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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Wave observations in outer planet magnetospheres

The first measurements of plasma waves and wave-particle interactions in the magnetospheres of the outer planets were provided by instruments on Voyager 1 and 2. At Jupiter, the observations yielded new information on upstream electrons and ions, bow shock dissipation processes, trapped radio waves in the magnetospheres and extended Jovian magnetotail, pitch angle diffusion mechanisms and whistlers from atmospheric lightning. Many of these same emissions were detected at Saturn. In addition, the Voyager plasma wave instruments detected dust particles associated with the tenuous outer rings of Saturn as they impacted the spacecraft. Most of the plasma wave activity at Jupiter and Saturn is in the audio range, and recordings of the wave observations have been useful for analysis.

Scarf, F. L.↗
NASA NTRS1986

Excitation of MHD waves upstream of Jupiter by energetic sulfur or oxygen ions

Large fluxes of heavy ions have been reported upstream of Jupiter's bow shock as Voyager 1 approached the planet (Zwickl et al., 1981; Krimigis et al., 1985). Enhanced low-frequency magnetic wave activity was also observed during the particle events. The fluctuations are left-handed, elliptically polarized in the plasma frame. The spectrum of these fluctuations contains a peak close to the Doppler-shifted resonance frequency of a sulfur or oxygen beam with streaming energy of approximately 30 keV. These fluctuations are also present in the spectrum of the magnitude of the field. It is concluded that the observations result from an instability driven by an energetic beam of either sulfur or oxygen. The wave observations can be described by a heavy ion distribution with both a streaming anisotropy and a temperature anisotropy. This class of heavy ion streaming instabilities may also play a role in wave-particle interactions in the vicinity of comets.

Goldstein, M. L.↗
NASA NTRS1986

Interaction of upgoing auroral H(+) and O(+) beams

Data from the S3-3 and DE 1 satellites are analyzed to study the interaction between H(+) and O(+) ions in upgoing auroral beams. Every data set analyzed showed some evidence of an interaction. The measured plasma was found to be unstable to a low-frequency electrostatic wave that propagates at an oblique angle to vector-B(0). A second wave, which can propagate parallel to vector-B(0), is weakly damped in the plasma studied in most detail. It is likely that the upgoing ion beams generate this parallel wave at lower altitudes. The resulting wave-particle interactions qualitatively can explain most of the features observed in ion distribution functions.

Kaufmann, R. L.↗
NASA NTRS1986

High-frequency waves generated by auroral electrons

Measurements of marginally unstable electron distribution functions and high-frequency plasma waves were made on a sounding rocket flight through a quiet auroral arc. The waves appeared near the electron plasma frequency and had a large parallel electric field component such that k-parallel is greater than k-perpendicular. The appearance of these waves was correlated with the presence of marginally unstable parallel electron distributions. Analysis has shown that the waves were produced by parallel electron distribution function greater than 0 rather than the small perpendicular electron distribution function greater than 0 features. Wave levels and growth rates inside the arc were small, and nonlinear wave-wave and wave-particle interactions appear to have been minimal.

Mcfadden, J. P.↗
NASA NTRS1986

Ion cyclotron waves observed near the plasmapause

Pc2 electromagnetic ion cyclotron waves at 0.1 Hz, near the oxygen cyclotron frequency, have been observed by ISEE-1 and -2 between L = 7.6 - 5.8 on an inbound near equatorial pass in the dusk sector. The waves occurred in a thick plasmapause of width about 1 earth radius and penetrated about 1 earth radius into the plasmasphere. Wave onset was accompanied by significant increases in the thermal (0-100 eV) He(+) and the warm (0.1-16 keV/e) O(+) and He(+) heavy ion populations. Wave polarization is predominantly left-handed with propagation almost parallel to the ambient magnetic field, and the spectral slot and polarization reversal predicted by multicomponent cold plasma propagation theory are identified in the wave data. The results are considered as an example of wave-particle interactions occurring during the outer plasmasphere refilling process at the time of the substorm recovery phase.

Fraser, B. J.↗
NASA NTRS1987

Detailed spectral structure of magnetospheric electron bursts precipitated by lightning

The temporal structure of electron fluxes precipitated by lightning that was measured at night over Wallops Island, Virginia, during August 1984 has been analyzed. A component of the precipitating electrons is almost certainly due to equatorial wave-particle interactions involving equatorial electron cyclotron resonance (EECR) with whistlers which produce pitch angle scattering. Precipitated electron fluxes of equatorial origin are characterized by a very steep spectral power exponent of about -20 above 100 keV. A second electron distribution from some other origin is also found whose time-integrated energy flux appears to be about equal in magnitude to the fluxes identified with the EECR processes.

