Shock collision in preheated argon

A new type of diaphragmless electrothermal shock tube is described. The device has the ability to generate well-developed shock regions with nonturbulent interfaces. This improvement in performance for diaphragmless tubes is achieved by preheating the downstream region using a high-power RF plasma heater. In the experiments reported here the shock tube is operated in a double-ended mode leading to highly reproducible shock collisions in the centre region of the tube. A high level of initial preionization ensures rapid equilibration across the incident and reflected regions, and shock-speed measurements in the two regions are used to determine uniquely the pre- and post shock states. Shock velocities of 3·5 mm μs −1 have been obtained in argon at initial pressures of 30 Torr, and higher speeds are possible.