Postbreakdown Transient Characteristics of a Gas-Filled Plasma Closing Switch

Gas-filled plasma closing switches (PCSs) are essential components of high energy density pulsed power systems used to generate short, high-power (tens MW to several GW) impulses. In practical applications, PCSs are required to operate in high-current (tens kA), high-voltage (10s-100s kV) regimes, to produce fast-rising ns and sub-ns HV impulses. The transient impedance of a PCS affects the rise time of the generated impulses and the power delivered to the load. Thus, the design and optimization of PCSs require detailed information on the dynamic plasma resistance. This article is focused on an investigation of the time-dependent resistance of the plasma channel(s) formed between the electrodes of a multielectrode PCS. Experimentally measured underdamped current and voltage waveforms were used to obtain the transient plasma resistance of the PCS. The PCS was filled with different gases: dry air, CO₂, N₂, and a 90%/10% Ar/O₂ mixture, in the pressure range from 0 up to 10 bar (gauge). It was found that the plasma resistance drops rapidly from a few hundreds of ohms to a few hundreds of milliohms due to the Joule heating of the breakdown channel. The methods proposed by Braginskii and Kushner to model the transient postbreakdown resistance were used to obtain analytical plasma resistances for all of the gases. These resistances have been compared with the transient resistance obtained using a Kirchhoff analysis of the lumped-element, postbreakdown RLC circuit. Based on this comparison, the suitability of the chosen analytical methods to determine the transient breakdown resistance in gases is discussed. The obtained results will help in the optimization of the operational performance of PCSs filled with environmentally friendly, low environmental impact gases.