Influence of electrode spacing and gas pressure on parameters of a runaway electron beam generating during the nanosecond breakdown in SF(6) and nitrogen

This study deals with experimental and theoretical simulation data showing the influence of electrode spacing and gas pressure on parameters of a supershort avalanche electron beam (SAEB) formed in SF(6) and nitrogen at different rise times and amplitudes of a voltage pulse. Using GIN-55-01, VPG-30-200, and SLEP-150M pulsers, tubular cathodes with a diameter of 6 mm, as well as gaps of 3, 5, and 8 mm, it was shown that the SAEB current amplitude can both increase and decrease depending on an electrode spacing, a waveform and a rise time of the voltage pulse, as well as the pressure of SF(6) and nitrogen. It was established as a result of simulation that maximal voltage across the gap during the process of generation of runaway electrons and the thickness of an anode foil have a major effect on the SAEB current pulse amplitude