Discharge dynamics and the production of active particles in a cathode-directed streamer

The emission spectroscopy technique is used to analyze a cathode-directed streamer discharge in air at atmospheric pressure in point-plane geometry at interelectrode distances of up to 100 mm and a high-voltage pulse amplitude of 18 kV. The densities of molecules in the N2(C 3Πu, v=0), N 2 + (B 2Σ u + , v=0) and NO(A 2Σ+, v=0) states are determined, and the reduced electric field in the streamer head is estimated. It is shown that the increase in the average electric field in the discharge gap substantially intensifies the production of active particles in the discharge plasma and makes the plasma more homogeneous. This effect is only related to the increase in the fraction of regions with a high electric field in the discharge gap and, as a result, the reduction of the discharge energy losses via rapidly thermalized degrees of freedom. The active particles are only produced in the streamer head, including the case in which the interelectrode gap is bridged by the streamer channel.