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Results for “collisionless plasma”

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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Gravitational Landau damping for an isotropic cluster of stars

The problem of ascertaining the dynamical stability and the existence of Landau damping in static, isotropic 'collisionless' star clusters is addressed. The second-order formalism of Kandrup and Sygnet (1985) is applied to a homogeneous and isotropic plasma, demonstrating formally that the unperturbed configuration will always be stable and that the modes must be purely oscillatory. The form of these modes is explicitly examined, culminating in an analytic expression for the time evolution of the density induced by an initial perturbation. It is shown how these considerations can be adapted trivially to localized, nonradial disturbances of a self-gravitating system of stars. The possible existence of gravitational Landau damping for more generic perturbations is discussed.

Habib, Salman↗
DOE OSTI2026

Understanding cold electron impact on parallel-propagating whistler chorus waves via moment-based quasilinear theory

Earth's magnetosphere hosts a wide range of collisionless particle populations that interact through various wave-particle processes. Among these, cold electrons, with energies below 100 eV, often dominate the plasma density but remain poorly characterized due to measurement challenges such as spacecraft charging and photoelectron contamination. Understanding the contribution of these cold populations to wave–particle interaction is of significant interest. Recent kinetic simulations identified a secondary drift-driven instability, in which parallel-propagating whistler-mode chorus waves excite oblique electrostatic whistler waves near the resonance cone and Bernstein-mode turbulence. These secondary modes enable a new channel of energy transfer from the parallel-propagating whistler wave to the cold electrons. In this work, we develop a moment-based quasilinear theory of the secondary instabilities to quantify such energy exchange. Our results show that these secondary instabilities persist for a wide range of parameters and, in many cases, lead to nearly complete damping of the primary wave. Such secondary instability might limit the amplitude of parallel-propagating whistler waves in Earth's magnetosphere and might explain why high-amplitude oblique whistler or electron Bernstein waves are rarely observed simultaneously with high-amplitude field-aligned whistler waves in the inner magnetosphere.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2010

Polycyclic Aromatic Hydrocarbons

Carbonaceous materials play an important role in space. Polycyclic Aromatic Hydrocarbons (PAHs) are a ubiquitous component of the carbonaceous materials. PAHs are the best-known candidates to account for the IR emission bands. They are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge is to reproduce in the laboratory the physical conditions that exist in the emission and absorption interstellar zones. The harsh physical conditions of the ISM -low temperature, collisionless, strong UV radiation fields- are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions and radicals are formed from the neutral precursors in an isolated environment at low temperature and probed with high-sensitivity cavity ringdown spectroscopy in the NUV-NIR range. Carbon nanoparticles are also formed during the short residence time of the precursors in the plasma and are characterized with time-offlight mass spectrometry. These experiments provide unique information on the spectra of large carbonaceous molecules and ions in the gas phase that can now be directly compared to interstellar and circumstellar observations (IR emission bands, DIBs, extinction curve). These findings also hold great potential for understanding the formation process of interstellar carbonaceous grains. We will review recent progress in the experimental and theoretical studies of PAHs, compare the laboratory data with astronomical observations and discuss the global implications.

Salama, Farid↗
NASA NTRS1973

Research in plasma physics

Three aspects of barium ion cloud dynamics are discussed. First, the effect of the ratio of ion cloud conductivity to background ionospheric conductivity on the motion of barium ion clouds is investigated and compared with observations of barium ion clouds. This study led to the suggestion that the conjugate ionosphere participates in the dynamics of barium ion clouds. Second, analytic work on the deformation of ion clouds is presented. Third, a linearized stability theory was extended to include the effect of the finite extent of an ion cloud, as well as the effect of the ratio of ion cloud to ionospheric conductivities. The stability properties of a plasma with contra-streaming ion beams parallel to a magnetic field are investigated. The results are interpreted in terms of parameters appropriate for collisionless shock waves. It is found that this particular instability can be operative only if the up-stream Alfven Mach number exceeds 5.5.

