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Large-Debye-distance effects in a homogeneous plasma

Published online by Cambridge University Press:  13 March 2009

Jan Scheffel  and
Bo Lehnert
Jan Scheffel
Affiliation:
The Royal Institute of Technology, S-100 44 Stockholm, Sweden
Bo Lehnert
Affiliation:
The Royal Institute of Technology, S-100 44 Stockholm, Sweden
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Abstract

The classical phenomenon of electron plasma oscillations has been investigated from new aspects. The applicability of standard normal-mode analysis of plasma perturbations has been judged from comparisons with exact numerical solutions to the linearized initial-value problem. We consider both Maxwellian and non-Maxwellian velocity distributions. Emphasis is on perturbations for which αλD is of order unity, where α is the wavenumber and λD the Debye distance. The corresponding large-Debye-distance (LDD) damping is found to substantially dominate over Landau damping. This limits the applicability of normal-mode analysis of non-Maxwellian distributions. The physics of LDD damping and its close connection to large-Larmor-radius (LLR) damping is discussed. A major discovery concerns perturbations of plasmas with non-Maxwellian, bump-in-tail, velocity distribution functions f0(ω). For sufficiently large αλD (of order unity) the plasma responds by damping perturbations that are initially unstable in the Landau sense, i.e. with phase velocities initially in the interval where df0/dw > 0. It is found that the plasma responds through shifting the phase velocity above the upper velocity limit of this interval. This is shown to be due to a resonance with the drifting electrons of the bump, and explains the Penrose criterion.

Type
Research Article
Information
Journal of Plasma Physics , Volume 41 , Issue 3 , June 1989 , pp. 493 - 516
Copyright
Copyright © Cambridge University Press 1989

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