Acceleration of charged particles by gyroresonant surfing at quasi-parallel shocks

Abstract

We discuss an acceleration mechanism of charged particles by magnetohydrodynamic (MHD) structures, such as quasi-parallel shocks and short-large amplitude magnetic structures (SLAMS). In the presence of electromagnetic waves and an electrostatic electric field, particles are accelerated efficiently in the perpendicular direction to the background magnetic field by the combination of two effects, the trapping of particles by the wave and the dragging by the electrostatic field to keep the resonance condition. This allows particles to propagate downstream even when they initially have smaller kinetic energy than the potential. We show the fundamental properties of this mechanism, referred to as gyroresonant surfing.