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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1997

Coordinated XTE/EUVE Observations of Algol

We performed a coordinated RXTE observation of the prototypical eclipsing binary Algol in conjunction with EUVE and ASCA observations. Observing the x-ray spectrum of Algol with ASCA, EUVE, and RXTE provides critical, near-simultaneous constraints on the distribution of the hottest temperature plasma in the Agol system: this is required to unambiguously determine the coronal Fe abundance. After some initial shuffling of observatory schedules with the help of mission planners, the coordinated multiwavelength observation was successfully performed in February, 1996. Analysis of the data, including development of new, IDL-based global model fitting routines, was accomplished from mid-1996 to mid-1997. The results indicate that the initial estimates of [Fe/H] approximately 0.3 dex (Stern et al.) are confirmed, and the Algol high temperature plasma thus has an Fe deficiency relative to the (Anders and Grevesse) solar abundance.

Stern, Robert A.↗
DOE OSTI2021

Propagation of positive discharges in an air bubble having an embedded water droplet

Low temperature plasmas generated inside gas bubbles immersed in water is an effective method of rapidly transferring plasma generated reactive species to the water for applications in biomedicine, agriculture and environment. Reactive species are generally produced in the gas phase plasma and then solvate into the liquid. The large surface-to-volume ratio (SVR) of the bubble accelerates this process. In generating bubbles in water, aerosols and droplets are also contained within the bubble. These droplets also have a large SVR and so can be rapidly plasma activated. However, the presence of the droplets can also impact the propagation of the plasma in the bubble. In this paper, results are discussed from computational and experimental investigations of the formation and evolution of discharges in an air bubble immersed in water with an embedded water droplet. The computations were performed with a two-dimensional plasma hydrodynamics model. Experiments were performed with a quasi-2D bubble apparatus. In bubbles having a droplet, a plasma filament typically bridges from the powered electrode to the droplet, and then from the droplet to the bubble surface. A surface-hugging streamer also occurs on the inner bubble surface and on the surface of the droplet. Both surface streamers result in part from surface charge accumulation and can dominate the formation of reactive species that transport into the droplet. Increasing droplet conductivity suppresses propagation of the surface discharge and leads to a lower density of aqueous reactive species. Increasing conductivity of the surrounding water does not change the overall structure of the discharge but does slightly elevate the discharge intensity. Finally, the size and shape of the embedded droplet can significantly affect the formation and propagation of the streamer.

2D fluid modelling↗
NASA NTRS1986

Unstable-magnetic-drift waves in a plasma with temperature anisotropy

It is pointed out that under certain conditions, such as a weak electron temperature anisotropy, the magnetic-drift wave instability can become rather important, and the growth rate can be greater than the ion gyrofrequency when the scale length of the density gradient is comparable to, or shorter than, the thermal ion gyroradius. The instability is attributed to wave-electron interactions, and the growth rate is far greater than the case investigated by Krall and Rosenbluth (1963) who attributed the instability to wave-ion interactions. The anticipated vanishing of the instability is observed as epsilon sub n/epsilon sub B approaches zero. The presently observed instability may be used to explain the low-frequency fluctuations evidenced by the Active Particle Tracer Explorer Ion Release Module magnetometer measurements, and may contribute to the acceleration of ions along the plasma cometary tail.

Wu, C. S.↗
NASA NTRS1993

The effects on the ionosphere of inertia in the high latitude neutral thermosphere

High-latitude ionospheric currents, plasma temperatures, densities, and composition are all affected by the time-dependent response of the neutral thermosphere to ion drag and Joule heating through a variety of complex feedback processes. These processes can best be studied numerically using the appropriate nonlinear numerical modeling techniques in conjunction with experimental case studies. In particular, the basic physics of these processes can be understood using a model, and these concepts can then be applied to more complex realistic situations by developing the appropriate simulations of real events. Finally, these model results can be compared with satellite-derived data from the thermosphere. We used numerical simulations from the National Center of Atmospheric Research Thermosphere/Ionosphere General Circulation Model (NCAR TIGCM) and data from the Dynamic Explorer 2 (DE 2) satellite to study the time-dependent effects of the inertia of the neutral thermosphere on ionospheric currents, plasma temperatures, densities, and composition. One particular case of these inertial effects is the so-called 'fly-wheel effect'. This effect occurs when the neutral gas, that has been spun-up by the large ionospheric winds associated with a geomagnetic storm, moves faster than the ions in the period after the end of the main phase of the storm. In these circumstances, the neutral gas can drag the ions along with them. It is this last effect, which is described in the next section, that we have studied under this grant.

