Cosmic-ray momentum diffusion in magnetosonic versus Alfvenic turbulent field

Energetic particle transport in a finite amplitude magnetosonic and Alfveni c turbulence is considered using the Monte Carlo particle simulations, whic h involve integration of particle equations of motion. We show that in the low-beta plasma the cosmic-ray acceleration can be the most important dampi ng process for magnetosonic waves. Assuming such conditions we derive the m omentum diffusion coefficient D-p, for relativistic particles in the presen ce of anisotropic finite-amplitude turbulent wave fields, for hat and Kolmo gorov-type turbulence spectra, respectively. We confirm the possibility of larger values of D-p occurring due to transit-time damping resonance intera ction in the presence of isotropic fast-mode waves in comparison to the Alf ven waves of the same amplitude (cf. Schlickeiser and Miller, 1997). The im portance of quasi-perpendicular fast-mode waves is stressed for the acceler ation of high velocity particles.