Evaluation of quasi-linear diffusion coefficients for whistler mode waves in a plasma with arbitrary density ratio
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Abstract |
Techniques are presented for efficiently evaluating quasi-linear diffusion coefficients for whistler mode waves propagating according to the full cold plasma index of refraction. In particular, the density ratio ωpe/Ωe can be small, which favors energy diffusion. This generalizes an approach, previously used for high-density hiss and electromagnetic ion cyclotron waves, of identifying (and omitting) ranges of wavenormal angle θ that are incompatible with cyclotron resonant frequencies ω occurring between sharp cutoffs of the modeled wave frequency spectrum. This requires a detailed analysis of the maximum and minimum values of the refractive index as a function of ω and θ, as has previously been performed in the high-density approximation. Sample calculations show the effect of low-density ratio on the pitch angle and energy diffusion coefficients modeling the effect of chorus waves on radiation belt electrons. The high-density approximation turns out to be quite robust, especially when the upper frequency cutoff is small compared with Ωe. The techniques greatly reduce the amount of computation needed for a sample calculation, while taking into account all resonant harmonic numbers n up to \textpm$\infty$.
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Year of Publication |
2005
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Journal |
Journal of Geophysical Research
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Volume |
110
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Date Published |
03/2005
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ISSN Number |
0148-0227
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URL |
http://onlinelibrary.wiley.com/doi/10.1029/2004JA010844/abstract
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DOI |
10.1029/2004JA010844
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