Confinement of nonequilibrium plasmas in microcavities with diamond or circular cross sections: Sealed arrays of Al/Al₂O₃/glass microplasma devices with radiating areas above 20 cm²

Arrays of Al Al2 O3 /glass microplasma devices with microcavities having diamond or circular cross-sectional geometries and radiating (active) areas >20 cm2 have been operated sealed-off in Ne, Ar, and Ar D2 gas mixtures. Microcavities are fabricated in only one of the two electrodes, and the thickness of the completed package is ∼170 μm (excluding the quartz output window). Excited by a sinusoidal 20 kHz voltage wave form, arrays with active areas of 4.5×3 cm2 exhibit ignition voltages as low as 110±5 V rms for Ne pressures of 400-700 Torr. Mixtures of 1% D2 in Ar at a total pressure of 300 Torr produce wavelength-integrated (λ∼250-400 nm) intensities of ∼1 mW cm-2 over a 25 cm2 area. Optical micrographs show the operation of the microplasmas in two well-defined modes. For current densities below a threshold value (∼53 mA cm-2 for 250 μm dia. cavities and pNe =400 Torr), diffuse uniform plasma is produced in each cavity but, with higher currents, a positive column having near-cylindrical geometry appears, as evidenced by the generation of intense emission localized in the region of weak electric field gradient near the axis of symmetry.