Self organization in cathode boundary layer discharges

Abstract

Summary form only given. Direct current glow discharges between a planar and a ring-shaped anode with a diameter on the order of one millimeter, separated by a gap of 100 to 250 /spl mu/m, was studied in xenon and argon in a pressure range from 75 to 760 Torr. The thickness of the cathode boundary layer (CBL) plasma, in the 100 /spl mu/m range, and a discharge sustaining voltage of approximately 200 V, indicates that the discharge is restricted to the fall and the negative glow, with the negative glow serving as virtual anode. The CBL plasma was found to be an efficient source of excimer radiation. In xenon, at 172 nm, the radiant excimer emittance reaches a value of 4 W/cm/sup 2/ for atmospheric pressure operation; in argon, at 128 nm, the maximum measured value was 1.6 W/cm/sup 2/ at 600 Torr. Efficiencies range from 2.5% for argon to 5% for xenon. When the discharge current is reduced below a critical value, the discharge in xenon, but not in argon, changes from an abnormal glow into a mode showing self-organization of the plasma. The plasma patterns, regularly arranged filaments that are most pronounced at lower pressures (100 Torr), show discrete changes when the current is decreased by fractions of mA. This self-organization of the plasma requires the presence of a second stable branch in addition to the abnormal fall in the voltage-current density characteristic of the cathode boundary layer (CBL) discharges. A model of the fall by von Engel and Steenbeck, which was modified to take thermal conduction through the 500 /spl mu/m thick as a loss process into account, in addition to radiation, indicates the presence of second stable mode of the glow discharge beyond the abnormal glow mode. The effect of the surface structure on the development of regularly arranged plasma filaments has been demonstrated by modifying the surface. The positive slope of the current-voltage characteristics of the CBL discharges over a wide range of currents (including that, where self-organization is observed) indicates the possibility of generating structured, large-area plasma layers, including flat excimer sources.