140-GHz High-Power Gyrotron Development for the Stellarator W7-X

G. Dammertz(1), D. Bariou(5), P. Brand(4), H. Braune(3), V. Erckmann(3),

G. Gantenbein(4), E. Giguet (5), W. Kasparek(4), H.P. Laqua(3), C. Lievin(5),

W. Leonhardt(1), G. Michel(3), G. Mueller(4), G. Neffe(1), B. Piosczyk(1),

M. Schmid(1), M. Thumm(1,2)

(1)FZK Karlsruhe, IHM, EURATOM-FZK, Postfach 3640, D-76021 Karlsruhe, Germany

(2)Universitaet Karlsruhe, IHE, Karlsruhe, Germany

(3)MPI fuer Plasmaphysik, Greifswald, Germany

(4)Universitaet Stuttgart, IPF, Stuttgart, Germany

(5) Thales ED, Vélizy, France

Electron cyclotron resonance heating (ECRH) has proven to be one of the most attractive heating schemes for stellarators, as it provides net current free plasma start up and heating. Extensive measurements on stellarators at IPP Garching yield a solid physical and technological basis for ECRH systems. Therefore, ECRH was decided to be the main heating method for the Wendelstein 7-X stellarator (W7-X) now under construction at IPP Greifswald/Germany. A 10 MW ECRH system with continuous wave possibilities operating at 140 GHz will be built up to meet the scientific goals of the stellarator with inherent steady-state capability at reactor relevant plasma parameters.

Two prototype gyrotrons with an output power of 1 MW were developed in collaboration between European research laboratories and European industry (Thales Electron Devices, France). The gyrotrons are equipped with a single-stage depressed collector, an optimized quasi-optical mode converter and a CVD-diamond window. The prototypes have been successfully tested at FZK. With the second one an output power of 0.89 MW at a pulse duration of 3 minutes and an output power of 0.54 MW for about 15 minutes has been obtained. The first prototype has been installed at IPP Greifswald and has been tested there successfully up to a pulse-length of 10 s. The development has been finished; the series gyrotrons and the superconducting magnet systems have been ordered. In a parallel development at CPI (Communications and Power Industries, Palo Alto, California) another tube had been tested at high power (920kW, 5 ms) and at a power of about 500 kW in pulse-lengths of 700 s.