Explosion Phenomena in Collisionless Plasmas at Super-Alfvenic Speed

Explosion events in plasmas widespread in both the Universe and Laboratories are investigated by numerical simulation of collisionless super-Alfvenic dense plasma clouds expanding through and decelerating in an ambient plasma background. Since the turbulent coupling of counterstreaming plasma flows at large Alfven-Mach numbers is inefficient, the laminar collisionless mechanism associated with electric fields arising at the leading edge of the expanding clouds is studied in detail. Using a universal hybrid kinetic-hydrodynamical description, the calculations are made for two cases, e.g., a. two-dimensional expansion of a spherical cloud into an initially (i) uniform and (ii)nonuniform background. The evolution of expanding plasma clouds and the dependence of cloud energy losses on time and on the ambient plasma nonuniformity are obtained.