ION INJECTION SIMULATIONS OF QUASI-PARALLEL SHOCK RE-FORMATION

The process of quasi-parallel shock re-formation is investigated using one-dimensional hybrid simulations. These simulations are used to study the coupling of a beam of ions reflected at the shock to the incoming solar wind. We have constructed a simple simulation configuration that allows us to control the properties of the background plasma and of the reflected ions. The simulations initially do not contain a shock, but rather include a background plasma, corresponding to the solar wind, into which we inject a counterstreaming ion beam, corresponding to shock-reflected ions. We investigate the length and time scales for the coupling of the reflected ions to the background plasma as functions of theta-Bn, beam density, and beam temperature. This coupling can lead to the formation of shocklike structures upstream from the injection location which we associate with quasi-parallel shock re-formation. In addition, we have perturbed the upstream plasma in a controlled manner to study the effect of upstream waves on the coupling process. We find that the coupling length and time scales vary systematically with the upstream magnetic field direction, theta-Bn. The coupling occurs at roughly the time and location where the injected ions become deflected transverse to the shock normal direction. Also, as seen in previous quasi-parallel shock simulations, the reflected (injected) ions become trapped downstream of the newly forming shock by the growing perturbations. In this way, shock-reflected ions may contribute directly to the downstream ion temperature.