Probe Measurement in a High-density lonized Gas

Abstract

Effects of probe temperature and probe material on electrostatic probe measurements in a partially-ionized high-density plasma were investigated. Probe measurements were performed in an atmospheric-pressure argon arc plasma and also in an argon arc plasma in which a small amount of hydrogen was added. Cylindrical probes of tungsten, rhenium and molybdenum were used at various temperatures. The work functions of these probes in atmospheric-pressure gases were estimated by the thermionic emission method. Further, ion saturation current to a cylindrical probe was calculated taking account of the local properties of the plasma. The ion current increases as the probe temperature rises but its increment is not large. The floating potential shifts in the negative direction at higher probe temperatures. This potential depends also on the material of the probe. These results are explained by the thermo-hydrodynamic effect and the variation in the work function of the probe.