Generation of atmospheric micro gap radio-frequency discharge plasma under controlled temperature conditions*

In dielectric barrier discharge, determining the temperature of a dielectric barrier is difficult owing to a rise in the temperature of a barrier and an electrode because heat generated in a discharge space exhibits a complex local distribution involving gas flow and heat transfer structures. In this study, we examined the effect of dielectric barrier temperature on plasma characteristics and a two-dimensional spatial distribution of the discharge in a radio-frequency atmospheric-pressure plasma. The temperature of the dielectric barrier was kept between 10 $^{\circ}$C and 50 $^{\circ}$C by circulating hot or cold water in a flow channel in a lower grounded electrode using a cooling water circulating device. Breakdown voltage tended to decrease with an increase in the temperature of the barrier. Depending on an increase in the applied voltage, the discharge aspect was observed to shift to the discharge having two regions, i.e., the bright and dark regions. The area of the bright region increased with an increase in the applied voltage and dielectric barrier temperature. In addition, the current density of the bright region was very high compared with that of the dark region, and therefore, the bright and dark regions were in the glow and Townsend-like modes, respectively.