Nanosecond Plasma: Peculiarities of Kinetics and Diagnostics*

In the last 20 years pulsed nanosecond discharges have been widely studied for the problems of flow control, ignition and stabilization of combustion, initiation of detonation. The parameters of the resulting plasma are usually determined by various aspects of the experiment: the composition of the gas mixture, the amplitude, duration and rise time of the high voltage pulse, the pulse repetition rate divided by the flow rate, the geometry of the electrode system.

We propose to consider the plasma produced by nanosecond discharges, paying attention to two key parameters: the specific energy deposited in the gas and the magnitude of the reduced electric field. We apply this approach to analyzing the electron density, densities of main radicals, as well as heat release and hydrodynamic perturbations. Volumetric and surface discharges in the pressure range from units of mbar to tens of bar will be considered. It will be shown that the use of the same pulse allows one to obtain dramatically different plasma parameters: specific energy in the range from 0.001 to 10 eV per particle, electron density from 10¹² to 10¹⁹ cm-3. The obtained plasma can vary from "classical" low-temperature to pulsed "arc" plasma, depending on the request of the application.

A special attention will be given to check of validity of diagnostics like E-field measurements by electrical probes, optical emission spectroscopy and laser E-FISH technique, actinometry and TALIF measurements of density of atoms. A fast, sub-nanosecond transition from streamer to filamentary nSDBD at high pressures will be analyzed by OES combined with a microimaging of high spatial (a few um) and temporal (0.5 ns) resolution.