Progress on the 10 MW, 140 GHz ECH System for the Stellarator W7-X

Summary form only given. During the last years electron cyclotron heating (ECH) has proven to be one of the most attractive heating schemes for stellarators, as it provides net current free plasma start up and heating. Both, the stellarator Wendelstein 7-X (W7-X), which is under construction at IPP-Greifswald, Germany, and the ITER tokamak, which will be built at Cadarache, France, will be equipped with a strong EC-heating and current drive system. Both systems are similar in frequency and have CW (continuous wave) capability (140 GHz, 10 MW for W7-X and 170 GHz, 24 MW for ITER). The commissioning of the ECH plant for W7-X is well underway, the status of the project and first integrated full power test results from two modules are reported and may provide valuable input for the ITER plant. The ten gyrotrons at W7-X are arranged in two sub-groups symmetrically to a central beam duct in the ECH hall. The RF-wave of each subgroup is combined and transmitted by a purely optical multi-beam waveguide transmission line from the gyrotrons to the torus. The combination of the five gyrotron beams to two beam lines each with a power of 5 MW reduces the complexity of the system considerably. The single-beam- as well as the multi-beam waveguide mirrors and the polarizers have been manufactured. Cold tests of a full size uncooled prototype line delivered an efficiency exceeding 90%. The microwave power will be launched to the plasma through ten CVD-diamond barrier windows and in-vessel quasi-optical plug-in launchers allowing each 1 MW RF-beam to be steered independently. The polarization as well as the poloidal and toroidal launch angle can be adjusted individually to provide optimum conditions for different heating and current drive scenarios.