Operation of a 500 kW, 84 GHz, long pulse gyrotron with collector potential depression

High-power, long-pulse or CW millimeter-wave sources are required in electron cyclotron heating or current drive for fusion experiments. Gyrotron oscillators have served as effective sources in this area for many years. Developments in using diamond for the output window have eliminated one of the obstacles to realizing high-power, long-pulse devices. At CPI, various programs are underway to deliver long-pulse or CW, high-power gyrotrons. In particular, we have completed the construction and test of an 84 GHz, 500 kW, 2-s-pulse gyrotron for Pohang University of Science and Technology. In addition to features that are similar to other high-power gyrotrons, like the internal converter, diode gun, and diamond window, the 84 GHz gyrotron also includes a single-stage depressed collector. In this paper, we summarize the basic design of the 84 GHz gyrotron and report on the experimental results of the 500 kW, long-pulse operation.