Progress report on the ECRH transmission system at the stellarator W7-X

The ECRH system of the stellarator W7-X, which is currently under construction, plays a dominant role for continuous plasma heating and current drive during the operation of the machine. The ECRH system will provide a power of 10 MW in continuous wave at 140 GHz. The RF power is generated by 10 gyrotrons which are placed 25-40 m away from the W7-X torus in a special building, the transmission of the power is performed by an optical system which includes in total about 160 reflecting mirrors.