests that the effective vertical electron heat conductivity may be comparable to the field-free value. The heat input to the thermal electron gas from the measured suprathermal electron flux is too small by a factor of at least five to maintain the observed electron temperature profile if the electron thermal conductivity is assumed to be close to the field-free value. It is thus inferred that most of the heat is supplied by the solar wind.

The theory of ionospheric focused heating

NASA Technical Reports Server (NTRS)

Bernhardt, P. A.; Duncan, L. M.

1987-01-01

Ionospheric modification by high power radio waves and by chemical releases are combined in a theoretical study of ionospheric focused heating. The release of materials which promote electron-ion recombination creates a hole in the bottomside ionosphere. The ionospheric hole focuses high power radio waves from a ground-based transmitter to give a 20 dB or greater enhancement in power density. The intense radio beam excites atomic oxygen by collisions with accelerated electrons. Airglow from the excited oxygen provides a visible trace of the focused beam. The large increase in the intensity of the radio beam stimulates new wave-plasma interactions. Numerical simulations show that the threshold for the two-plasmon decay instability is exceeded. The interaction of the pump electromagnetic wave with the backward plasmon produces a scattered electromagnetic wave at 3/2 the pump frequency. The scattered wave provides a unique signature of the two-plasmon decay process for ground-based detection.

An experimental system for spectral line ratio measurements in the TJ-II stellarator.

PubMed

Zurro, B; Baciero, A; Fontdecaba, J M; Peláez, R; Jiménez-Rey, D

2008-10-01

The chord-integrated emissions of spectral lines have been monitored in the TJ-II stellarator by using a spectral system with time and space scanning capabilities and relative calibration over the entire UV-visible spectral range. This system has been used to study the line ratio of lines of different ionization stages of carbon (C(5+) 5290 A and C(4+) 2271 A) for plasma diagnostic purposes. The local emissivity of these ions has been reconstructed, for quasistationary profiles, by means of the inversion Fisher method described previously. The experimental line ratio is being empirically studied and in parallel a simple spectroscopic model has been developed to account for that ratio. We are investigating whether the role played by charge exchange processes with neutrals and the existence of non-Maxwellian electrons, intrinsic to Electron Cyclotron Resonance Heating (ECRH) heating, leave any distinguishable mark on this diagnostic method.

Photon-enhanced thermionic emission for solar concentrator systems.

PubMed

Schwede, Jared W; Bargatin, Igor; Riley, Daniel C; Hardin, Brian E; Rosenthal, Samuel J; Sun, Yun; Schmitt, Felix; Pianetta, Piero; Howe, Roger T; Shen, Zhi-Xun; Melosh, Nicholas A

2010-09-01

Solar-energy conversion usually takes one of two forms: the 'quantum' approach, which uses the large per-photon energy of solar radiation to excite electrons, as in photovoltaic cells, or the 'thermal' approach, which uses concentrated sunlight as a thermal-energy source to indirectly produce electricity using a heat engine. Here we present a new concept for solar electricity generation, photon-enhanced thermionic emission, which combines quantum and thermal mechanisms into a single physical process. The device is based on thermionic emission of photoexcited electrons from a semiconductor cathode at high temperature. Temperature-dependent photoemission-yield measurements from GaN show strong evidence for photon-enhanced thermionic emission, and calculated efficiencies for idealized devices can exceed the theoretical limits of single-junction photovoltaic cells. The proposed solar converter would operate at temperatures exceeding 200 degrees C, enabling its waste heat to be used to power a secondary thermal engine, boosting theoretical combined conversion efficiencies above 50%.

Self-healing of cracks in Ag joining layer for die-attachment in power devices

NASA Astrophysics Data System (ADS)

Chen, Chuantong; Nagao, Shijo; Suganuma, Katsuaki; Jiu, Jinting; Zhang, Hao; Sugahara, Tohru; Iwashige, Tomohito; Sugiura, Kazuhiko; Tsuruta, Kazuhiro

2016-08-01

Sintered silver (Ag) joining has attracted significant interest in power devices modules for its ability to form stable joints with a porous interconnection layer. A function for the self-healing of cracks in sintered porous Ag interlayers at high temperatures is discovered and reported here. A crack which was prepared on a Ag joining layer was closed after heating at 200 °C in air. The tensile strength of pre-cracked Ag joining layer specimens recovers to the value of non-cracked specimens after heating treatment. Transmission electron microscopy (TEM) was used to probe the self-healing mechanism. TEM images and electron diffraction patterns show that a large quantity of Ag nanoparticles formed at the gap with the size less than 10 nm, which bridges the crack in the self-healing process. This discovery provides additional motivation for the application of Ag as an interconnection material for power devices at high temperature.

Thermoplasmonic Ignition of Metal Nanoparticles.

PubMed

Mutlu, Mehmet; Kang, Ju-Hyung; Raza, Søren; Schoen, David; Zheng, Xiaolin; Kik, Pieter G; Brongersma, Mark L

2018-03-14

Explosives, propellants, and pyrotechnics are energetic materials that can store and quickly release tremendous amounts of chemical energy. Aluminum (Al) is a particularly important fuel in many applications because of its high energy density, which can be released in a highly exothermic oxidation process. The diffusive oxidation mechanism (DOM) and melt-dispersion mechanism (MDM) explain the ways powders of Al nanoparticles (NPs) can burn, but little is known about the possible use of plasmonic resonances in NPs to manipulate photoignition. This is complicated by the inhomogeneous nature of powders and very fast heating and burning rates. Here, we generate Al NPs with well-defined sizes, shapes, and spacings by electron beam lithography and demonstrate that their plasmonic resonances can be exploited to heat and ignite them with a laser. By combining simulations with thermal-emission, electron-, and optical-microscopy studies, we reveal how an improved control over NP ignition can be attained.

