Two-fluid simulations of shock wave propagation and shock-bubble interaction in collisionless plasma

The propagation of collisionless shock waves and the influence of the space-charge field on the development of fluid instabilities induced by a collisionless shock wave are investigated by solving the two-fluid plasma equations numerically in two space-dimensions. A second-order accurate Riemann solver is employed to sharply capture the shock wave and contact discontinuity. First, a series of shock-tube problems is solved to verify the method. The shock structure similar to that obtained in a previous particle-in-cell (PIC) simulation is reproduced. However, it is found that the shock wave propagates at speeds higher than the PIC results for high initial density ratios at the shock tube diaphragm. Second, the interactions between a collisionless shock wave of Mach number 1.6 and an isolated cylindrical bubble of Atwood number 0.81 are investigated. It is found that in addition to the well-known Richtmyer-Meshkov instability, filamentary fluid-instability is induced at the bubble interface introducing turbulence in the region ahead of the shock wave.