Pressure Dependences of Gas Temperature and Electron Density in Microhollow Cathode Discharges in He and He+H2O Gases

Abstract

Microplasmas were generated using a cylindrical hollow cathode with a diameter of 0.5 mm and a length of 3 mm in He and He+H2O gases at pressures in the range of 20 to 765 Torr. Spectral line profiles of He I (667.8 nm) and Hα (656.3 nm) were measured to determine the plasma parameters. Gas temperature and electron density were evaluated by the analysis of spectral line broadening. These parameters linearly increased with gas pressure in the range of 300 to 765 Torr. The gas temperatures and electron densities at atmospheric pressure were obtained to be 610 K and 5.0×1014 cm-3 for He and 820 K and 3.5×1014 cm-3 for He+H2O microplasmas, respectively. A comparison of these values with those obtained in a previous work [M. Miclea et al.: J. Phys. D 38 (2005) 1709] demonstrated that our device could generate high-density plasmas with a large volume and a high degree of nonequilibrium. The influences of an admixture of H2O on the discharge properties and plasma parameters were also discussed.