Simulation Study of Trapped Electron Effects on Positron Acceleration by a Shock Wave in an Electron–Ion–Positron Plasma

Abstract

Positron acceleration by a shock wave in an electro-ion-positron plasma is studied with a two-dimensional, relativistic, electromagnetic particle simulation, with special attention to effects of electrons trapped in the shock wave. It is demonstrated that ultrarelativistic positron acceleration can occur even when the fluctuations along the shock front, which we call 2D fluctuations, excited by the trapped electrons grow to large amplitudes. Further, by comparing the results of the simulation and the calculation of test positrons not influenced by the 2D fluctuations, we show that the positrons influenced by the 2D fluctuations are accelerated to higher energies than the positrons not influenced by them. In addition to the parallel electric field formed in the shock transition region, the perpendicular electric field in the shock wave greatly contributes to the ultrarelativistic positron acceleration under the influence of the 2D fluctuations. Effects of the accelerated positrons on the 2D fluctuations are also discussed.