Progress towards full feedback control of MHD instabilities by ECRH on TEXTOR

E. Westerhof, M.R. Baar, de, B.A. Hennen, J.W. Oosterbeek, W.A. Bongers, A. Bürger, E.M.M. Demarteau, S. Korsholm, S.K. Nielsen, P.W.J.M. Nuij, D.J. Thoen, M. Steinbuch

Research output: Chapter in Book/Report/Conference proceedingConference contributionAcademic

Abstract

Electron cyclotron resonance heating (ECRH) or current drive (ECCD) are often used for control of plasma instabilities, like neoclassical tearing modes orsawteeth. To perform this task under feedback control requires both identification, and localization of the mode as well as steering of the ECRH wave beam. Thispaper describes the implementation of different parts of the control loop on the TEXTOR tokamak.For the ECRH launcher, a dedicated controller is developed on the basis of its mechanical properties obtained from Frequency Response Function measurements.The performance of the controller will be tested on a mechanical mock-up of the actual launcher.For the identification and localization of the instabilities a dedicated electron cyclotron emission (ECE) diagnostic has been implemented based on the "same line-of-sight" principle.1,2 An ECE-receiver is located in the ECRH transmission line looking along the sight-line of the ECRH beam. Through steering of the ECRH/ECE wave beam, a magnetic island or sawtooth inversion radius then only needs to be localized in the ECE spectrum at the gyrotron frequency (or justabove or below) in order to deposit the ECRH power exactly on top of it (or on its high or low field side). At TEXTOR, the ECE power (of the order of a few nW) is separated from the ECRH power (of 1 MW) by a 25.75 mm thick quartz plate acting as Fabry-Pérot etalon. First ECE measurements have been obtained during high power ECRH (400 kW up to 2s), which demonstrate the capability of the system to localize rotating magnetic islands and sawtooth inversion.
Original languageEnglish
Title of host publication7. International workshop 'Strong microwaves: Sources and applications', Nizhny Novgorod, 13-18 October 2008
Publication statusPublished - 2008

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