Diagnostic signatures of magnetized collisionless shocks in laboratory experiments

Magnetized collisionless shocks commonly occur in the heliosphere and astrophysics, and have recently become the subject of laboratory investigations at HED facilities. We describe the modeling and interpretation of a campaign of laser experiments designed to generate high Mach number magnetized collisionless shocks on OMEGA-EP. In the experiment, a laser-produced high velocity plasma collides with a magnetized, pre-ablated plasma. Proton radiography shows a moving region of proton deficit followed by a sharp enhancement of proton density. These features are produced by gradients in propagating compressed magnetic field. We compare the data to the results of 3D PIC simulations of plasma collisions, and describe the signatures of magnetized shock formation, including the early electrostatic-dominated stage, and a later magnetic reflection with magnetic overshoots. We point out the importance of the contact discontinuity between the flows, and its dependence on the magnetization of plasma. We explain the geometrical effects on the radiography introduced by density gradients in expanding plasma and by the curvature of the imposed magnetic field. We conclude that our experiments have reproducibly achieved magnetized shocks with Alfvenic Mach number 3 to 9 in laboratory conditions.