An investigation of non-equilibrium effects in an argon free-jet plasma

摘要

The non-equilibrium effects present in the formation of a strong normal shock wave in a low density, slightly ionized argon flow field, particularly as evidenced by the appearance of a dark region upstream of the shock wave, have been analyzed both theoretically and experimentally. A model for the flow through the shock wave was formulated which incorporates a quantum mechanical theory to explain the existence of the dark region, and the problem was solved numerically to yield flow field property distributions. A precursor region of high electron temperature was found to exist upstream of the main body of the heavy-particle shock wave.ududAn experimental investigation of the phenomenon was carried out in an arc heated free jet flow field. A test facility was constructed in which the goal has been to attain operation at low enough enthalpies to allow precise and extensive diagnostic testing while still high enough to exhibit the interesting non-equilibrium effects. Extensive study was carried out on the effect of electrode design and gas flow phenomena on the stability of the arc discharge. The completed unit was instrumented fully for measurement of the operating parameters and a computer program was developed to monitor its operation as a supply of slightly ionized argon for free-jet experiments.ududThe non-equilibrium aspects of the free-jet were analyzed both theoretically and experimentally. A theoretical model was developed and numerically solved for the free-jet expansion of slightly ionized argon. Pitot pressure measurements were completed and compared favorably with predictions calculated from this theoretical model.ududElectron temperature and ion density profiles were measured both along the axis of the empty free-jet and through the normal shock wave in front of a cooled blunt body using a new type of cooled Langmuir probe, the operation of which was theoretically analyzed. The existence of a region of electron temperature in front of a strong normal shock wave coincident with the observed dark region was experimentally verified.