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The unstable modes of a two-component electron plasma

Published online by Cambridge University Press:  13 March 2009

P. McQuillan
Affiliation:
Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QW, Scotland
K. G. McClements
Affiliation:
Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QW, Scotland

Abstract

In this paper we investigate the linear generation of electrostatic waves in a homogeneous, collisionless, unmagnetized plasma with two Maxwellian electron components, one drifting with respect to the other. The ions are assumed to be infinitely massive. It is shown that such a system may be unstable to a beam mode rather than the well-known Langmuir mode, if the drifting electron component is sufficiently dense and has a sufficiently low temperature. This ‘electron-beam instability’ is driven by the free energy in the particle distribution, and the associated phase velocity is greater than the electron thermal speed. The dispersion characteristics of the electron-beam instability and the Langmuir instability at the critical drift velocity for wave growth are determined for a wide range of parameters. The results of our investigation are applied to electron beams producing hard X-ray emission in solar flares, and it is argued that such beams may be unstable to the generation of electrostatic waves at frequencies below the electron plasma frequency.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1988

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