Acceleration of energetic ions by nonlinear magnetosonic waves

Abstract

Interactions of nonthermal energetic ions with nonlinear magnetosonic waves are studied by means of a one-dimensional (one space coordinate and three velocity components), relativistic, electromagnetic particle simulation code with full ion and electron dynamics. It is found that, if ions with gyration speeds much greater than the Alfvén speed encounter a shock wave, some of them can gain great energies. The acceleration takes place when the particle velocity becomes nearly parallel to the transverse electric field in the shock. On the basis of a simple physical picture, the increase in the energy is theoretically obtained. Both the theory and simulation show that the ions with higher energies can obtain greater energies. Thus, in a plasma with strong magnetohydrodynamic turbulence some of the ions could be repeatedly accelerated to higher energies by many nonlinear pulses.