Simulation studies of positron acceleration in a shock wave in a nonuniform external magnetic field

摘要

Positron acceleration in a shock wave in an electron-positron-ion plasma is studied with one-dimensional, fully kinetic, electromagnetic particle simulations, with particular attention paid to the effect of inhomogeneity of external magnetic field B _0. First, acceleration to γ ～ 10 ~4, where γ is the Lorentz factor, is demonstrated for a shock wave in a uniform B _0 with the shock speed v _(sh) close to c cos θ, where c is the speed of light and θ is the angle between B _0 and the wave normal. The acceleration is not saturated till the end of the simulation run. Then, the effect of nonuniformity of B _0 is investigated: Comparisons are made between the case in which the difference (v _(sh) - c cosθ) at the shock front changes from negative to positive values as the shock wave propagates and the case with this relation reversed. The latter is found to create a greater number of high-energy particles than the former