One dimensional shock refraction at a plasma-cold gas interface

Refraction and reflection of a shockwave at a plasma/cold gas interface has been studied using an R.F. preheated section in an electrothermal shock tube. The gas used in the experiment was Argon at initial pressures from 10 to 30 Torr, with initial temperature of 9000 K. A detailed numerical analysis of the refraction event has been undertaken using a method that does not require definition of an effective γ. Methods that do use such a γ are not accurate, except for very weak shocks. Because of short ionization times it has been possible to assume equilibrium behind the various shock waves. Calculations suggest that in the region of interest, reflected and refracted shock velocities depend primarily on initial shock velocity, slightly on initial plasma temperature and very weakly on initial pressure. The analysis covers initial temperatures of 6000 to 12 000 K and initial pressures of 10 to 50 Torr. Calculations and experimental results are presented. These show that a step function discontinuity is a good approximation to the nature of the plasma cold gas interface in this situation.