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Weakly nonlinear waves in magnetized plasma with a slightly non-Maxwellian electron distribution. Part 2. Stability of cnoidal waves

Published online by Cambridge University Press:  01 December 2007

S. PHIBANCHON
Affiliation:
Physics Department, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand
M. A. ALLEN*
Affiliation:
Physics Department, Mahidol University, Rama 6 Road, Bangkok 10400, Thailand
G. ROWLANDS
Affiliation:
Department of Physics, University of Warwick, Coventry CV4 7AL, UK
*
Corresponding author: frmaa@mahidol.ac.th

Abstract

We determine the growth rate of linear instabilities resulting from long-wavelength transverse perturbations applied to periodic nonlinear wave solutions to the Schamel–Korteweg–de Vries–Zakharov–Kuznetsov (SKdVZK) equation which governs weakly nonlinear waves in a strongly magnetized cold-ion plasma whose electron distribution is given by two Maxwellians at slightly different temperatures. To obtain the growth rate it is necessary to evaluate non-trivial integrals whose number is kept to a minimum by using recursion relations. It is shown that a key instance of one such relation cannot be used for classes of solution whose minimum value is zero, and an additional integral must be evaluated explicitly instead. The SKdVZK equation contains two nonlinear terms whose ratio b increases as the electron distribution becomes increasingly flat-topped. As b and hence the deviation from electron isothermality increases, it is found that for cnoidal wave solutions that travel faster than long-wavelength linear waves, there is a more pronounced variation of the growth rate with the angle θ at which the perturbation is applied. Solutions whose minimum values are zero and which travel slower than long-wavelength linear waves are found, at first order, to be stable to perpendicular perturbations and have a relatively narrow range of θ for which the first-order growth rate is not zero.

Type
Papers
Copyright
Copyright © Cambridge University Press 2007

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