Numerical Simulation of Stationary AC Tungsten Inert Gas Welding of Aluminum Plate in Consideration of Oxide Layer Cleaning

NASA Astrophysics Data System (ADS)

Tashiro, Shinichi; Tanaka, Manabu

An unified numerical simulation model of AC TIG welding of the aluminum plate considering energy balance among the electrode, the arc and the base metal and employing an analytical model for calculating cleaning rate of the oxide layer has been developed for investigating heat transport properties and weld pool formation process in AC TIG welding of aluminum plate. As a result of this simulation, it was shown that although the heat flux from the arc onto the base metal increases in EN (Electrode Negative) phase due to the electron condensation, that in EP (Electrode Positive) phase conversely decreases because mainly of cooling caused by the electron emission. Furthermore, the validity of the simulation model was confirmed by comparing to experimental results such as the arc voltage, the area of cleaning zone and the shape of weld pool.

Electronic transport properties of intermediately coupled superconductors: PdTe2 and Cu0.04PdTe2

NASA Astrophysics Data System (ADS)

Hooda, M. K.; Yadav, C. S.

2018-01-01

We have investigated the electrical resistivity (1.8-480 K), Seebeck coefficient (2.5-300 K) and thermal conductivity (2.5-300 K) of PdTe2 and 4% Cu intercalated PdTe2 compounds. The electrical resistivity for the compounds shows a Bloch-Gruneisen-type linear temperature (T) dependence for 100 \\text{K}, and Fermi liquid behavior (ρ (T) \\propto T2) for T<50 \\text{K} . Seebeck coefficient data exhibit a strong competition between Normal (N) and Umklapp (U) scattering processes at low T. The low-T, thermal conductivity (κ) of the compounds is strongly dominated by the electronic contribution, and exhibits a rare linear T-dependence below 10 K. However, high-T, κ (T) shows the usual 1/T -dependence, dominated by the U-scattering process. The electron-phonon coupling parameters, estimated from the low-T, specific-heat data and first-principle electronic structure calculations suggest that PdTe2 and Cu0.04PdTe2 are intermediately coupled superconductors.

Cubic nitride templates

DOEpatents

Burrell, Anthony K; McCleskey, Thomas Mark; Jia, Quanxi; Mueller, Alexander H; Luo, Hongmei

2013-04-30

A polymer-assisted deposition process for deposition of epitaxial cubic metal nitride films and the like is presented. The process includes solutions of one or more metal precursor and soluble polymers having binding properties for the one or more metal precursor. After a coating operation, the resultant coating is heated at high temperatures under a suitable atmosphere to yield metal nitride films and the like. Such films can be used as templates for the development of high quality cubic GaN based electronic devices.

Optimization of porous microchannel heat exchanger

NASA Astrophysics Data System (ADS)

Kozhukhov, N. N.; Konovalov, D. A.

2017-11-01

The technical progress in information and communication sphere leads to a sharp increase in the use of radio electronic devices. Functioning of radio electronics is accompanied by release of thermal energy, which must be diverted from the heat-stressed element. Moreover, using of electronics at negative temperatures, on the contrary, requires supply of a certain amount of heat to start the system. There arises the task of creating a system that allows both to supply and to divert the necessary amount of thermal energy. The development of complex thermostabilization systems for radio electronic equipment is due to increasing the efficiency of each of its elements separately. For more efficient operation of a heat exchanger, which directly affects the temperature of the heat-stressed element, it is necessary to calculate the mode characteristics and to take into account the effect of its design parameters. The results of optimizing the microchannel heat exchanger are presented in the article. The target optimization functions are the mass, pressure drop and temperature. The parameters of optimization are the layout of porous fins, their geometric dimensions and coolant flow. For the given conditions, the optimum variant of porous microchannel heat exchanger is selected.

Heat-Flux Measurements in Laser-Produced Plasmas Using Thomson Scattering from Electron Plasma Waves

NASA Astrophysics Data System (ADS)

Henchen, R. J.; Goncharov, V. N.; Cao, D.; Katz, J.; Froula, D. H.; Rozmus, W.

2017-10-01

An experiment was designed to measure heat flux in coronal plasmas using collective Thomson scattering. Adjustments to the electron distribution function resulting from heat flux affect the shape of the collective Thomson scattering features through wave-particle resonance. The amplitude of the Spitzer-Härm electron distribution function correction term (f1) was varied to match the data and determines the value of the heat flux. Independent measurements of temperature and density obtained from Thomson scattering were used to infer the classical heat flux (q = - κ∇Te) . Time-resolved Thomson-scattering data were obtained at five locations in the corona along the target normal in a blowoff plasma formed from a planar Al target with 1.5 kJ of 351-nm laser light in a 2-ns square pulse. The flux measured through the Thomson-scattering spectra is a factor of 5 less than the κ∇Te measurements. The lack of collisions of heat-carrying electrons suggests a nonlocal model is needed to accurately describe the heat flux. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Industrial femtosecond lasers for machining of heat-sensitive polymers (Conference Presentation)

NASA Astrophysics Data System (ADS)

Hendricks, Frank; Bernard, Benjamin; Matylitsky, Victor V.

2017-03-01

Heat-sensitive materials, such as polymers, are used increasingly in various industrial sectors such as medical device manufacturing and organic electronics. Medical applications include implantable devices like stents, catheters and wires, which need to be structured and cut with minimum heat damage. Also the flat panel display market moves from LCD displays to organic LED (OLED) solutions, which utilize heat-sensitive polymer substrates. In both areas, the substrates often consist of multilayer stacks with different types of materials, such as metals, dielectric layers and polymers with different physical characteristic. The different thermal behavior and laser absorption properties of the materials used makes these stacks difficult to machine using conventional laser sources. Femtosecond lasers are an enabling technology for micromachining of these materials since it is possible to machine ultrafine structures with minimum thermal impact and very precise control over material removed. An industrial femtosecond Spirit HE laser system from Spectra-Physics with pulse duration <400 fs, pulse energies of >120 μJ and average output powers of >16 W is an ideal tool for industrial micromachining of a wide range of materials with highest quality and efficiency. The laser offers process flexibility with programmable pulse energy, repetition rate, and pulse width. In this paper, we provide an overview of machining heat-sensitive materials using Spirit HE laser. In particular, we show how the laser parameters (e.g. laser wavelength, pulse duration, applied energy and repetition rate) and the processing strategy (gas assisted single pass cut vs. multi-scan process) influence the efficiency and quality of laser processing.

