Laser discharges in attaching gases, June 25, 1976--June 24, 1977. Final report

A significant problem in the development of high-power gas discharge lasers is the glow-to-arc transition, which limits the electrical energy that can be deposited in the diffuse glow plasma, especially in attaching gases. A combined experimental and theoretical study of the maintenance and stability of glow discharges in attaching gas mixtures similar to those used in rare gas-halide excimer laser discharges is described. A discharge test apparatus has been constructed for establishing uv-preionized, self-sustained, diffuse glow discharges in halogen-containing mixtures. Quasi-steady, diffuse discharges have been established in 0.5% SF/sub 6/:15-15% Kr:He mixtures at 100-800 Torr, and have been maintained for up to 1 ..mu..sec, the limit of the pulse-forming network used. Measured electric fields in the positive column agree well with fields calculated from a steady-state model based on electron production by one- and two-step electron impact ionization and loss by attachment to SF/sup 6/. The discharge duration is limited above some values of pressure, Kr concentration, and/or current density by the glow-to-arc transition, i.e., by filament formation within the diffuse glow. Discharge operation is not limited by the instability analyzed by Daugherty, Mangano, and Jacob