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The ion-ion acoustic instability

Published online by Cambridge University Press:  13 March 2009

S. Peter Gary
Affiliation:
Earth and Space Science Division, Los Alamos National Laboratory, Los Alamos, NM 87545
Nojan Omidi
Affiliation:
Instituts of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90024

Abstract

This paper considers the linear theory of ion-acoustic-like instabilities in a homogeneous Vlasov plasma with two ion components, a less dense beam and a more dense core, with a relative drift velocity. Numerical solutions of the full electrostatic dispersion equation are presented, and the properties of the ion–ion acoustic instability are studied in detail. The following properties are demonstrated: (i) At relatively cold beam temperatures, the instability is fluid-like, but it becomes a beam resonant kinetic instability as the beam temperature becomes of the order of the core temperature; (ii) if the mode is unstable, its threshold lies well below the threshold of the electron–ion acoustic instability; (iii) an electron temperature anisotropy T⊥/T‖e > 1 enhances the instability and (iv) at sufficiently large beam-core relative drift speeds, electron magnetization can either detract from or enhance the instability. If field-aligned ion beams are to drive the ion-acoustic-like enhanced fluctuations observed upstream of the Earth's bow shock, the effective beam temperature must be much smaller than values quoted in the literature.

Information

Type
Research Article
Copyright
Copyright © Cambridge University Press 1987

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