Switches for pulsed-power conditioning in high energy applications

This dissertation presents theoretical and experimental results from a research program that was aimed at finding practical ways of transferring energy to various loads, mainly from an inductive energy store fluxed by a primary store such as a capacitor bank. The main obj ecti ves of the work were to investigate and develop high power opening and closing switches, together with the transfer circuits needed to generate the fast (less than lOOns duration) high energy, pulses required in many applications. The study was to include a feasibility study of the use of the Plasma Erosion Opening Switch (PEOS) in such a system. To produce the large fast pulses required, an opening switch is required that: * Carry a current of the order of several kA during the inductor storage time. It should also be able to interrupt this current and to withstand the high voltage it will experience as the current is subsequently transferred to a load. * Conduct for as long as possible (up to one quarter period of the current waveform), to maximise the inductively stored energy which can be transferred to xhe load when the switch opens. * Open to an impedance that is large compared to the load impedance . This ensures that most of the inductively stored energy is transferred to the load. Open sufficiently rapidly to produce the required sharp pulse of voltage. In pulsed-power applications, energy is usually supplied from slow and relatively inexpensive power sources such as a capacitor bank, or an explosive flux-compression generator, which deliver large quantities of energy in the lO-lOO time range. Although no single switch is currently available which has such a long conduction time, together with a nanosecond opening time, the PEOS is a potential candidate. To overcome its short conduction time, while still obtaining an opening time of less than lOOns, the PEOS is used together with an additional slower stage or stages of switching. The key to this method is that each successive switching stage produces a considerably increased voltage. Various different types of switch were investigated and these are described in the thesis. Particular consideration is paid to the performance of the PEOS, as the final conditioning stage. Exploding foils are also investigated, together with a novel Automatic Exploding Foil Change-Over Switch, since an exploding foil opening switch is needed to condition the output of the capacitor bank before the PEOS. The initial resistance of the PEOS is very low, and the change-over switch is required to ensure that the current transfer takes place when the voltage across the fuse approaches its peak value. An important part of the investigation was to develop a mathematical model of the PEOS, as a part of the power condi tioning circuit, in order to simulate the system for different load conditions. The thesis explains the design, operation and performance characteristics of the various pulsed-power components, such as capacitor banks, closing and opening switches, pulse transformer, the vacuum system required for a PEOS, and high voltage and current measurement techniques.