ION KINETIC SIMULATIONS OF THE FORMATION AND PROPAGATION OF A PLANAR COLLISIONAL SHOCK-WAVE IN A PLASMA

Ion kinetic simulations of the formation and propagation of planar sho ck waves in a hydrogen plasma have been performed at Mach numbers 2 an d 5, and compared to fluid simulations. At Mach 5, the shock transitio n is far wider than expected on the basis of comparative fluid calcula tions. This enlargement is due to hot ions streaming from the hot plas ma into the cold plasma and is found to be limited by the electron pre heating layer, essentially because electron-ion collisions slow down t hese energetic ions very effectively in the cold upstream region. Doub le-humped ion velocity distributions formed in the transition region, which are particularly prominent during the shock formation, are found not to be unstable to any electrostatic mode, due to electron Landau damping. At Mach numbers of 2 and below, no such features are seen in velocity space, and there is very little difference between the profil es from the kinetic and fluid simulations.