Source record↗
NASA NTRS1989

Ion reflection and downstream thermalization at the quasi-parallel bow shock

Using the results of ISEE 2 plasma and magnetic field measurements, two features related to the ion thermalization process at high-Mach-number (M above 2) quasi-parallel collisionless shocks are discussed. These are the presence of a coherent secondary beam of ions within the shock layer which is considered to be produced by reflection, and downstream ion distributions which contain both a relatively cold core of directly transmitted ions and a hotter 'shell' of ions, which appear to result from the disruption and scattering of ions initially reflected at the shock. Evidence is presented that coherent ion reflection is an important element of the ion energy dissipation process at high-Mach-number quasi-parallel shocks.

Gosling, J. T.↗
NASA NTRS1972

VLF/ELF input impedance of an arbitrarily oriented loop antenna in a cold collisionless multicomponent magnetoplasma.

A study is made of the input impedance Z of a small strip-loop antenna with arbitrary orientation in a cold collisionless uniform multicomponent magnetoplasma. Assuming a uniform current distribution, an integral expression for Z is derived which is valid for arbitrary values of driving frequency, plasma composition and density, loop orientation angle, and static magnetic field strength. The integral expression is evaluated numerically for the VLF/ELF range in a plasma modeled upon the inner magnetosphere. Approximate closed-form expressions for Z are also developed. It is found that the loop VLF/ELF input reactance is essentially identical to its free space self inductance. Also the loop radiation resistance is found to be a strong function of the loop orientation angle for frequencies near the lower-hybrid-resonance frequency or below the proton gyrofrequency.

Wang, T. N. C.↗
NASA NTRS1973

Kinetic theory analysis of solar wind interaction with planetary objects

A purely kinetic treatment is proposed for the interaction of the solar wind with any small planetary object. Small refers to those cases where the solar wind proton's thermal gyroradius is arbitrarily taken to be greater than 0.1 radius of the object under investigation. The 'object' may possibly include an ionosphere or magnetosphere. The collisionless Boltzmann equation, neglecting the magnetic field, is used to calculate steady-state profiles of density and velocity around the obstacle. A low density plasma void in the umbral region and a compression in the penumbral region are clearly found. The present technique, despite its neglect of the interplanetary magnetic field, is proposed as an alternative zeroth order approach to the continuum, local magnetic anomaly, and guiding center approaches used by others for the particular case of moon. Some recent, potentially relevant, observations on and in front of the moon are discussed.

Wu, S. T.↗
NASA NTRS1987

Electric potential distributions at the interface between plasmasheet clouds

At the interface between two plasma clouds with different densities, temperatures, and/or bulk velocities, there are large charge separation electric fields which can be modeled in the framework of a collisionless theory for tangential discontinuities. Two different classes of layers were identified: the first one corresponds to (stable) ion layers which are thicker than one ion Lamor radius; the second one corresponds to (unstable) electron layers which are only a few electron Larmor radii thick. It is suggested that these thin electron layers with large electric potential gradients (up to 400 mV/m) are the regions where large-amplitude electrostatic waves are spontaneously generated. These waves scatter the pitch angles of the ambient plasmasheet electron into the atmospheric loss cone. The unstable electron layers can therefore be considered as the seat of strong pitch angle scattering for the primary auroral electrons.

Evans, D. S.↗
NASA NTRS2012

MESSENGER Magnetic Field Observations of Upstream Ultra-Low Frequency Waves at Mercury

The region upstream from a planetary bow shock is a natural plasma laboratory containing a variety of wave particle phenomena. The study of foreshocks other than the Earth's is important for extending our understanding of collisionless shocks and foreshock physics since the bow shock strength varies with heliocentric distance from the Sun, and the sizes of the bow shocks are different at different planets. The Mercury's bow shock is unique in our solar system as it is produced by low Mach number solar wind blowing over a small magnetized body with a predominately radial interplanetary magnetic field. Previous observations of Mercury upstream ultra-low frequency (ULF) waves came exclusively from two Mercury flybys of Mariner 10. The MESSENGER orbiter data enable us to study of upstream waves in the Mercury's foreshock in depth. This paper reports an overview of upstream ULF waves in the Mercury's foreshock using high-time resolution magnetic field data, 20 samples per second, from the MESSENGER spacecraft. The most common foreshock waves have frequencies near 2 Hz, with properties similar to the I-Hz waves in the Earth's foreshock. They are present in both the flyby data and in every orbit of the orbital data we have surveyed. The most common wave phenomenon in the Earth's foreshock is the large-amplitude 30-s waves, but similar waves at Mercury have frequencies at near 0.1 Hz and occur only sporadically with short durations (a few wave cycles). Superposed on the "30-s" waves, there are spectral peaks at near 0.6 Hz, not reported previously in Mariner 10 data. We will discuss wave properties and their occurrence characteristics in this paper.

