Engineering topics

Gray, Perry C.

Publications and source records attributed to Gray, Perry C..

5 records

NASA NTRS2012

Observation of Bernstein Waves Excited by Newborn Interstellar Pickup Ions in the Solar Wind

A recent examination of 1.9 s magnetic field data recorded by the Voyager 2 spacecraft in transit to Jupiter revealed several instances of strongly aliased spectra suggestive of unresolved high-frequency magnetic fluctuations at 4.4 AU. A closer examination of these intervals using the highest resolution data available revealed one clear instance of wave activity at spacecraft frame frequencies from 0.2 to 1 Hz. Using various analysis techniques, we have characterized these fluctuations as Bernstein mode waves excited by newborn interstellar pickup ions. We can find no other interpretation or source consistent with the observations, but this interpretation is not without questions. In this paper, we report a detailed analysis of the waves, including their frequency and polarization, that supports our interpretation.

magnetic fields↗

NASA NTRS1992

Acoustic double layers in multispecies plasma

The formation of acoustic double layers in the presence of two ion species is examined via a particle simulation in a 1D bounded system. The effect of having two ion components, an H(+) and an O(+) beam, on double-layer evolution from ion acoustic turbulence driven by an electron drift relative to the H(+) beam of about 0.5 u sub e, where u sub e is the electron thermal speed, is examined. It is found that acoustic double layers form in either ion species on a time scale of about 100 omega sub ps exp -1, where omega sub ps is the ion plasma frequency for species 's' and s = H or O, and for drifts relative to the electrons lower than that required for double layer formation in simulations of single ion component plasma.

Gray, Perry C.↗

NASA NTRS1992

MHD turbulence, reconnection, and test-particle acceleration

We examine homogeneous MHD turbulence and turbulent magnetic reconnection as possible mechanisms for accelerating cosmic ray particles. Test particle calculations are performed using fields from MHD simulations, and initially Maxwellian particle distributions are shown to evolve into power-law distributions. Simple estimates for both the maximum energy attainable and the mean energies of the accelerated particles are fairly successful and are consistent with timescales for flares and cosmic rays.

Gray, Perry C.↗

NASA NTRS1991

Heat flow between species in one-dimensional particle plasma simulations

The theory of Eldridge and Feix (1962) is presently applied to characterize the rate of heat flow between two one-dimensional particle species. Formulas derived assuming initial Maxwellian distributions, while complex, are judged applicable to simulators. Tests of the theory by simulations using Langdon and Birdsall's (1985) standard code yield results which indicate that heat flow between species may become rapid when the actual (not necessarily the intended) temperatures differ: thereby presenting a substantial hazard.

Lawson, William S.↗

NASA NTRS1990

Simulation study of ion two-stream instability in the auroral acceleration region

Particle in cell plasma simulation technique has been used to study the effect of the ion two-stream instability on hydrogen and oxygen distributions at small relative drifts. Whether heating due to parallel modes which are unstable at low drifts might be sufficient to quench oblique modes which are unstable at higher drifts is investigated. It is found that this is not the case and that the oblique modes contribute significantly to heating.

Gray, Perry C.↗