Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Plasma Physics
Volume 57, Number 12
Monday–Friday, October 29–November 2 2012; Providence, Rhode Island
Session TO6: General Tokamak; Heating and Current Drive; Diagnostics |
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Chair: Ted Strait, General Atomics Room: 555AB |
Thursday, November 1, 2012 9:30AM - 9:42AM |
TO6.00001: Active Control of Power Exhaust in Strongly Heated ASDEX Upgrade Plasmas Ralph Dux, Arne Kallenbach, Matthias Bernert, Thomas Eich, Christoph Fuchs, Louis Giannone, Albrecht Herrmann, Josef Schweinzer, Wolfgang Treutterer Due to the absence of carbon as an intrinsic low-Z radiator, and tight limits for the acceptable power load on the divertor target, ITER will rely on impurity seeding for radiative power dissipation and for generation of partial detachment. The injection of more than one radiating species is required to optimise the power removal in the main plasma and in the divertor region, i.e. a low-Z species for radiation in the divertor and a medium-Z species for radiation in the outer core plasma. In ASDEX Upgrade, a set of robust sensors, which is suitable to feedback control the radiated power in the main chamber and the divertor as well as the electron temperature at the target, has been developed. Different feedback schemes were applied in H-mode discharges with a maximum heating power of up to 23\,MW, i.e. at ITER values of $P/R$ (power per major radius) to control all combinations of power flux into the divertor region, power flux onto the target or electron temperature at the target through injection of nitrogen as the divertor radiator and argon as the main chamber radiator. Even at the highest heating powers the peak heat flux density at the target is kept at benign values. The control schemes and the plasma behaviour in these discharges will be discussed. [Preview Abstract] |
Thursday, November 1, 2012 9:42AM - 9:54AM |
TO6.00002: Advanced ECCD based NTM control in closed-loop operation at ASDEX Upgrade (AUG) Matthias Reich, Laura Barrera-Orte, Karl Behler, Alexander Bock, Louis Giannone, Marc Maraschek, Emanuele Poli, Chris Rapson, J\"org Stober, Wolfgang Treutterer In high performance plasmas, Neoclassical Tearing Modes (NTMs) are regularly observed at reactor-grade beta-values. They limit the achievable normalized beta, which is undesirable because fusion performance scales as beta squared. The method of choice for controlling and avoiding NTMs at AUG is the deposition of ECCD inside the magnetic island for stabilization in real-time (rt). Our approach to tackling such complex control problems using real-time diagnostics allows rigorous optimization of all subsystems. Recent progress in rt-equilibrium reconstruction ($<$~3.5~ms), rt-localization of NTMs ($<$~8~ms) and rt beam tracing ($<$~25~ms) allows closed-loop feedback operation using multiple movable mirrors as the ECCD deposition actuator. The rt-equilibrium uses function parametrization or a fast Grad-Shafranov solver with an option to include rt-MSE measurements. The island localization is based on a correlation of ECE and filtered Mirnov signals. The rt beam-tracing module provides deposition locations and their derivative versus actuator position of multiple gyrotrons. The ``MHD controller'' finally drives the actuators. Results utilizing closed-loop operation with multiple gyrotrons and their effect on NTMs are shown. [Preview Abstract] |
Thursday, November 1, 2012 9:54AM - 10:06AM |
TO6.00003: Simulation of suppression of neoclassical tearing modes with ECCD J. Pratt, E. Westerhof Above a critical value of the plasma beta, neoclassical tearing modes (NTMs) destabilize, reducing confinement and causing disruptions. The primary tactic for controlling NTMs in ITER is to apply localized electron cyclotron current drive (ECCD) inside the magnetic islands. Theoretical description of the evolution of nonlinear, resistive magnetic islands is currently based on the generalized Rutherford equation (GRE), obtained by averaging Ohm's law for the perturbed helical current over the entire island region. In order to study the stabilization processes inside an island in more detail than the GRE allows, we extend the nonlinear 3D reduced-MHD simulation JOREK [1-2] to include ECCD effects. With the extended simulation, we investigate detailed evolution of the inside of magnetic islands during their stabilization by ECCD. We discuss implications of our results for the GRE. \\[4pt] [1] G. T. A. Huysmans, S. Pamela, E. van der Plas, and P. Ramet, Plasma Physics and Controlled Fusion 51, 124012 (2009).\\[0pt] [2] M. H\"olzl, S. G\"unter, R. P. Wenninger, W.-C. M\"uller, G. Huysmans, K. Lackner, I. Krebs, and ASDEX Upgrade Team, arXiv:1201.5765v2 (2012). [Preview Abstract] |
