Nanosecond Discharge in Non-Boiling Liquid Nitrogen

Nanosecond discharge has been studied in non-boiling liquid nitrogen. The discharge is initiated in the gap in the central conductor of a coaxial waveguide with an impedance of $50~\Omega $ . The gap varied within 10– $100~\mu $ m. The dielectric of the waveguide and the discharge medium is non-boiling liquid nitrogen at atmospheric pressure and temperature 65 K. The amplitude of the voltage pulse is +/–12–25 kV, the duration is 7 ns, the voltage rise time is 150 ps. It is found that the leading edge of the discharge current is less than 80 ps. According to estimates, the electron ionization rate $\nu _{i}$ is more than $7.5\cdot 10^{{10}}$ ${\mathrm {s}}^{-{1}}$ and the ionization rate constant ${k} _{i}$ is more than $4.2\cdot 10^{-{12}}$ cm3 ${\mathrm {s}}^{-{1}}$ in non-boiling liquid nitrogen at 65 K. A passing electromagnetic coupling wave with amplitude about 10 kV and duration 150 ps is detected behind the discharge gap in the waveguide. The formation of electromagnetic coupling wave is numerically demonstrated. The dependence of the discharge delay time on the electric field in the gap is measured. The formation of $20~\mu $ m size erosion craters is found at the surface of the electrodes demonstrating the possible role of the micro-explosive processes in the discharge mechanism.