Observations of a helium-air gas-confined barrier discharge operated in diffuse mode

With ambient air instead of solid dielectric operating as the insulating layer, a diffuse helium/air gas-confined barrier discharge with a coaxial jet configuration is demonstrated for the first time. The effects of the helium gas flow rate, the diameter, and the vertical position of the helium gas flow on the breakdown characteristics of the diffuse mode are investigated. As the applied voltage increases, a diffuse plasma layer is first ignited within the helium gas column followed by a typical filamentary discharge bridging the whole gap. With the replacement of ambient air by N-2 or O-2 gas, the diffuse mode can be achieved with relatively lower breakdown voltage in the case of N-2 gas while it is not observable in the case of O-2 gas. The dynamics of the diffuse discharge show that the plasma front crosses the helium gas column vertically at an average velocity of similar to 10(4) m/s, and then splits into two horizontally counter-propagating plasma fronts with the dark channel left behind. Published by AIP Publishing.