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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Scaling of the beam-plasma discharge

A theoretical analysis is presented of the scaling of the critical beam current required for ignition and the narrow band emissions observed for beam currents less than critical in a beam plasma discharge experiment. The theory of the two-stream interaction between a nonrelativistic cold electron beam and a plasma in the presence of a magnetic field is developed, and conditions for the two-stream instability and the resulting amplification are derived. It is shown that the experimentally observed scaling is consistent with the assumption that the ignition triggering occurs when an instability near the electron plasma frequency is excited. Finally, it is shown that the wave emissions observed in the subthreshold range can be explained by the excitation of the kinetic instability of the upper branch and convective saturation.

Rowland, H. L.↗
NASA NTRS1976

Plasma processes in space

Elementary microscopic interactions in plasmas are described. The importance of plasma physics in space studies is illustrated by examining several phenomena which cannot be explained satisfactorily by MHD theory. These include kinetic instabilities, plasma turbulence in the bow shock, magnetic turbulence near the moon, VLF emissions in the magnetosphere, planetary and solar radio emissions, and interaction of planetary and cometary plasmas with the solar wind. Evidence for the existence of anomalous transport processes in terrestrial and planetary magnetospheres is presented.

Wu, C. S.↗
NASA NTRS1985

Thermalization of neutral-beam-injected ions by lower hybrid waves in Jupiter's magnetosphere

A theoretical analysis of lower-hybrid wave generation by a ring distribution of superthermal ions is presented. A kinetic instability of waves traveling across the magnetic field occurs when fast neutrals escaping from the Io plasma torus are reionized and accelerated to corotation speed in Jupiter's magnetosphere. Instability is possible for modest threshold values of V/a0 = 3 - 7 where V is the pickup gyrospeed and a0 is the background-ion thermal speed. Consequent effects include the relaxation of the pickup-ion distribution and the acceleration of superthermal electrons.

Barbosa, D. D.↗
NASA NTRS1998

Increased Stability in Crystal Growth Kinetics in Response to Bulk Transport Enhancement

High-resolution interferometry on facets of lysozyme crystals growing under steady external conditions revealed intrinsic kinetics instabilities that occur as fluctuations in the spacing of growth steps. The amplitude of these fluctuations is reduced by forced solution flow. This increased stability is interpreted in terms of the ratio of the characteristic rates of lattice incorporation and bulk transport. Apparently a steady state is approached as an asymptote of a continuous family of unsteady states.

Vekilov, Peter G.↗
NASA NTRS1998

Intrinsic Kinetics Fluctuations as Cause of Growth Inhomogeneity in Protein Crystals

Intrinsic kinetics instabilities in the form of growth step bunching during the crystallization of the protein lysozyme from solution were characterized by in situ high-resolution optical interferometry. Compositional variations (striations) in the crystal, which potentially decrease its utility, e.g., for molecular structure studies by diffraction methods, were visualized by polarized light reflection microscopy. A spatiotemporal correlation was established between the sequence of moving step bunches and the striations.

Vekilov, Peter G.↗
NASA NTRS2002

Fundamentals of Plasma Sails Propulsion Concept

The Mini-Magnetospheric Plasma Propulsion (M2P2), originally proposed by Winglee et al. [2000], is based on the two-fluid plasma model and requires a 15-km frontal standoff distance (or 20-km cross-sectional diameter) in order for the magnetic bubble to absorb sufficient momentum from the SW to accelerate a spacecraft to the unprecedented speeds of 50-80 km/s after an acceleration period of about three months. Winglee et al. [2000] derived the above size requirement based on an extrapolation of their simulated results in which a system much smaller than a M2P2 was used (p. 21,074 of their study). We submit, however, that a fluid model has no validity for such a small scale size-even in the region near the plasma source! It is assumed in the MHD fluid model, normally applied to the magnetosphere, that the characteristic scale-size is much greater than the Larmor radius and ion skin depth of the SW. In the case of the M2P2, however, the size of the magnetic bubble is actually less than or, at best, comparable to, the scale of these characteristic parameters and, therefore, a kinetic approach, which addresses the smallscale physical mechanisms involved, must be used. A fully three-dimensional version of the hybrid code is used in our M2P2 (Plasma Sails) studies was originally developed by Delamere et al. [1999]. The M2P2 plasma sail is an excellent application for this hybrid code. The primary advantage of this code is the seamless interface between fluid and kinetic descriptions of the ion populations. A kinetic description is not necessary for the dense inner regions of the magnetic bubble and tremendous computational savings can be realized by treating this dense, magnetized ion population with the fluid description. It is essential, however, that the outer bubble regions be treated kinetically as well as the SW protons. Comparison of full size M2P2 simulation based on 3D MHD and kinetic models show that kinetic treatment introduces much more asymmetry to the considering problem and the possibility of kinetic instabilities development.