Le, G.↗
NASA NTRS2012

MESSENGER Observations of ULF Waves in Mercury's Foreshock Region

The region upstream from a planetary bow shock is a natural plasma laboratory containing a variety of wave particle phenomena. The study of foreshocks other than the Earth s is important for extending our understanding of collisionless shocks and foreshock physics since the bow shock strength varies with heliocentric distance from the Sun, and the sizes of the bow shocks are different at different planets. The Mercury s bow shock is unique in our solar system as it is produced by low Mach number solar wind blowing over a small magnetized body with a predominately radial interplanetary magnetic field. Previous observations of Mercury upstream ultra-low frequency (ULF) waves came exclusively from two Mercury flybys of Mariner 10. The MESSENGER orbiter data enable us to study of upstream waves in the Mercury s foreshock in depth. This paper reports an overview of upstream ULF waves in the Mercury s foreshock using high-time resolution magnetic field data, 20 samples per second, from the MESSENGER spacecraft. The most common foreshock waves have frequencies near 2 Hz, with properties similar to the 1-Hz waves in the Earth s foreshock. They are present in both the flyby data and in every orbit of the orbital data we have surveyed. The most common wave phenomenon in the Earth s foreshock is the large-amplitude 30-s waves, but similar waves at Mercury have frequencies at ~ 0.1 Hz and occur only sporadically with short durations (a few wave cycles). Superposed on the "30-s" waves, there are spectral peaks at ~ 0.6 Hz, not reported previously in Mariner 10 data. We will discuss wave properties and their occurrence characteristics in this paper.

Le, Guan↗
DOE OSTI2026

Verification of global gyrokinetic simulation of low frequency mode excited by thermal plasma in spherical tokamak

A low frequency Alfven eigenmode in the ST40 spherical tokamak (ST) is found to be resonantly excited by thermal ions from global gyrokinetic GTC simulations. The analyses of phase-space resonances and wave-particle energy exchanges show that the Beta-induced Alfvén-Acoustic Eigenmode (BAAE) is primarily driven unstable by thermal ions, but is stabilized by energetic particles (EPs). When all kinetic effects are artificially suppressed, GTC simulations in the ideal magnetohydrodynamic (MHD) limit confirm the existence of the MHD eigenmode with a frequency in the BAAEs gap, as previously found by the ideal MHD code NOVA. The kinetic effects of thermal ions induce a frequency downshift compared to the stable BAAE in the MHD simulations. These results support the verification for global gyrokinetic simulations of the BAAE in the ST. However, the simulations do not explain the experimental observations of the BAAE in the ST40, possibly owing to the limitation of the collisionless gyrokinetic Monte Carlo model for the EPs.

Alfvén eigenmode↗
NASA NTRS1979

Temperature anisotropy of the Jovian sulfur nebula

The apparent paradox between the reported observation of a 3-eV gyration energy of Jupiter's ionized sulfur nebula and its observed thickness is discussed. An observation of the thickness of the cloud taken nearly edge-on is presented and shown to imply a large bounce-averaged anisotropy of the sulfur in temperature. These observations are used to construct a self-consistent model of the sulfur nebula in which the sulfur ions are injected by Io as ions and remain sufficiently collisionless in the magnetosphere to maintain the anisotropy for a time longer than a characteristic diffusion time. It is also shown that the proton-electron plasma is collisionally thermalized and provides an adequate means of tapping the rotational energy of the planet to provide the power radiated in the sulfur lines.

