Spectroscopic investigation of high-pressure micro-hollow cathode discharges

Abstract

Micro-hollow cathode discharge (MHCD), as a high-pressure glow discharge, has many applications in industry. Theclosed-MHCD is investigated experimentally in argon in the paper. The relations between breakdown voltages of glow discharge and gas pressure in argon are measured. Minimum breakdown voltages obtained, are about 520V at 200Torr argon. The differential resistivity of the <i>voltage-current</i> characteristics for all of the pressure studied is positive. Strong optical emission from the closed-MHCD is also observed. Measurement of electron temperature is carried out by optical emission spectroscopy. The electron temperature was about 1eV at the pressure from 200Torr to 760Torr and at the discharge current from 0.5mA to 10mA. An increase in pressure of the working gas leads to a slight decrease in electron temperature. The electron number density and gas temperature of closed-MHCD was investigated by diode laser atomic absorption spectroscopy. The gas temperature and the electron number density were evaluated from the analysis of the absorption line profiles, taking into account significant Stark broadening mechanisms. The gas temperature was found to increase with pressure from 1100K to 2100K. The electron number density was calculated from Stark broadening and shift, and it ranges from 7×10¹⁴ to 1.5×10¹⁵cm^-3. Thus, the closed-MHCD is similar to MHCD, which has the non-equilibrium character with the advantage of high-pressure. And it can also be used for non-thermal plasma processing e.g. surface treatment, plasma chemistry and generation of UV and VUV radiation.