2X II 10-Megajoule Ignitron Crowbar

A 10-MJ Ignitron Crowbar Array for the 2X II fusion machine has been installed, and is now in operation. It is designed to handle about three times the energy of the previous array used with the 2X machine, which has been supplanted by the 2X II. In addition, this array is expected to be considerably more reliable than previous designs. Furthermore, the floor utilization of the assembly is considerably improved, access to all components is better, and the overall cost per kilojoule is substantially reduced. Two insulated identical main pulse coils are incorporated in the 2XII machine. Similarly, the crowbar array is split into two equal parts, with each connected permanently across its pulse coil. The crowbar array is expected to handle 10 MJ at 40 kV. However, because of reliability limitations of the capacitor banks above 30 kV, operation above this value is not planned except for possible special tests. With the present coils, the decay time constant of current to I/¿ of its peak value will be about 7 msec. A mechanical switch, actuated by exploding a copper foil against one electrode, has been built and installed within a foot of the coil terminals. It has not yet been perfected adequately for use, but calculations indicate that it could extend the time constant above 20 msec.