Power POWER modulation MODULATION CAPABILITIEScapabilities OF THE

140 GHz / 1 MW GYROTRON FOR THE STELLARATOR WENDELSTEIN 7-Xof the 140GHz/1MW gyrotron for Wendelstein 7-X.

G. Dammertz¹, S. Alberti², D. Fasel², E. Giguet⁶, K. Koppenburg¹, M. Kuntze¹,

F. Legrand⁶, W. Leonhardt¹, C. Lievin⁶, G. Müller⁵, G. Neffe¹, B. Piosczyk¹,

M. Schmid¹, A. Sterk⁴, M. Thumm^1,3, M. Q. Tran², A.G.A Verhoeven⁴

¹Forschungszentrum Karlsruhe, Association Euratom-FZK, IHM,

Postfach 3640, D-76021 Karlsruhe, Germany

²Centre de Recherches en Physique des Plasmas, Association Euratom-Confédération Suisse, EPFL Ecublens, CH-1015 Lausanne, Suisse

³ Universität Karlsruhe, Institut für Höchstfrequenztechnik und Elektronik,

Kaiserstr. 12, D-76128 Karlsruhe, Germany

⁴ FOM Instituut foor Plasmafisica Rijnhuizen, Association EURATOM-FOM, P.O.Box 1207, 3430 BE Nieuwegen, Netherlands

⁵Institut für Plasmaforschung, Universität Stuttgart, Pfaffenwaldring 31, D-70569 Stuttgart, Germany

⁶Thales Electron Devices, 2 Rue de Latécoère, F-78141Vélizy-Villacoublay, France

S. Alberti¹, G. Dammertz², D. Fasel¹, K. Koppenburg², G. Mueller⁴, M. Schmidt², A.Sterk³, A.G.A Verhoeven³, + other suggestions

¹Centre de Recherches en Physique des Plasmas, Ecole Polytechnique Fédérale de Lausanne, Association EURATOM-Confédération Suisse, CH-1015 Lausanne, EPFL, Switzerland.

²Euratom/FZK

³Euratom-FOM

⁴Euratom-IPP-Garching

In present Tokamakstokamaks, and in particular for in future larger devices as ITER, the control of Neo-classical Tearing Modes (NTM) is essential for achieving high performance in terms of the beta limit. A commonly used scheme for NTM stabilisations stabilization consists in driving a helical current at the resonance surface of interest with Electron-Cyclotron-Current-Drive (ECCD). Depending on the ratio between the magnetic island size and the RF beam width, complete stabilization of the NTM will only be achieved with deep RF power modulation in phase with the mode and, for JET or ITER, recent studies indicate that a modulation depth as high as 70% at frequencies ranging between 1 and 10 kHz would be needed.

In the frame of the European development programmeprogram of high power sources for ECRH applications between FZK Karlsruhe, IPP Garching/Greifswald, EPFL Lausanne, IPF Stuttgart and Thales Electron Devices, the modulation capabilities of the 140 GHz/1MW gyrotron developpeddeveloped for the Wendelstein 7-X stelleratorstellarator at Greifswald, Germany, have been experimentally investigated. In short RF pulse lengths of 1 s, operation (1s), RF power modulation depths higher thanas high as 705% have been obtained either by modulating the main voltage (MVM) or the depressed collector voltage (CVM). Frequency modulation as high as 50 kHz have been obtained with MVM and 1KHz 1 kHz with CVM, in both cases the limitaionlimitation was given by the corresponding power supply and not by the gyrotron itself. Detailed analysis of the collector loading with respect to the modulation scheme will be presented and the intrinsic gyrotron limitations for long pulse length in theoperation with deep modulation regime will be discussed.

als Vortrag: 22th SOFT, Helsinki, Finnland, Sept. 2002

F+E: 31.20.10