Electronegative gas components and gas pressure significantly change residual charge dynamics, which are critical for pulse-periodic streamer discharge behaviors. Evolutions of repetitively pulsed positive streamer discharge and the streamer-to-spark transitions were investigated at high pressures and compared between typical weak (O2) and strong (SF6) electronegative gas mixtures. Pulse-sequence resolved electrical and optical diagnostics were implemented to capture discharge evolutions in long pulse trains. We observe that streamer inception and propagation under subsequent pulses in N2 and N2–O2 mixtures are similar, including the earlier inception of the primary streamer and the accelerated propagation of the secondary streamer. The repetitively pulsed breakdown is extended to the low pulse repetition frequency region with the addition of O2. Discharge evolutions are unexpectedly different in N2–SF6 mixtures. Subsequent discharge channels prefer to propagate around the periphery of the inception cloud region with large radial deviations. Another difference is the precursor channel identified besides multiple streamer channels. Effects of electronegative gas on streamer evolutions under positive repetitive pulses have been qualitatively analyzed. Collisional electron detachment and photo-ionization are crucial in N2–O2 mixtures. With the presence of strong electronegative gas (SF6), the leader formation is probably induced by the earlier corona inception and longer voltage stressing period under following pulses in a pulse train, which are caused by the strong electronegativity of SF6 and the small ion mobility.

The corona-stabilized switch has a great potential in pulsed power systems where high pulse repetition frequencies are required. Corona discharge in SF 6 in highly inhomogeneous electric field is utilized to improve repetitive performance of this kind of switch. To clarify how the repetitive performance (insulation recovery and repetitive breakdown stability) of the switch depends on the field inhomogeneity, the insulation recovery and repetitive breakdown stability of a corona-stabilized switch are experimentally investigated and theoretically analyzed. An innovative double-pulse method combining breakdown voltage and discharge channel images is used to measure the insulation recovery of the switch. For different electrodes, their voltage jitters at pulse repetition frequencies of 1-2000 Hz are measured to illustrate the stability of repetitive breakdown. The experimental results are theoretically analyzed from the memory effect and behavior characteristics of the residual plasma, the critical volume and its dynamic characteristics. The results reveal the corona stabilization enhancement effect during the repetitive breakdown in SF 6 in extremely inhomogeneous field. The influence of electrode profile on the propagation of discharge channel shock wave, the decay of residual plasma and the recovery of neutral gas density are clarified. Effect of the electrostatic conditions, including the critical volume and its dynamic characteristics, and the intensity of corona discharge, on the repetitive performance of the switch are also clarified. INDEX TERMS Corona stabilization, electric field inhomogeneity, gas discharge devices, insulation recovery, memory effect.

The corona-stabilized plasma closing switch, which utilizes the stabilization effect resulted from the movement and accumulation of corona-generated space charge to improve the repetitive performance, has a great potential in repetitive pulsed power systems. In this paper, the influence of gas type on the recovery performance and repetitive breakdown stability of a corona-stabilized plasma closing switch is investigated. The results are analyzed from the memory effect of residual plasma, the development and propagation characteristics of streamer corona, and the thermo-hydrodynamic process of discharge channel. The enhancement effect of residual plasma on corona stabilization of the subsequent breakdown in the repetitive operation of the gas gap with highly inhomogeneous electric field and strong electronegative gas is proposed. The development and propagation characteristics of streamer corona in different gases that can lead to significant differences in the corona stabilization effect of breakdown are clarified. It is also found that the gas with small molecular mass and higher gas velocity exhibits excellent insulation recovery in the gas switch with uniform fields, but displays poor repetitive performance in the corona-stabilized switch with a rod-plate electrode.

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