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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Ion dynamics during the parametric instabilities of a left-hand polarized Alfvén wave in a proton-electron-alpha plasma

The parametric instabilities of an Alfvén wave in a proton-electron plasma system are found to have great influence on proton dynamics, where part of the protons can be accelerated through the Landau resonance with the excited ion acoustic waves, and a beam component along the background magnetic field is formed. In this paper, with a one-dimensional hybrid simulation model, we investigate the evolution of the parametric instabilities of a monochromatic left-hand polarized Alfvén wave in a proton-electron-alpha plasma with a low beta. When the drift velocity between the protons and alpha particles is sufficiently large, the wave numbers of the backward daughter Alfvén waves can be cascaded toward higher values due to the modulational instability during the nonlinear evolution of the parametric instabilities, and the alpha particles are resonantly heated in both the parallel and perpendicular direction by the backward waves. On the other hand, when the drift velocity of alpha particles is small, the alpha particles are heated in the linear growth stage of the parametric instabilities due to the Landau resonance with the excited ion acoustic waves. Therefore, the heating occurs only in the parallel direction, and there is no obvious heating in the perpendicular direction. The relevance of our results to the preferential heating of heavy ions observed in the solar wind within 0.3 AU is also discussed in this paper.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

Simulation studies of plasma waves in the electron foreshock - The transition from reactive to kinetic instability

Particle simulation experiments were used to analyze the electron beam-plasma instability. It is shown that there is a transition from the reactive state of the electron beam-plasma instability to the kinetic instability of Langmuir waves. Quantitative tests, which include an evaluation of the dispersion relation for the evolving non-Maxwellian beam distribution, show that a quasi-linear theory describes the onset of this transition and applies again fully to the kinetic stage. This stage is practically identical to the late stage seen in simulations of plasma waves in the electron foreshock described by Dum (1990).

Dum, C. T.↗
DOE OSTI2013

Parametric instability of a monochromatic Alfven wave: Perpendicular decay in low beta plasma

Two-dimensional hybrid simulations are performed to investigate the parametric decay of a monochromatic Alfven wave in low beta plasma. Both the linearly and left-hand polarized pump Alfven waves are considered in the paper. For the linearly polarized pump Alfven wave, either a parallel or obliquely propagating wave can lead to the decay along the perpendicular direction. Initially, the parametric decay takes place along the propagating direction of the pump wave, and then the decay occurs in the perpendicular direction. With the increase of the amplitude and the propagating angle of the pump wave (the angle between the propagating direction of the pump wave and the ambient magnetic field), the spectral range of the excited waves becomes broad in the perpendicular direction. But the effects of the plasma beta on the spectral range of the excited waves in perpendicular direction are negligible. However, for the left-hand polarized pump Alfven wave, when the pump wave propagates along the ambient magnetic field, the parametric decay occurs nearly along the ambient magnetic field, and there is no obvious decay in the perpendicular direction. Significant decay in the perpendicular direction can only be found when the pump wave propagates obliquely.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Dual-mode resonant instabilities of the surface dust-acoustic wave in a Lorentzian plasma slab

The dual-mode resonant instabilities of the dust-acoustic surface wave propagating at the plasma-vacuum interfaces of the generalized Lorentzian dusty plasma slab are kinetically investigated. The dispersion relation is derived for the two propagation modes: symmetric and anti-symmetric waves. We have found that the temporal growth rate of the resonant instability increases with an increase of the slab thickness for both modes. Especially, the nonthermality of plasmas enhances the growth rate of the anti-symmetric resonant wave, and the nonthermal effect is enhanced as the slab thickness is increased. It is also found that the growth rate increases with increasing angular frequency of the rotating dust grain due to the enhanced resonant energy exchange.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Rotational and magnetic field instabilities in neutron stars

