Electron density and electron temperature in argon microhollow cathode discharges

Summary form only given, as follows. Direct current microhollow cathode discharges (MHCDs) operated in noble gases and in mixtures of rare gases and halides have been shown to emit excimer radiation with efficiency in the 0.5-10% range. Even higher values in efficiency have been obtained (20% in xenon) when the discharge was pulsed with 20 ns pulses. These relatively high values indicate a substantial density of electrons with energies greater than the excitation energy of rare gas atoms. We have measured, electron density and electron energy, for a microdischarge plasma with typical dimensions of 100 /spl mu/m in argon at a pressure of 300 Torr, with 1% of hydrogen added. The discharge current was 4 mA, and the sustaining voltage 180 V. The electron density was obtained by measuring the Stark broadening of the hydrogen Balmer-/spl square/line at 486.1 nm. In direct current operation, the electron density was found to be 4/spl times/10/sup 14/ cm/sup -3/. Applying a 20 ns pulse of 750 V to a low current dc discharge resulted in an increase of the electron density by more than two orders of magnitude (10/sup 17/ cm/sup -3/). The temporal increase in electron density followed the current pulse; the exponential decay had a time constant of 50 ns. Electron temperature was obtained from line emission ratios of two argon lines at 810.6 and 811.8 nm by assuming a Maxwell-Boltzmann distribution for the electron energies. For dc operation the electron temperature was found to be approximately 60 eV. For the pulsed mode it is more than twice this value: approximately 140 eV. The data indicate that the efficiency of MHCD argon excimer emission at 128 nm can be substantially increased beyond the dc value of 0.7% by pulsing the discharge.