Postbreakdown Transient Characteristics of a Gas-Filled Plasma Closing Switch

Abstract

Gas-filled plasma closing switches (PCSs) are essential components of high energy density pulsed power systems, used to generate short, high-power (10s MW to several GW) impulses. In practical applications, PCSs are required to operate in high current (10s 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, design and optimisation of PCSs require detailed information on the dynamic plasma resistance. The present paper is focused on an investigation of the timedependent resistance of the plasma channel(s) formed between the electrodes of a multi-electrode 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 bar 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 milli-Ohms due to the Joule heating of the breakdown channel. The methods proposed by Braginskii and Kushner to model the transient post-breakdown resistance were used to obtain analytical plasma resistances for all of the gasses. These resistances have been compared with the transient resistance obtained using a Kirchhoff analysis of the lumped-element, post-breakdown 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 optimisation of the operational performance of PCSs filled with environmentallyfriendly, low environmental impact gases.

Development and Test of a 500-kV Compact Marx Generator Operating at 100-Hz PRF

“…, where R OFF is the resistance in the nonconductive state (R OFF = 1 M) and v(ch_cntl) is the channel control signal described below. R br is the resistance calculated using the following formula: R br = d/(πσ a 2 ) [26], where d is the interelectrode distance and a(t) is the radius of the plasma arc calculated by the Braginskii formula [26].…”