Energy Efficiency Analysis of the Discharge Circuit of Caltech Spheromak Experiment

The Caltech spheromak experiment uses a size A ignitron in switching a 59-??F capacitor bank (charged up to 8 kV) across an inductive plasma load. Typical power levels in the discharge circuit are ~200 MW for a duration of ~10 ??s. This paper describes the setup of the circuit and the measurements of various impedances in the circuit. The combined impedance of the size A ignitron and the cables was found to be significantly larger than the plasma impedance. This causes the circuit to behave like a current source with low energy transfer efficiency. This behavior is expected to be common with other pulsed plasma experiments of similar size that employ an ignitron switch.