Cherenkov radiation of shear Alfvén waves in plasmas with two ion species

Abstract

A calculation is presented of the radiation pattern of shear Alfvén waves generated by a burst of charged particles in a charge-neutral plasma with two-ions of differing charge-to-mass ratios. The wake pattern is obtained for the inertial and kinetic regimes of wave propagation. Due to the presence of two ion-species, the Alfvén waves propagate within two different frequency bands separated by a gap. One band is restricted to frequencies below the cyclotron frequency of the heavier species and the other to frequencies between the ion-ion hybrid frequency and the cyclotron frequency of the lighter species. The radiation pattern in the lower frequency band is found to exhibit essentially the same properties reported in a previous study [Van Compernolle et al., Phys. Plasmas 15, 082101 (2008)] of a single species plasma. However, the upper frequency band differs from the lower one in that it always allows for the Cherenkov radiation condition to be met. The methodology is extended to examine the Alfvénic wake of point-charges in the inertial and adiabatic regimes. The adiabatic regime is illustrated for conditions applicable to fusion-born alpha particles in ITER.