Thursday, November 1, 2012 10:06AM - 10:18AM |
TO6.00004: Sawtooth and Triggering Mechanism for Tearing Modes on the Tokamak a Configuration Variable Duccio Testa, Gustavo Canal, Stefano Coda, Federico Felici, Timothy Goodman, Miho Janvier, Josef Kamleitner, Donhyun Kim, Holger Reimerdes, Olivier Sauter The onset and sawtooth triggering mechanisms for Tearing Modes (TMs) has been extensively investigated during recent experimental campaigns on the Tokamak a Configuration Variable. The main long-term aim of this work is to provide understanding of the relation between sawteeth and TMs so that reliable real-time schemes can be devised for combined sawtooth and TM control in burning plasma experiments such as ITER. Hence, our work has focused on studying the dynamical relation between sawtooth crash and subsequent onset of TMs, sometimes leading to disruptions, using control techniques for the duration of the sawtooth period and the TM seeding mechanism via real-time pacing and localized electron cyclotron heating and current drive. [Preview Abstract] |
Thursday, November 1, 2012 10:18AM - 10:30AM |
TO6.00005: The application of optimal control theory to the vertical plasmas stabilization at TCV N. Cruz, A.P. Rodrigues, C.A.F. Varandas, J.-M. Moret, S. Coda, B.P. Duval From an axisymmetric circular shape plasma device, most present tokamaks have become axisymmetric elongated cross section shaped plasma devices, aiming at increasing energy confinement times. However, the elongated cross section of the plasma shape makes its vertical position unstable and a real-time feed-back control loop is necessary to stabilize it. The Tokamak\`{a} Configuration Variable (TCV) uses in-vessel poloidal field coils driven by a pair of fast switching power supplies to achieve highly elongated plasmas vertical stabilization. This contribution describes a new vertical stabilization non-linear digital controller developed for TCV, aiming at improving the performance of the power supplies and in-vessel coils stabilizing the vertical position of the plasma. From the modeling of the plasma response to the actuators, a state-space model is obtained, that is used to calculate a high order transfer function (TF) of the plasma position response to the voltage applied to the power supplies. This TF must go through a model reduction algorithm to obtain a lower-order model that may then be used to establish the bang-bang time-optimal controller. A state-space map of the controllable region and switching points is derived for the calculation of the bang-bang controller. From this map the switching-time is optimized to minimize the time to reach the set point. A description of the control algorithm development and hardware/software implementation is presented, with preliminary results of the controller. [Preview Abstract] |
Thursday, November 1, 2012 10:30AM - 10:42AM |
TO6.00006: The Preliminary Experimental Results of Resonant Magnetic Perturbation Coils on J-TEXT Tokamak Bo Rao, Yonghua Ding, Wei Jin, Qiming Hu, Nengchao Wang, Bin Yi, Quanlin Li, Wubing Zeng, Ge Zhuang A set of saddle coils system designed for generating rotating resonant magnetic perturbations (RMPs) has been installed inside the vacuum vessel of the J-TEXT tokamak and recently operated in DC mode and produced mainly m/n=2/1 mode perturbations. This system named as DRMP consists of 12 coils divided into 4 groups which equivalently locate in the toroidal direction. Another set of saddle coils system (now given a new name as SRMP) originally designed for TEXT-U has also been reconstructed outside the J-TEXT vessel wall. The SRMP mainly generates 2/1, 3/1 and some other higher m modes perturbations. In a J-TEXT Ohmic discharge, when the visible tearing modes with a high frequency ( $>$ 6 kHz, typically), the SRMP applied on a suitable spatial phase can suppress the modes completely, but if the SRMP operates at the opposite spatial phase, a locked mode would be stimulated afterward even though the modes have been suppressed. Nevertheless, if the mode frequency is too low, RMP will directly lead to mode locking. With some discharges without any visible tearing modes, mode penetration by DRMP is observed. The experimental results and their possible explanations will be given in the meeting. [Preview Abstract] |
