The 10 MW, 140 GHz, Continuous Wave ECRH-System for the Stellarator W7-X

Manfred Thumm

Karlsruhe Research Center

Institute for Pulsed Power and Microwave Technology

and

University of Karlsruhe

Institute of High Frequency Techniques and Electronics

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 European stellarator line and is presently under construction at IPP Greifswald. The experiment aims at demonstrating the inherent steady state capability of stellarators at fusion reactor relevant plasma parameters. W7-X (major radius 5.5 m, minor radius 0.55 m) is equipped with a superconducting coil system operating at 2.5 T for steady state operation and a divertor for 10 MW steady state heat removal. A 10 MW ECRH 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 European R&D program aiming at the development of a prototype gyrotron for W7-X has been successfully terminated by fall of 2002. A prototype gyrotron with the same specifications was developed for W7-X at CPI (USA). Test results and limitations are reported. The distinct microwave beams from each gyrotron are combined and transmitted to the W7-X Stellarator ports by an open quasi-optical transmission system with high transmission efficiency, which runs at normal pressure and consists of water cooled imaging copper mirrors. Cold tests of a full size, uncooled prototype line and the related RF-diagnostics are presented. The microwave power is launched to the plasma through 10 synthetic diamond barrier windows and in-vessel quasi-optical plug-in launchers, which allow an independent steering of each beam. The commissioning of the ECRH plant is well under way and the status is presented.