A magnetized, spherical plasma expansion in an inhomogeneous plasma: Transition from super- to sub-Alfvénic

Abstract

[1] In this letter the transition of a strong 3-D collisionless shock into sub-Alfvenic waves is numerically. The transition occurs due to changes in the background plasma parameters. The Alfven speed eventually exceeds the shock speed; the shock does not run out of energy. At this velocity transition, the shock disassembles into two types of waves: the usual compressional Alfven wave and a left-hand polarized electromagnetic shear Alfven wave. This latter wave shows remarkable 3-D coherence, and preliminary analysis suggests that there are two possible sources of energy: one is coupling to the strong electromagnetic waves that exist within the collisionless shock and the other is the density and magnetic field gradients at the interface.