Pickup ion energization by shock surfing

Energization at a quasi‐perpendicular shock is described for ions which approach the shock with a speed much less than that of the incoming plasma. These ions may be trapped between the shock electrostatic potential and the upstream Lorentz force and accelerated by “surfing” along the shock surface, before eventually escaping the shock into the upstream or downstream plasma. The process is described in detail, extending previous work on the mechanism, and energy gains are calculated. It is pointed out that pickup ions in the solar wind are ideally configured, so that a reasonable fraction of the ions can be accelerated by this mechanism at cometary bow shocks, the solar wind termination shock, and interplanetary traveling shocks. The mechanism may provide the required “injection” or preacceleration at quasi‐perpendicular shocks for subsequent diffusive shock acceleration.