Protection system for the gyrotrons at TJ-II

Abstract Two 500 kW gyrotrons are used in ECRH experiment at TJ-II device. High voltage low output capacity power supply based on fast switching high frequency technology feeds the tubes. Different energy surge components and its destructive influence on a load are analyzed to elaborate design concept of the gyrotron protection system when breakdown occurs. Calculation of energy dissipation shows the necessity of additional protection even in case the switching-off time of the power supply is about 5–10 μs. Crowbar protection is highly recommended for this case. Several TVS-31 vacuum switches connected in series are proposed for such a protection system. It allows up to 10 kA short circuit current and 80 kV (130 kV) hold-off voltage. Switching-on time is less than 1 μs, total time delay is less than 3–5 μs. The system consists of the main switch, triggering unit and arcing sensor to detect the current or current derivation excess. Results of design and HV tests are presented.