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On the kinetic instabilities of uniform magnetized plasmas with generalized loss-cone distribution functions

Published online by Cambridge University Press:  13 March 2009

L. Gomberoff
Affiliation:
Department of Physics and Astronomy, Tel-Aviv University, Ramat Aviv, Israel
S. Cuperman
Affiliation:
Department of Physics and Astronomy, Tel-Aviv University, Ramat Aviv, Israel

Abstract

A general proof is given that in uniform magnetized plasmas described by generalized loss-cone distribution functions (loss-cone index l, thermal velocity α, and perpendicular spread α⊥), electromagnetic, electrostatic, or coupled-mode instabilities are insensitive to the separate values of l and (α); they depend rather, on the effective thermal anisotropy Aeff ≡ (T/T)eff-1, where (T/T)eff ≡ (l + 1) (α22). In the case of parallel propagation this statement is limited only by the linearization assumption; in the oblique propagation case, the additional condition λ/rL ≫ 1 is required (λ = 1/k, where k is the wave vector perpendicular to the external magnetic field, and rL is the Larmor radius). Thus, dispersion relations and their solutions obtained by using simple bi-Maxwellian distribution functions can be used directly for the complex case of generalized loss-cone distribution functions by simply replacing the anisotropy factor, A ≡α22-1, by Aeff defined above. This result explains earlier conclusions that the growth rate of the whistler instability is independent of the explicit value of the loss-cone index l, for a given thermal anisotropy.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1981

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References

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