Space and Missile Systems Center Standard: Technical Requirements for Electronic Parts, Materials, and Processes used in Space Vehicles

DTIC Science & Technology

2013-04-12

DTL-38999 Connector, Electrical, Circular, Miniature, High Density, Quick Disconnect (Bayonet, Threaded , and Breach Coupling), Environment Resistant ...186 Table 1160-1. Resistance Tolerance and Required Derating...For MIL-DTL-5015 Connector, Electrical, Circular Threaded , AN Type, General Specification for MIL-H-6088G(1) Heat Treatment of Aluminum Alloys

Enrichment Wastes' Processing of Manganiferous Ores with the Use of Mechanochemical Methods

ERIC Educational Resources Information Center

Kubekova, Sholpan N.; Kapralova, Viktoria I.; Ibraimova, Gulnur T.; Batyrbayeva, Aigul A.

2016-01-01

The aim of the research is the study of the chemical and phase composition of enrichment wastes of manganiferous ore in Ushkatyn-III deposit and the synthesis of new materials by mechanochemical activation and subsequent heat treatment of the mechanical activation products. The use of XFA, infrared spectroscopy and electron probe microanalysis…

ECR ion source with electron gun

DOEpatents

Xie, Zu Q.; Lyneis, Claude M.

1993-01-01

An Advanced Electron Cyclotron Resonance ion source (10) having an electron gun (52) for introducing electrons into the plasma chamber (18) of the ion source (10). The ion source (10) has a injection enclosure (12) and a plasma chamber tank (14). The plasma chamber (18) is defined by a plurality of longitudinal magnets (16). The electron gun (52) injects electrons axially into the plasma chamber (18) such that ionization within the plasma chamber (18) occurs in the presence of the additional electrons produced by the electron gun (52). The electron gun (52) has a cathode (116) for emitting electrons therefrom which is heated by current supplied from an AC power supply (96) while bias potential is provided by a bias power supply (118). A concentric inner conductor (60) and Outer conductor (62) carry heating current to a carbon chuck (104) and carbon pusher (114) Which hold the cathode (116) in place and also heat the cathode (16). In the Advanced Electron Cyclotron Resonance ion source (10), the electron gun (52) replaces the conventional first stage used in prior art electron cyclotron resonance ion generators.

Low-pressure hydrogen discharge maintenance in a large-size plasma source with localized high radio-frequency power deposition

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

Todorov, D.; Shivarova, A., E-mail: ashiva@phys.uni-sofia.bg; Paunska, Ts.

2015-03-15

The development of the two-dimensional fluid-plasma model of a low-pressure hydrogen discharge, presented in the study, is regarding description of the plasma maintenance in a discharge vessel with the configuration of the SPIDER source. The SPIDER source, planned for the neutral-beam-injection plasma-heating system of ITER, is with localized high RF power deposition to its eight drivers (cylindrical-coil inductive discharges) and a large-area second chamber, common for all the drivers. The continuity equations for the charged particles (electrons and the three types of positive ions) and for the neutral species (atoms and molecules), their momentum equations, the energy balance equations formore » electrons, atoms and molecules and the Poisson equations are involved in the discharge description. In addition to the local processes in the plasma volume, the surface processes of particle reflection and conversion on the walls as well as for a heat exchange with the walls are included in the model. The analysis of the results stresses on the role of the fluxes (particle and energy fluxes) in the formation of the discharge structure. The conclusion is that the discharge behavior is completely obeyed to non-locality. The latter is displayed by: (i) maximum values of plasma parameters (charged particle densities and temperatures of the neutral species) outside the region of the RF power deposition, (ii) shifted maxima of the electron density and temperature, of the plasma potential and of the electron production, (iii) an electron flux, with a vortex structure, strongly exceeding the total ion flux which gives evidence of a discharge regime of non-ambipolarity and (iv) a spatial distribution of the densities of the neutral species resulting from their fluxes.« less

Synthesis of {111} Facet-Exposed MgO with Surface Oxygen Vacancies for Reactive Oxygen Species Generation in the Dark.

PubMed

Hao, Ying-Juan; Liu, Bing; Tian, Li-Gang; Li, Fa-Tang; Ren, Jie; Liu, Shao-Jia; Liu, Ying; Zhao, Jun; Wang, Xiao-Jing

2017-04-12

Seeking a simple and moderate route to generate reactive oxygen species (ROS) for antibiosis is of great interest and challenge. This work demonstrates that molecule transition and electron rearrangement processes can directly occur only through chemisorption interaction between the adsorbed O 2 and high-energy {111} facet-exposed MgO with abundant surface oxygen vacancies (SOVs), hence producing singlet oxygen and superoxide anion radicals without light irradiation. These ROS were confirmed by electron paramagnetic resonance, in situ Raman, and scavenger experiments. Furthermore, heat plays a crucial role for the electron transfer process to accelerate the formation of ·O 2 - , which is verified by temperature kinetic experiments of nitro blue tetrazolium reduction in the dark. Therefore, the presence of oxygen vacancy can be considered as an intensification of the activation process. The designed MgO is acquired in one step via constructing a reduction atmosphere during the combustion reaction process, which has an ability similar to that of noble metal Pd to activate molecular oxygen and can be used as an effective bacteriocide in the dark.

Self-consistent discharge growing model of helicon plasma

NASA Astrophysics Data System (ADS)

Isayama, Shogo; Hada, Tohru; Shinohara, Shunjiro; Tanikawa, Takao

2015-11-01

Helicon plasma is a high-density and low-temperature plasma generated by the electromagnetic (Helicon) wave excited in the plasma. It is thought to be useful for various applications including electric thrusters. Physics of helicon plasma production involves such fundamental processes as the wave propagation (dispersion relation), collisional and non-collisional wave damping, plasma heating, ionization/recombination of neutral particles, and modification of the dispersion relation by newly ionized plasma. There remain a number of unsolved physical issues such as, how the Helicon and the TG modes influence the plasma density, electron temperature and their spatial profiles. While the Helicon mode is absorbed in the bulk plasma, the TG mode is mostly absorbed near the edge of the plasma. The local power deposition in the helicon plasma is mostly balanced by collisional loss. This local power balance can give rise to the inhomogeneous electron temperature profile that leads to time evolution of density profile and dispersion relation. In our study, we construct a self-consistent model of the discharge evolution that includes the wave excitation, electron heat transfer, and diffusion of charged particles.

