Heavy Ion Acceleration by Super-Alfvenic Waves

A generation mechanism of super Alfv\'{e}nic (SPA) waves in multi-ion species plasma is proposed and the associated heavy ion acceleration process is discussed. The SPA waves are thought to play important roles in particle acceleration since they have large wave electric field because of their high phase velocity. It is demonstrated by using full particle-in-cell simulation that large amplitude proton cyclotron waves, excited due to proton temperature anisotropy, nonlinearly destabilize SPA waves through parametric decay instability in a three component plasma composed of electrons, protons, and $\alpha$ particles. At the same time, $\alpha$ cyclotron waves get excited via another decay instability. A pre-accelerated $\alpha$ particle resonates simultaneously with the two daughter waves, the SPA waves and the $\alpha$ cyclotron waves, and it is further accelerated perpendicular to the ambient magnetic field. The process may work in astrophysical environments where sufficiently large temperature anisotropy of lower mass ions occurs.
Comment: 4 figures