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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Plasma wave phenomena at interplanetary shocks observed by the Ulysses URAP experiment

We present Ulysses URAP observations of plasma waves at seven interplanetary shocks detected between approximately 1 and 3 AU. The URAP data allows ready correlation of wave phenomena from .1 Hz to 1 MHz. Wave phenomena observed in the shock vicinity include abrupt changes in the quasi-thermal noise continuum, Langmuir wave activity, ion acoustic noise, whistler waves and low frequency electrostatic waves. We focus on the forward/reverse shock pair of May 27, 1991 to demonstrate the characteristics of the URAP data.

Lengyel-Frey, D.↗
NASA NTRS1993

Generation of waves in the Venus mantle by the ion acoustic beam instability

The ion acoustic beam instability is suggested as a mechanism to produce wave turbulence observed in the Venus mantle at frequencies 100 Hz and 730 Hz. The plasma is assumed to consist of a stationary cold O(+) ion plasma and a flowing, shocked solar wind plasma. The O(+) ions appear as a beam relative to the flowing ionosheath plasma which provides the free energy to drive the instability. The plasma is driven unstable by inverse electron Landau damping of an ion acoustic wave associated with the cold ionospheric O(+) ions. The instability can directly generate the observed 100 Hz waves in the Venus mantle as well as the observed 730 Hz waves through the Doppler shift of the frequency caused by the satellite motion.

Huba, J. D.↗
NASA NTRS1985

Ion-acoustic instabilities driven by an ion velocity ring

A ring distribution of ions in velocity space can generate electrostatic waves which propagate predominantly along an ambient magnetic field at frequencies comparable with the ion plasma frequency. A dispersion equation which accounts for these waves is presented, and solved analytically and numerically. It was found that ion-acoustic-like waves are excited in a plasma even if the electron temperature is comparable with the in temperature under the assumption of an anisotropic ion distribution.

Akimoto, K.↗
DOE OSTI2022

Direct Measurement of the Return Current Instability in a Laser-Produced Plasma

Measurements were made of the return current instability growth rate, demonstrating its concurrence with nonlocal transport. Thomson scattering was used to measure a maximum growth rate of 5.1 × 10 9 Hz, which was 3 times less than classical Spitzer-Härm theory predicts. Here, the measured plasma conditions indicate the heat flux was nonlocal, and Vlasov–Fokker-Planck simulations that account for nonlocality reproduce the measured growth rates. Furthermore, the threshold for the return current instability was measured (δ T = 0.017 ± 0.002) to be in good agreement with previous theoretical models.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1972

Structure of ion acoustic solitons and shock waves in a two-component plasma.

Time-independent solitary waves and shocks are investigated in a two-component plasma using a fluid model and kinetic theory. It is found that very small concentrations of a light ion can drastically alter the structure, changing the potential maximum by an order of magnitude. For a fixed Mach number, a critical density ratio of light to heavy ions is found at which the potential maximum changes discontinuously from a value large enough to reflect the light ions to one which allows them to traverse the shock front and enter the downstream flow. The downstream oscillatory structure normally seen in a shock is completely quenched by dissipation due to light ion reflection at concentrations of 3-8% He in an Ar plasma for typical electron to ion temperature ratios and Mach number values.

White, R. B.↗
NASA NTRS1981

Stationary electrostatic solitary waves in the auroral plasma

Time-stationary fluid equations are used to describe electrostatic solitons in an auroral plasma of cold ionospheric and hot plasma sheet particles. A one-dimensional fluid analysis of the four component model auroral plasma indicates that at least two different, weakly damped, small amplitude electrostatic solitons can propagate along the geomagnetic field. The slower of the two is a generalization of an ion-acoustic solitary wave in a multi-component plasma, and ion inertia is negligible for the faster mode which is supported by the two electron components and resembles a clump of shielded negative space charge convected by the drifting plasma sheet electrons. Some expected features of the large amplitude properties are indicated qualitatively, and an analogy is considered between the theory of ion-acoustic shocks and a theory of double layers.