40 CFR 90.421 - Dilute gaseous exhaust sampling and analytical system description.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Volume Sampler (PDP-CVS) system with a heat exchanger, or a Critical Flow Venturi—Constant Volume Sampler (CFV-CVS) system with CFV sample probes and/or a heat exchanger or electronic flow compensation. Figure... sampling point. (ii) For the CFV-CVS, either a heat exchanger or electronic flow compensation is required...

40 CFR 91.421 - Dilute gaseous exhaust sampling and analytical system description.

Code of Federal Regulations, 2014 CFR

2014-07-01

... Pump—Constant Volume Sampler (PDP-CVS) system with a heat exchanger, or a Critical Flow Venturi—Constant Volume Sampler (CFV-CVS) system with CVS sample probes and/or a heat exchanger or electronic flow... sampling point. (ii) For the CFV-CVS, either a heat exchanger or electronic flow compensation is required...

40 CFR 91.421 - Dilute gaseous exhaust sampling and analytical system description.

Code of Federal Regulations, 2012 CFR

2012-07-01

... Pump—Constant Volume Sampler (PDP-CVS) system with a heat exchanger, or a Critical Flow Venturi—Constant Volume Sampler (CFV-CVS) system with CVS sample probes and/or a heat exchanger or electronic flow... sampling point. (ii) For the CFV-CVS, either a heat exchanger or electronic flow compensation is required...

40 CFR 90.421 - Dilute gaseous exhaust sampling and analytical system description.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Volume Sampler (PDP-CVS) system with a heat exchanger, or a Critical Flow Venturi—Constant Volume Sampler (CFV-CVS) system with CFV sample probes and/or a heat exchanger or electronic flow compensation. Figure... sampling point. (ii) For the CFV-CVS, either a heat exchanger or electronic flow compensation is required...

40 CFR 91.421 - Dilute gaseous exhaust sampling and analytical system description.

Code of Federal Regulations, 2013 CFR

2013-07-01

... Pump—Constant Volume Sampler (PDP-CVS) system with a heat exchanger, or a Critical Flow Venturi—Constant Volume Sampler (CFV-CVS) system with CVS sample probes and/or a heat exchanger or electronic flow... sampling point. (ii) For the CFV-CVS, either a heat exchanger or electronic flow compensation is required...

40 CFR 90.421 - Dilute gaseous exhaust sampling and analytical system description.

Code of Federal Regulations, 2012 CFR

2012-07-01

... Volume Sampler (PDP-CVS) system with a heat exchanger, or a Critical Flow Venturi—Constant Volume Sampler (CFV-CVS) system with CFV sample probes and/or a heat exchanger or electronic flow compensation. Figure... sampling point. (ii) For the CFV-CVS, either a heat exchanger or electronic flow compensation is required...

The role of electron heating physics in images and variability of the Galactic Centre black hole Sagittarius A*

NASA Astrophysics Data System (ADS)

Chael, Andrew; Rowan, Michael; Narayan, Ramesh; Johnson, Michael; Sironi, Lorenzo

2018-05-01

The accretion flow around the Galactic Centre black hole Sagittarius A* (Sgr A*) is expected to have an electron temperature that is distinct from the ion temperature, due to weak Coulomb coupling in the low-density plasma. We present four two-temperature general relativistic radiative magnetohydrodynamic (GRRMHD) simulations of Sgr A* performed with the code KORAL. These simulations use different electron heating prescriptions, motivated by different models of the underlying plasma microphysics. We compare the Landau-damped turbulent cascade model used in previous work with a new prescription we introduce based on the results of particle-in-cell simulations of magnetic reconnection. With the turbulent heating model, electrons are preferentially heated in the polar outflow, whereas with the reconnection model electrons are heated by nearly the same fraction everywhere in the accretion flow. The spectra of the two models are similar around the submillimetre synchrotron peak, but the models heated by magnetic reconnection produce variability more consistent with the level observed from Sgr A*. All models produce 230 GHz images with distinct black hole shadows which are consistent with the image size measured by the Event Horizon Telescope, but only the turbulent heating produces an anisotropic `disc-jet' structure where the image is dominated by a polar outflow or jet at frequencies below the synchrotron peak. None of our models can reproduce the observed radio spectral slope, the large near-infrared and X-ray flares, or the near-infrared spectral index, all of which suggest non-thermal electrons are needed to fully explain the emission from Sgr A*.

Thickness-dependent electron–lattice equilibration in laser-excited thin bismuth films

DOE PAGES

Sokolowski-Tinten, K.; Li, R. K.; Reid, A. H.; ...

2015-11-19

Electron–phonon coupling processes determine electronic transport properties of materials and are responsible for the transfer of electronic excess energy to the lattice. With decreasing device dimensions an understanding of these processes in nanoscale materials is becoming increasingly important. We use time-resolved electron diffraction to directly study energy relaxation in thin bismuth films after optical excitation. Precise measurements of the transient Debye–Waller-effect for various film thicknesses and over an extended range of excitation fluences allow to separate different contributions to the incoherent lattice response. While phonon softening in the electronically excited state is responsible for an immediate increase of the r.m.s.more » atomic displacement within a few hundred fs, 'ordinary' electron–phonon coupling leads to subsequent heating of the material on a few ps time-scale. Moreover, the data reveal distinct changes in the energy transfer dynamics which becomes faster for stronger excitation and smaller film thickness, respectively. The latter effect is attributed to a cross-interfacial coupling of excited electrons to phonons in the substrate.« less

Conditions for Aeronomic Applicability of the Classical Electron Heat Conduction Formula

NASA Technical Reports Server (NTRS)

Cole, K. D.; Hoegy, W. R.

