The dynamics of a nanosecond gas discharge development with an extended slot cathode in argon

The article presents the results of an experimental study and numerical modelling for the formation and development dynamics of a high-voltage transverse nanosecond discharge generated by a slot cathode in an argon medium at a pressure range of 1–10 Torr. Numerical modelling was carried out under similar experimental conditions for the processes of formation and propagation of ionisation waves, electron density distribution, excited atom and average electron energy in the discharge gap, including the cavity inside the cathode. At a pressure of p = 1 Torr, a classical version of a high-voltage discharge is demonstrated to take place with no penetration of the plasma into the cathode cavity and no observed hollow cathode effect. An increase in gas pressure to 5 Torr leads to a penetration of plasma into the cathode cavity with the formation of a cathodic potential drop (CPD) region. Electrons emitted from the side surfaces of the cavity pass through the CPD region without collisions, oscillate inside the cathode cavity; the hollow cathode effect is fully manifested. At р = 10 Torr, the modelling results qualitatively coincide with the results at р = 5 Torr; in this case, however, hardly any accelerated electrons are observed in the gap between the electrodes, due to their energetic relaxation both inside the cathode cavity and when exiting from it. In both cases, the plasma structure formed at the exit of the cathode cavity involves a concentration of charged particles an order of magnitude higher than that in the rest of the gap, leading to a self-limiting discharge current effect. The results of the numerical modelling are in good agreement with experimental data.