Shock and Current-Sheet Separation in Magnetic Shock Tubes

The problem of separation of a shock wave from the current driving it, is experimentally investigated over a wide range of Mach numbers in a single gas. In order to do this, a parallel plate shock tube was developed which produces repeatable shocks in hydrogen from Mach 20-180 at initial pressures from 75-460 μHg. In the present work, no preheating or external magnetic fields were used and the shock is completely collision dominated. The shock-wave and current-sheet trajectories were determined by piezoelectric pressure probes and magnetic pickup loops, respectively, and separation of the shock wave from the driving current was measured directly at speeds above 8.0 cm/μsec and initial pressures above 250 μHg. Experiments were performed at speeds up to 22 cm/μsec at lower pressures, but separation was not observed at these conditions. The electron temperature behind the shock and within the current layer was determined by using the ratio of continuum intensities across the Balmer series limit, and these temperature measurements were used in connection with the other data to explain most of the observed results. The data are also used to examine the applicability of the skindepth model and shock-formation theory in predicting separation in magnetic shock tubes.