1998-01-01

Conditions for the applicability of the classical formula for heat conduction in the electrons in ionized gas are investigated. In a fully ionised gas ( V(sub en) much greater than V(sub ei)), when the mean free path for electron-electron (or electron-ion) collisions is much larger than the characteristic thermal scale length of the observed system, the conditions for applicability break down. In the case of the Venus ionosphere this breakdown is indicated for a large fraction of the electron temperature data from altitudes greater than 180 km, for electron densities less than 10(exp 4)/cc cm. In a partially ionised gas such that V(sub en) much greater than V(sub ei) there is breakdown of the formula not only when the mean free path of electrons greatly exceeds the thermal scale length, but also when the gradient of neutral particle density exceeds the electron thermal gradient. It is shown that electron heat conduction may be neglected in estimating the temperature of joule heated electrons by observed strong 100 Hz electric fields when the conduction flux is limited by the saturation flux. The results of this paper support our earlier aeronomical arguments against the hypothesis of planetary scale whistlers for the 100 Hz electric field signal. In turn this means that data from the 100 Hz signal may not be used to support the case for lightning on Venus.

Efficient electron heating in relativistic shocks and gamma-ray-burst afterglow.

PubMed

Gedalin, M; Balikhin, M A; Eichler, D

2008-02-01

Electrons in shocks are efficiently energized due to the cross-shock potential, which develops because of differential deflection of electrons and ions by the magnetic field in the shock front. The electron energization is necessarily accompanied by scattering and thermalization. The mechanism is efficient in both magnetized and nonmagnetized relativistic electron-ion shocks. It is proposed that the synchrotron emission from the heated electrons in a layer of strongly enhanced magnetic field is responsible for gamma-ray-burst afterglows.

Method and apparatus for studying high-temperature properties of conductive materials in the interests of nuclear power engineering

NASA Astrophysics Data System (ADS)

Savvatimskiy, A. I.; Onufriev, S. V.

2016-12-01

Physical processes during a rapid (microsecond) heating of metals, carbon, and their compounds by a single pulse of electric current are discussed. Effects arising in such short-term heating near the melting point are noted: the electron emission and heat capacity anomalies and the possible occurrence of Frenkel pair (interstitial atom and vacancy). The problem of measuring the temperature using optical methods under pulse heating is considered, including the use of a specimen in the form of a blackbody model. The melting temperature of carbon (4800-4900 K) is measured at increased pulse pressure. The results of studying the properties of metals (by example of zirconium and hafnium) and of zirconium carbide at high temperatures are discussed. The schematics of the pulse setups and the instrumentation, as well as specimens for a pulse experiment, are presented.

Empirical Modeling of ICMEs Using ACE/SWICS Ionic Distributions

NASA Astrophysics Data System (ADS)

Rivera, Y.; Landi, E.; Lepri, S. T.; Gilbert, J. A.

2017-12-01

Coronal Mass Ejections (CMEs) are some of the largest, most energetic events in the solar system releasing an immense amount of plasma and magnetic field into the Heliosphere. The Earth-bound plasma plays a large role in space weather, causing geomagnetic storms that can damage space and ground based instrumentation. As a CME is released, the plasma experiences heating, expansion and acceleration; however, the physical mechanism supplying the heating as it lifts out of the corona still remains uncertain. From previous work we know the ionic composition of solar ejecta undergoes a gradual transition to a state where ionization and recombination processes become ineffective rendering the ionic composition static along its trajectory. This property makes them a good indicator of thermal conditions in the corona, where the CME plasma likely receives most of its heating. We model this so-called `freeze-in' process in Earth-directed CMEs using an ionization code to empirically determine the electron temperature, density and bulk velocity. `Frozen-in' ions from an ensemble of independently modeled plasmas within the CME are added together to fit the full range of observational ionic abundances collected by ACE/SWICS during ICME events. The models derived using this method are used to estimate the CME energy budget to determine a heating rate used to compare with a variety of heating mechanisms that can sustain the required heating with a compatible timescale.

Investigation of ion and electron heat transport of high- T e ECH heated discharges in the large helical device

DOE PAGES

Pablant, N. A.; Satake, S.; Yokoyama, M.; ...

2016-01-28

An analysis of the radial electric field and heat transport, both for ions and electrons, is presented for a high-more » $${{T}_{\\text{e}}}$$ electron cyclotron heated (ECH) discharge on the large helical device (LHD). Transport analysis is done using the task3d transport suite utilizing experimentally measured profiles for both ions and electrons. Ion temperature and perpendicular flow profiles are measured using the recently installed x-ray imaging crystal spectrometer diagnostic (XICS), while electron temperature and density profiles are measured using Thomson scattering. The analysis also includes calculated ECH power deposition profiles as determined through the travis ray-tracing code. This is the first time on LHD that this type of integrated transport analysis with measured ion temperature profiles has been performed without NBI, allowing the heat transport properties of plasmas with only ECH heating to be more clearly examined. For this study, a plasma discharge is chosen which develops a high central electron temperature ($${{T}_{\\text{eo}}}=9$$ keV) at moderately low densities ($${{n}_{\\text{eo}}}=1.5\\times {{10}^{19}}$$ m-3). The experimentally determined transport properties from task3d are compared to neoclassical predictions as calculated by the gsrake and fortec-3d codes. The predicted electron fluxes are seen to be an order of magnitude less than the measured fluxes, indicating that electron transport is largely anomalous, while the neoclassical and measured ion heat fluxes are of the same magnitude. Neoclassical predictions of a strong positive ambipolar electric field ($${{E}_{\\text{r}}}$$ ) in the plasma core are validated through comparisons to perpendicular flow measurements from the XICS diagnostic. Furthermore, this provides confidence that the predictions are producing physically meaningful results for the particle fluxes and radial electric field, which are a key component in correctly predicting plasma confinement.« less

Performance improvement of optical fiber coupler with electric heating versus gas heating.

PubMed

Shuai, Cijun; Gao, Chengde; Nie, Yi; Peng, Shuping

2010-08-20

Gas heating has been widely used in the process of fused biconical tapering. However, as the instability and asymmetric flame temperature of gas heating exist, the performance of the optical devices fabricated by this method was affected. To overcome the problems resulting from gas combustion, an electric heater is designed and manufactured using a metal-ceramic (MoSi(2)) as a heating material. Our experimental data show that the fused-taper machine with an electric heater has improved the performance of optical devices by increasing the consistency of the extinction ratio, excess loss, and the splitting ratio over that of the previous gas heating mode. Microcrystallizations and microcracks were observed at the fused region of the polarization-maintaining (PM) fiber coupler and at the taper region with scanning electron microscopy and atomic force microscopy respectively. The distribution of the microcrystallizations and microcracks are nonuniform along the fiber with gas heating, while their distribution is rather uniform with electric heating. These findings show that the novel optical fiber coupler with an electric heater has improved the performance of optical fiber devices by affecting the consistency of the optical parameters and micromorphology of the surface of PM fiber.

