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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Electrostatic beam instabilities in a positive/negative ion plasma

This paper examines the linear theory of electrostatic waves and instabilities in an unmagnetized, homogeneous Vlasov plasma. The first configuration considered is that of a stable plasma with three Maxwellian components: electrons, positive ions, and negative ions. The dispersion properties of the lightly damped ion modes are studied as a function of relative electron density and relative component temperatures. The second configuration considered is that of a tenuous electron-ion beam with drift speed streaming through a negative/positive ion plasma. If the beam is very tenuous, an electron beam instability is excited; if the beam is more dense, the instability becomes Buneman-like with parabolic dispersion. The thresholds and maximum growth rates of these instabilities are described as functions of the beam density and drift speed.

Galvez, Miguel↗
NASA NTRS1986

A review of broad-band electrostatic waves in the magnetotail

Recent results showing that ions beams are the cause of generating broad-band electrostatic waves in the magnetotail, as well as theoretical work in good agreement with the spectrum observed, is reviewed. The implications of this for the transport and other dynamics of the magnetotail are discussed.

Grabbe, Crockett L.↗
NASA NTRS1987

Numerical study of the spectrum of broadband electrostatic noise in the magnetotail

A numerical study of the spectrum of broadband electrostatic noise (BEN) generated by ion beams in the plasma sheet boundary layer (PSBL) is presented, in which two cases are analyzed. The first case is concerned with a single hot-electron species. In the second case, a second population of cold electrons (arising from diffusion from the lobe into the PSBL) is introduced. The presence of the second electron component in the dispersion relation for generating BEN was found to significantly increase the upper frequency range of the unstable spectrum, enhancing the associated growth rates. It is shown that ion beam instabilities can explain most major features of the observed BEN spectrum. The results explain the gradual rise in the upper frequency range of BEN as a spacecraft approaches the plasma sheet from the lobe, and the sudden jump in that frequency up to near the plasma frequency upon crossing the PSBL.

Grabbe, Crockett L.↗
NASA NTRS1987

An analysis of the shocklike electrostatic noise observed during AMPTE solar wind ion releases

Electrostatic waves produced by the interaction of the ion cloud with the solar wind are analyzed in order to explain the shocklike noise detected by the Ion Release Module instruments during the Active Magnetospheric Particle Tracer Explorers solar wind ion releases. The results indicate that the shocklike noise can be generated by two instabilities, an ion-electron instability that occurs for waves propagating parallel to the solar wind velocity and an ion-ion instability that occurs for waves propagating at a large angle to the solar wind direction. Both instabilities give high growth rates for both the lithium and barium releases. The calculated results agree with the observed ones in all main features. In the earlier stage of the ion cloud expansion, both instabilities are likely to occur, while in the later stage the ion-ion instability is more likely to occur.

Ma, T. Z.↗
NASA NTRS1986

Effects of warm streaming electrons on electrostatic shock solutions

A plasma model consisting of warm downward streaming electrons, cool Boltzmann electrons, cold upward streaming ions, and hot Boltzmann ions is considered. It is shown that there is little difference between having a finite temperature in the electron beam and leaving the beam cold. This implies a greater utility for a cold electron beam model, and adds weight to the idea that the smaller amplitude electrostatic shocks seen in conjunction with ion beams are nonlinear ion acoustic modes.

Witt, Earl↗
NASA NTRS1987

Experimental tests of a toroidal electrostatic analyzer

A toroidal electrostatic analyzer of a design suitable for space plasma instrumentation has been constructed and tested. Experimental results are compared with second-order ion optical theory and are in good agreement. Verifying the ion optics of the toroid was simplified by use of a position-sensing microchannel-plate detector mounted on a positioning system with three translational degrees of freedom located at the toroid exit. The toroidal analyzer described here is the first optical element in a fully toroidal mass spectrograph intended for analysis of kilovolt magnetospheric plasmas.

Young, D. T.↗
NASA NTRS1988

Electrostatic Liquid-Drop-Levitation System

Electrostatic levitator has levitated drops of liquid up to 4 mm in diameter while maintaining spherical drop shapes. Stable levitation of spherical drops valuable in experiments involving super-cooling, solidification, and crystal growth.

