Transient phenomena connected with the operation of large low inductance capacitor banks

Capacitor banks with an energy storage of the order of several megajoules and an internal inductance of the order of 1 $m\mu H$ are of interest in plasma physics, especially in experiments on the fast magnetic compression of plasmas. One method of obtaining both the de sired low inductance and a maximum of safety against the effects of an electric breakdown anywhere in the bank is shown schematically in fig. 1. The bank is split up into many units each switched by its own spark-gap and connected to the load by cables which are generally of equal length. All units are interconnected by high ohmic charging resistors. At the moment of firing the spark gaps, all the units are connected in parallel to the load thus representing a low inductive discharge path, though the impedance of any one unit is largecompared to the impedance of the load. In this way overvoltaging of other gaps, and initiation of a random chain discharge of the whole bank by a prefiring unit, is precluded. This scheme has one serious disadvantage if the impedance of the load is es sentially inductive. The spark-gap of one of the units, though triggered, can fail to break down at the proper time. Breakdown then occurs during the second quarter cycle leading to high voltage transients at the capacitor terminals of this unit which may have an amplitude much higher than the charging voltage and therefore cause breakdown of the insulation. To provide insulation for a voltage, much higher than the charging voltage, is expensive. For a large bank it is therefore necessary to investigate ways of avoiding these transients . Part I describes theresults of such an investigation as far as the properties of the sparkgaps are concerned. [...