Monitoring and Control Interface Based on Virtual Sensors

PubMed Central

Escobar, Ricardo F.; Adam-Medina, Manuel; García-Beltrán, Carlos D.; Olivares-Peregrino, Víctor H.; Juárez-Romero, David; Guerrero-Ramírez, Gerardo V.

2014-01-01

In this article, a toolbox based on a monitoring and control interface (MCI) is presented and applied in a heat exchanger. The MCI was programed in order to realize sensor fault detection and isolation and fault tolerance using virtual sensors. The virtual sensors were designed from model-based high-gain observers. To develop the control task, different kinds of control laws were included in the monitoring and control interface. These control laws are PID, MPC and a non-linear model-based control law. The MCI helps to maintain the heat exchanger under operation, even if a temperature outlet sensor fault occurs; in the case of outlet temperature sensor failure, the MCI will display an alarm. The monitoring and control interface is used as a practical tool to support electronic engineering students with heat transfer and control concepts to be applied in a double-pipe heat exchanger pilot plant. The method aims to teach the students through the observation and manipulation of the main variables of the process and by the interaction with the monitoring and control interface (MCI) developed in LabVIEW©. The MCI provides the electronic engineering students with the knowledge of heat exchanger behavior, since the interface is provided with a thermodynamic model that approximates the temperatures and the physical properties of the fluid (density and heat capacity). An advantage of the interface is the easy manipulation of the actuator for an automatic or manual operation. Another advantage of the monitoring and control interface is that all algorithms can be manipulated and modified by the users. PMID:25365462

The multi-species Farley-Buneman instability in the solar chromosphere

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

Madsen, Chad A.; Dimant, Yakov S.; Oppenheim, Meers M.

2014-03-10

Empirical models of the solar chromosphere show intense electron heating immediately above its temperature minimum. Mechanisms such as resistive dissipation and shock waves appear insufficient to account for the persistence and uniformity of this heating as inferred from both UV lines and continuum measurements. This paper further develops the theory of the Farley-Buneman instability (FBI) which could contribute substantially to this heating. It expands upon the single-ion theory presented by Fontenla by developing a multiple-ion-species approach that better models the diverse, metal-dominated ion plasma of the solar chromosphere. This analysis generates a linear dispersion relationship that predicts the critical electronmore » drift velocity needed to trigger the instability. Using careful estimates of collision frequencies and a one-dimensional, semi-empirical model of the chromosphere, this new theory predicts that the instability may be triggered by velocities as low as 4 km s{sup -1}, well below the neutral acoustic speed. In the Earth's ionosphere, the FBI occurs frequently in situations where the instability trigger speed significantly exceeds the neutral acoustic speed. From this, we expect neutral flows rising from the photosphere to have enough energy to easily create electric fields and electron Hall drifts with sufficient amplitude to make the FBI common in the chromosphere. If so, this process will provide a mechanism to convert neutral flow and turbulence energy into electron thermal energy in the quiet Sun.« less

Finned Carbon-Carbon Heat Pipe with Potassium Working Fluid

NASA Technical Reports Server (NTRS)

Juhasz, Albert J.

2010-01-01

This elemental space radiator heat pipe is designed to operate in the 700 to 875 K temperature range. It consists of a C-C (carbon-carbon) shell made from poly-acrylonitride fibers that are woven in an angle interlock pattern and densified with pitch at high process temperature with integrally woven fins. The fins are 2.5 cm long and 1 mm thick, and provide an extended radiating surface at the colder condenser section of the heat pipe. The weave pattern features a continuous fiber bath from the inner tube surface to the outside edges of the fins to maximize the thermal conductance, and to thus minimize the temperature drop at the condenser end. The heat pipe and radiator element together are less than one-third the mass of conventional heat pipes of the same heat rejection surface area. To prevent the molten potassium working fluid from eroding the C C heat pipe wall, the shell is lined with a thin-walled, metallic tube liner (Nb-1 wt.% Zr), which is an integral part of a hermetic metal subassembly which is furnace-brazed to the inner surface of the C-C tube. The hermetic metal liner subassembly includes end caps and fill tubes fabricated from the same Nb-1Zr alloy. A combination of laser and electron beam methods is used to weld the end caps and fill tubes. A tungsten/inert gas weld seals the fill tubes after cleaning and charging the heat pipes with potassium. The external section of this liner, which was formed by a "Uniscan" rolling process, transitions to a larger wall thickness. This section, which protrudes beyond the C-C shell, constitutes the "evaporator" part of the heat pipe, while the section inside the shell constitutes the condenser of the heat pipe (see figure).

Investigation on the hot melting temperature field simulation of HDPE water supply pipeline in gymnasium pool

NASA Astrophysics Data System (ADS)

Cai, Zhiqiang; Dai, Hongbin; Fu, Xibin

2018-06-01

In view of the special needs of the water supply and drainage system of swimming pool in gymnasium, the correlation of high density polyethylene (HDPE) pipe and the temperature field distribution during welding was investigated. It showed that the temperature field distribution has significant influence on the quality of welding. Moreover, the mechanical properties of the welded joint were analyzed by the bending test of the weld joint, and the micro-structure of the welded joint was evaluated by scanning electron microscope (SEM). The one-dimensional unsteady heat transfer model of polyethylene pipe welding joints was established by MARC. The temperature field distribution during welding process was simulated, and the temperature field changes during welding were also detected and compared by the thermo-couple temperature automatic acquisition system. Results indicated that the temperature of the end surface of the pipe does not reach the maximum value, when it is at the end of welding heating. Instead, it reaches the maximum value at 300 sand latent heat occurs during the welding process. It concludes that the weld quality is the highest when the welding pressure is 0.2 MPa, and the heating temperature of HDPE heat fusion welding is in the range of 210 °C-230 °C.

