Schematic of shock wave generation: In the top picture the green block represents the driver gas expanding from the driver section into the driven section. The bottom diagram shows the position of the shock wave, the contact surface (interface between driver and driven gases) and the rarefaction wave (from the expansion of the driver gas) with time in the shock tube.

In the high-pressure shock tube shock waves are generated by filling the driver section with helium until the diaphragm separating the driver and driven sections ruptures. The driver gas then expands into the driven section and compresses the test gas in the driven section resulting in the formation of a series of compression waves. These compression waves coalesce within a short distance to form a shock wave which travels along the shock tube. When the shock wave reaches the end of the driven section it is reflected and travels back towards the driver section and causes a second heating event. The conditions are chosen so that the reaction conditions are obtained behind the reflected shock wave

13000 psi Shock Wave. Note the rapid increase in pressure

The gases behind a shock wave are at a much higher temperature, pressure and density than the gases in front of the shock wave. The time taken to alter the properties from those ahead of the shock wave to those behind the shock wave is approximately the time it takes for the head of the shock wave to traverse a distance equivalent to the thickness of the shock front i.e. the change is effectively instantaneous. The instantaneous change in temperature, pressure and density is one of the main benefits of using a shock tube for investigating high-temperature gas kinetics.

Shock wave Generation