Streamer-to-filament transition is a general feature of high pressure high voltage nanosecond surface dielectric barrier discharges [1]. The transition was studied experimentally using time- and space-resolved optical emission in UV and visible parts of spectra. The discharge was initiated by HV pulses 20 ns in duration and 2 ns rise time, positive or negative polarity, 20 - 60 kV in amplitude on the HV electrode. The experiments were carried out at initial pressures P > 3 atm and ambient initial temperature in air, H2 : N2 and O2 : Ar mixtures. It was shown that the transition to filamentary mode is accompanied by the appearance of intense continuous radiation and broad atomic lines. Electron density calculated from line broadening is characterized by high absolute values Ne ≥ 1018 cm-3 at P > 5 atm and long decay time. Possible mechanisms of the contraction of high-pressure nanosecond discharges and possible reasons of the appearance of a continuous spectrum and a high electron density in the filament channels are discussed in detail.
-
