Recent Results of 28 GHz 400 kW Long Pulse Gyrotrons at IAE-CAEP

Recently, 28GHz, 400kW gyrotrons have been built and tested at IAE-CAEP. The gyrotrons were developed for ECRH experiments with a spherical tokamak. The gyrotrons have a single anode magnetron injection gun to produce gyrating electron beam. The operational cavity mode is TE8,3, which is converted into a Gaussian mode by an internal quasi-optical mode converter. In order to enhance the overall efficiency, single stage depressed collectors are used. In the test, output frequency of the gyrotron is 28.1 GHz. With the cathode voltage -52kV, anode voltage about 20 kV, excited by different beam currents, the gyrotron (#2) has realized long pulse, high power output of 200 kW / 5 s, 300 kW / 3 s, and 400 kW / 1 s. Another tube (gyrotron #3) has been tested in May and delivered 400 kW / 5 s output power on May 21, 2021. Now the gyrotrons have been installed on the spherical tokamak and successfully used as trial products in the ECRH experiment. Further test of several optimized gyrotrons will continue during the next several months.