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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Data-driven linear time advance operators for the acceleration of plasma physics simulation

In this study, we demonstrate the application of data-driven linear operator construction for time advance with a goal of accelerating plasma physics simulation. We apply dynamic mode decomposition (DMD) to data produced by the nonlinear SOLPS-ITER (Scrape-off Layer Plasma Simulator - International Thermonuclear Experimental Reactor) plasma boundary code suite in order to estimate a series of linear operators and monitor their predictive accuracy via online error analysis. We find that this approach defines when these dynamics can be represented by a sequence of approximate linear operators and is essential for providing consistent projections when compared to an unconstrained application. For linear diffusion and advection–diffusion fluid test problems, we construct and apply operators within explicit and implicit time advance schemes, demonstrating that stability can be robustly guaranteed in each case. We further investigate the use of the linear time advance operators within several integration methods including forward Euler, backward Euler, and the matrix exponential. The application of this method to simulation data from SOLPS-ITER, with varying levels of Markov chain Monte Carlo numerical noise, shows that constrained DMD operators yield a capability to identify, extract, and integrate a (slow) subset of the present timescales. Example applications show that for projected speedup factors of [Formula: see text], and [Formula: see text], a mean relative error of 3%, 5%, and 8% and maximum relative error less than 20% are achievable, which appears acceptable for typical SOLPS-ITER steady-state simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1990

Electron distributions in the plasma sheet boundary layer - Time-of-flight effects

The electron edge of the plasma sheet boundary layer lies lobeward of the ion edge. Measurements obtained near the electron edge of the boundary layer reveal low-speed cutoffs for earthward and tailward-flowing electrons. These cutoffs progress to lower speeds with deeper penetration into the boundary layer, and are consistently lower for the earthward-directed electrons than for the tailward-direction electrons. The cutoffs and their variation with distance from the edge of the boundary layer can be consistently interpreted in terms of a time-of-flight effect on recently reconnected magnetic field lines. The observed cutoff speeds are used to estimate the downtail location of the reconnection site.

Onsager, T. G.↗
NASA NTRS1988

On the need for space tests of plasma contactors as electron collectors

An analysis is presented of laboratory experiments that have shown that hollow plasma sources can provide low-impedance contact with a background plasma. In particular, some experiments show an report an 'ignited mode' of electron collection using plasma sources where almost an ampere was collected at a potential of 100 volts. The experimental results are compared with theoretical and computational models of plasma layers. Preliminary results indicate that the measured potential profiles and collected currents during the 'ignited mode' correspond to an increase in the background plasma thermal current of more than an order of magnitude. The results imply that the 'ignited mode' results are substantially impacted by the laboratory electron source and the tank size. Only experiments performed in space will be able to provide the correct boundary conditions for reliably testing high electron collection by plasma contactors.

Katz, Ira↗
DOE OSTI2024

Effect of parallel flow on resonant layer responses in high beta plasmas

Abstract Resonant layers in a tokamak respond to non-axisymmetric magnetic perturbations by amplifying the mode amplitude and balancing the plasma rotation through magnetic reconnection and force balance, respectively. This resonant response can be characterized by local layer parameters and especially by a single quantity in the linear regime, the so-called inner-layer Δ. The computation of Δ under two-fluid drift-MHD formalism has been progressed by reducing the order of the system in the phase space, where the shielding current is approximated as being only carried by electrons, a posteriori . In this study, we relax the approximation and compute Δ accounted for by the parallel flow associated with the ion shielding current. The posteriori is numerically verified in great agreement with the original SLAYER developed in a previous paper (J.-K. Park 2022 Phys. Plasmas 29 072506). Extending the resonant layer response theory to high β plasmas, our research findings answer two important questions: how the parallel flow influences the resonant layer response and why the parallel flow effect appears in high β plasmas. The complicated plasma compression in high β regime allows the parallel flow response to give rise to the ion shielding current, which not only shifts the zero-crossing condition of the ExB flow but also enhances the field penetration threshold. Technically, the Riccati matrix transformation method is adapted to handle the numerical stiffness due to the increased order of the system. The high fidelity of this numerical method makes use of further extension of the model to higher-order systems to take other physical phenomena into account. This work is envisaged to predict the resonant layer response under high β fusion reactor conditions.