Goldberg, R. A.↗
NASA NTRS1987

Small scale MHD wave processes in the solar atmosphere and solar wind

Solar wind observations suggesting wave-particle interactions via ion-cyclotron resonances are reviewed. The required power at high frequencies is presumably supplied via a turbulent cascade. Tu's (1987) model, which considers a turbulent cascade explicitly, is outlined. In the solar atmosphere, resonance absorption is considered. The meanings of the cusp and Alfven resonances are discussed, and it is shown how energy gets pumped into small scales. It is shown that resonance absorption can heat the corona and spicules in a manner consistent with observations, if turbulence provides an eddy viscosity.

Hollweg, Joseph V.↗
NASA NTRS1987

Generation of plasma waves by thick-target electron beams, and the expected radiation signature

The production of plasma waves by a nonthermal beam of high-energy electrons injected into a background thermal plasma was investigated. The coupled kinetic equations for nonthermal electrons were solved, and the level of the plasma waves produced by the bump-on-tail instability arising as a result of the Coulomb collisions of nonthermal electrons with background plasma was estimated. In addition, the radiation signatures of these waves were examined. It is shown that the wave-particle interactions have a significant effect on the overall distribution of the electrons and that it is unlikely that such effects can be discerned in the observed bremsstrahlung or synchrotron radiation of the nonthermal electrons. However, a significant fraction of the energy lost by the beam is transferred to plasma waves and is then dissipated by the thermal plasma.

Hamilton, Russell J.↗
NASA NTRS1987

Counterstreaming ion events in the magnetosphere

This paper presents general characteristics of more than 60 counterstreaming ion (CSI) events observed by the ISEE 1 satellite. Often, both oxygen and hydrogen ions at a number of energy levels were observed among the CSIs, but some events showed only one of these ions at one or more energy levels involved. In a number of cases, either only H(+) or O(+) ions at just one energy level were seen counterstreaming, and in a few cases, the CSIs were observed to involve ions of one energy traveling parallel to the magnetic field and ions of another energy traveling simultaneously in the antiparallel direction. Moreover, some of the CSI events correlated well with electric wave activity. It is suggested that, in some CSI events, wave-particle interaction may be involved.

Horita, R. E.↗
NASA NTRS1987

Energetic ion and electron phase space densities in the magnetosphere of Uranus

Proton and electron phase space density profiles are constructed from an analysis of Voyager 2 low-energy charged particle data from the magnetosphere of Uranus. The Uranus proton profiles reveal an approximately exponential decline with decreasing radius for L less than about 9 in a relatively dense thermal plasma region with intense plasma wave activity. Among the distributed loss mechanisms at Uranus are satellite sweeping, wave-particle interactions, and charge exchange of protons with an extended hydrogen corona.

Cheng, Andrew F.↗
NASA NTRS1987

Voyager 2 plasma wave observations at Uranus

At Uranus, the Voyager 2 plasma wave investigation observed very significant phenomena related to radio emissions, dust impacts, and magnetospheric wave-particle interactions. On January 19, 1986 (R = 270 R-sub U) the plasma wave investigation detected an intense radio burst at 31 and 56 kHz, and this provided the first indication that Uranus had a magnetosphere. During the encounter, more of these sporadic bursts were observed along with relatively continuous radio emissions extending down to 10 kHz, and a sporadic narrowband radio signal with f near 5 kHz. As Voyager passed through the ring plane, the plasma wave investigation recorded a large number of dust impacts. The Voyager 2 plasma wave instrument also detected many strong electromagnetic and electrostatic plasma waves, with intensity peaks in the region within 12 Uranus radii. These waves have characteristics that can interact strongly with the local plasma and with the trapped energetic particles, leading to precipitation into the atmosphere, charged particle acceleration, and charged particle diffusion. In addition, strong wave activity was detected in the region of the bow and shock and moderate levels in the magnetic tail.

