Pulse operation of involute gate 125 mm thyristor

The limits of operation of a 125 mm thyristor with a six point "snowflake" gate design have been previously reported. Tests were performed at the Army Research Laboratory (ARL) using a 10 m/spl Omega/, 0.5 ms (FWHM) pulse forming network. With the snowflake gate design, single shot operation was limited to 140 kA at 600 A//spl mu/s. Operation with a modified PFN and a shorted load at 3 kV, 111 kA and a di/dt of 800 A//spl mu/s was demonstrated under rep rate conditions. The thyristor failed when the di/dt was increased to 1 kA//spl mu/s. Under both sets of operating conditions, the failure occurred in the vicinity of the gate structure. The thyristor has been modified to include a high current involute gate design. Computer simulations have shown that the new design will operate at 200 kA with di/dt's in excess of 1 kA//spl mu/s. Operation was demonstrated in our circuit at 165 kA with a di/dt of 2.6 kA//spl mu/s. Detailed results on the temporal behavior with respect to voltage drop, charge transfer and action as a function of operating levels under matched load conditions are presented. The new design has significantly improved performance and will permit construction of the compact, light weight high voltage series switch strings required for electric guns.