A dual, high speed, real-time visible light camera setup was installed on the TCV tokamak to reconstruct optically and in real-time the plasma boundary shape. Localized light emission from the plasma boundary in tangential view, broadband visible images results in clearly resolved boundary edge-features. These projected features are detected in real-time and transformed to the poloidal plane to obtain a measurement of the plasma boundary. Plasma boundary reconstructions of diverted plasma discharges are presented, showing agreement of within 1 cm compared with magnetic equilibrium reconstruction. The resulting real-time plasma shape measurement is applied in a feedback control loop for the plasma position, demonstrating effective stabilization and tracking of the plasma vertical position.

VL - 54 U1 -FP

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U5 - 6dc862485b6b1045595d0c48e382998f ER - TY - JOUR T1 - Development of real-time plasma analysis and control algorithms for the TCV tokamak using Simulink JF - Fusion Engineering and Design Y1 - 2014 A1 - Felici, F. A1 - Le, H. B. A1 - J. I. Paley A1 - Duval, B. P. A1 - Coda, S. A1 - Moret, J. M. A1 - Bortolon, A. A1 - L. Federspiel A1 - Goodman, T. P. A1 - Hommen, G. A1 - A. Karpushov A1 - Piras, F. A1 - A. Pitzschke A1 - J. Romero A1 - G. Sevillano A1 - Sauter, O. A1 - Vijvers, W. A1 - TCV team KW - diagnostics KW - MHD control KW - Plasma control KW - Simulink KW - TCV KW - TOKAMAK AB - One of the key features of the new digital plasma control system installed on the TCV tokamak is the possibility to rapidly design, test and deploy real-time algorithms. With this flexibility the new control system has been used for a large number of new experiments which exploit TCV's powerful actuators consisting of 16 individually controllable poloidal field coils and 7 real-time steerable electron cyclotron (EC) launchers. The system has been used for various applications, ranging from event-based real-time MHD control to real-time current diffusion simulations. These advances have propelled real-time control to one of the cornerstones of the TCV experimental program. Use of the Simulink graphical programming language to directly program the control system has greatly facilitated algorithm development and allowed a multitude of different algorithms to be deployed in a short time. This paper will give an overview of the developed algorithms and their application in physics experiments. VL - 89 IS - 3 U1 - FP U2 - TP U5 - fd3e636fc3f0786cd773655181eb821f ER - TY - JOUR T1 - A fast, magnetics-free flux surface estimation and q-profile reconstruction algorithm for feedback control of plasma profiles JF - Plasma Physics and Controlled Fusion Y1 - 2013 A1 - Hommen, G. A1 - de M. Baar A1 - Citrin, J. A1 - de Blank, H. J. A1 - Voorhoeve, R. J. A1 - de Bock, M. F. M. A1 - Steinbuch, M. AB -The flux surfaces' layout and the magnetic winding number q are important quantities for the performance and stability of tokamak plasmas. Normally, these quantities are iteratively derived by solving the plasma equilibrium for the poloidal and toroidal flux. In this work, a fast, non-iterative and magnetics-free numerical method is proposed to estimate the shape of the flux surfaces by an inward propagation of the plasma boundary shape, as can be determined for example by optical boundary reconstruction described in Hommen (2010 Rev. Sci. Instrum. 81 113504), toward the magnetic axis, as can be determined independently with the motional Stark effect (MSE) diagnostic. Flux surfaces are estimated for various plasma regimes in the ITER, JET and MAST tokamaks and are compared with results of CRONOS reconstructions and simulations, showing agreement to within 1% of the minor radius for almost all treated plasmas. The availability of the flux surface shapes combined with the pitch angles measured using MSE allow the reconstruction of the plasma q-profile, by evaluating the contour-integral over the flux surfaces of the magnetic field pitch angle. This method provides a direct and exact measure of the q-profile for arbitrary flux surface shapes, which does not rely on magnetic measurements. Results based on estimated flux surface shapes show agreement with CRONOS q-profiles of better than 10%. The impact of the shape of the flux surfaces on the q-profile, particularly the profiles of elongation and Shafranov shift, and offsets in plasma boundary and the magnetic axis are assessed. OFIT+ was conceived for real-time plasma profile control experiments and advanced tokamak operation, and provides quickly and reliably the mapping of actuators and sensors to the minor radius as well as the plasma q-profile, independent of magnetic measurements.