Scarf, F. L.↗
NASA NTRS1982

Dissipation of ionospheric irregularities by wave-particle and collisional interactions

The nonlinear dissipation of plasma irregularities aligned parallel to an ambient magnetic field is studied numerically using a model which employs both wave-particle and collisional diffusion. A wave-particle diffusion coefficient derived from a local theory of the universal drift instability is used. This coefficient is effective in regions of nonzero plasma gradients and produces triangular-shaped irregularities with spectra which vary as f to the -4th, where f is the spatial frequency. Collisional diffusion acts rapidly on the vertices of the irregularities to reduce their amplitude. The simultaneous action of the two dissipative processes is more efficient than collisions acting alone. In this model, wave-particle diffusion mimics the forward cascade process of wave-wave coupling.

Bernhardt, P. A.↗
NASA NTRS1983

Terrestrial versus Jovian VLF chorus - A comparative study

The relevant parameters of the magnetospheres of Jupiter and earth are investigated based on the wave-particle resonant interactions that are believed to be responsible for the generation of VLF chorus emissions observed on Voyager 1. Expressions are derived for the wave-particle interaction length and the nonlinearity parameter, and the values of these parameters are compared with those calculated for the earth's magnetosphere. It is determined that the typical interaction lengths are at least 2-5 times larger in the Jovian than in the terrestrial magnetosphere, and that the wave intensity necessary to reach the threshold of nonlinearity in the Jovian magnetosphere is 5-100 times lower. Measurements by Voyager 1 show that the inferred wave magnetic field intensities of the Jovian chorus are in the range of reported intensities for terrestrial chorus, probably due to the fact that the fluxes of few keV resonant particles found in the Jovian magnetosphere were typically two orders of magnitude higher. Growth rate measurements on Voyager 1 broadband wave data are employed to confirm that the temporal growth rates of Jovian chorus bursts are higher than for the earth.

Inan, U. S.↗
DOE OSTI2026

Collisionless ion-electron energy exchange in magnetized shocks

Energy partition between ions and electrons in collisionless shocks has been a long-standing unsolved fundamental physical question. Here, we show that kinetic simulations of moderate Alfv´enic Mach number, magnetized, collisionless shocks reveal rapid, faster-than-Coulomb, energy exchange between ions and electrons when the plasma is sufficiently magnetized. Using kinetic and multi-fluid models with counter-streaming ions, we identify resonances between electron whistler and ion magnetohydrodynamic waves that account for this rapid energy exchange.

High-energy-density plasmas↗
DOE OSTI2026

First Demonstration of Resonant Pitch-Angle Scattering of Relativistic Electrons by Externally Launched Helicon Waves

Helicon waves (a.k.a whistler waves) satisfying the normal wave-particle cyclotron resonance are observed to limit the growth and maximum energy of relativistic electrons (REs) in low-density Ohmic DIII-D tokamak plasmas. Following the application of helicon waves, pitch-angle scattering of high-energy REs causes an increase in both synchrotron and electron-cyclotron emissions. The hard x-ray emission, a proxy for the RE population, ceases to grow. Energy-resolved hard x-ray measurements also show a striking decrease in the number of high-energy REs (above the resonance at approximately 8MeV) to below the noise floor and an increase in low-energy (∼ 4 MeV) REs. This occurs despite the toroidal electric field remaining high enough to drive exponential RE growth in the absence of helicon waves. Furthermore, these results open new directions for limiting the maximum energy of RE populations in laboratory and fusion plasmas.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2026

Measurement of the Alfvén Wave Parametric Decay Instability Growth Rate

Alfvén waves, a fundamental mode of magnetized plasmas, are ubiquitous in space and laboratory plasmas. The nonlinear behavior of these modes is thought to play a key role in important problems in space plasma, such as the heating of the solar corona and solar wind turbulence. In particular, theoretical predictions show that these Alfvén waves may be unstable to various parametric instabilities, but space observations of these processes are limited. We demonstrate the first measurement of the Alfvén wave parametric decay instability (PDI) growth rate. Experiments are conducted on the Large Plasma Device at UCLA in which a high amplitude 𝛿⁢𝐵/𝐵 0 ∼ 0.7% pump Alfvén wave is launched from one end of the device and a smaller seed Alfvén wave is launched from the other side. When the frequency of the seed wave is chosen to match the backward wave expected from PDI, damping of the seed wave is reduced. We compare this reduction in damping to the theoretically expected PDI growth rate while accounting for acoustic mode damping. Results show agreement between measurements and theoretical predictions. As a result, this not only provides critical validation for PDI theories and simulations that could help interpret future space observations but also suggests a new way of studying similar nonlinear wave phenomena.

Alfvén waves↗