Developing the science and technology for the Material Plasma Exposure eXperiment

NASA Astrophysics Data System (ADS)

Rapp, J.; Biewer, T. M.; Bigelow, T. S.; Caneses, J. F.; Caughman, J. B. O.; Diem, S. J.; Goulding, R. H.; Isler, R. C.; Lumsdaine, A.; Beers, C. J.; Bjorholm, T.; Bradley, C.; Canik, J. M.; Donovan, D.; Duckworth, R. C.; Ellis, R. J.; Graves, V.; Giuliano, D.; Green, D. L.; Hillis, D. L.; Howard, R. H.; Kafle, N.; Katoh, Y.; Lasa, A.; Lessard, T.; Martin, E. H.; Meitner, S. J.; Luo, G.-N.; McGinnis, W. D.; Owen, L. W.; Ray, H. B.; Shaw, G. C.; Showers, M.; Varma, V.; the MPEX Team

2017-11-01

Linear plasma generators are cost effective facilities to simulate divertor plasma conditions of present and future fusion reactors. They are used to address important R&D gaps in the science of plasma material interactions and towards viable plasma facing components for fusion reactors. Next generation plasma generators have to be able to access the plasma conditions expected on the divertor targets in ITER and future devices. The steady-state linear plasma device MPEX will address this regime with electron temperatures of 1-10 eV and electron densities of 1021{\\text{}}-1020 m-3 . The resulting heat fluxes are about 10 MW m-2 . MPEX is designed to deliver those plasma conditions with a novel Radio Frequency plasma source able to produce high density plasmas and heat electron and ions separately with electron Bernstein wave (EBW) heating and ion cyclotron resonance heating with a total installed power of 800 kW. The linear device Proto-MPEX, forerunner of MPEX consisting of 12 water-cooled copper coils, has been operational since May 2014. Its helicon antenna (100 kW, 13.56 MHz) and EC heating systems (200 kW, 28 GHz) have been commissioned and 14 MW m-2 was delivered on target. Furthermore, electron temperatures of about 20 eV have been achieved in combined helicon and ECH heating schemes at low electron densities. Overdense heating with EBW was achieved at low heating powers. The operational space of the density production by the helicon antenna was pushed up to 1.1 × 1020 m-3 at high magnetic fields of 1.0 T at the target. The experimental results from Proto-MPEX will be used for code validation to enable predictions of the source and heating performance for MPEX. MPEX, in its last phase, will be capable to expose neutron-irradiated samples. In this concept, targets will be irradiated in ORNL’s High Flux Isotope Reactor and then subsequently exposed to fusion reactor relevant plasmas in MPEX.

Electron density inversed by plasma lines induced by suprathermal electron in the ionospheric modification experiment

NASA Astrophysics Data System (ADS)

Wang, Xiang; Zhou, Chen

2018-05-01

Incoherent scatter radar (ISR) is the most powerful ground-based measurement facility to study the ionosphere. The plasma lines are not routinely detected by the incoherent scatter radar due to the low intensity, which falls below the measured spectral noise level of the incoherent scatter radar. The plasma lines are occasionally enhanced by suprathermal electrons through the Landau damping process and detectable to the incoherent scatter radar. In this study, by using the European Incoherent Scatter Association (EISCAT) UHF incoherent scatter radar, the experiment observation presents that the enhanced plasma lines were observed. These plasma lines were considered as manifest of the suprathermal electrons generated by the high-frequency heating wave during the ionospheric modification. The electron density profile is also obtained from the enhanced plasma lines. This study can be a promising technique for obtaining the accurate electron density during ionospheric modification experiment.

TiO2/water Nanofluid Heat Transfer in Heat Exchanger Equipped with Double Twisted-Tape Inserts

NASA Astrophysics Data System (ADS)

Eiamsa-ard, S.; Ketrain, R.; Chuwattanakul, V.

2018-05-01

Nowadays, heat transfer enhancement plays an important role in improving efficiency of heat transfer and thermal systems for numerous areas such as heat recovery processes, chemical reactors, air-conditioning/refrigeration system, food engineering, solar air/water heater, cooling of high power electronics etc. The present work presents the experimental results of the heat transfer enhancement of TiO2/water nanofluid in a heat exchanger tube fitted with double twisted tapes. The study covered twist ratios of twisted tapes (y/w) of 1.5, 2.0, and 2.5) while the concentration of the nanofluid was kept constant at 0.05% by volume. Observations show that heat transfer, friction loss and thermal performance increase as twist ratio (y/w) decreases. The use of the nanofluid in the tube equipped with the double twisted-tapes with the smallest twist ratio (y/w = 1.5) results in the increases of heat transfer rates and friction factor up to 224.8% and 8.98 times, respectively as compared to those of water. In addition, the experimental results performed that double twisted tapes induced dual swirling-flows which played an important role in improving fluid mixing and heat transfer enhancement. It is also observed that the TiO2/water nanofluid was responsible for low pressure loss behaviors.

Electron density window for best frequency performance, lowest phase noise and slowest degradation of GaN heterostructure field-effect transistors

NASA Astrophysics Data System (ADS)

Matulionis, Arvydas

2013-07-01

The problems in the realm of nitride heterostructure field-effect transistors (HFETs) are discussed in terms of a novel fluctuation-dissipation-based approach impelled by a recent demonstration of strong correlation of hot-electron fluctuations with frequency performance and degradation of the devices. The correlation has its genesis in the dissipation of the LO-mode heat accumulated by the non-equilibrium longitudinal optical phonons (hot phonons) confined in the channel that hosts the high-density hot-electron gas subjected to a high electric field. The LO-mode heat causes additional scattering of hot electrons and facilitates defect formation in a different manner than the conventional heat contained mainly in the acoustic phonon mode. We treat the heat dissipation problem in terms of the hot-phonon lifetime responsible for the conversion of the non-migrant hot phonons into migrant acoustic modes and other vibrations. The lifetime is measured over a wide range of electron density and supplied electric power. The optimal conditions for the dissipation of the LO-mode heat are associated with the plasmon-assisted disintegration of hot phonons. Signatures of plasmons are experimentally resolved in fluctuations, dissipation, hot-electron transport, transistor frequency performance, transistor phase noise and transistor reliability. In particular, a slower degradation and a faster operation of GaN-based HFETs take place inside the electron density window where the resonant plasmon-assisted ultrafast dissipation of the LO-mode heat comes into play. A novel heterostructure design for the possible improvement of HFET performance is proposed, implemented and tested.

