Status of the 140 GHz / 10 MW CW Transmission System for ECRH on the Stellarator W7-X

W. Kasparek(1), H.Braune(2), G.Dammertz(3), V.Erckmann(2), G.Gantenbein(1), F.Hollmann(2), M.Grünert(1), W. KasparekH.Kumric(1), L.Jonitz(2), H.P.Laqua(2), W.Leonhardt(3), G.Michel(2), F.Noke(2), B.Plaum(1), M.Schmid(3), T.Schulz(2), K.Schwörer(1), M.Thumm(3), M.Weissgerber(2)

(1) IPF, Universität Stuttgart, Pfaffenwaldring 31, D-70569 Stuttgart, Germany.

(2) MPI für Plasmaphysik, EURATOM-Association, Greifswald, Germany.

(3) FZ Karlsruhe, IHM, Association Euratom-FZK, Karlsruhe, Germany.

Abstract

The stellarator W7-X which is currently under construction in at IPP-Greifswald, Germany, will be equipped with a powerful 10 MW ECRH system, working at 140 GHz. The ECRH system is designed to operate in cw regime. The microwave power will be generated by 10 gyrotrons delivering 1 MW each and will be transmitted from the gyrotron hall to the machine W7-X stellarator ports via a fully optical system. .. The transmission system consists of 10 short single-beam waveguides (SBWG)mirror sections including matching optics and polarizers for each gyrotron, and two multi-beam waveguides (MBWGs,mirror sections ( length appr. 44 m) which transmit 5 beams each to the torus hall. Near to the stellarator ports, the beams are separated again and launched by individual antennas to the plasma. The launchers allow for arbitrary toroidal (EC-current drive) and poloidal (on/off axis heating) launch angle of each beam. All mirrors (more than 160) are water- cooled and can be adjusted remotely.

In the talk, Tthe status of the construction of the transmission lines and the design of the launchers is reported. Low-power tests of a prototype system at IPF Stuttgart are reviewed, showing high transmission performance (efficiency 90 %, mode purity 98 %).

The first gyrotron is now operating at IPP Greifswald, and high-power long-pulse tests have started. Measurements on transmission performance, behaviour of the water-cooled mirrors under thermal and microwave loads as well as alignment issues, characteristics of directional couplers, calorimetric loads and other diagnostics are discussed.

At present, Tthe system is presently being prepared for high-power tests of a mock-up for a the remote steering antenna as planned for ECRH/ECCD on ITER. and possibleFirst results of these experiments are presented.