Experimental study of energy delivered to the filaments in high pressure nanosecond surface discharge

of energy delivered to the filaments in high pressure discharge. discharges driven by repetitive high frequency (typically at least tens of kHz) nanosecond pulses; constriction of the discharges corresponding to sharp increase of the electron density in a nanosecond time scale has been experimentally observed. Filamentary surface dielectric barrier discharge provides similar plasma properties in the filaments but instead of a single shot channel, multiply equidistant filaments (30-50 in our case) appear along the edge of the high-voltage electrode. A regular "grid" of the filaments results in efficient and stable ignition of combustible mixtures. Our recent experiments shown high, more than 7 eV/particle, specific delivered energy for the filaments in air initiated by pulses of negative polarity 30-45 kV on the electrode at gas pressure equal to 8 bar. Developed physical model of the filamentary nanosecond surface DBD suggests extra-raid fast gas heating (tens of kK during parts of nanoseconds) in discharges at high electric field and high energy density at elevated pressures. In this case the efficiency of ignition is explained by high temperature and quasi-equilibrium plasma formed in the filaments; high density of O-atoms and high hydrodynamic perturbations in the vicinity of each filaments. One of open questions is the initial stage, namely how streamer-to-filament transition happens and what is a physical reason of sub-nanosecond single-shot construction. The aim of the present work is an experimental study of appearance of the filaments using microimaging; of the value of specific delivered energy and study of character of hydrodynamic perturbations for the filamentary nSDBD discharge of positive polarity. negative polarity streamers. During the a few channels move faster than the surrounding streamers; the distribution of these channels around the edge of the electrode is arbitrary. At higher voltages, a regular set of filaments is developed. Difference in morphology is linked to the different polarities of the