Design and analysis of multifunctional structures for embedded electronics in unmanned aerial vehicles

NASA Astrophysics Data System (ADS)

Kothari, Rushabh M.

Multifunctional structures are a new trend in the aerospace industry for the next generation structural design. Many future structures are expected to be something in addition to a load bearing structure. The design and analysis of multifunctional structures combining structural, electrical and thermal functionalities are presented here. The sandwich beam is considered as a starting point for the load bearing structure and then it is modified with a cavity to embed avionics and thermal controls. The embedded avionics inside the load bearing structure would allow weight reduction of the aerospace vehicle due to elimination of separate electronics housing, interconnects, cables etc. The cavity reduces strength of the structure so various reinforcements methods are evaluated. The result of various reinforcements and their effectiveness are presented. The current generation of electronics produce massive amount of heat. In the case of embedded electronics, the excessive heat presents a major challenge to the structural and heat transfer engineers. The embedded nature of electronics prevents the use of the classical heat dissipative methods such as fans and high velocity air flows, etc. The integrated thermal control of the electronics has been designed using passive heat transfer device and highly optimized particulate composite thermal interface material (TIM). The TIMs are used to fill the air gaps and reduce contact resistance between two surfaces, such as electronics and heat dissipators. The efficiency of TIM directly affects the overall heat transfer ability of the integrated thermal control system. The effect of the particles at micron and nano scales are studied for the particulate composite TIM. The thermal boundary resistance study for the particulate composite TIM with nano silica particles is presented in this thesis. The FEA analysis is used to model thermal boundary resistance and compared with the theoretical micromechanics model. The heat pipes are chosen as a part of passive heat transfer device due to their durability and excellent thermal conductivities. The multifunctional system consisting of all above components is modeled for unmanned aerial vehicle (UAV) at subsonic air speeds to demonstrate the validity of the design.

Electron and ion distribution functions in magnetopause reconnection

NASA Astrophysics Data System (ADS)

Wang, S.; Chen, L. J.; Bessho, N.; Hesse, M.; Kistler, L. M.; Torbert, R. B.; Mouikis, C.; Pollock, C. J.

2015-12-01

We investigate electron and ion velocity distribution functions in dayside magnetopause reconnection events observed by the Cluster and MMS spacecraft. The goal is to build a spatial map of electron and ion distribution features to enable the indication of the spacecraft location in the reconnection structure, and to understand plasma energization processes. Distribution functions, together with electromagnetic field structures, plasma densities, and bulk velocities, are organized and compared with particle-in-cell simulation results to indicate the proximities to the reconnection X-line. Anisotropic features in the distributions of magnetospheric- and magnetosheath- origin electrons at different locations in the reconnection inflow and exhaust are identified. In particular, parallel electron heating is observed in both the magnetosheath and magnetosphere inflow regions. Possible effects of the guide field strength, waves, and upstream density and temperature asymmetries on the distribution features will be discussed.

Effect of remote inductively coupled plasma (ICP) on the electron energy probability function of an in-tandem main ICP

NASA Astrophysics Data System (ADS)

Lee, Jaewon; Kim, Kyung-Hyun; Chung, Chin-Wook

2017-02-01

The remote plasma has been generally used as the auxiliary plasma source for indirect plasma processes such as cleaning or ashing. When tandem plasma sources that contain main and remote plasma sources are discharged, the main plasma is affected by the remote plasma and vice versa. Charged particles can move between two chambers due to the potential difference between the two plasmas. For this reason, the electron energy possibility function of the main plasma can be controlled by adjusting the remote plasma state. In our study, low energy electrons in the main plasma are effectively heated with varying remote plasma powers, and high energy electrons which overcome potential differences between two plasmas—are exchanged with no remarkable change in the plasma density and the effective electron temperature.

Control of plasma properties in a short direct-current glow discharge with active boundaries

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

Adams, S. F.; Demidov, V. I., E-mail: vladimir.demidov@mail.wvu.edu; West Virginia University, Morgantown, West Virginia 26506

2016-02-15

To demonstrate controlling electron/metastable density ratio and electron temperature by applying negative voltages to the active (conducting) discharge wall in a low-pressure plasma with nonlocal electron energy distribution function, modeling has been performed in a short (lacking the positive-column region) direct-current glow discharge with a cold cathode. The applied negative voltage can modify the trapping of the low-energy part of the energetic electrons that are emitted from the cathode sheath and that arise from the atomic and molecular processes in the plasma within the device volume. These electrons are responsible for heating the slow, thermal electrons, while production of slowmore » electrons (ions) and metastable atoms is mostly due to the energetic electrons with higher energies. Increasing electron temperature results in increasing decay rate of slow, thermal electrons (ions), while decay rate of metastable atoms and production rates of slow electrons (ions) and metastable atoms practically are unchanged. The result is in the variation of electron/metastable density ratio and electron temperature with the variation of the wall negative voltage.« less

Dependence of L-mode confinement on the electron cyclotron power deposition profile in the TCV tokamak

NASA Astrophysics Data System (ADS)

Kirneva, N. A.; Razumova, K. A.; Pochelon, A.; Behn, R.; Coda, S.; Curchod, L.; Duval, B. P.; Goodman, T. P.; Labit, B.; Karpushov, A. N.; Rancic, M.; Sauter, O.; Silva, M.; TCV Team

2012-01-01

Scenarios with different electron cyclotron heating power profile distributions and widths were compared for the first time in experiments on the Tokamak à Configuration Variable (TCV). The heating profile was changed from shot to shot over a wide range from localized on-axis, with normalized minor radius half-width at half maximum σ1/2 ~ 0.1, up to a widely distributed heating power profile with σ1/2 ~ 0.4 and finally to a profile peaked far off-axis. The global confinement, MHD activity, density, temperature and electron pressure profile evolution were compared. In particular, the energy confinement properties of discharges with localized on-axis heating and distributed on-axis heating were very similar, with degradation close to that predicted by the ITER L-mode scaling; in the case of off-axis heating, on the other hand, the confinement degradation was even stronger.