Burns, Alan↗
DOE OSTI2023

Inertial and anisotropic pressure effects on cross-field electron transport in low-temperature magnetized plasmas

In this paper, a one-dimensional (1D) particle-in-cell Monte Carlo collision (PIC-MCC) model is developed to investigate the effects of anisotropic pressure and inertial terms due to non-Maxwellian velocity distribution functions on cross-field electron transport. The conservation of momentum is evaluated by taking the moments of the first-principles gas-kinetic equation. A steady-state discharge is obtained without any low-frequency ionization oscillations by considering an anomalous electron scattering profile. Further, the results obtained from the 1D PIC-MCC model are compared with fluid models, including the quasi-neutral drift-diffusion (DD), non-neutral DD, and full fluid moment models. The discharge current obtained from the PIC-MCC model is in good agreement with the fluid models. The cross-field electron transport due to the inertial terms, i.e. the gradient of axial and azimuthal drift, is evaluated. Moreover, PIC-MCC simulation results show non-zero, anisotropic, off-diagonal pressure tensor terms due to asymmetric non-Maxwellian electron velocity distribution function, potentially contributing to cross-field electron transport.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

2 H(p,γ) 3 He cross section measurement using high-energy-density plasmas

An absolute cross section for the radiative capture reaction 2 H(p,γ) 3 He has been measured at the OMEGA laser facility using inertially confined plasmas. These high-temperature plasmas are created by imploding a fuel-containing capsule using laser ablation, and are advantageous in that they better mimic astrophysical systems. We measure an S factor for this reaction of 0.429 ± 0.026 stat ± 0.072 sys eV b at E c.m . = 16.35 ± 0.40 keV, which is higher than the adopted evaluations. Furthermore, this reaction is important as a source of nuclear energy in protostars and brown dwarfs. It is also a critical reaction during big-bang nucleosynthesis, and an accurate cross section can be used as a constraint on cosmology.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Dataset, Code, and Models for Training Deep Learning Potentials for Low Temperature Plasma-Surface Interactions

This repository contains datasets, training scripts, and finished models, and test simulations used in the development of DeepREBO— a machine-learned interatomic potential trained to emulate the REBO2 empirical potential. The data was generated to study deep potential development for simulations of plasma-surface interactions. It uses an active learning framework, starting from a minimal dataset and iteratively expanding it. Included are those generated datasets, the trained models, and simulations used to evaluate the performance of the training process. This resource supports reproducibility and provides a reference framework for training deep potentials in plasma-surface interaction studies.

active learning↗
DOE OSTI2021

2H(p, gamma) 3He cross section measurement using high-energy-density plasmas

An absolute cross section for the radiative capture reaction 2H(p, γ ) 3He has been measured at the OMEGA laser facility using inertially confined plasmas. These high-temperature plasmas are created by imploding a fuel containing capsule using laser ablation, and are advantageous in that they better mimic astrophysical systems. We measure an S factor for this reaction of 0.429 ± 0.026stat ± 0.072sys eV b at Ec.m. = 16.35 ± 0.40 keV, which is higher than the adopted evaluations. This reaction is important as a source of nuclear energy in protostars and brown dwarfs. It is also a critical reaction during big-bang nucleosynthesis, and an accurate cross section can be used as a constraint on cosmology.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1968

Nonlinear interactions of electromagnetic waves with a thermally generated cesium plasma.

The interaction of a large‐amplitude disturbing wave with a thermally generated, highly ionized cesium plasma has been investigated using a small‐amplitude sensing wave as a probe. The subsequent interaction between the disturbing and sensing waves is related to the plasma electron temperature. The plasma was contained in a magnetic field of 500–1000 G and had an electron plasma frequency near 10 GHz and an electron gyromagnetic frequency around 2 GHz. The sensing wave was a 10 GHz plane wave of approximately 1.5 mW input power and the disturbing wave was 7.5 GHz plane wave of about 1.2 W peak power. Measurements of the sensing‐wave transmitted power were made using standard microwave techniques. A notch filter in the sensing‐wave receiving circuit reduced the scattered disturbing‐wave interference to an immeasurably low level. Langmuir probes were used to detect disturbing‐wave modulation and to measure plasma temperatures and densities. Measurements of the interaction were correlated with a solution of the Boltzmann transport equation for a perturbed Maxwellian distribution function with binary Coulomb collisions.

Jack G Hewitt, Jr↗