Operation of high power 84-GHz gyrotron for KSTAR ECH system

The initial objective of the KSTAR ECH system is to produce seed plasmas by irradiation of powerful millimeter waves for the main ohmic discharges. A specially designed gyrotron, manufactured by CPI, has specifications of 500 kW, 84 GHz, and 2- second pulse duration. It adopts the state-of-arts technologies of a diode gun, a depressed potential collector, an internal mode converter, and a diamond window. As a part of the final acceptance tests of the gyrotron, we constructed a test and including a test modulator to confirm its operating conditions. With short-pulses of 20 microseconds, we produced the output peak power of 500 kW at 84 GHz. The output power distribution is confirmed to be a Gaussian by IR images on targets. In this experimental study, we describe details of the gyrotron, the test stand, and experimental results.