Injection and acceleration of ions at collisionless shocks: Kinetic simulations

Kinetic simulations of collisionless shocks have provided a wealth of information on injection and acceleration of thermal ions into a diffusive acceleration process. At quasi-parallel shocks upstream diffuse ions and the induced upstream turbulence are an integral part of the collisionless shock structure. Before injected into a diffusive acceleration process thermal ions are trapped near the shock and are accelerated to higher energies. The injection and acceleration process for thermal ions at quasi-perpendicular shocks depends on the possibility of these ions to recross the shock many times. A viable mechanism for injection is cross-field diffusion of the specularly reflected ions after they have crossed the shock into the downstream region. Determination of the cross-field diffusion coefficient in strong turbulence suggests that specularly reflected ions can recross the quasi-perpendicular shock and can get further accelerated. At more oblique shocks the same injection process as at quasi-parallel sh...