Parametric instabilities in a two ion species plasma as a driver of super Alfvénic waves

Linear dispersion relation of parametric instabilities of a left hand circularly polarized wave in a three species plasma consisting electrons, protons, and α particles is derived and the obtained dispersion relation is numerically solved. It is shown that the so-called super Alfvénic waves, which are thought to play important roles in preferential acceleration of heavy ions, can get excited through a parametric decay instability when the parent wave is on the proton cyclotron branch and the plasma beta is sufficiently low. A variety of other parametric instabilities are also generated.