Rhim, Won Kyu↗
NASA NTRS1988

Approximations For Predicting Electrostatic Discharges

Report provides approximate equations for capacitances and ratios of maximum electrostatic field strengths to potentials of variously shaped electrodes in vicinity of ground planes. Maximum-field-strength/potential ratio of given electrode used in conjunction with measured or estimated potential to determine whether discharge is likely. Capacitance and potential give measure of maximum energy release and maximum damage done by discharge.

Edmonds, Larry D.↗
NASA NTRS1987

GRADIO three-axis electrostatic accelerometers

Dedicated accelerometers for satellite gravity gradiometry (GRADIO project) are described. The design profits from experience acquired with the CACTUS accelerometer payload of the satellite CASTOR-D5B and studies of highly accurate accelerometers for inertial navigation. The principle of operation, based on a three-axis electrostatic suspension of a cubic proof mass, is well suited for the measurements of accelerations less than 0.0001 m/sec/sec. A resolution better than 10 to the minus 11th power m/sec/sec/sq root Hz is expected.

Bernard, A.↗
NASA NTRS1987

Particle and fluid simulations of resistive current-driven electrostatic ion cyclotron waves

The results from 1-D numerical simulations of electrostatic ion cyclotron waves (EIC) are presented for a model in which the electrons are a resistive (collisional) fluid. Simulations of both the kinetic and fluid descriptions are performed and compared in order to assess the fundamental limitations of fluid theory for EIC waves. The effect of ion-neutral collisions is also included using a simple Monte Carlo technique. It is found that a small ion-neutral collision frequency destroys the frequency harmonic coupling of kinetic EIC waves and tends to validate the fluid description. The saturation amplitude of the current-driven EIC instability is in agreement with recent laboratory experiments. The coherent nature (extremely narrow spectral width) and phase velocity agree with ground based (coherent backscatter radars) and in situ observations of current-driven EIC waves in the high latitude ionosphere.

Seyler, Charles E.↗
NASA NTRS1987

The emissions of broadband electrostatic noise in the near vicinity of the Shuttle Orbiter

Measurements of the Space Shuttle environment from the STS-3 and Spacelab 2 missions indicate the presence of oblique ion streams and broadband electrostatic noise. A two-dimensional theoretical model is applied to study a possible causal relationship between the ion streams and the broadband noise, especially in terms of the ion acoustic wave and ion-ion wave modes. This model predicts the generation of waves with frequencies ranging from the ion cyclotron frequency up to values greater than the ion plasma frequency, with the maximum growth rate occurring in the 10-kHz range. These results are consistent with the observational data from the STS-3 mission. The model also shows that these two wave modes can coexist only when the wave vectors of the two wave modes are nearly perpendicular. The parametric dependence of the wave instabilities on the plasma parameters and the inclination of the wave propagation vector is also studied.

Hwang, K. S.↗
NASA NTRS1987

Electrostatic waves in the magnetosphere of Uranus

Observations of electrostatic waves in the magnetosphere of Uranus are discussed with attention focused on the Bernstein emissions. The most intense Bernstein waves were observed near the magnetic equator of the planet, even though the tilt of the Uranian magnetic moment is very large relative to the rotational axis. In addition to the Bernstein modes, a number of highly sporadic emissions were detected in the vicinity of the Miranda L shell.

Kurth, W. S↗
NASA NTRS1988

Electrostatic ion instabilities in the presence of parallel currents and transverse electric fields

The electrostatic ion instabilities are studied for oblique propagation in the presence of magnetic field-aligned currents and transverse localized electric fields in a weakly collisional plasma. The presence of transverse electric fields result in mode excitation for magnetic field aligned current values that are otherwise stable. The electron collisions enhance the growth while ion collisions have a damping effect. These results are discussed in the context of observations of low frequency ion modes in the auroral ionosphere by radar and rocket experiments.

