ION PITCH-ANGLE SCATTERING BY ALFVEN WAVES

Freshly created ions can be picked up by a moving plasma without relyi ng on collisions. It is well known that such an ion pickup process can be accomplished via the interaction with Alfven waves. However, it sh ould be stressed that in generation pickup is attributed to two distin ctly different sub-processes, namely, pitch-angle diffusion and pitch- angle scattering. In this article their difference is discussed and fu rthermore, some new results from a recent theoretical study are report ed. It is found that under some conditions the usual quasilinear theor y which describes the pitch-angle diffusion process cannot be justifie d even when the turbulence level is low. Another significant finding i s that in the presence of strong Alfven turbulence, thermal ions can b e intensely heated by a nonlinear damping of the waves, which does not depend upon the usual ion cyclotron resonance. (C) 1997 American Inst itute of Physics. [S1070-664X(97)00111-0].