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Parametric instability driven by density modulation in velocity space

Published online by Cambridge University Press:  13 March 2009

D. Sherwell
Affiliation:
Atomic Energy Board, Private Bag X256, Pretoria, South Africa
R. A. Cairns
Affiliation:
Department of Applied Mathematics, University of St Andrews, Fife, Scotland

Abstract

Any ion distribution f;i =(θ—ώit) is an exact solution of the Vlasov equation for a uniformly magnetized plasma. Here θ is the phase angle in velocity space and ώi is the Larmor frequency. Then fi rotates rigidly in velocity space with frequency ώ;i about an axis along a magnetic field line. If fi has anisotropy in the perpendicular velocity plane of the form fi(V, t) = fi(V) [1+A cos 2(θ— ώit)], then it represents a density modulation of frequency 2ώ;i which is confined to velocity space. This non-Maxwellian distribution is an oscillating source of free energy (a pump) which may stimulate certain ion Bernstein modes, their frequencies being near harmonics of Ωi. We here investigate the linear kinetic theory of the system. Linearization implies the parametric approximation of a strong constant pump. Application of the theory may be found in the earth's bow shock.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1980

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