Time resolved evolution of runaway nanosecond discharge in air and He gases

Summary form only given. Investigation carried out with fast-framing camera showed different character of discharge evolution in He and air gases under pressure of 10⁵ Pa. Discharge was initiated by application of high-voltage (HV) pulse with amplitude up to 160 kV and duration of 5 ns at Full Width at Half Maximum, to a blade shaped stainless steel cathode. Experimental results show that while the first stage of the discharge, i.e. the stage in which initial plasma channel is formed in the gap is similar in both gases, further development differs a lot. Namely, it was shown that the later development of the discharge in He is influenced by formation of explosive emission centers on the edge of the cathode, which apparently is favored in He.