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The results of recent experimental and numerical studies of nanosecond high-voltage discharges in pressurized gases are reviewed. The discharges were ignited in a diode filled by different gases within a wide range of pressures by an applied pulsed voltage or by a laser pulse in the gas-filled charged resonant microwave cavity. Fast-framing imaging of light emission, optical emission spectroscopy, x-ray foil spectrometry and coherent anti-Stokes Raman scattering were used to study temporal and spatial evolution of the discharge plasma density and temperature, energy distribution function of runaway electrons and dynamics of the electric field in the plasma channel. The results obtained allow a deeper understanding of discharge dynamical properties in the nanosecond timescale, which is important for various applications of these types of discharges in pressurized gases.

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Time-resolved optical-emission spectroscopy measurements are used to evaluate plasma density in an interference switch during the extraction of a nanosecond output pulse from a high-power microwave compressor. The compressor represents a resonant cavity connected to an H-plane waveguide tee with a shorted side arm filled with helium at a pressure of 2 • 10 5 Pa; the plasma discharge in the tee side arm is triggered by a Surelite laser. A nanosecond-scale dynamics of the plasma density is obtained by analyzing the shape of the helium spectral lines. The analysis of the experimental data evidences a correlation between the rise time of the plasma density and the peak power of the microwave output pulse. Numerical simulations of the microwave energy release from the cavity with the appearance of the plasma yield results in good agreement with the measured output pulse peak power and waveform.