Recent Results of a 50 GHz High Power Gyrotron for ECRH at XL-50 Tokamak

Recently, a 50 GHz high power gyrotron has been developed at IAE-CAEP. This gyrotron was developed for ECRH experiments at the spherical tokamak XL-50. The gyrotron has a diode type magnetron injection gun (MIG). The operating cavity mode is TE 8,3 , which is converted into a Gaussian mode by an internal quasi-optical mode converter. In order to enhance the overall efficiency, a single stage depressed collector with a sweeping coil is used. According to the simulation results, 500 kW output power could be expected. A prototype of the gyrotron was completed and tested. In the high power operation, output power of 200 kW with 5 s pulse duration at 50.05 GHz was achieved. The efficiency is ~38%. And 300 kW for 3 s with 30% efficiency was obtained. However, the output efficiency is low and some unstable problems occurred in the operation. Some improvements should be made to enhance both power and efficiency. Now the prototype has been installed at the XL-50 tokamak and used as a trial product in the ECRH experiments.