Breakdown development in helium in high voltage open discharge with subnanosecond current front

Abstract

High-voltage open discharge experiments in helium [, ] showed a possibility to control the electron avalanche development on a subnanosecond timescale. The controlled current growth rate was of 500 A (cmns) for an applied voltage of 20 kV and gas pressure of 6 Torr. Here, a kinetic model of the breakdown is developed to analyze the mechanism of current growth, which takes into account the kinetics of electrons, ions, fast atoms and photons with a Doppler shift (DS). Using particle-in-cells simulations, we show a critical role of DS photons in the secondary electron emission during the breakdown. DS photons appear in discharge due to (a) electronic excitations in the background gas by heavy particles (ions and fast atoms) and (b) in collisional excitation transfer reactions between fast atoms (He f ) and atoms excited by electron impact (He), He f He He He. The latter, newly analysed, mechanism is dominant in the DS photons production during the breakdown in high-voltage open discharges. Our experimental and calculation results show a decrease of the breakdown timescale with increasing gas pressure from 3 Torr to 16 Torr.