In this short review we present recent results on the dynamics of neutron stars and their magnetic fields. We discuss the progress that has been made, during the last 5 years, in understanding the rotational instabilities with emphasis to the one due to the f-mode, the possibility of using gravitational wave detection in constraining the parameters of neutron stars and revealing the equation of state as well as the detectability of gravitational waves produced during the unstable phase of a neutron star’s life. In addition we discuss the dynamics of extremely strong magnetic fields observed in a class of neutron stars (magnetars). Magnetic fields of that strength are responsible for highly energetic phenomena (giant flares) and we demonstrate that the analysis of the emitted electromagnetic radiation can lead in constraining the parameters of neutron stars. Furthermore, we present our results from the study of such violent phenomena in association with the emission of gravitational radiation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

EVIDENCE AGAINST THE OSCILLATING TWO-STREAM INSTABILITY AND SPATIAL COLLAPSE OF LANGMUIR WAVES IN SOLAR TYPE III RADIO BURSTS

Recently Thejappa et al. studied a specific Langmuir wave packet observed by STEREO A and argued based on the electric field from one of the three antennas that this packet satisfied the conditions for the oscillating two-stream instability (OTSI) and was undergoing wave collapse. We analyze the same event using all three electric components and show that, while the wave packet has structure consistent with collapse simulations and theory, the field strength is well below that required for collapse to proceed. Analyzing the three electric field components shows that the power spectrum and dominance of wave power perpendicular to the local magnetic field are inconsistent with OTSI. We show that this packet and other more intense packets are inconsistent with collapse and show no evidence of OTSI, but are likely trapped eigenmodes in density wells. Therefore, OTSI and collapse are unlikely explanations for intense Langmuir events observed in the solar wind.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2026

Capturing Secondary Kinetic Instabilities in Three‐Dimensional Dayside Reconnection Using an Improved Gradient‐Based Closure

Magnetic reconnection is a highly dynamic process that excites a wide variety of kinetic waves and instabilities. Transverse current sheet instabilities such as the lower-hybrid drift and secondary drift-kink instabilities in particular have been shown by kinetic simulations to modify the reconnection and introduce significant turbulence and mixing to the reconnection layer. Past studies using the ten-moment fluid model to capture important kinetic physics such as the electron inertia and full representation of the pressure tensor proved advantageous to a two-fluid representation of reconnection, but the model struggled when using a local relaxation closure for the heat flux to replicate the current sheet instabilities and subsequent mixing seen in kinetic simulations. This work uses the Gkeyll software framework to perform simulations of asymmetric reconnection based on the 16 October 2015 MMS crossing of a diffusion region, the Burch event. An improved gradient-based heat flux closure is implemented, showing significant improvement in secondary kinetic instabilities that grow in the current sheet. These instabilities generate turbulence which leads to growth of secondary magnetic islands and flux ropes.

Bradshaw, K. [Princeton University, NJ (United Sta↗
DOE OSTI2022

Observation and analysis of lower-hybrid-current-drive density limit in EAST

Lower hybrid current drive (LHCD) experiments with line-averaged density up to ~5.1 × 10 19 m –3 were performed in EAST L-mode plasmas. When the line-averaged density rises above a critical value, the hard x-ray (HXR) emission falls to the noise level, indicating that the LHCD density limit is encountered. The experimental results show that the LHCD density limit can be increased with higher wave source frequency (ƒ 0 ) and higher magnetic field (B t ). Although a higher LHCD density limit is obtained by a higher magnetic field for both 2.45 GHz and 4.6 GHz waves, the results show a stronger dependence on the magnetic field for the 4.6 GHz case. Analysis suggests that, for normal operation with a relatively low magnetic field (1.6 T $\leqslant$ B t $\leqslant$ 2.5 T) on EAST, the dominant mechanisms responsible for the LHCD density limit are different between the 2.45 GHz and 4.6 GHz waves. The wave accessibility plays a more significant role during 4.6 GHz LHCD experiments, while parasitic losses due to parametric decay instability (PDIs) dominate the accessibility issue in the 2.45 GHz case. Collisional loss in the scrape-off layer (SOL) may explain the 4.6 GHz result when combined with the accessibility limit at high density and low temperature.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1988

Multisatellite studies of ULF waves

Multisatellite studies of ULF waves are reviewed, with a special emphasis on compressional Pc 5 waves. The observations of the radial extent, azimuthal wave number and the field-aligned standing wave structure of the waves are described. When combined with plasma data, the waves appear to be consistent with drift-mirror waves originating from the pressure anisotropy of the ring current plasma. The most recent observations revealed some features not considered in previous theories of the drift-mirror wave: antisymmetric standing wave structure and rather small pressure anisotropy that can drive the waves to instability. Recent theoretical work shows that these observations can be explained if the coupling of the drift-mirror wave to the shear Alfven wave is properly treated in a realistic magnetic field geometry.