Lee, Yeongsun (ORCID:000000034474416X)↗
NASA NTRS1995

Nature and location of the source of plasma sheet boundary layer ion beams

Onsager et al. (1991) have put forward a model of the formation of the plasma sheet boundary layer (PSBL) which relies on a steady source of plasma from a spatially extended plasma sheet, together with steady equatorward and earthward ExB convection of field lines due to reconnection at a downtail neutral line. This model is a synthesis of earlier proposals and it explains such features as an electron layer exterior to the ion boundary layer, ion velocity dispersion, counter streaming beams, low-speed cutoffs in the beams. It also explains the apparent evolution of the ion beams through 'kidney bean' shaped velocity-space distributions toward quasi-isotropic shells without invoking pitch angle scattering or energy diffusion. In this paper we explore two ramifications of the model. In principle we can map, as a function of time, the downtail neutral line distance and establish whether or not it is retreating during substorm recovery. We can also reconstruct the plasma distribution function near the neutral line to see if it is most consistent with mantle or plasma sheet plasma. We perform this analysis using International Sun Earth Explorer (ISEE) Fast Plasma Experiment (FPE) data for two plasma sheet recovery events, one on March 1, 1978, and the other on April 18, 1978. On March 1, 1978, we find evidence for an initial retreat from around 110 to 160 R(sub E) in the first 15 min; little further retreat occurs thereafter. On April 18, 1978, the neutral line location ranges from as little as 40 R(sub E) tailward of the satellite to as much as 200 R(sub E), but there is no evidence for a systematic retreat. The reconstructed ion distributions for these events are most consistent with a plasma sheet origin for the March 1 case and possibly plasma mantle or low-latitude boundary layer for the April 18 case.

Elphic, R. C.↗
DOE OSTI2021

Comparison of AlF 3 thin films grown by thermal and plasma enhanced atomic layer deposition

Films of aluminum fluoride (AlF 3 ) deposited by thermal and plasma enhanced atomic layer deposition (PEALD) have been compared using in situ multiwavelength ellipsometry (MWE) and monochromatic x-ray photoelectron spectroscopy (XPS). The AlF 3 films were grown using cyclic exposures of trimethylaluminum, hydrogen fluoride, and H radicals from a remote H 2 inductively coupled plasma. Films were characterized in situ using MWE and XPS for growth rate, film composition, and impurity incorporation. The MWE showed a growth rate of 1.1 and 0.7 Å per cycle, at 100 °C, for thermal and plasma enhanced ALD AlF 3 films, respectively. Carbon incorporation was below the XPS detection limit. The plasma enhanced ALD AlF 3 film showed the presence of Al-Al chemical states, in the Al 2p scans, suggesting the presence of Al-rich clusters with a concentration of 14%. The Al-rich clusters are thought to originate during the hydrogen plasma step of the PEALD process. Finally, the Al-rich clusters were not detected in thermal ALD AlF 3 films using the same precursors and substrate temperature.

36 MATERIALS SCIENCE↗
NASA NTRS1982

The fine structure of the front side magnetopause during two successive crossings

The magnetopause crossings of November 10, 1977, which are considered to be representative of a class of structures, are investigated, and a procedure is developed to derive approximate surface currents near the magnetopause from ISEE 1 magnetic field data by assuming a constant speed of the magnetopause along its normal for each crossing of the magnetopause layer. Changes in the magnetic field indicate that current sheets exist on each side of the magnetopause layer, which is characterized by an irregular magnetic field and a magnetosheath-like energy distribution. No boundary layer plasma is observed on the magnetospheric field lines inside the magnetopause, and electromagnetic energy is found to be dissipated at the two edges of the magnetopause layer where the current layers are observed.

Formisano, V.↗
NASA NTRS1980

Significance of thermal contact resistance in two-layer thermal-barrier-coated turbine vanes

The importance of thermal contact resistance between layers in heat transfer through two layer, plasma sprayed, thermal barrier coatings applied to turbine vanes was investigated. Results obtained with a system of NiCrAlY bond and yttria stabilized zirconia ceramic show that thermal contact resistance between layers is negligible. These results also verified other studies which showed that thermal contact resistance is negligible for a different coating system of NiCr bond calcia stabilized zirconia ceramic. The zirconia stabilized ceramic thermal conductivity data scatter presented in the literature is ?20 to -10 percent about a curve fit of the data. More accurate predictions of heat transfer and metal wall temperatures are obtained when the thermal conductivity values are used at the ?20 percent level.

