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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Effect of electron thermal anisotropy on the kinetic cross-field streaming instability

The investigation of the kinetic cross-field streaming instability, motivated by the research of collisionless shock waves and previously studied by Wu et al. (1983), is discussed more fully. Since in the ramp region of a quasi-perpendicular shock electrons can be preferentially heated in the direction transverse to the ambient magnetic field, it is both desirable and necessary to include the effect of the thermal anisotropy on the instability associated with a shock. It is found that Te-perpendicular greater than Te-parallel can significantly enhance the peak growth rate of the cross-field streaming instability when the electron beta is sufficiently high. Furthermore, the present analysis also improves the analytical and numerical solutions previously obtained.

Tsai, S. T.↗
NASA NTRS1973

Thermal electron energy distribution measurements in the ionosphere.

A recoverable payload instrumented for twilight airglow studies was launched by an Aerobee 150 from the White Sands Test Range on Feb. 8, 1971 at 13.56 UT. The payload included a low energy electron spectrometer (HARP) and a cylindrical Langmuir probe. The HARP electron spectrometer is a new device designed to make high resolution differential electron flux measurements. Measurements of ionospheric electron energy distribution in the range from about 0.2 to 4.0 eV are presented.

Hays, P. B.↗
NASA NTRS1987

Rapid temporal evolution of radiation from non-thermal electrons in solar flares

Solutions of the time dependent Fokker-Planck equation was found for accelerated electrons undergoing Coulomb collisions in a magnetized, fully ionized plasma. An exact solution was found for arbitrary pitch angle and energy distribution in a uniform background plasma. Then, for an inhomogeneous plasma, a solution was found for particles with small pitch angles. These solutions were used to calculate the temporal evolution of bremsstrahlung x-rays from short bursts of nonthermal electron beams, and these spectra were compared with observed high time resolution spectra of short timescale solar hard x-ray bursts. It is shown that the observed softening in time of the spectra rules out a homogeneous background and therefore the possibility of electrons being confined to the corona either because of converging magnetic field or high densities. The inhomogeneous solution was also applied to a model with constant coronal density and exponentially rising chromospheric density. The spectra are shown to be consistent with that produced by a collimated beam of electrons accelerated in the corona with certain given conditions. These conditions could be violated if large pitch angle electrons are present.

Lu, Edward T.↗
NASA NTRS1989

Anisotropic thermal electron distributions in the solar wind

This paper presents data on ISEE 3 observations of unusually anisotropic core electrons detected in the solar wind near 1 AU, which exhibited temperature (T) ratios T-parallel/T-perpendicular of 1.5 to 4. Distinct anisotropy events are described, together with the observed correlations between core temperature anisotropy and various other solar wind parameters. It was found that the periods of extreme electron anisotropy tended to be coincident with intervals of double ion beam, suggesting similar causal mechanisms for the two phenomena.

Phillips, J. L.↗
NASA NTRS1989

ISEE 3 observations of solar wind thermal electrons with T-perpendicular greater than T-parallel

This study presents ISEE 3 observations of anomalous electron distributions for which T-perpendicular exceeds T-parallel in the solar wind near 1 AU. Twelve anomaly events were identified, lasting from 24 min to 6 hours. These events generally share the following characteristics: (1) high plasma density, (2) low solar wind speed, (3) magnetic field which is nearly transverse to the flow, and (4) low electron and ion temperatures. The processes of solar wind adiabatic expansion and isotropization via Coulomb collisions could be expected to lead to such anomalous anisotropies under conditions similar to those observed. However, these conditions actually produce T-perpendicular greater than T-parallel for only a small fraction of the time, suggesting that other mechanisms are also important in regulating solar wind electron distributions.

Phillips, J. L.↗
NASA NTRS2002

The Non-Thermal Electron Spectrum of the Supernova Remnant SN 1006

We present the results of a spectral analysis of a compilation of X-ray, radio, and gamma-ray data for the supernova remnant SN 1006. The data are used to constrain models of the electron spectrum of the remnant. We present the results for the electron spectrum and review the implications for cosmic-ray acceleration and the strength of the magnetic field in the remnant.

Allen, Glenn E.↗
NASA NTRSDate not supplied

How Auroral Electron Precipitations Contribute to the Formation of Electron Heat Fluxes to the Ionosphere?

