Self-Triggering Spark Gap ``Crowbar''

A self-triggering spark gap has been developed for use as a simple ``crowbar'' at the output of a high-voltage dc power supply to protect the load in case of load failure. The system consists of three spheres arranged in a triggered spark gap system, with the center sphere maintained at a fixed potential with respect to the other two spheres (one at ground, one at high voltage) under steady-state conditions. When the load fails, capacitive coupling drives the triggering sphere to a voltage that causes break-down between the high-voltage sphere and the triggering sphere, with subsequent firing of the entire protective gap system. Advantages over thyratrons for this ``crowbar'' application include the following: 1) the voltage rating is unlimited, 2) the current rating is of the order of tens of thousands of amperes, 3) reliability is greater than that of a thyratron, due to lack of filament supply requirements, auxiliary triggering circuits, etc., 4) less costly than the thyratron circuit.