Lotko, W.↗
NASA NTRS2021

ARTEMIS Observations of Plasma Waves in Laminar and Perturbed Interplanetary Shocks

The ‘Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon's Interaction with the Sun’ (ARTEMIS) mission provides a unique opportunity to study the structure of interplanetary shocks and the associated generation of plasma waves with frequencies between ~50-8000 Hz due to its long duration electric and magnetic field burst waveform captures. We compare wave properties and occurrence rates at 11 quasi-perpendicular interplanetary shocks with burst data within 10 minutes (~3200 proton gyroradii upstream, ~1900 downstream) of the shock ramp. A perturbed shock is defined as possessing a large amplitude whistler precursor in the quasi-static magnetic field with an amplitude greater than ⅓ the difference between the upstream and downstream average magnetic field magnitudes; laminar shocks lack these large precursors and have a smooth, step function-like transition. In addition to wave modes previously observed, including ion acoustic, whistler, and electrostatic solitary waves, waves in the ion acoustic frequency range that show rapid temporal frequency change are common. Three shocks had burst captures in the ramp; of these, the two laminar shocks with burst data in the ramp contained a wide range of large amplitude wave modes in the ramp whereas the one perturbed shock contained no such waves. Thus, energy dissipation through wave-particle interactions is more prominent in these two laminar shocks than in the perturbed shock. Based on observations from all 11 shocks, the The wave occurrence rates for laminar shocks are higher in the transition region, especially the ramp, than downstream. In contrast, perturbed shocks have approximately 2-3 times the wave occurrence rate downstream than laminar shocks.

L. A. Davis↗
NASA NTRS1985

High time resolution plasma wave and magnetic field observations of the Jovian bow shock

High time resolution (60 ms) Voyager magnetometer and plasma wave measurements of a strong (fast Mach number 16), quasi-perpendicular Jovian bow shock reveal an abrupt change in the plasma wave spectrum at the leading edge of the shock foot. Upstream electron plasma waves terminate at the leading edge, and are replaced by a lower-frequency broadband spectrum of ion-acoustic-like waves, which terminates at the main shock ramp. The clear association with the foot region of the lower frequency component suggests that it is generated by reflected ions. If the upstream plasma waves are generated by an escaping electron heat flux, their termination at the leading edge suggests that electrons are heated by the low-frequency waves in the shock foot.

Moses, S. L.↗
NASA NTRS1992

A new tool for analyzing microinstabilities in space plasmas modeled by a generalized Lorentzian (kappa) distribution

The modified plasma dispersion function Z* sub kappa (xi) based on the generalized Lorentzian distribution, which was introduced by Summers and Thorne (1991), is used to analyze three classical problems of plasma physics. These include the Landau damping of Langmuir waves, the ion acoustic instability in a current-carrying plasma, and the cyclotron resonant instability of electromagnetic R mode waves propagating parallel to an ambient magnetic field. It was found that, in each case, the results for a generalized Lorentzian plasma can differ significantly from those for a Maxwellian plasma. It is suggested that previous calculations based on a Maxwellian plasma distribution function Z(xi) have to be reexamined.

Summers, Danny↗
DOE OSTI2025

Nonlinear evolution, propagation, electron-trapping, and damping effects of ion-acoustic solitons using fully kinetic PIC simulations

We investigate ion acoustic solitary waves (solitons) of varying amplitudes in a one-dimensional plasma using fully kinetic particle-in-cell simulations. The initial soliton conditions are based on the Korteweg–de Vries (KdV) equation, treating ions as a cold species and electrons with finite temperature. Our findings reveal that KdV solitons evolve nonlinearly to a saturated state at higher amplitude, deviating from KdV predictions for ion density and electric potential, and from the Boltzmann relation for electron density. At this saturated state, the KdV model cannot accurately describe the soliton behavior. For small amplitudes, Sagdeev's model describes the saturated state, but not the soliton width; for larger amplitudes, it models the width accurately, but not the amplitude. These discrepancies arise from assuming a Boltzmann relation for electron density, while electron trapping creates non-Boltzmann densities—a deviation that increases with soliton amplitude. Additionally, we observe that the soliton amplitude oscillates roughly at the electron bounce frequency. The soliton is better described by Schamel's electron density formulation and a modified KdV equation incorporating electron trapping. The soliton velocity matches best with predictions from Sagdeev's and Schamel's models. Moreover, the soliton speed–amplitude relationship differs from existing theoretical predictions. Finally, we find minimal ion and electron Landau damping effects.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1997

