Diffuse discharges at high-current density

Diffuse discharges were studied in an impedance-matched experimental system. A traveling-wave transmission line system was used to produce a high-voltage pulse (up to 40 kV), with a rise time of approximately 2 ns and a total pulse width of approximately 100 ns. Gas mixtures of C3F8 and c-C4F8 with He in a pressure range between 100 and 600 Torr were investigated. Plane parallel electrodes with 10-cm diameter and electrode spacings from 0.25 to 1.5 cm provided uniform field conditions in the discharge region. UV radiation produced by a flashboard placed behind a perforated anode surface provided the volumetric preionization necessary for maintenance of the diffuse discharge. A low ionization potential seedant was used to assure a uniform preionization. High-current-density diffuse discharges were maintained for approximately 100 ns. At low-current density, the diffuse discharge in an electronegative gas mixture operated under balanced electron growth conditions with constant voltage. At high-current densities (above 100 A/cm2), the discharge operating voltage decreased and was found to be as much as two times lower than the low-current glow-discharge voltage. The operating voltage also decreased with time during individual discharge under such conditions.