Ultrafast Ionization, Heating, Thermalization and Constriction of High-Pressure Nanosecond Pulsed Discharge Plasmas*

We present our approach for investigating the mechanisms of the fast transition of partially ionized atmospheric pressure nonequilibrium discharges to fully ionized thermal spark discharges on nanosecond time scales. A suite of ultrafast optical diagnostics including streaked optical emission spectroscopy (OES), picosecond Thomson scattering, streaked absolute continuum emission, coherent anti-Stokes Raman scattering (CARS) and coherent Rayleigh-Brillouin scattering (CRBS) will be performed. This study is expected to produce new insights in the underpinning plasma physics of nanosecond repetitively pulsed (NRPs) discharges. In addition, we will leverage the huge range of ionization degrees and gas temperatures encountered in NRPs to assess the applicability range of several optical diagnostics in the partially and fully ionized regimes as well as during the transition phase between these two regimes. The outcomes of this study are expected to elucidate new insights in electron kinetics, gas heating and thermalization mechanisms responsible for the occurrence of instabilities in atmospheric pressure plasmas.