Low power tests on a TE/sub 28.8/-gyrotron mode converter system

For the ERCH system of the plasma fusion experiment W7-X in Greifswald, Germany, ten 140 GHz gyrotrons each giving 1 MW continuous output power are foreseen. They include a quasi-optical mode converter system to convert the field distribution of the resonator mode (TE/sub 28.8/) to a Gaussian like output beam. A cold test set-up of this system consisting of an advanced launcher and three beam forming mirrors was was built for low power measurements and for comparison with the design calculations.