Progress in the 10 MW ECRH system for the stellarator W7-X

Summary form only given, as follows. Electron cyclotron resonance heating (ECRH) has proven during the last few years to be one of the most attractive heating schemes for stellarators, as it provides net current free plasma start tip and heating. Extensive measurements on stellarators at IPP Garching provide a solid physical and technological basis for ECRH systems. Therefore, ECRH will be the main heating method for the Wendelstein 7-X stellarator (W7-X) now under construction at Greifswald / Germany. A 10 MW ECRH system with continuous wave (CW) possibilities operating at 140 GHz will be built to meet the scientific goals of the stellarator at Greifswald with inherent steady-state capability at reactor relevant plasma parameters. A prototype gyrotron with an output power of 1 MW was developed in collaboration between European research laboratories, and European industries. The gyrotron is equipped with a single stage depressed collector for increasing the efficiency, an optimized quasi-optical mode converter and a CVD-diamond window. The prototype gyrotron has been successfully tested with an output power of 0.89 MW at a pulse duration of three minutes and all output power of 0.54 MW for about 15 minutes. The specified value of Gaussian beam output power exceeding 0.9 MW has been obtained for about 1 minute. Further results will be given.