A theory for the Langmuir waves in the electron foreshock

Journal Article · Sun Mar 01 04:00:00 EST 1987 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA092iA03p02329· OSTI ID:5557962

Cairns, I H ^[1]

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1. Univ. of Sydney, New South Wales (Australia)

A theory for the Langmuir (L) waves observed in the electron foreshock is suggested. Free energy for the Langmuir wave growth is contained in cutoff distributions of energetic electrons streaming from the bow shock. These cutoff distributions drive Langmuir wave growth primarily by the kinetic version of the beam instability, and wave growth is limited by quasi-linear relaxation. The observed bump-on-tail electron distributions are interpreted as the remnants of cutoff distributions after quasi-linear relaxation has limited the wave growth. Only plausibility arguments for this theory are given since suitable treatments of quasi-linear relaxation are not presently available. However, it is shown that the wave processes L {plus minus} S {yields} L{prime} and L {plus minus} S {yields} T (where S and T denote ion sound and transverse waves, respectively), refraction in steady-state density structures, diffusion due to interactions with ion sound turbulence, and effects due to wave convection and spatial gradients in the beam velocity, are unable to suppress the beam instability. The theory leads to natural interpretations of the Langmuir electric field waveforms observed and of the decrease in the Langmuir wave electric fields with increasing distance from the foreshock boundary. The theory for the beam instability is reviewed, and previous analytic and numerical treatments of the beam instability are related.

• OSTI ID: 5557962
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 92:A3; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

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