Test wire for high voltage power supply crowbar system

The klystron microwave amplifier tubes used in the low energy demonstration accelerator (LEDA) and to be used in the accelerator production of tritium (APT) plant have a strict upper limit on the amount of energy which can be safely dissipated within the klystron's vacuum envelope during a high voltage arc. One way to prevent damage from occurring to the klystron microwave amplifier tube is through the use of a crowbar circuit which diverts the energy stored in the power supply filter capacitors from the tube arc. The crowbar circuit must be extremely reliable. To test the crowbar circuit, a wire that is designed to fuse when it absorbs a predetermined amount of energy is switched between the high voltage output terminals. The energy required to fuse the wire was investigated for a variety of circuits that simulated the power supply circuit. Techniques for calculating wire length and energy are presented along with verifying experimental data.