Spectroscopic investigations of high-pressure microhollow cathode discharges

Summary form only given, as follows. Stable DC operation of microhollow cathode discharges up to atmospheric pressure has been obtained by reducing the diameter of the electrodes and the cathode opening to values in the order of 100 microns in argon and nitrogen. The discharges presented were operated DC and pulsed in a wide current range up to 30 mA with a forward voltage drop up to 200 V for argon and 400 V for nitrogen. Optical emission spectroscopy was used to get information about the plasma properties of the microhollow cathode discharge, which were not available until now. The electron density was measured in pulsed and DC operation by Stark broadening of the hydrogen Balmer H/sub α/ and H/sub β/ line. Hydrogen was added for this purpose with a partial pressure of 10-20 % in argon. The measured electron densities scale linear with discharge current in the order of 10/sup 15/ cm/sup 3/ in the cathode cavity. In parallel the mean electron temperature was determined to about 1 eV from the line intensities ratios of numerous neutral and single ionized argon states by a Boltzmann plot. The temperature of the neutral gas atoms was determined using the rotational-vibrational spectra of the second positive system of molecular nitrogen. It was found that the gas temperature varies from 700-1800 K as function of discharge current and depends on the mode of operation. Under pulsed operation the gas temperature in microhollow cathode discharges can be strongly reduced.