Performance measurements on high order gyrotron mode generators

For ECRH system of the plasma fusion experiment W7-X in Griefswald, Germany, ten 140 GHz gyrotrons each delivering 1 MW continous output power are foreseen. This system is used for cold test verification of the design calculations and studies on installation tolerances and their effect on the output beam. This simplifies the development process as design errors or mechanical errors are difficult to be corrected as soon as the system is installed in the gyrotron resonator mode. The mode in the gyrotron is fully rotating because of the geometrically asymmetric power injection. To prevent this influence a new mode generator was constructed which made the reduction of a mode's counter rotating with less than 1% of power.