(FT/P2-24) Experimental Results of Series Gyrotrons for the Stellarator W7-X

G. Gantenbein1), H. Braune2), G. Dammertz1), V. Erckmann2), S. Illy1), S. Kern1), W. Kasparek3), H.P. Laqua2), C. Lechte3), F. Legrand4), W. Leonhardt1), C. Liévin4), G. Michel2), B. Piosczyk1), O. Prinz1), 5), M. Schmid1), M. Thumm1), 5)
1) Forschungszentrum Karlsruhe, Association EURATOM-FZK, Institut fuer Hochleistungsimpuls- und Mikrowellentechnik, Postfach 3640, D-76021 Karlsruhe, Germany
2) Max-Planck-Institut fuer Plasmaphysik, Teilinstitut Greifswald, Association EURATOM, Wendelsteinstr. 1, D-17491 Greifswald, Germany
3) Universitaet Stuttgart, Institut fuer Plasmaforschung, Pfaffenwaldring 31, D-70569 Stuttgart, Germany
4) Thales Electron Devices, 2 Rue de Latécoère, F-78141 Vélizy-Villacoublay, France
5) Universitaet Karlsruhe, Institut fuer Hoechstfrequenztechnik und Elektronik, Kaiserstr. 12, D-76131 Karlsruhe, Germany

Abstract.  A powerful ECRH system with 10 MW RF power at 140 GHz and CW operation is foreseen for the stellarator W7-X, being under construction at IPP Greifswald. The RF power will be delivered by 10 gyrotrons, each capable of 1 MW, CW. Nine gyrotrons are being manufactured by Thales Electron Devices (TED), Vélizy, France, one gyrotron was produced by CPI, Palo Alto, CA. Testing of the TED gyrotrons is performed at the test stand at FZK (pulse duration 3 min) and the final tests are performed at IPP (pulse length 30 min). Both, the first TED series gyrotron and the CPI gyrotron have passed the acceptance tests successfully. The acceptance tests of the TED series gyrotrons are ongoing. The RF output beam quality of all tubes tested so far is at a constant high level of about 97% in the Gaussian beam. In short pulse operation the gyrotrons have achieved the specified parameters. However, for long pulse operation the performance decreases due to the occurrence of parasitic oscillations which are assumed to be excited by the electron beam in the beam tunnel close to the cavity. Experimental results of this effect and possible modifications of the beam tunnel geometry will be discussed.

Full paper available (PDF)