The 10 MW ECRH system for W7-X

Summary form only given, as follows. Electron Cyclotron Resonance Heating (ECRH) is the main heating method for the Wendelstein 7-X Stellarator (W7-X),which is the next step device in the stellarator line of IPP and is presently under construction. The experiment aims at demonstrating the inherent steady state capability of stellarators at reactor relevant plasma parameters and is therefore equipped with a superconducting coil system. A 10 MW ECRH power plant with CW-capability at 140 GHz is under construction to meet the scientific objectives. The microwave power is generated by 10 gyrotrons with 1 MW each. A prototype gyrotron is presently being developed in collaboration between European research-laboratories and industry and incorporates advanced features like single stage depressed collector, optimized quasi-optical mode converter and a CVD-diamond window. The first prototype was successfully tested and an output power of up to 1 MW, a pulse duration of up to 180 s (at reduced power) and an efficiency of up to 50% was achieved. Recent test results are reported. The gyrotrons are supplied by 10 modular solid state HV-supplies (65 kV, 50 A each) providing fast power control and high flexibility. The first power supply module is presently under test. The ten individual microwave beams are combined and transmitted to the main torus hall by an open quasi-optical transmission system with high transmission efficiency, which runs at normal pressure and consists of water cooled imaging mirrors. Cold tests of a full size, uncooled prototype line and the related RF-diagnostics are discussed. The microwave power is launched to the plasma through 10 diamond barrier windows and in-vessel quasi-optical plug-in launchers, which allow an independent steering of each beam. The polarization as well as the poloidal and toroidal launch angle of each microwave beam can be individually controlled to provide optimal conditions for different heating and current drive scenarios. The co- struction of the ECRH plant is well under way and the status is presented.