Parametric Studies of Ultrarelativistic Electron Acceleration by an Oblique Shock Wave

Abstract

A magnetosonic shock wave propagating obliquely to an external magnetic field can trap and accelerate electrons to ultrarelativistic energies when vsh is close to c cos θ, where vsh is the propagation speed of the shock wave, c is the light speed, and θ is the propagation angle of the shock wave. Because of instabilities driven by the trapped electrons, some electrons can be detrapped from the main pulse retaining their high energies and can then be further accelerated to higher energies as a result of their gyromotions. The dependence of electron motions on the parameters vsh and θ is investigated by two-dimensional electromagnetic particle simulations with full ion and electron dynamics. If θ is fixed, electron energies become maximum when vsh is slightly smaller than c cos θ. If the value of vsh/(c cos θ) is fixed, the maximum energy of electrons tends to increase with decreasing θ for the range vsh/(c cos θ) < 1. The number of electrons that are detrapped to the upstream region and suffer the subsequent acceleration is also examined.