Experiments with background gas in a vacuum arc centrifuge

A vacuum arc centrifuge has been operated with an initial filling gas of either argon or hydrogen for pressures ranging from 10/sup -3/ to 10/sup -1/ Pa. The angular velocity /spl omega/ of the plasma has been determined by cross-correlating the signals from potential probes, and the electron temperature T has been deduced from Langmuir probe data. At high gas pressures and early times during the 14 ms plasma lifetime, high-frequency nonuniformities frequently observed in the vacuum discharge disappear, suggesting that the associated instability is suppressed. Under the same conditions, nonuniformities rotating with much lower angular velocities are observed in the plasma. Temperatures are reduced in the presence of the background gas, and the theoretical figure of merit for separation proportional to /spl omega//sup 2//T is increased compared to its value in the vacuum discharge for both argon and hydrogen gas fillings.