A self-closing water switch for load decoupling

One of the most popular methods of generating high voltage impulses is to employ a Marx generator. In general, the output voltage pulse of a Marx generator can rapidly energise a pulsed power load in a few tens of ns, depending upon the load capacitance, and thereafter the pulse will decay with a time constant determined by the rate of charge removal from the generator. In some applications, the Marx generator may be required to apply a fairly constant voltage for only a few hundred of ns. This can be achieved by increasing the discharging time constant of the impulse generator to a few μs. However, the long wavetail of the impulse waveform in this situation may become damaging to the load after a few hundred ns, and in this case a crowbar circuit is usually incorporated into the system in order to isolate the load. This paper reports on work which was undertaken to develop a simple high voltage switch which can operate as a crowbar device to divert the energy contained in the Marx wavetail away from sensitive loads following the period of interest. The work describes the design and characterisation of a water filled switch developed for this purpose