Liebert, C. H.↗
NASA NTRS1985

The generation of electrostatic noise in the plasma sheet boundary layer

The one and two ion beam instability is considered as a possible explanation for the observations of broadband electrostatic noise in the plasma sheet region of the geomagnetic tail. When only hot streaming plasma sheet boundary layer ions are present, no broadband waves are excited. Cold, streaming ionospheric ions can generate electrostatic broadband waves propagating in the slow beam acoustic mode, but the growth rates of the waves are significantly enhanced when hot boundary layer ions are present. (Both the slow and fast beam acoustic modes can be excited, depending on the relative ion drift.) This model predicts that the wave intensity of the broad band noise should peak in the plasma sheet boundary layer. Observations of less intense electrostatic waves in the lobes and plasma sheet are likely a result of the absence of hot ion beams or large ion temperatures, respectively, which result in smaller growth rates. The ion beam instability may play an important role in the formation of the central plasma sheet.

Dusenbery, P. B.↗
DOE OSTI2023

Growth of nanostructured molybdenum disulfide (MoS 2 ) thin films on a nanohole-patterned substrate using plasma-enhanced atomic layer deposition (ALD)

Nanostructured molybdenum disulfide (MoS 2 ) thin films were grown on a nanohole-patterned silicon substrate using plasma-enhanced atomic layer deposition. A nanoscale hole-patterned silicon substrate was fabricated for the growth of MoS 2 film using the self-assembly-based nanofabrication method. The nanoscale holes can significantly increase the surface area of the substrate while the formation and growth of nanostructures normally start at the surface of the substrate. Hydrogen sulfide (H 2 S) gas was used as the S source in the growth of molybdenum disulfide (MoS 2 ) while molybdenum (V) chloride (MoCl 5 ) powder was used as the Mo source. The MoS 2 film had a stoichiometric ratio of 1 (Mo) to 2 (S), and had peaks of E 1 2g and A 1g , which represent the in-plane and out-plane vibration modes of the Mo–S bond, respectively. It was found that the MoS 2 film grown in the nanoscale hole, especially at the wall of the hole, has more hexagonal-like structures due to the effects of nanoscale space confinement and the nanoscale interface although the film shows an amorphous structure. Post-growth high-temperature annealing ranging from 800 to 900 °C produced local crystalline structures in the film, which are compatible with those reported by other researchers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Simulation of Liquid Lithium Divertor Geometry Using SOLPS-ITER

Here, plasma-facing component (PFC) geometries are evaluated for a Fusion Nuclear Science Facility (FNSF) design to find solutions that are compatible with flowing liquid lithium components while satisfying requirements from the perspective of plasma and neutral particle transport. Flowing liquid metal (LM) divertor systems offer important advantages due to continual regeneration of the surface material, but may require modifications from standard optimized tokamak divertor designs. Scrape Off Layer Plasma Simulator for the International Thermonuclear Experimental Reactor (SOLPS-ITER) simulations are used to compare standard vertical target, open, and balanced baffled geometries. It is found that the open geometry offers little control of neutral particles and has narrow operating windows where the divertor fluxes can be lowered to acceptable levels, while maintaining the required upstream density. The addition of neutral baffles allows greater control over the divertor conditions with less impact on the upstream density. The divertor neutral pressure in the baffled geometry is slightly higher than the open divertor, but not as large with a vertical target. A first-pass coupling of the SOLPS solution with sheath and implantation/erosion models to compute the lithium emission shows that the lithium is largely confined to the near-surface region due to the small ionization mean free path and large main ion flow toward the surface. The lithium source was varied by three orders of magnitude. At the highest rate, when the sourced lithium approaches the level of the main ion recycling flux, a high core lithium concentration (~10%) is observed with only moderate power dissipation to affect the divertor plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1972

Magnetogasdynamic heat transfer to a hemispherical body in a supersonic argon plasma.

Measurements of the heat transfer to a hemispherical body in a Mach 4.6, low density, argon plasma are reported. The experiments demonstrated that local wall currents affected the heat flux to the electrically conducting surface, both without and with internally applied magnetic fields. Such currents were induced by a nonuniform shock-layer plasma potential; but with applied fields, Hall currents dominated. Magnetic fields significantly increased the stagnation-region heat flux while causing a reduction over the remainder of the hemisphere. For an electrically nonconducting surface, the local heat flux was reduced, and magnetic fields insignificantly affected the heat flux. Analytical treatments indicate that joule and radiation heating were negligible.

Nowak, R. J.↗
NASA NTRS1980

Plasma double-layers produced by ponderomotive force

Non-linear rectification of the RF electric fields excited in a convectively amplifying electron beam-plasma interaction results in a dc electric field, and a corresponding ponderomotive force acting on the charged particles to produce a space-charge separation, i.e. a type of plasma double-layer. This paper analyses the effect, taking into account plasma electron temperature and electron-neutral collisions. To measure such double-layers, an electron beam probe constitutes a convenient non-perturbing diagnostic technique, but great care is required in its calibration. An analysis is presented taking into account significant non-linear effects which had been neglected in previous work. The paper concludes with some preliminary experimental results illustrating the use of the technique in a beam-plasma interaction for which a weak double-layer electric field is predicted.

