Experimental Investigations of Normal Ionizing Shock Waves

Experiments have been conducted on normal ionizing shock waves produced in a coaxial electromagnetic shock tube. Steady shock velocities were measured as a function of initial gas pressure, drive current, and applied axial magnetic field. The speeds agreed well with theoretical values. Measurements were made of the switch-on magnetic field, the upstream transverse electric field, and the density ratio across the front. The data all show that trans-Alfvénic shocks (uA l f1 < us ≲ 3uA l f1) exhibit Chapman-Jouguet behavior, with current flow in the shock front, and no separation of shock and drive currents. In contrast, super-Alfvénic shocks (us ≳ 3uA l f1) appear to be gas dynamic in nature. Spectroscopic measurements and shock-reflection studies demonstrated the presence of a nonluminous front and shock-heated gas preceding the luminous drive current.