Evaluation of quasi-linear diffusion coefficients for whistler mode waves in a plasma with arbitrary density ratio

[1] 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 omega(pe)/Omega(e) 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 theta that are incompatible with cyclotron resonant frequencies omega 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 omega and theta, 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 Omega(e). The techniques greatly reduce the amount of computation needed for a sample calculation, while taking into account all resonant harmonic numbers n up to +/-infinity.