Reforming perpendicular shocks in the presence of pickup protons: initial ion acceleration

Abstract

Abstract. Acceleration processes associated with the heliospheric termination shock may provide a source of anomalous cosmic rays (ACRs). Recent kinetic simulations of supercritical, quasi-perpendicular shocks have yielded time varying shock solutions that cyclically reform on the spatio-temporal scales of the incoming protons. Whether a shock solution is stationary or reforming depends upon the plasma parameters which, for the termination shock, are ill defined but believed to be within the time-dependent regime. Here we present results from high phase space resolution particle-in-cell simulations for a three-component plasma (solar wind protons, electrons and pickup protons) appropriate for the termination shock. We find reforming shock solutions which generate suprathermal populations for both proton components, with the pickup ions reaching energies of order twenty times the solar wind inflow energy. This suprathermal "injection" population is required as a seed population for subsequent acceleration at the shock which can in turn generate ACRs.