Experimental Study of Normal Ionizing Shock Waves

A coaxial electromagnetic shock tube has been used to study normal ionizing shocks propagating through hydrogen. An experiment is described which produced plane switch-on ionizing shocks. Quantitative studies were conducted covering the sub-Alfvénic and trans-Alfvénic regimes. Data are presented that support the existence of switch-on fronts in both these regimes, thereby demonstrating the significant effect of the initial electric field on the shock jump conditions. The results are interpreted by appeal to Taussig's theory of normal ionizing shocks. To choose from among the several theoretically predicted ionizing waves propagating at a given speed, Taussig's theory is supplemented by a simple physical criterion modeled on the Chapman-Jouguet hypothesis of Gross and Kunkel. This criterion has strong intuitive support and results in a picture of ionizing shock propagation that is in general agreement with the experimental observations.