Abstract and subjects
The Field-Reversed Configuration Heating Experiment (FRCHX) was designed to form closed-field-line magnetized target plasmas for magneto-inertial fusion and other high energy density plasma research. These plasmas are in a field-reversed configuration (FRC) and are formed via a reversed-field theta pinch on an already-magnetized background plasma. To extend the duration and uniformity of the pinch, the capacitor bank driving the reversed-field discharge is crowbarred near the current peak. Four parallel rail-gap switches are used on FRCHX for this application to ensure a low-inductance crowbar discharge path and to accommodate the large magnitude of the discharge current (often greater than 1 MA). Parallel operation of spark gap switches in a crowbarring arrangement, however, has often proved to be difficult due to the very low voltage present on the bank and across the switches at the time of peak current. This paper reports on the successful efforts made to develop a low-inductance crowbar switch for FRCHX and to ultimately enable successful triggering and operation of the four parallel rail-gap switches used in the crowbar. The design of the parallel switch assembly is presented first, followed by a description of the triggering scheme employed to ensure conduction of all four switches.