Takahashi, Kazue↗
DOE OSTI2021

A co-axial electron gun to generate millimeter-wave RF using the two-stream instability

A novel source for broadband millimeter-wave RF is being designed at Los Alamos National Laboratory utilizing the two-stream instability. This RF source offers the potential for consistent output power over a large bandwidth on a single device. The source is designed to use two co-axial electron beams coupled into solenoidal magnetic fields. This is accomplished using two cathodes independently modulated nested in each other. The electron beam energy from the innermost cathode will fall in the range between 15 and 20 keV with the beam energy from the outer cathode being 75%–95% of the inner beam energy. In order to efficiently match the beam from the outer cathode into the solenoidal magnetic field, shields are used around the cathodes to shape the electric field in the gun region to extend the electrostatic focal length of the beams for better coupling into the magnetic field. As a result, we present the design of electron guns and expected performance using Trak simulations.

47 OTHER INSTRUMENTATION↗
DOE OSTI2014

Density gradient effects on transverse shear driven lower hybrid waves

Shear driven instabilities are commonly observed in the near-Earth space, particularly in boundary layer plasmas. When the shear scale length (L{sub E}) is much less than the ion gyro-radius (ρ{sub i}) but greater than the electron gyro-radius (ρ{sub e}), the electrons are magnetized in the shear layer, but the ions are effectively un-magnetized. The resulting shear driven instability, the electron-ion hybrid (EIH) instability, is investigated in a new interpenetrating plasma configuration in the Auburn Linear EXperiment for Instability Studies. In order to understand the dynamics of magnetospheric boundary layers, the EIH instability is studied in the presence of a density gradient located at the boundary layer between two plasmas. This paper reports on a recent experiment in which electrostatic lower hybrid waves are identified as the EIH instability, and the effect of a density gradient on the instability properties are investigated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2012

Multi-dimensional instability of dust-acoustic solitary waves in a magnetized plasma with opposite polarity dust

Dust-acoustic (DA) solitary structures and their multi-dimensional instability in a magnetized dusty plasma (containing inertial negatively and positively charged dust particles, and Boltzmann electrons and ions) have been theoretically investigated by the reductive perturbation method, and the small-k perturbation expansion technique. It has been found that the basic features (polarity, speed, height, thickness, etc.) of such DA solitary structures, and their multi-dimensional instability criterion or growth rate are significantly modified by the presence of opposite polarity dust particles and external magnetic field. The implications of our results in space and laboratory dusty plasma systems have been briefly discussed.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2014

Modulational instability and associated rogue structures of slow magnetosonic wave in Hall magnetohydrodynamic plasmas

The modulational instability and associated rogue structures of a slow magnetosonic wave are investigated for a Hall magnetohydrodynamic plasma. Nonlinear Schrodinger equation is obtained by using the multiple scale method, which shows a modulationally unstable slow magnetosonic mode evolving into bright wavepackets. The dispersive effects induced by the Hall electron current increase with the increase in plasma β and become weaker as the angle of propagation increases. The growth rate of the modulational instability also increases with the increase in plasma β. The growth rate is greatest for the parallel propagation and drops to zero for perpendicular propagation. The envelope wavepacket of a slow magnetosonic is widened with less oscillations as plasma β increases. But the wavepacket becomes slightly narrower and more oscillatory as the angle of propagation increases. Further a non-stationary envelope solution of the Peregrine soliton is analyzed for rogue waves. The Peregrine soliton contracts temporally and expands spatially with increase in plasma β. However, the width of a slow magnetosonic Peregrine soliton decreases both temporally and spatially with increase of the propagation angle.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2021

Drift waves enstrophy, zonal flow, and nonlinear evolution of the modulational instability

