PRESSURE-DEPENDENCE OF PLASMA PARAMETERS IN MEDIUM-VACUUM NITROGEN ARC-DISCHARGE WITH THE TITANIUM CATHODE

This paper is concerned with plasma properties of a medium-vacuum nitrogen arc discharge with the titanium cathode. The arc chamber used is 400 mm in diameter and 600 mm in length. The cathode diameter and thickness are 64 and 25 mm, respectively. The experimental conditions are as follows: Pressure range = 1 x 10(-3) approximately 2 x 10(-1) torr; N2 gas flow rate = 6 ml/min; arc current = 50 A. Electric probe characteristics are measured as a function of pressure and distance from the cathode surface. The analytical results obtained from these measurements show that the electron energy distribution takes 1-Mx at pressures above 1 x 10(-2) torr, whereas 2-Mx at pressure under 4 x 10(-2) torr and the electron density have a maximum value at a certain pressure. Furthermore, Ti+, Ti++, and N2+ ion spectral intensities are measured as a function of pressure and distance from the cathode surface. On comparison of those results and the electron density, the pressure dependence of the Ti+ spectral intensity turns out to that of the electron density. This suggests that the major ion in the plasma volume is Ti+ species.