Eviatar, A.↗
NASA NTRS1995

Investigation of intrinsic variability in one-dimensional parallel shocks using steady state hybrid simulations

We have developed a means of producing a steady state hybrid simulation of a collisionless shock. The shock is stopped in the simulation box by transforming into the shock frame and by modifying the downstream boundary conditions to allow the plasma to flow through the simulation box. Once the shock is stationary in the box frame, the simulation can be run for an arbitrary time with a fixed box size and a fixed number of simulation particles. Using this technique, we have shown that certain gross properties associated with the shock, such as the particle distribution function (including energetic particles produced by Fermi acceleration) and the flow speed profile, are constant (except for statistical variations) over hundreds of gyroperiods when averaged over times short compared to the average residence time of energetic particles. Our results imply that any microphysical processes responsible for particle heating and/or injection into the Fermi mechanism can be viewed as smooth and continuous on timescales longer than a few gyroperiods.

Bennett, Lee↗
DOE OSTI2023

Electron heating in kinetic-Alfvén-wave turbulence

We report analytical and numerical investigations of subion-scale turbulence in low-beta plasmas using a rigorous reduced kinetic model. We show that efficient electron heating occurs and is primarily due to Landau damping of kinetic Alfvén waves, as opposed to Ohmic dissipation. This collisionless damping is facilitated by the local weakening of advective nonlinearities and the ensuing unimpeded phase mixing near intermittent current sheets, where free energy concentrates. The linearly damped energy of electromagnetic fluctuations at each scale explains the steepening of their energy spectrum with respect to a fluid model where such damping is excluded (i.e., a model that imposes an isothermal electron closure). In conclusion, the use of a Hermite polynomial representation to express the velocity-space dependence of the electron distribution function enables us to obtain an analytical, lowest-order solution for the Hermite moments of the distribution, which is borne out by numerical simulations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1983

Hydromagnetic waves, turbulence, and collisionless processes in the interplanetary medium

An extended discussion is conducted concerning the origin and evolution of interplanetary hydromagnetic waves and turbulence, and their influence on the large scale dynamics of the solar wind. The solar wind is at present the preeminent medium for the study of hydromagnetic waves and turbulence, providing an opportunity for advancement of understanding of the most fundamental processes of the astrophysical plasmas. All interplanetary fluctuations whose time scale is observed to be greater than 1 sec can be regarded as hydromagnetic fluctuations. It has been found to be simplest, and generally very satisfactory, to model interplanetary variations as fluctuations in an MHD fluid. Attention is given to the classification of wave modes, geometrical hydromagnetics, Alfven wave pressure, rugged invariants, and the kinetic theory of collisionless processes.

Barnes, A.↗
NASA NTRS1992

Semikinetic and generalized transport models of the polar and solar winds

In order to gain a better understanding of the relative merits of the transport and kinetic approaches to modeling thermal space plasmas, a comparison is presented of a transport (bi-Maxwellian-based 16-moment equations) and a semikinetic description of supersonic flow in the solar wind and also of both supersonic and subsonic flows in the polar wind for 'steady state' conditions. The study shows: remarkable agreement between the two models for supersonic collisionless flows, even for the higher-order moments; the inadequacy of the semikinetic approach for modeling subsonic flows; and the superiority of the 16-moment transport over the semikinetic approach for modeling the solar wind. Further evidence that the bi-Maxwellian-based transport equations are a useful tool for studying 'thermal' space plasmas that develop non-Maxwellian features is provided.

Demars, H. G.↗
DOE OSTI2023

Isolation and phase-space energization analysis of the instabilities in collisionless shocks

We analyse the generation of kinetic instabilities and their effect on the energization of ions in non-relativistic, oblique collisionless shocks using a 3D-3V (three spatial with three velocity components) simulation by dHybridR, a hybrid particle-in-cell code. At sufficiently high Mach number, quasi-perpendicular and oblique shocks can experience rippling of the shock surface caused by kinetic instabilities arising from free energy in the ion velocity distribution due to the combination of the incoming ion beam and the population of ions reflected at the shock front. To understand the role of the ripple on particle energization, we devise a new instability isolation method to identify the unstable modes underlying the ripple and interpret the results in terms of the governing kinetic instability. We generate velocity-space signatures using the field–particle correlation technique to look at energy transfer in phase space from the isolated instability driving the shock ripple, providing a viewpoint on the different dynamics of distinct populations of ions in phase space. Together, the field–particle correlation technique and our new instability isolation method provide a unique viewpoint on the different dynamics of distinct populations of ions in phase space and allow us to completely characterize the energetics of the collisionless shock under investigation.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