Characterization of the Basic Operationa L Properties of the Capillary Plasma Electrode (CPE) Discharge

Summary form only given. Various approaches have been pursued to create stable atmospheric pressure discharges by extending the lifetime of the diffuse phase of the discharge to hundreds of microseconds. Previous research showed that the stability of the diffuse mode is dependent on the frequency (in the kHz range), gas type, power, mode of the excitation, and geometrical confinement. Some of the most promising approaches are based on the recognition that arc formation in high-pressure plasmas can be avoided and stable high-pressure plasmas can be generated and maintained when the plasmas are spatially constricted to dimensions of tens to hundreds of microns. The capillary plasma electrode (CPE) discharge (US Patent 5872426 and E.E. Kunhardt, 2000) is able to produce stable atmospheric pressure nonequilibrium plasmas. The CPE is similar in design to a barrier-electrode discharge, but has perforated dielectrics. This configuration, aside from exhibiting a diffuse mode of operation, also exhibits the so-called "capillary jet" mode, in which the capillaries "turn on" and a bright plasma jet emerges from the capillaries. The capillary jets from adjacent capillaries overlap so that the discharge appears uniform when the electrode contains an array of holes. There appears to be a threshold frequency for the capillary jet formation, which is strongly dependent on the L/D ratio of the capillaries, where D is the diameter of a capillary and L its length. However, the operating principles and basic properties of this behavior are not well understood. This current work explores these modes of operation of the CPE by characterizing the electrical and optical emission properties of this discharge by examining a multi-hole discharge as well as a single-capillary discharge reactor.