FOM-Institute for Plasma Physics Rijnhuizen Association Euratom-FOM, Trilateral Euregio Cluster Feedback controlled ECRH power deposition for control of MHD instabilities on TEXTOR E. Westerhof With contributions from: M. de Baar, B.A. Hennen, J.W. Oosterbeek, W.A. Bongers, A. Bürger, S.B. Korsholm, S.K. Nielsen, P. Nuij, D.J. Thoen, M. Steinbuch, and the TEXTOR-Team

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Quick overview A brief reminder of why –Feedback control of MHD instabilities –Feedback control of ECRH power deposition How –A holistic view –TEXTOR Selected elements of control loop –Mechanical launcher –Mode detection & ECRH localization What comes next

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Why control MHD instabilities? Neoclassical Tearing Modes (NTMs) –deteriorate confinement –cause disruptive discharge termination © O. Sauter et al., Phys. Plasmas 4 (1997) 1654 DIII-D

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Why control MHD instabilities? Sawteeth –limit central pressure –trigger NTMs –redistribute fusion alphas and He-ash © E. Westerhof et al., Nucl. Fusion 42 (2002) 1324 O. Sauter et al., Phys. Rev. Letters 88 (2002) JET

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Why control ECRH deposition? Effect of ECRH on sawteeth and NTM depends strongly on localization –co-ECCD for sawtooth period control in TEXTOR © E. Westerhof et al., Proceedings EC

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Why control ECRH deposition? Effect of ECRH on sawteeth and NTM depends strongly on localization –(modulated) ECCD for 3/2 NTM control in AUG B T -ramp to achieve localization Advantage of modulation with O-point rotation © M. Maraschek et al., Phys. Rev. Letters 98 (2007)

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e TEXTOR as test bed for MHD control Dynamic Ergodic Divertor (DED) for controlled generation of tearing modes High power ECRH system with flexible launcher for MHD control

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e How: a holistic view of NTM control

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e The TEXTOR team Bart Hennen et al. (collaboration TU/e) –Mechanical launcher control –Control algorithms –Modeling of full control loop Diego De Lazzari –Modeling of plasma response: Rutherford Eqn Hans Oosterbeek –Inline ECE diagnostic for mode detection and ECRH localization and many others

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Selected elements of control loop

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Launcher control Launcher design features –AC perm. magnet synchronous motor + servo amplifier –Actuation in 2 rotational degrees of freedom (DOFs) range: -30° to 30° poloidal / -45° to 45° toroidal Fast, accurate steering of ECRH launcher requires detailed knowledge of its mechanics –10° in 100 ms, with a position accuracy of 1°

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Launcher control Mechanics characterized by Frequency Response Function techniques Derived linear plant + friction model used in design of advanced launcher feedback controller

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Modeled controller response Speed of response: ~ 25° rotation in 100 [ms] Max. positioning error: 0.4°

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Inline ECE for localization an phase tracking Single system for mode detection & ECRH steering Principle: localizing it … in the ECE spectrum on the gyrotron frequency ensures power deposition on top of it

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Major technical challenge for inline ECE To separate the ~1 MW gyrotron radiation from the ~100 pW expected ECE power at the radiometer – mW of power can destroy radiometer –Requires a 130 dB rejection of the gyrotron component to level ECRH and ECE components at the input of the mixer

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Implementation in Quasi Optical environment Frequency Selective Coupler based on the Fabry-Pérot principle Constructive interference for transmitted waves at gyrotron frequency Constructive interference of reflected waves at ECE frequencies Destructive interference for reflected gyrotron waves Spacing of ECE channels determined by thickness of plate Trade off between ECE resolution and losses through plate absorption Transmission Reflection f gyr f ECE

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e 140 GHz 800 kW, 10 seconds (3 s for FB project) Reflected ECRH down by 50 dB from the two dielectric plates Final design of in-line ECE optics ECE from plasma ECRH from gyrotron mm thick dielectric plate in 96 mm waist Expected ECE ~ 100 pW

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Geometry in plasma of final system 6 ECE channels spaced 3 GHz –132.5,..., GHz Each channel 500 MHz wide Larger coverage by varying of launcher elevation

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Experimental results: discharge with sawteeth Plasma conditions: B  = 2.3 T I p = 300 kA 400 kW co-ECCD Sawtooth inversion clearly visible between and GHz ECRH outside q=1 sawteeth stabilized © J.W. Oosterbeek et al., Proceedings EC

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Discharge with tearing mode Plasma conditions: B  = 2.25 T I p = 300 kA 400 kW co-ECCD (  = -10 o ) Elevation scan -15 o to +15 o ECRH outside r s at start of scan: phase reversal from to Mode stabilized early in scan when r EC approaches r s Strong perturbations in presence if island © J.W. Oosterbeek et al., Proceedings EC

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Discharge with tearing mode Plasma conditions: B  = 2.25 T I p = 300 kA 400 kW co-ECCD (  = -10 o ) Elevation scan -15 o to +15 o ECRH outside r s at start of scan: phase reversal from to Mode stabilized early in scan when r EC approaches r s Strong perturbations in presence if island © J.W. Oosterbeek et al., Proceedings EC

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e Discharge with tearing mode Plasma conditions: B  = 2.25 T I p = 300 kA 400 kW co-ECCD (  = -10 o ) Elevation scan -15 o to +15 o ECRH outside r s at start of scan: phase reversal from to Mode stabilized early in scan when r EC approaches r s Strong perturbations in presence of islands: in phase with island rotation © J.W. Oosterbeek et al., Proceedings EC

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e In summary Control of mechanical ECRH launcher designed and tested in software Inline ECE diagnostic for integrated mode detection, phase tracking and ECRH launcher steering developed and tested In parallel work has progressed on –Mode location and phase detection algorithms –Installation of controller hardware –Modeling of effect of ECRH on mode growth –Et cetera

E. Westerhof, Workshop Control for Nuclear Fusion, 7&8 May 2008, TU/e What comes next Mechanical tests of launcher controller Integration of complete feedback loop Tests of algorithms for mode localization and launcher steering Tests of algorithms for phase tracking and gyrotron power modulation Physics studies of back-scattered ECRH in inline ECE diagnostic Development of CW wave guide compatible frequency selective couplers for inline ECE