Cosmic Ray Momentum Diffusion in Magnetosonic versus Alfvénic Turbulent Fields

Energetic particle transport in a finite amplitude magnetosonic and Alfvénic turbulence is considered using Monte Carlo particle simulations, which involve an integration of particle equations of motion. We show that in a low-β plasma cosmic ray acceleration can be the most important damping process for magnetosonic waves. Assuming such conditions we derive the momentum diffusion coefficient Dp for relativistic particles in the presence of anisotropic finite-amplitude turbulent wave fields, for flat and Kolmogorov-type turbulence spectra. We confirm the possibility of larger values of Dp occurring due to transit-time damping resonance interaction in the presence of isotropic fast-mode waves in comparison to the Alfvén waves of the same amplitude (cf. Schlickeiser & Miller 1998). The importance of quasi-perpendicular fast-mode waves is stressed for the acceleration of high velocity particles.