Design of the evacuated waveguide transmission lines for JET-EP

An over moded evacuated waveguide line was chosen to be used in the transmission system for the proposed JET-EP ECRH project. The system includes 6 lines of 63.5mm waveguide for transmitting the 6.0MW(10s) at 113.3GHz from the gyrotrons to the launching antenna. The lines will be on average 72m in length and consist of 9 miter bends for an estimated transmission efficiency of 91%. Each line will include an evacuated switch leading to a calorimetric load, two DC breaks, two gate valves, one pumpout Tee, a power monitor miter bend and a double disk CVD window near the torus. The location of waveguide supports will be positioned to minimize power converted to higher order modes from waveguide sagging and misalignment. The two gate valves and CVD window will be used as tritium barriers at the torus and between J1T and J1D. The last leg of the waveguide leading to the torus will be designed to accommodate for the torus movement during disruptions and thermal cycles. All lines will also be designed to be compatible for 170GHz operation. A brief description of the line and discussion of the above topics will be presented.