Sensitivity of Ignitrons to Stray Capacitance
LAWRENCE LIVERMORE NATIONAL LAB CA
Pagination or Media Count:
The surprising sensitivity of ignitors was encountered on RACE, a compact torus device. Its capacitor bank has both the common reverse-crowbar circuit and an unusual forward-crowbar circuit that made this investigation necessary. The ignitors were fired with high-capacitance coaxial-cable pulse transformers. When the bank fired, because of negative bank charge, forward-crowbar ignitrons saw both positive anode voltage and a positive pulse to their ignitors coupled through pulse transformer capacitance. One tube prefired as low as 3 kV. Prefires ceased when coaxial transformers were replaced with double-shielded transformers. Pulse duration and energy were much less than expected. The computed ignitor pulse RC time was only 5.6 ns, far less than a typical 250-ns anode firing delay. The positive capacitive energy input to the ignitor was 0.14 mJ, more than 3 orders of magnitude less than the ignitron firing chassis.
- Electricity and Magnetism