SUPERSONIC EXPANSION OF NONEQUILIBRIUM PLASMAS.

In the light of the important role that K//R (recombination rate constant) in any numerical solution of nonequilibrium expansion flow of plasmas, details of experiments on a 15-degree corner expansion flow of ionized argon are given. In these experiments the plasma flow which was generated by driving strong normal shock waves into quiescent argon, was studied mainly by optical diagnostics. Using a dual-frequency-laser interferometer, the plasma properties around a corner expansion were recorded. The analysis of the interferograms has yielded values for the recombination rate constant as a function of the plasma macroscopic properties. The range of shock Mach-number, electron number density, temperature and initial channel pressure and temperature were as follows: 13 less than M//s less than 19; 10**1**6 less than n//e less than 1. 5 multiplied by 10**1**7 cm** minus **3; 9,000 degree K less than T less than 13,000 degree K; 2. 2 less than p//I less than 10 torr; T//1 congruent 300 degree K. It was found that the theoretically predicted values for the three-body, electron-ion-electron collisional-recombination rate are in good agreement with those measured gasdynamically in a well-defined flow. The measured flow quantities substantiate a previous analysis based on the method of characteristics.