Investigation of nanosecond discharge in pressurized air sustained by high-voltage pulses with different rise-times

Summary form only given. Results of a study of nanosecond duration discharge, supplied by high-voltage (HV) pulses of durations 1,5 and 20 ns, in discharge gaps of 1-3 cm and pressures of 1-8×10⁵ Pa, are compared. Energetic runaway electrons (RAE) presence^1,2,3 was noted and their spectrum has been derived via computer simulations⁴ compared with results of experimental x-ray absorption spectroscopy⁵ for various values of discharge gap length and pressure. The influence of the gap length and pressure on the RAE spectrum is discussed. No “anomalous” electrons^6,7 were detected via both methods. It has been shown that under an atmospheric pressure the discharge sustained by 5 and 20 ns HV pulses has two distinctive stages, namely high- impedance and low-impedance stages⁸. During the high-impedance stage the discharge gap is bridged by a plasma channel whose conductivity is not sufficient to terminate the HV stage of HV pulse, and allows an expansion of denser, secondary plasma channel across the gap and a further generation of RAE as well. It has also been shown that in case of 5 and 20 ns HV pulses RAE with energies ≥15 keV are only generated during the low-impedance stage and thus are not responsible for discharge ignition⁸.