Levine, J. S.↗
DOE OSTI2020

Baking and plasma pretreatment of sapphire surfaces as a way to facilitate the epitaxial plasma-enhanced atomic layer deposition of GaN thin films

The growth of high-quality epitaxial gallium nitride (GaN) thin films is achieved by using a baking and plasma pretreatment of the substrate prior to the GaN plasma-enhanced atomic layer deposition (PE-ALD). In this work, it is found that such pretreatment makes the GaN films grow coherently on sapphire substrates, following a layer-by-layer growth mechanism. The deposited GaN film shows high crystalline quality, a sharp GaN/sapphire interface, and a flat surface. The possibility of growing high-quality GaN epilayers in this way broadens the range of applications for PE-ALD in GaN-based devices.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effects of radial transport on divertor power and particle flux widths under different operational regimes in EAST

Here, a study of the effects of radial transport on the outer divertor particle and power flux widths (λ js and λ q ) is carried out using plasmas under different operational regimes in the Experimental Advanced Superconducting Tokamak (EAST). In the EAST experiments, the λ js values measured during the grassy intra- and inter-ELM phases are similar, and the averaged value of λ js during grassy ELMy discharges is found to be smaller than that of the intra-ELM phase of type-I ELMy discharges but larger than that of the inter-ELM phase of type-I ELMy discharges. Simulations of scans of the radial particle and heat transport coefficients, D and χ e , performed using the BOUT++ transport code show that both λq and λjs increase with D and χe, especially when D or χ e is larger than a threshold value, indicating that background turbulence starts to matter in the determination of λ q and λ js when D or χ e surpasses the threshold value. A comparison between the simulation of the D scan and the experimental results shows that the different values of λ js obtained under different plasma operational regimes are probably due to the different intensities of background turbulence, which is beyond the scope of Goldston's heuristic drift-based model as reported by Goldston et al (2012 Nucl. Fusion 52 013009), since their model was derived by assuming that turbulent transport does not exceed a certain level. The ratio of λ js to λ q is greatly affected by the radial transport; however, simulations carried out using Scrape-off Layer Plasma Simulation (SOLPS) show that divertor geometry and plasma density have big influences on λ js , and thus could also affect the ratio of λ js to λ q .

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

A software package for plasma facing component analysis and design: the Heat flux Engineering Analysis Toolkit (HEAT)

The engineering limits of plasma facing components (PFCs) constrain the allowable operational space of tokamaks. Poorly managed heat fluxes that push the PFCs beyond their limits not only degrade core plasma performance via elevated impurities, but can also result in PFC failure due to thermal stresses or melting. Simple axisymmetric assumptions fail to capture the complex interaction between 3D PFC geometry and 2D or 3D plasmas. This results in fusion systems that must either operate with increased risk or reduce PFC loads, potentially through lower core plasma performance, to maintain a nominal safety factor. High precision 3D heat flux predictions are necessary to accurately ascertain the state of a PFC given the evolution of the magnetic equilibrium. A new code, the Heat flux Engineering Analysis Toolkit (HEAT), has been developed to provide high precision 3D predictions and analysis for PFCs. HEAT couples many otherwise disparate computational tools together into a single open source python package. Magnetic equilibrium, engineering CAD, finite volume solvers, scrape off layer plasma physics, visualization, high performace computing, and more, are connected in a single web-based user interface. Linux users may use HEAT without any software prerequisites via an appImage. This manuscript introduces HEAT, discusses the software architecture, presents first HEAT results, and outlines physics modules in development.

divertor physics↗
NASA NTRS1979

Plasma wave turbulence at the magnetopause - Observations from ISEE 1 and 2

An investigation of plasma wave electric and magnetic fields in the vicinity of the magnetopause using measurements from the ISEE 1 and 2 spacecraft is presented. Strong electric and magnetic field turbulence is often observed at the magnetopause; the electric field spectrum of this turbulence extends from less than a few hertz to over 100 kHz, and the magnetic field from a few hertz to about 1 kHz. Similar turbulence spectra are observed in association with flux transfer events and possible 'inclusions' of boundary layer plasma in the magnetosphere. Two possible plasma instabilities, the electrostatic ion-cyclotron and the lower-hybrid-drift instability, should explain the broad-band electric field turbulence; the narrow-band electrostatic emissions near the local electron plasma frequency are believed to be plasma oscillations or electrostatic waves near the upper-hybrid-resonance frequency.

Gurnett, D. A.↗