Long-Pulse Testing of a 110 GHz Gyrotron with a Single-Stage Depressed Collector

Summary form only given. High-power, long-pulse or CW millimeter-wave sources are required for electron cyclotron heating (ECH) and current drive in magnetic fusion experiments. To further reduce system cost and improve reliability we have developed and built a prototype 110 GHz, with output power greater than 1 MW and a single-stage, depressed collector. In this paper, we report on the long-pulse test results of this gyrotron, which will be referred to as VGT-8115. The basic design of VGT-8115 is similar to that of the earlier 110 GHz, 1 MW devices, but it utilizes a single-stage, depressed collector. The fabrication of this gyrotron was completed in September 2004 and test began the same month. In short-pulse testing, we have obtained an output power of 1.28 MW with a collector voltage of 73.3 kV, a body voltage of 26 kV and a beam current of 41.2 A. We are restricted to a maximum beam current of 25 A for long-pulse testing because of test set limitations. In long-pulse testing, we have obtained 10-second pulses at output power levels of 500 kW with a collector voltage of 73.5 kV and a body voltage of 20.9 kV (94.4 kV accelerating voltage) and beam currents of 24.5 A