Alpha particles in field‐aligned beams upstream of the bow shock: Simulations

The results of self‐consistent hybrid simulations of an oblique collisionless, supercritical shock are presented in order to study the possibility that field‐aligned ion beams (FABs) formed by direct reflection could contain alpha particles. Alpha particles are included in the simulations self‐consistently, with care taken to ensure that sufficient simulation particles are present to give reasonable statistics. It is found that alpha particles can backstream from a shock with θ Bn = 45°, but less readily than protons. The deficit of alpha particles in the FABs, expressed as a relative density ratio to H + (normalized to the solar wind He ++ to H + density ratio), varies between about 0.1 and < 0.01, and depends strongly on the upstream H + and He ++ temperatures.