Fast particles and metal vapors from electrodes with small radii of curvature during nanosecond discharges in gases

In gaps with a non-uniform electric field, the high electric fields (>1 MV/cm) are achieved with a short volt- age pulse front, which are enhanced by the accumulation of positive ions at the cathode and the formation of plasma. Based on the known experimental and theoretical studies of vacuum discharge, we hypothesized that the mechanism of destructive mechanical stresses in the surface layer of electrodes should also take place during nanosecond breakdown in gases. In this paper, the radiation of diffuse discharge plasma formed be- tween two electrodes with a small radius of curvature was investigated when the discharge gaps were filled with air, nitrogen, argon, and helium at atmospheric pressure. With a nanosecond voltage pulse duration and energy inputs into the gas of <1 mJ/cm3, the tracks of particles emitted from bright spots on the electrodes, including those at a right angle to their surface, were recorded. It is shown that the length of the tracks de- pends on the polarity of the electrode and that at low energy inputs in the air the tracks end with a brighter glow region. It is established that the greatest radiation intensity during discharges in four different gases (air, nitrogen, argon and helium) are found in tracks that are formed in the air. From this result, as well as from the recorded duration of track glow pulses in hundreds of microseconds, it follows that the increase in the bright- ness of the radiation of the ends of the tracks during propagation in the air is determined by the heating of the electrode material during the interaction of the emitted particles with oxygen.