Test-particle simulations of Fermi acceleration of electrons at quasiperpendicular shocks

Abstract

Summary form only. A type of first-order Fermi electron acceleration associated with quasi-perpendicular shocks has been studied. Ion-scale transverse waves in the magnetic field upstream of the shock do not scatter electrons. However, when these waves are advanced into the shock, the leading edges are compressed first, producing mirror points for a large fraction of the electrons. Thus a population of electrons is trapped in a flux tube between two such mirror points that converge as the field continues to advect into the shock. A similar trap is formed when straight field lines are advected into a concave region of a corrugated shock. In either case, the population is longitudinally accelerated by compression between converging mirrors. A few electrons, having special initial conditions, can be accelerated by this means to energies thousands of times greater than their injection energies. Starting from a Maxwellian distribution of initial energies, the resulting particle energy spectrum is a mildly heated (factors of two to five) Maxwellian plus a power law to very high energies with an index -2.6.<>