Pattern Transition in a Surface Microdischarge in Atmospheric-Pressure Helium

The surface microdischarge in atmospheric helium is studied for the dynamic evolution of plasma patterns in the glow mode. It is found that there are two distinct patterns in the positive half cycle. This indicates that the influence of space-charge electric field caused by surface deposited charges not only exists in the negative half cycle for the evolution process, but also exists between the half cycles. It is in agreement with the phenomenon which the originating regions of discharge in positive half cycle depend on the number of the current pulse in negative half cycle. The emission pattern of the positive half cycle is dominated by the last strong current pulse in the negative half cycle.