Measurement of heavy particle and electron densities in supersonic nonequilibrium corner expansion of ionised argon and neon

Dual-wavelength interferometry is employed to study ionized high-temperature corner expansions of argon and neon. The expansion flow is generated by passing a strong shock wave over a 36-deg sharp convex corner produced by a wedge mounted inside the Mach cone at the exit of the Australian National University's double-diaphragm shock tube DDT, operated in the single diaphragm mode. The Mach number of this primary shock wave was 15.3 for argon and 19.4 for neon. The experimental results are compared with theoretical models that account for recombination processes in the expansion fan. For argon, the comparison shows that nonequilibrium flow exists; for neon, the flow is essentially in equilibrium for the initial part of the flow, but it departs from equilibrium further downstream