10 MW, 140 GHz, CW GYROTRON AND OPTICAL TRANSMISSION SYSTEM FOR MILLIMETER WAVE HEATING OF PLASMAS IN THE STELLARATOR W7-X

M. Thumm*, G. Dammertz, G. Gantenbein, S. Illy,
W. Leonhardt, G. Neffe, B. Piosczyk, M. Schmid

Forschungszentrum Karlsruhe, Association Euratom-FZK, IHM, Postfach 3640,

76021 Karlsruhe, Germany

*and Universitaet Karlsruhe, Institut fuer Hoechstfrequenztechnik und Elektronik,
Kaiserstr. 12, 76131 Karlsruhe, Germany

manfred.thumm@ihm.fzk.de

H. Braune, V. Erckmann, H.P. Laqua, G. Michel, M. Weissgerber

Max-Planck-Institut fuer Plasmaphysik (IPP),

Wendelsteinstr. 1, 17491 Greifswald, Germany

P. Brand, W. Kasparek, C. Lechte

Institut fuer Plasmaphysik, Universitaet Stuttgart,

Pfaffenwaldring 31, 70569 Stuttgart Germany

During the last years electron cyclotron heating (ECH) has proven to be one of the most attractive heating schemes for stellarators, as it provides net current free plasma start up and heating. Both, the stellarator Wendelstein 7-X (W7-X), which is under construction at IPP-Greifswald, Germany, and the ITER tokamak, which will be built at Cadarache, France, will be equipped with a strong EC-heating and current drive system. Both systems are similar in frequency and have CW (continuous wave) capability (140 GHz, 10 MW for W7-X and 170 GHz, 24 MW for ITER). The commissioning of the ECH plant for W7-X is well underway, the status of the project and first integrated full power test results from two modules are reported and may provide valuable input for the ITER plant.

The ten 1 MW gyrotrons at W7-X are arranged in two sub-groups symmetrically to a central beam duct in the ECH hall. The RF-waves of each subgroup are combined and transmitted by a purely optical multibeam waveguide transmission line (copper mirrors) from the gyrotrons to the plasma torus. The combination of the five gyrotron beams to two beam lines each with a power of 5  MW reduces the complexity of the system considerably. The single-beam- as well as the multi-beam waveguide mirrors and the grating polarizers have been manufactured. Cold tests of a full size uncooled prototype line delivered an efficiency exceeding 90%. The microwave power will be launched to the plasma through ten CVD-diamond barrier windows and in-vessel quasi-optical plug-in launchers allowing each 1 MW RF-beam to be steered independently. The polarization as well as the poloidal and toroidal launch angle can be adjusted individually to provide optimum conditions for different heating and current drive scenarios.

The first series gyrotron was tested and yielded a total output power of 0.98 MW, with an efficiency of 31% (without a single-stage 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 0.90 MW and the power measured in a calorimetric load after a 25-m-long quasi-optical transmission line (seven mirrors) was 0.87 MW.

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*Work supported by the European Communities, EFDA