In situ wave phenomena in the upstream and downstream regions of interplanetary shocks: Implications for type 2 burst theories

The results are presented of in situ waves observed by the Ulyssess unified radio and plasma wave experiment (URAP) in the upstream and downstream regions of a large number of interplanetary shocks. The Langmuir waves which are the most essential ingredients for the type 2 radio emission are observed only in the upstream regions of a limited number of shocks. On the other hand, the ion-acoustic-like waves (0.5 to 5 kHz) are observed near most of the interplanetary shocks. Implications of observations made for the electron acceleration mechanisms at the collisionless shocks and for type 2 burst theories are presented.

Thejappa, G.↗
DOE OSTI2021

Slow and Fast Light in Plasma Using Optical Wave Mixing

Slow and fast light, or large changes in the group velocity of light, have been observed in a range of optical media, but the fine optical control necessary to induce an observable effect has not been achieved in a plasma. Here, we describe how the ion-acoustic response in a fully ionized plasma can produce large and measurable changes in the group velocity of light. In this work, we show the first experimental demonstration of slow and fast light in a plasma, measuring group velocities between 0.12c and -0.34c.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2001

Thermal Electron Contributions to Current-Driven Instabilities: SCIFER Observations in the 1400-km Cleft Ion Fountain and Their Implications to Thermal Ion Energization

SCIFER TECHS observations of the variations in the thermal electron distribution in the 1400-km altitude cleft are associated with periods of intense ion heating and field-aligned currents. Energization of the thermal ion plasma in the mid-altitude cleft occurs within density cavities accompanied by enhanced thermal electron temperatures, large field-aligned thermal electron plasma flows and broadband low-frequency electric fields. Variations in the thermal electron contribution to field-aligned current densities indicate small scale (approximately 100's m) filamentary structure embedded within the ion energization periods. TECHS observations of the field-aligned drift velocities and temperatures of the thermal electron distribution are presented to evaluate the critical velocity thresholds necessary for the generation of electrostatic ion cyclotron and ion acoustic instabilities. This analysis suggests that, during periods of thermal ion energization, sufficient drift exists in the thermal electron distribution to excite the electrostatic ion cyclotron instability. In addition, brief periods exist within the same interval where the drift of the thermal electron distribution is sufficient to marginally excite the ion acoustic instability. In addition, the presence an enhancement in Langmuir emission at the plasma frequency at the center of the ion energization region, accompanied by the emission's second-harmonic, and collocated with observations of high-frequency electric field solitary structures suggest the presence of electron beam driven decay of Langmuir waves to ion acoustic modes as an additional free energy source for ion energization.

Adrian, Mark L.↗
NASA NTRS1991

Lower-hybrid turbulence in a nonuniform magnetoplasma

An experimental study of a pressure-gradient-driven instability in a large discharge plasma is presented. When the electron diamagnetic drift exceeds the sound speed, ion-acoustic-like waves are driven unstable. The growth rate maximizes near the lower-hybrid frequency and the waves propagate essentially across B. The sound waves grow to large amplitudes and saturate by wave steepening and refraction away from the destabilizing drift. Magnetic fluctuations result from electron diamagnetic currents and opposing Hall currents associated with the wave density fluctuations. Ions are essentially unmagnetized and slow compared to the magnetized electrons. In spite of the large amplitude waves little acceleration of electrons or ions is observed.

