Measurements of electron density and electric field in plasma produced in nanosecond discharge in pressurized gases

Summary form only given. This talk outlines the main experimental results regarding the research of nanosecond time-scale discharge in gases as air, H₂ and He, conducted at pressures P≥10⁵ Pa. Discharges were ignited in gas filled chambers, with interelectrode gap 0.5-3 cm, by application of high-voltage (HV) pulses with amplitudes ~100-200 kV and duration 1-7 ns at FWHM to a blade shaped cathode with sharp edge. The discharge in such conditions is ignited by high-energy runaway electrons (RAE), which are considered responsible for pre-ionization of the gas in the interelectrode gap.We have investigated this discharge using a variety of non-disturbing, experimental techniques with temporal resolution close to a single nanosecond, such as: fast-framing imaging, x-ray foil spectroscopy, electron beam imaging and electron beam foil spectroscopy. Profound conclusions were drawn according the experimental results, regarding the dynamics of the discharge evolution and dependence on the gas and pressure, energy spectrum of RAE and the x-ray radiation, RAE emission mechanism. Temporal evolution of plasma parameters such as electron density and temperature were determined using Optical Emission Spectroscopy. These results predicted a presence of significant electric fields (~10 kV/cm) in the plasma. Lately we have measured the intensity of electric fields using Coherent anti-Stokes Raman Scattering, which also allows calculating the conductivity of plasma.