Ganguli, G.↗
NASA NTRS1988

Kinetic theory for electrostatic waves due to transverse velocity shears

A kinetic theory in the form of an integral equation is provided to study the electrostatic oscillations in a collisionless plasma immersed in a uniform magnetic field and a nonuniform transverse electric field. In the low temperature limit the dispersion differential equation is recovered for the transverse Kelvin-Helmholtz modes for arbitrary values of K parallel, where K parallel is the component of the wave vector in the direction of the external magnetic field assumed in the z direction. For higher temperatures the ion-cyclotron-like modes described earlier in the literature by Ganguli, Lee and Plamadesso are recovered. In this article, the integral equation is reduced to a second-order differential equation and a study is made of the kinetic Kelvin-Helmholtz and ion-cyclotron-like modes that constitute the two branches of oscillation in a magnetized plasma including a transverse inhomogeneous dc electric field.

Ganguli, G.↗
NASA NTRS1988

A new quasi-thermal trap model for solar flare hard X-ray bursts - An electrostatic trap model

A new quasi-thermal trap model of solar flare hard X-ray bursts is presented. The new model utilizes the trapping ability of a magnetic mirror and a magnetic field-aligned electrostatic potential produced by differences in anisotropies of the electron and ion distribution function. It is demonstrated that this potential can, together with the magnetic mirror itself, effectively confine electrons in a trap, thereby enhancing their bremsstrahlung yield per electron. This analysis makes even more untenable models involving precipitation of the bremsstrahlung-producing electrons onto a cold target.

Spicer, D. S.↗
NASA NTRS1988

Generation, saturation, and convection of electrostatic waves in Jupiter's shock foot

In this paper, a model is developed for the analysis of the electrostatic waves produced in the shock foot at Jupiter. It is shown that an ion beam instability involving the ions reflected at the shock ramp and the incoming solar-wind electrons produces waves at the observed frequencies and that saturation via orbit diffusion limits the waves to amplitudes near to what is observed. Results from a two-dimensional model of the reflected beam in the foot indicate that the waves propagate against the solar wind away from the shock ramp and are amplified up to their saturation amplitudes. The saturation results, combined with the electron temperature profile due to wave-particle interactions predicted by quasi-linear theory, reproduce a wave amplitude profile for the shock foot that is in reasonable agreement with the observations.

Moses, S. L.↗
NASA NTRS1988

Nature and the nonlinear evolution of electrostatic waves associated with the AMPTE solar wind releases

The nonlinear evolution of the electrostatic waves observed during the AMPTE (Active Magnetosphere Particle Tracer Explorers) solar wind releases is investigated. Previous linear studies indicate two distinct sets of instabilities may be responsible for the generation. One set consists of ion-acoustic type instabilities which are insensitive to the presence of a background magnetic field, while the other group corresponds to the modified two stream instabilities and requires the solar wind flow to be across the ambient magnetic field. To establish which set of instabilities is more viable a detailed linear Vlasov theory has been conducted by numerically solving the full electromagnetic dispersion relation. In addition both the plasma wave as well as the magnetic field measurements by the IRM (Ion Release Module) spacecraft were used to correlate the frequency and the power of the observed waves with the magnitude and the direction of the solar wind magnetic field. The results of these analyses indicate that the ion-acoustic type instabilities have growth rates that are an order of magnitude or more larger than those of the modified two stream instabilities. Results show that both the solar wind protons and the released ions may be heated and accelerated in the directions oblique to the solar wind flow velocity.

Omidi, N.↗
NASA NTRS1988

A description of electron heating with an electrostatic potential jump in a parallel, collisionless, fire hose shock

The electron heating required if protons scatter elastically in a parallel, collisionless shock is calculated. Near-elastic proton scattering off large amplitude background magnetic field fluctuations might be expected if the waves responsible for the shock dissipation are generated by the fire hose instability. The effects of an electrostatic potential jump in the shock layer are included by assuming that the energy lost by protons in traversing the potential jump is converted into electron thermal pressure. It is found that the electron temperature increase is a strong function of the potential jump. Comparison is made to the parallel shock plasma simulation of Quest (1987).

Ellison, Donald C.↗