GLOW-TO-ARC TRANSITION IN A PULSED HIGH-PRESSURE GAS DISCHARGE.

The glow-to-arc transition that occurs at high repetition rate operation in near-atmospheric pressure, transverse electric gas discharges has been investigated experimentally in helium and mixtures of helium and other gases (CO//2, CO, Ne, A, Kr, Xe). Various aspects of the discharge including the ionization phase, output power and wavelength (for lasing gas mixtures), electron density, gas current and voltage, visible emission from reaction products, refractive effects in the gas, and the distribution of cathode hot spots, have been measured as the excitation current, repetition rate, and preionization were changed. The effects on the discharge of cathode material, added contaminants, and magnetic field were also observed. The results indicate that one of the main causes of the glow-to-arc transition at high repetition rate operation is a thermal instability, similar to the Benard instability, driven by the temperature gradient at the cathode.