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 ${{\mathrm{(u}}_{\mathrm{A\; l\; f}}}_1{\mathrm{<\; u}}_s{{\text{≲ 3u}}_{\mathrm{A\; l\; f}}}_1)$ exhibit Chapman‐Jouguet behavior, with current flow in the shock front, and no separation of shock and drive currents. In contrast, super‐Alfvénic shocks ${\mathrm{(u}}_s{{\text{≳ 3u}}_{\mathrm{A\; l\; f}}}_1)$ 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.