Spectral micro–scale measurements of the initial stage of streamer–to–filament transition in high pressure nanosecond surface dielectric barrier discharge

The paper presents the recent study of spectral composition of the filament during its propagation process in the single shot surface nanosecond dielectric barrier discharge (nSDBD) at high pressures. The micro–images and spectra at specific moments were recorded by the ICCD camera and spectrometer accompanied with the long distance microscope. This is the first time that we analysis nSDBD in the micrometer scale. The discharge starts with the streamer generated from the high–voltage electrode. A few nanoseconds later, there are a few protrusions passing through the streamer front. After the protrusions’ propagation, the filaments are formed in the whole channel connecting the high–voltage electrode and the tip of protrusions. It is found that in the early stage of the streamer–to–filament transition, both the streamer and the protrusion are contributed by the second positive system of nitrogen while only when the whole filament is formed, the cw emission can be seen.