VL - 55 SN - 0741-3335 UR - http://www.euro-fusionscipub.org/wp-content/uploads/2014/11/EFDP12014.pdf IS - 2 U1 -FP

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U5 - 0b2acdc2ac4dbfe79e66d33160ef64d5 ER - TY - JOUR T1 - Nonlinear control for stabilization of small neoclassical tearing modes in ITER JF - Nuclear Fusion Y1 - 2012 A1 - Hennen, B.A. A1 - Lauret, M. A1 - Hommen, G. A1 - Heemels, Wpmh A1 - M.R. de Baar A1 - Westerhof, E. KW - CURRENT DRIVE KW - ELECTRON-CYCLOTRON WAVES KW - TOKAMAK AB - In this paper, the feasibility of feedback stabilization of neoclassical tearing modes at small island sizes, corresponding to otherwise unstable island sizes in ITER scenario 2, is demonstrated. The islands are stabilized by application of electron cyclotron resonance heating and current drive in a regime where the application of current drive in open loop normally results in a complete suppression of the island. By applying current drive in closed loop with feedback of real-time measurements of the island width, complete suppression is avoided and the island is stabilized at a specific reduced size. In contrast to complete suppression, control of islands at a specific size will allow the manipulation of a plasma's current density profile in hybrid scenarios. Three conceptual (non-)linear feedback controllers with varying complexity, performance, robustness and required model knowledge are introduced. Simulations show the theoretical feasibility of small island stabilization at a specific reduced width. The controllers are applied to the generalized Rutherford equation, which governs the island evolution subject to electron cyclotron current drive. A strategy for the gradual implementation of the controllers is suggested. Stabilization of small islands by feedback control will allow the use of system identification to extend the model knowledge on the evolution of small islands, and in addition will extend the operational regime. VL - 52 SN - 0029-5515 N1 - ISI Document Delivery No.: 956LNTimes Cited: 0Cited Reference Count: 28 U1 - FP U2 - TP U5 - 462408b12d9999bed675160bb4c26465 ER - TY - JOUR T1 - Optical boundary reconstruction of tokamak plasmas for feedback control of plasma position and shape JF - Review of Scientific Instruments Y1 - 2010 A1 - Hommen, G. A1 - de M. Baar A1 - Nuij, P. A1 - McArdle, G. A1 - Akers, R. A1 - Steinbuch, M. KW - ASDEX KW - CONFINEMENT KW - EDGE KW - H-mode KW - MAST AB - A new diagnostic is developed to reconstruct the plasma boundary using visible wavelength images. Exploiting the plasma's edge localized and toroidally symmetric emission profile, a new coordinate transform is presented to reconstruct the plasma boundary from a poloidal view image. The plasma boundary reconstruction is implemented in MATLAB and applied to camera images of Mega-Ampere Spherical Tokamak discharges. The optically reconstructed plasma boundaries are compared to magnetic reconstructions from the offline reconstruction code EFIT, showing very good qualitative and quantitative agreement. Average errors are within 2 cm and correlation is high. In the current software implementation, plasma boundary reconstruction from a single image takes 3 ms. The applicability and system requirements of the new optical boundary reconstruction, called OFIT, for use in both feedback control of plasma position and shape and in offline reconstruction tools are discussed. (C) 2010 American Institute of Physics. [doi:10.1063/1.3499219] VL - 81 SN - 0034-6748 UR -