Heating and acceleration of ions in nonresonant Alfv́nic turbulence

Nonlinear scattering of protons and alpha particles during the dissipation of the finite amplitude, low-frequency Alfv́nic turbulence is studied. The process discussed here is not the coherent scattering and acceleration, as those often treated in the past studies, but is an incoherent process in which it is essential that the Alfv́nic turbulence has a broadband spectrum. The presence of such an Alfv́nic turbulence is widely recognized observationally both in the solar corona and in the solar wind. Numerical results suggest that, although there is no apparent sign of the occurrence of any parametric instabilities, the ions are heated efficiently by the nonlinear Landau damping, i.e., trapping and phase mixing by Alfv́n wave packets which are generated by beating of finite amplitude Alfv́n waves. The heating occurs both in the parallel and in the perpendicular directions, and the ion distribution function which is asymmetric with respect to the parallel velocity is produced. Eventual perpendicular energy of ions is much influenced by the spectrum and polarization of the given Alfv́nic turbulence since the turbulence initially possess transverse energy as specified by Walen's relation.