Design and operation of a 700 kV, 700 A modulator

A 700 kV, 700 A pulse modulator capable of repetitive operation is under development for use in our high power microwave program. The output pulse is designed to give a flat top of about 200 ns at the rated voltage. The transformer consists of two sets of ferrite cores with their primaries driven in parallel and their secondaries connected in series. The primary on each core consists of 24 windings of 2 turns each, distributing the flux evenly throughout the core. The secondary winding has 20 turns which links both cores, giving a 20:1 step-up transformer for a 1 kΩ matched load. A novel pulser arrangement has been used to drive the transformer. Each core is driven by two 5Ω pulse lines plus/minus charged to ~40 kV with a switch connecting the two lines. In matched conditions this gives a 40 kV voltage across the load. This configuration produces a fast rising pulse eliminating the pulse rise time degradation associated with the transfer function of a discrete element pulseline. The transformer has been tested at 100 kV with a variety of dummy loads at low repetition rate. Preliminary results are also reported at high voltage with the modulator under oil