International Journal of Terahertz Science and Technology
  TST >> Vol.1, No.2, June 2008: PP. 73-99

10 MW, 0.14 THz, CW Gyrotron and Optical Transmission System for Millimeter Wave Heating of Plasmas in the Stellarator W7-X

M.Thumm 2*, G. Dammertz 1, G. Gantenbein 1, S. Illy 1, S. Kern 1, W. Leonhardt 1, G. Neffe 1, B. Piosczyk 1, M. Schmid 1, H. Braune 3, V. Erckmann 3, F. Hollmann 3, L. Jonitz 3, H.P. Laqua 3, G. Michel 3, F. Noke 3, F. Purps 3, T. Schulz 3, M. Weissgerber 3, P. Brand 4, M. Grünert 4, W. Kasparek 4, H. Kumric 4, C. Lechte 4, B. Plaum 4
1 Forschungszentrum Karlsruhe, Association Euratom-FZK, Institut für Hochleistungsimpuls- und Mikrowellentechnik, Postfach 3640, 76021 Karlsruhe, Germany
2 Universität Karlsruhe, Institut für Höchstfrequenztechnik und Elektronik, Kaiserstr. 12, 76131 Karlsruhe, Germany
3 Max-Planck-Institut für Plasmaphysik (IPP), Wendelsteinstr. 1, 17491 Greifswald, Germany.
4 Institut für Plasmaforschung, Universität Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany
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Abstract: 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 comparable in frequency and have CW (continuous wave) capability (0.14 THz, 10 MW for W7-X and 0.17 THz, 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 10 gyrotrons at W7-X will be arranged in two sub-groups symmetrically to a central beam duct in the ECH hall. The RF-wave of each subgroup will be combined and transmitted by a purely optical multibeam wave guide transmission line (copper mirrors) from the gyrotrons to the plasma torus. The combination of the 5 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 polarizers have been already manufactured. Cold tests of a full size uncooled prototype line delivered an efficiency exceeding 90%. The mm-wave power will be launched to the plasma through ten synthetic-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 will be adjusted individually to provide optimum conditions for different heating and current drive scenarios. The first series gyrotrons were 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.

Keywords: Electron cyclotron heating, Fusion plasmas, Stellarator, High power CW gyrotron, Quasi-Optical transmission

Published: 2008-06-26

Acknowledgments: The authors wish to thank the technical staff at FZK Karlsruhe, IPF Stuttgart and IPP Greifswald for their excellent contributions in solving numerous technological problems during the R&D of sophisticated ECH-components. We are grateful to the key persons at TED Velizy and CPI Palo Alto for their great effort and their readiness to incorporate innovative concepts in the gyrotron-R&D. Finally we would like to thank all partners in the collaborating European research laboratories for their stimulating discussions and active support.

This work was supported by the European Communities under the contract of Association between EURATOM and Forschungszentrum Karlsruhe, and was carried out within the framework of the European Fusion Development Agreement. The views and opinions expressed herein do not necessarily reflect those of the European Commission.

Cite this article:
M.Thumm, G. Dammertz, G. Gantenbein, S. Illy, S. Kern, W. Leonhardt, G. Neffe, B. Piosczyk, M. Schmid, H. Braune, V. Erckmann, F. Hollmann, L. Jonitz, H.P. Laqua, G. Michel, F. Noke, F. Purps, T. Schulz, M. Weissgerber, P. Brand, M. Grünert, W. Kasparek, H. Kumric, C. Lechte, B. Plaum. 10 MW, 0.14 THz, CW Gyrotron and Optical Transmission System for Millimeter Wave Heating of Plasmas in the Stellarator W7-X[J]. International Journal of Terahertz Science and Technology, 2008, Vol.1, No.2: 73-99.  DOI:10.11906/TST.073-099.2008.06.09




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