Self-organized patterns in cathode boundary layer discharges

Summary form only given. The cathode boundary layer (CBL) discharge is a high-pressure glow discharge between a planar cathode and a ring-shaped anode, separated by a dielectric layer with a thickness of several hundred micrometers. Self-organized patterns of CBL discharges in direct current operation have been studied in a pressure range of 75 to 760 torr in xenon. The plasma patterns, i.e. regularly arranged filaments in the negative glow, are most distinct at lower pressures (50 to 150 torr). The number of filaments decreases with decreasing current down to a single filament for the cathode area with a diameter of 300 mum. Side-on observations of the discharges show a significant decrease of cathode fall thickness in the self-organized mode. This and a simultaneous decrease in sustaining voltage indicate an enhanced secondary emission coefficient possibly due to increased Xe metastable states. The pattern structure is likely due to electrostatic interaction between the positively charged cathode fall region of the filaments in a potential well. This potential well may be due to a positive space charge on the surrounding dielectric layer generated through photoemission of electrons. Spectroscopic studies revealed that the excimer emission at 172 nm is enhanced in this regime. The absolute value of the VUV radiant power is reaching values of 1.5 W/cm² at an internal efficiency of 4% for a discharge at 250 torr with aluminum as cathode material