140GHz high-power gyrotron development for the stellarator W7-X

Electron cyclotron resonance heating (ECRH) has proven to be one of the most attractive heating schemes for stellarators. Therefore, ECRH was chosen to be the main heating method for the Wendelstein 7-X stellarator (W7-X) now under construction at IPP Greifswald, Germany. A 10MW ECRH system with continuous wave (CW) possibilities, operating at 140GHz will be built up to meet the scientific goals of the stellarator. Two prototype gyrotrons with an output power of 1MW were developed in collaboration between European research laboratories and European industry (Thales Electron Devices, France). The gyrotrons are equipped with a single-stage depressed collector, an optimised quasi-optical mode converter and a CVD-diamond window. The prototypes have been successfully tested at FZK. With the second one, an output power of 0.89MW at a pulse duration of 3min and an output power of 0.54MW for about 15min have been obtained.