Experimental study on the ionization of argon behind reflected shock waves

The electron temperature and density along with the ion temperature in argon gas behind reflected shock waves were measured by laser light scattering, while the spectroscopic temperature was measured from the ArI line emissions. The values of these three temperatures are different from each other for a few hundred microseconds after arrival of the reflected shock front. Both the electron and ion temperatures are much higher than the theoretical gasdynamic temperature, while the spectroscopic temperature is lower than the theoretical one. The degree of ionization is much higher than that in the equilibrium state. The stochastic character of the ArI line emissions was observed, indicating that the gas is inhomogeneous. These phenomena are explained as follows: initially, the gas behind the reflected shock wave is inhomogeneous, and an associative ionization is initiated at some points. The gas becomes homogeneous mainly through diffusion. (author)