Stenzel, R. L.↗
NASA NTRS1999

Generation of Electron Suprathermal Tails in the Upper Solar Atmosphere: Implications for Coronal Heating

We present a mechanism for the generation of non-Maxwellian electron distribution function in the upper regions of the solar atmosphere in the presence of collisional damping. It is suggested that finite amplitude, low frequency, obliquely propagating electromagnetic waves can carry a substantial electric field component parallel to the mean magnetic field that can be significantly larger than the Dreicer electric field. This long wavelength electric fluctuation is capable of generating high frequency electron plasma oscillations and low frequency ion acoustic-like waves. The analysis has been performed using 1-1/2D Vlasov and PIC numerical simulations in which both electrons and ions are treated kinetically and self consistently. The simulation results indicate that high frequency electron plasma oscillations and low frequency ion acoustic-like waves are generated. The high frequency electron plasma oscillation drives electron plasma turbulence, which subsequently is damped out by the background electrons. The turbulence damping results in electron acceleration and the generation of non-Maxwellian suprathermal tails on time scales short compared to collisional damping. Bulk heating also occurs if the fluctuating parallel electric field is strong enough. This study suggests that finite amplitude, low frequency, obliquely propagating, electromagnetic waves can play a significant role in the acceleration and heating of the solar corona electrons and in the coupling of medium and small-scale phenomena.

Vinas, Adolfo F.↗
NASA NTRS1993

Plasma waves observed at low altitudes in the tenuous Venus nightside ionosphere

The Pioneer Venus (PV) Orbiter Electric Field Detector (OEFD) measured many plasma wave bursts throughout the low altitude ionosphere during the final entry phase of the spacecraft. Apart from 100 Hz bursts observed at very low altitudes (approx. 130 km), the bursts fall into two classes. The first of these is a wideband signal that is observed in regions of low magnetic field, but average densities, in comparison to the prevailing ionospheric condition. This wideband signal is not observed in the 30 kHz channel of the OEFD, but is resricted to the 5.4 kHz channel and lower. Since these bursts are observed with roughly constant burst rate above 160 km altitude, we attribute them to ion acoustic mode waves generated by precipitating solar wind electrons. The second type of signal is restricted to 100 Hz only, and is observed in the regions of low electron beta, consistent with whistler-mode waves. These waves could be generated by lightning in the Venus atmosphere if the vertical component of the magnetic field greater than 3.6 nT. Because the ionosphere is very different during the entry phase, compared to the ionosphere as observed early in the Pioneer Venus mission, any conclusions regarding the source of the plasma waves detected during entry phase cannot be applied directly to the earlier observations.

Strangeway, R. J.↗
NASA NTRS1993

Plasma Waves Observed at Low Altitudes in the Tenuous Venus Nightside Ionosphere

The Pioneer Venus Orbiter Electric Field Detector (OEFD) measured many plasma wave bursts throughout the low altitude ionosphere during the final entry phase of the spacecraft. Apart from 100 Hz bursts observed at very low altitudes (approx. 130 km), the bursts fall into two classes. The first of these is a wideband signal that is observed in regions of low magnetic field, but average densities, in comparison to the prevailing ionospheric condition. This wideband signal is not observed in the 30 kHz channel of the OEFD, but is restricted to the 5.4 kHz channel and lower. Since these bursts are observed with roughly constant burst rate above 160 km altitude, we attribute them to ion acoustic mode waves generated by precipitating solar wind electrons. The second type of signal is restricted to 100 Hz only, and is observed in regions of low electron beta, consistent with whistler-mode waves. These waves could be generated by lightning in the Venus atmosphere if the vertical component of the magnetic field greater than 3.6 nT. Unfortunately, the spacecraft spin axis is mainly horizontal, and only that component of magnetic field can be measured. Alternatively, the 100 Hz bursts could be generated locally through gradient drift instabilities, provided the ambient magnetic field is horizontal. Because the ionosphere is very different during the entry phase, compared to the ionosphere as observed early in the Pioneer Venus mission, any conclusions regarding the source of the plasma waves detected during entry phase cannot be applied directly to the earlier observations.

Strangeway, R. J.↗