Khazanov, G. V.↗
NASA NTRS2016

Special Issue the 12th International Conference on Substorms

The 12th International Conference on Substorms (ICS-12) was held at the Ise-Shima Royal Hotel in Shima, Japan, on November 10-14, 2014. There were 125 attendees including 68 from foreign countries. The ICS has been held every 2 years since 1992 to discuss substorms, which are fundamental global-scale disturbances in the Earth's magnetosphere. The year 2014 marked the 50th anniversary of the first publication about substorms (Akasofu 1964). The conference included three tutorial lecturers (Profs. S.-I. Akasofu, V. Angelopoulous, and D. Baker), as well as many international scientists, to discuss substorm processes in the tail, their Interactions with the inner magnetosphere and the ionosphere, substorm currents and their dynamics and energetics, the role of MagnetoHydroDynamics (MHD) and kinetic instabilities, storm-substorm relationships, ULFELFVLF waves, and non-Earth substorm-like features. Prof. Akasofu also gave an evening talk about the history of auroral research since the nineteenth century with photographs that inspired and intrigued the young scientists and students in attendance.

Shiokawa, Kazuo↗
NASA NTRS1992

Kinetic effects on the velocity-shear-driven instability

A comparison is made between the properties of the low-frequency long-wavelength velocity-shear-driven instability in kinetic theory and magnetohydrodynamics (MHD). The results show that the removal of adiabaticity along the magnetic field line in kinetic theory leads to modifications in the nature of the instability. Although the threshold for the instability in the two formalisms is the same, the kinetic growth rate and the unstable range in wave-number space can be larger or smaller than the MHD values depending on the ratio between the thermal speed, Alfven speed, and flow speed. When the thermal speed is much larger than the flow speed and the flow speed is larger than the Alfven speed, the kinetic formalism gives a larger maximum growth rate and broader unstable range in wave-number space. In this regime, the normalized wave number for instability can be larger than unity, while in MHD it is always less than unity. The normal mode profile in the kinetic case has a wider spatial extent across the shear layer.

Wang, Z.↗
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 NTRS1995

Heating and scattering of ring-beam distributions by turbulence

Pickup ions in the solar wind are initially are born in ring-beam distributions, i.e. f(v) varies as delta(v(sub perpendicular) - V(sub sw)sin(Theta)) delta(v(sub parallel) - V(sub sw)cos(Theta)), where Theta is the angle between the solar wind velocity and the IMF(Interplanetary Magnetic Field), and V(sub sw) is the solar wind speed. Often the distribution has been presumed to relax to a distribution that is isotropic in Theta and essentially mono-energetic, a shell or a 'bi-spherical distribution.' However solar wind turbulence is capable of heating the ring distribution on the timescale of a few tens of gyroperiods, a timescale not greatly distinct from that required for pitch angle scattering to a shell. To describe this effect, we have performed test-particle studies of the heating/scattering of the ring beam distribution by MHD turbulence, adopting various models for the MHD fluctuations, including slab and fully dynamic 2D and 3D incompressible turbulence. Furthermore, a system composed of a cold ion ring and a background plasma is unstable to several kinetic plasma instabilities. We carried out kinetic simulations of the ring beam distribution, showing that plasma instabilities also rapidly energize and scatter particles. Results will be presented comparing relaxation and heating rates of the ring-beam distribution by the various mechanisms.

Gray, P. C.↗
NASA NTRS1985

Plasma heating at collisionless shocks due to the kinetic cross-field streaming instability

Heating at collisionless shocks due to the kinetic cross-field streaming instability, which is the finite beta (ratio of plasma to magnetic pressure) extension of the modified two stream instability, is studied. Heating rates are derived from quasi-linear theory and compared with results from particle simulations to show that electron heating relative to ion heating and heating parallel to the magnetic field relative to perpendicular heating for both the electrons and ions increase with beta. The simulations suggest that electron dynamics determine the saturation level of the instability, which is manifested by the formation of a flattop electron distribution parallel to the magnetic field. As a result, both the saturation levels of the fluctuations and the heating rates decrease sharply with beta. Applications of these results to plasma heating in simulations of shocks and the earth's bow shock are described.

Winske, D.↗
NASA NTRS1995

Kinetic Kelvin-Helmholtz instability at a finite sized object

Two-dimensional hybrid simulations with particle ions and fluid electrons are used to calculate the kinetic evolution of the self-consistent flow around a two-dimensional obstacle with zero intrinsic magnetic field. Plasma outlfow from the obstacle is used to establish a boundary layer between the incoming solar wind and the outgoing plasma. Because the self-consistent flow solution, a velocity shear is naturally set up at this interface, and since the magnetic field for these simulations is transverse to this flow, the Kelvin-Helmholtz (K-H) instability can be excited at low-velocity shear. Simulations demonstrate the existence of the instability even near the subsolar location, which normally is thought to be stable to this instability. The apparent reason for this result is the overall time dependence at the boundary layer, which gives rise to a Rayleigh-Taylor like instability which provides seed perturbations for the K-H instability. These results are directly applicable to Venus, comets, artificial plasma releases, and laser target experiments. This result has potentially important ramifications for the interpretation of observational results as well as for an estimation of the cross-field transport. The results suggest that the K-H instability may play a role in dayside processes and the Venus ionopause, and may exist within the context of more general situations, for example, the Earth's magnetopause.

