Simulations relevant to the beam instability in the foreshock

Journal Article · Sun Jan 01 04:00:00 EST 1989 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA094iA01p00079· OSTI ID:5941192

Cairns, I H; Nishikawa, K I ^[1]

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1. Univ. of Iowa, Iowa City (United States)

Electrons backstreaming into Earth's foreshock generate waves near the plasma frequency f{sub p} by the beam instability. Tow versions of the beam instability exist: the reactive version, in which narrow-band waves grow by bunching the electrons in space, and the kinetic version, in which broadband growth occurs by a maser mechanism. Recently, it has been suggested that (1) the backstreaming electrons have steep-sided cutoff distributions which are initially unstable to the reactive instability, (2) the back reaction to the wave growth causes the instability to pass into its kinetic phase, and (3) the kinetic instability saturates by quasi-linear relaxation. In this paper the authors present two-dimensional simulations of the reactive instability for Maxwellian beams and cutoff distributions. They demonstrate that the reactive instability is a bunching instability and that the reactive instability saturates and passes over into the kinetic phase by particle trapping.A reactive/kinetic transition is shown to most likely occur within 1 km and 50 km of the bow shock. They suggest that the frequency of the intense narrow-band waves decrease from above f{sub p} to perhaps 0.9f{sub p} (dependent on the beam density) with increasing penetration into the high beam speed region of the foreshock, before the wave frequency rises again as the waves become broadband deeper in the foreshock. Both the simulation results and numerical solutions of the dispersion equation indicate that for the observed beam parameters the center frequency of the waves near the foreshock boundary should be between 0.9f{sub p} and 0.98f{sub p}, rather than above f{sub p} as previously believed. The simulation results indicate that the effects of spatial inhomogeneity are vital for a quantitative understanding of the foreshock waves.

• OSTI ID: 5941192
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 94:A1; ISSN JGREA; ISSN 0148-0227
• Country of Publication: United States
• Language: English

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71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
AMPLIFIERS
COMPUTERIZED SIMULATION
DISTRIBUTION
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
ELECTRONIC EQUIPMENT
ELECTRONS
ELEMENTARY PARTICLES
ENERGY
EQUIPMENT
FERMIONS
FREE ENERGY
INSTABILITY
INTERACTIONS
LEPTONS
MASERS
MICROWAVE AMPLIFIERS
MICROWAVE EQUIPMENT
NUMERICAL SOLUTION
PHYSICAL PROPERTIES
PLASMA INSTABILITY
PLASMA MICROINSTABILITIES
PLASMA WAVES
QUASILINEAR PROBLEMS
SATURATION
SIMULATION
SOLAR ACTIVITY
SOLAR WIND
SPATIAL DISTRIBUTION
THERMODYNAMIC PROPERTIES
TRAPPING
TWO-DIMENSIONAL CALCULATIONS