Exploring Transition Regions of Collisionality, Criticality, and Magnetization in Parallel Shock Experiments

A series of parallel shock experiments were performed on the Big Red Ball (BRB) at the Wisconsin Plasma Physics Lab (WiPPL). An upgraded compact toroid injector produced a supersonic piston (60 - 100 km/s) that collided with a target plasma. Plasma densities (0.5 < n_e < 50 \cdot 10¹⁸\ m^-3) were adjusted by varying the number of plasma guns, with the experiment length (L = 3 m) always much larger than the ion skin depth (3 < d_i < 30 cm). The variable magnetic field (0 ∼ 10 mT) allowed for target plasma betas of 0.1 < β < 10. Together, this amounts to a substantial parameter space in magnetosonic Mach number (M_{ms} ∼ 0.5 - 5), in collisionality (ν _e / ω _ce ∼ 0.1 - 5), and in magnetization (ρ _i / L ∼ 0.1 - 2). Results and analysis to identify the transitions from subcritical to supercritical, from collisional to collisionless, and from Hall-MHD to MHD, will be presented. This work was also presented at APS-DPP.