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1 MW, 140 GHZ SERIES GYROTRONS FOR THE W7-X STELLARATOR

M. Thumm^1,5, H. Braune², G. Dammertz¹, V. Erckmann², G. Gantenbein¹, S. Illy¹, S. Kern¹, W. Kasparek³, H. P. Laqua², C. Lechte³, F. Legrand⁴, W. Leonhardt¹, C. Liévin⁴, G. Michel², B. Piosczyk¹, O. Prinz^1,5, M. Schmid¹

¹Forschungszentrum Karlsruhe, Association EURATOM-FZK, Institut fuer Hochleistungsimpuls- und Mikrowellentechnik, Postfach 3640, D-76021 Karlsruhe, Germany

²Max-Planck-Institut fuer Plasmaphysik, Teilinstitut Greifswald, Association EURATOM,

Wendelsteinstr. 1, D-17491 Greifswald, Germany

³Universitaet Stuttgart, Institut fuer Plasmaforschung, Pfaffenwaldring 31,

D-70569 Stuttgart, Germany

⁴Thales Electron Devices, 2 Rue de Latécoère, F-78141 Vélizy-Villacoublay, France

⁵Universitaet Karlsruhe, Institut fuer Hoechstfrequenztechnik und Elektronik, Kaiserstr. 12,

D-76131 Karlsruhe, Germany

e-mail: manfred.thumm@ihm.fzk.de

A powerful ECRH system with 10 MW mm-wave power at 140 GHz in CW operation is foreseen for the stellarator W7-X, being under construction at IPP Greifswald, Germany. The mm-wave power will be delivered by 10 gyrotrons, each capable of 1 MW, CW. Nine gyrotrons (cavity mode: TE_28.8) are being manufactured by Thales Electron Devices (TED), Vélizy, France, one gyrotron (cavity mode: TE_28.7) was produced by CPI, Palo Alto, CA, USA. Testing of the TED gyrotrons is being performed in the test facility at FZK (pulse duration 3 min) and the final tests are being performed at IPP (pulse length 30 min).

Both, the first TED series gyrotron and the CPI gyrotron have passed the acceptance tests successfully. The first TED series tube yielded a total output power of 0.98 MW, with an efficiency of 31% (with non-depressed collector) in short pulse operation and of 0.92 MW in pulses of 1800 s (efficiency of almost 45% at a depression voltage of 29 kV). The Gaussian mode output power was 0.91 MW. The mm-wave power, measured in a calorimetric load at the end of a 24 m long quasi-optical transmission line with seven mirrors, was 0.87 MW.

The acceptance tests of the TED series gyrotrons are ongoing. The mm-wave output beam quality of all tubes tested so far is at a constant high level of about 97 % in the fundamental Gaussian beam. In short pulse operation (1 ms) the gyrotrons have achieved the specified parameters. However, for long pulse operation the performance of some tubes 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 entrance of the cavity.

Experimental results employing a slightly modified beam tunnel geometry will be discussed.