Electron heat fluxes (also called electron thermal fluxes) in the ionosphere are carried by thermal electrons whose energy is below a few eV. Electron heat fluxes greatly impact on electron temperature, which is a fundamental parameter in the ionospheric dynamics. At the high latitude in the auroral regions electron heat flux is originated dominantly from the magnetosphere through high-energy electron energy fluxes. High-energy electron fluxes in the diffuse auroral region can undergo multiple backscatters between the magnetically conjugated regions of both hemispheres, and different kind of wave-particle interactions along the magnetic field line. High-energy electron fluxes in discrete auroral region can be trapped below the auroral acceleration region and can also undergo backscatter and multiple reflection. These processes, in turn, amplify super-thermal electrons (<~500-600 eV) that dominantly form electron heat fluxes through Coulomb collision between thermal electrons. Such electron heat fluxes play an important role to determine electron temperature profile in the ionosphere, which is one of the key parameters that controls the ionospheric dynamics. Thus, it is necessary to include electron heat flux as a topside energy input in all global ionospheric models. We demonstrate all above results based on Superthermal Electron Transport (STET), Superthermal Proton, Electron and Atomic Hydrogen tRansport in the Ionosphere and Thermosphere (SPEAH-RIT), and Comprehensive Inner Magnetosphere and Ionospheres (CIMI) codes developed at NASA Goddard Space Flight Center.

George V. Khazanov↗
DOE OSTI2020

Evidence of restricted heat transport in National Ignition Facility Hohlraums

We present experimental evidence of restricted electron thermal conduction in the high-Z coronal plasma regions of laser-driven Hohlraums on the National Ignition Facility. Four separate measurements, three of which are direct observations of Hohlraum dynamics, corroborate this finding. (1) The velocity of the coronal plasma ablated and heated by the outer-cone laser beams is determined by time-dependent imaging of the gold plasma plume, or “bubble.” The velocities of the incoming plume (perpendicular to the Hohlraum axis) are consistent with high-fidelity 2D radiation-hydrodynamic simulations using flux-limited thermal electron conduction with a flux multiplier f = 0.03. Simulations using f = 0.15, which is very nearly classical Spitzer–Härm transport, predict plume velocities slower than measured. (2) Specific features in time-resolved images of the Hohlraum wall at an angle of 19° are also more consistent with f = 0.03 simulations compared to f = 0.15. (3) Spectroscopic tracers were added to the Hohlraum wall in the outer-beam bubble region. The ratios of hydrogen-like to helium-like line emission are sensitive to the electron temperature of the bubble. The hydrogen-like to helium-like ratios extracted from the time-integrated spectra of manganese and cobalt tracers from two observation angles are consistent with f = 0.03 and not with f = 0.15. (4) The time of peak capsule emission, or “bang time,” an integrated measurement, is also more consistent with f = 0.03 than with f = 0.15. Overall, while these findings do not identify the causes of restricted thermal conduction in Hohlraums, they motivate future experiments to test specific hypotheses and focus on model development in the regions of the plasma exhibiting restricted transport.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Neural network model of the multi-mode anomalous transport module for accelerated transport simulations

Here, a neural network version of the Multi-Mode Anomalous Transport Module, known as MMMnet, has been developed to calculate plasma turbulent diffusivities in DIII-D with a calculation time suitable for control applications. MMMnet uses a simple artificial neural network structure to predict the ion thermal, electron thermal, and toroidal momentum diffusivities while reproducing Multi-Mode Model (MMM) data with good accuracy and keeping the calculation time as a fraction of that associated with MMM. Model-based control techniques require models with fast calculation times, making many existing physics-oriented predictive codes unsuitable. The control-oriented predictive code COTSIM (Control Oriented Transport SIMulator) calculates the most significant plasma dynamics in response to the different actuators while running at a speed useful for control design. In order to achieve this calculation speed, COTSIM often relies on scaling laws and control-level models. Replacing some of these scaling laws and control-level models with neural network versions of more complex physics-level models has the potential of increasing the range of validity and the level of accuracy of COTSIM without compromising its computational speed. In this work, MMMnet is integrated into COTSIM to improve the turbulent diffusivity predictions, which will in turn improve the prediction accuracy associated with the dynamics of many plasma properties.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