Cosmic ray transport in anisotropic magnetohydrodynamic turbulence - III. Mixed magnetosonic and Alfvenic turbulence

Observations of interstellar turbulence imply that the power spectrum of the wave turbulence must be highly anisotropic. This anisotropy has to be included when transport of high energy cosmic rays in the Galaxy is discussed. Here we evaluate the relevant cosmic ray transport parameters in the presence of anisotropic plasma wave turbulence, consisting of a mixture of shear Alfven waves and fast magnetosonic waves. By averaging the respective Fokker-Planck coefficient over the particle pitch-angle we calculate the momentum and spatial diffusion coefficients for different anisotropy parameters. For strongly perpendicular turbulence (Lambda much less than 1) we obtain that the momentum diffusion coefficient is proportional to Lambda(-1/2) [ln epsilon(-1) + ln Lambda(1/2)], whereas for strongly parallel turbulence (Lambda much greater than 1) the momentum diffusion coefficient is a constant. We also calculate the anisotropy dependence of the spatial diffusion coefficient and the parallel mean free path for the mixed turbulence. For all coefficients we discuss the rigidity dependence for different cosmic ray particles.