Thomas, V. A.↗
NASA NTRS1994

Coalescence of two current loops with a kink instability simulated by a three-dimensional electromagnetic particle code

We have studied the dynamics of a coalescence of current loops using three-dimensional electromagnetic (EM) particle simulation code. Our focus is the investigation of such kinetic processes as energy trasnfer, heating particles, and electromagnetic emissions associated with a current loop coalescence which cannot be studied by MHD simulations. First, the two loops undergo a pinching oscillation due to a pressure imbalance between the inside and outside of the current loop. During the pinching oscillation, a kinetic kink instability is excited and electrons in the loops are heated perpendicularly to an ambient magnetic field. Next, the two current loops collide and coalesce, while at the same time a helical structure grows further. Subsequently, the perturbed current, which is due to these helically bunched electrons, can drive a whistler instability. It should be noted in this case that the whistler wave is excited by the kinetic kink instability and not a beam instability. After the coalescence of two helical loops, tilting motions can be observed in the direction of left-hand rotation, and the helical structure will relax resulting in strong plasma heating mostly in the direction perpendicular to the ambient magnetic field. It is also shown that high-frequency electromagnetic waves can be emitted from the region where the two loops coalesce and propagate strongly in the direction of the electron drift velocity. These processes may be important in understanding heating mechansims for coronal loops as well as radio wave emission mechanisms from active regions of solar plasmas.

Nishikawa, K.-I.↗
NASA NTRS1987

A theory for the Langmuir waves in the electron foreshock

A comprehensive theory for the Langmuir waves in the earth's foreshock involving saturation of the kinetic version of the beam instability by quasi-linear relaxation is proposed in this paper. Reactive and kinetic beam instabilities are shown to be the two limiting versions of a single instability whose analytically and numerically derived descriptions are shown to form a consistent picture. It is pointed out that the reactive instability gives rise only to narrow-band growth while the kinetic instability gives rise to wide-band growth. Arguments for describing the Langmuir wave growth in terms of the kinetic instability are given, and four suppression mechanisms for the kinetic instability are discussed. It is suggested that quasi-linear relaxation limits the Langmuir growth and gives rise to distributions qualitatively similar to the observed distribution functions, and arguments in favor of this hypothesis are presented.

Cairns, Iver H.↗
NASA NTRS1985

Kinetic cyclotron and synchrotron maser instabilities - Radio emission processes by direct amplification of radiation

This article reviews the theory of the kinetic (cyclotron and synchroton) mase instabilities. The subject has been extensively developed in recent years by many authors, who have been incited by the research of the auroral kilometric radiation and other applications. The maser mechanism is appealing because it is simple and efficient, and can lead to direct amplification of radiation. Two types of electron distribution functions have been investigated so far. These are the loss-cone and hollow-beam disributions which may exist pervasively in many regions within and beyond the solar system. It is likely that the maser instabilities can have many potentially important applications to numerous radio emission processes observed in astrophysical research.

Wu, C. S.↗
NASA NTRS1983

A kinetic cross-field streaming instability

In a high-beta plasma the so-called modified-two-stream instability, which results from strongly magnetized electrons drifting relative to unmagnetized ions across a homogeneous magnetic field, is misnamed because the mode is highly kinetic, particularly when the relative streaming velocity exceeds the Alfven speed of the plasma. This kinetic cross-field streaming instability is investigated in detail, examining the effect of the electromagnetic terms and the stability boundaries in both low- and high-beta plasmas. An approximate dispersion relation showing the relation of this mode to the whistler is derived and solutions of it are compared with those obtained from the exact dispersion relation. The kinetic mode, unlike the usual modified-two-stream instability, is not stabilized by electromagnetic effects when the relative electron-ion drift speed exceeds the Alfven speed.

Wu, C. S.↗
NASA NTRS1984

Kinetic theory of current and density drift instabilities with weak charged-neutral collisions

This paper describes the linear kinetic theory of electrostatic instabilities driven by a density gradient drift and a magnetic-field-aligned current in a plasma with weak charged neutral collisions. The configuration is that of a uniform magnetic field B, a weak, uniform density gradient in the x direction and a weak, uniform electric field in the z direction. Collisions are represented by the BGK model. The transition from the (kinetic) universal density drift instability to the (fluidlike) current convective instability is studied in detail, and the short wavelength properties of the latter mode are investigated.

Gary, S. P.↗