The interaction of the drift wave (DW) turbulence and zonal flow (ZF) is investigated with the modified Hasegawa–Mima equation taking into account the backreaction of ZF velocity on DW turbulence. It is shown that the y-averaged enstrophy of DW turbulence and the velocity of ZF are intrinsically related. By utilizing this feature, a nonlinear stage of DW modulational instability is considered within the framework of the wave kinetic equation. It is shown that in this approximation, the nonlinear stage of the modulational instability results in the collapsing solutions, accompanied by the “wave breaking” phenomenon. Numerical simulations based on the Hasegawa–Mima equation show that for a weak DW turbulence, Φ ̃ = ( e φ ̃ / T e ) ( L n / ρ s ) ⪝ 1 , the collapsing-like features on both ZF and y-averaged enstrophy of DW turbulence decay in time and then re-emerge again at different locations. For the case of a strong DW turbulence, Φ ̃ > 1 , where nonlinear interactions of DW harmonics dominate, stable spatial structures of ZF and y-averaged enstrophy of DW turbulence emerge.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1985

Simultaneous excitation of large-scale geomagnetic field fluctuations and plasma density irregularities by powerful radio waves

The physical mechanism of thermal filamentation instability of radio waves whose frequencies can be as low as in the VLF band and as high as in the SHF band are investigated. This instability can excite large-scale magnetic and plasma density fluctuations simultaneously in the ionosphere and magnetosphere. Relevant experiments are reviewed in terms of this instability and other mechanisms.

Lee, M. C.↗
NASA NTRS1976

Filamentation instability of a large amplitude whistler wave

Experiments performed in a pulsed afterglow plasma column with specified parameters revealed a filamentation instability of a large-amplitude whistler wave launched from antennas which produce a diverging energy flow in the linear regime. The difficult problem of diagnosing local density perturbations in a magnetized plasma in the presence of large-amplitude RF signals and nonuniform anisotropic electron distributions is discussed. Since Langmuir probes are too unreliable under these conditions, a microwave probe is developed based on the principle of the cavity shift method. The temporal and spatial evolution of the duct formation and wave propagation are shown. The role of the observed electron heating in the filamentation process is examined. The observed self-focusing process appears to be the result of the reinforcing interaction between the wave-induced density depression and the density-induced wave refraction. Interesting applications are noted.

Stenzel, R. L.↗
NASA NTRS1997

Hydrodynamic Instability in an Extended Landau/Levich Model of Liquid-Propellant Combustion at Normal and Reduced Gravity

The classical Landau/Levich models of liquid-propellant combustion, despite their relative simplicity, serve as seminal examples that correctly describe the onset of hydrodynamic instability in reactive systems. Recently, these two separate models have been combined and extended to account for a dynamic dependence, absent in the original formulations, of the local burning rate on the local pressure and temperature fields. The resulting model admits an extremely rich variety of both hydrodynamic and reactive/diffusive instabilities that can be analyzed either numerically or analytically in various limiting parameter regimes. In the present work, a formal asymptotic analysis, based on the realistic smallness of the gas-to-liquid density ratio, is developed to investigate the combined effects of gravity and other parameters on the hydrodynamic instability of the propagating liquid/gas interface. In particular, an analytical expression is derived for the neutral stability boundary A(p)(k), where A(p) is the pressure sensitivity of the burning rate and k is the wavenumber of the disturbance. The results demonstrate explicitly the stabilizing effect of gravity on long-wave disturbances, the stabilizing effect of viscosity (both liquid and gas) and surface tension on short-wave perturbations, and the instability associated with intermediate wavenumbers for negative values of A(p). In the limiting case of weak gravity, it is shown that hydrodynamic instability in liquid-propellant combustion is a long-wave instability phenomenon, whereas at normal gravity, this instability is first manifested through O(1) wavenumber disturbances. it is also demonstrated that, in general, surface tension and the viscosity of both the liquid and gas phases each produce comparable stabilizing effects in the long-wavenumber regime, thereby providing important modifications to previous analyses in which one or more of these effects were neglected.

Margolis, S. B.↗