Thursday, November 1, 2012 10:42AM - 10:54AM |
TO6.00007: ABSTRACT WITHDRAWN |
Thursday, November 1, 2012 10:54AM - 11:06AM |
TO6.00008: 3-D ECE imaging on KSTAR for enhanced understanding of MHD and transport physics Gunsu S. Yun, Woochang Lee, Jaehyun Lee, Minjun Choi, Hyeon K. Park, Calvin W. Domier, Neville C. Luhmann, Jr. The electron cyclotron emission imaging (ECE-I) system on the KSTAR, an advanced diagnostic tool for 2D visualization of MHD instabilities, has enabled the study of sawteeth [1], tearing modes, and edge-localized modes (ELMs) [2] in unprecedented detail with a broad spatial coverage (each of the two views $\sim $50cm$\times \sim $15cm vertical$\times $radial) and a fast time resolution ($\sim $1 $\mu $s). To further advance the diagnostic capability, a second ECEI system is being installed at a location toroidally separated from the first ECEI system by 1/16$^{th}$ of the circumference. The combined ECEI systems will provide quasi-3D visualization of MHD instabilities and address many critical issues such as mode rotation (both poloidal and toroidal velocities) and toroidal nonuniformity (mode beating and localization of the fast crash) of the MHD instabilities. In addition to the MHD studies, other important diagnostic applications, such as pitch angle measurement, 3D heat transport in various time scales, and toroidal correlation of turbulent fluctuations, are envisioned.\\[4pt] [1] Yun et al., submitted to PRL.\\[0pt] [2] Yun et al., PRL 107 (2011) [Preview Abstract] |
Thursday, November 1, 2012 11:06AM - 11:18AM |
TO6.00009: Alternative Design Concepts for the ITER Core Ion-Temperature Diagnostics Manfred Bitter, Luis Delgado-Aparicio, Philip Efthimion, Russell Feder, Kenneth Hill, David Johnson, Novimir Pablant, Brent Stratton, Kenneth Young, Peter Beiersdorfer, Eric Wang, Robin Barnsley Measurements of the ion temperature and plasma flow velocities in the ITER core must be made with spatial and temporal resolutions of 10 cm and 10 ms, respectively, over the range r/a=0-0.85. These requirements can be met by Doppler measurements of the spectral lines of neon- or helium-like, ion of tungsten, iron, and krypton with high-resolution x-ray imaging crystal spectrometers consisting of one spherically bent crystal and an array of two-dimensional pixilated detectors in a Johann configuration. One detector dimension displays spectral information and the other displays spatial information in a direction perpendicular to the toroidal magnetic field. It is challenging to implement this type of spectrometer on ITER due to neutron and gamma streaming through the viewing apertures. This paper discusses the feasibility of two alternative design concepts: a spectrometer with two concentric, spherically bent (convex and concave) crystals and a new von Hamos type spectrometer with one spherically bent (concave) crystal. [Preview Abstract] |
Thursday, November 1, 2012 11:18AM - 11:30AM |
TO6.00010: ITER Plasma at Electron Cyclotron Frequency Domain: Tokamak Core Plasma Diagnostics Based on the Synergy of Stimulated Raman and Brillouin Scatterings V. Alexander Stefan A novel plasma diagnostic method is proposed based on the synergy of stimulated Raman and Brillouin scatterings. A nonlinear plasma mode is excited in a 4-wave coupling,\footnote{V. Alexander STEFAN, \textit{Nonlinear Electromagnetic Radiation Plasma Interactions}, (S-U-Press, 2008).} leading to the appearance of suprathermal electrons and accelerated ions at the plasma edge\footnote{V. Alexander Stefan, Abstract: D1.00018 : ITER Plasma at Electron Cyclotron Frequency Domain: Stimulated Raman Scattering off Gould-Trivelpiece Modes and Generation of Suprathermal Electrons and Energetic Ions; Bulletin of the American Physical Society APS April Meeting 2011 Volume 56, Number 4.} with the parameters directly dependent on the plasma parameters in the core of tokamak. Accordingly, plasma diagnostic in the core region, (ion temperature), can be performed by the diagnostics of suprathermal electrons and accelerated ions at the edge plasma. [Preview Abstract] |
Thursday, November 1, 2012 11:30AM - 11:42AM |
TO6.00011: Tomographic reconstruction of tokamak plasma light emission using wavelet-vaguelette decomposition Kai Schneider, Romain Nguyen van yen, Nicolas Fedorczak, Frederic Brochard, Gerard Bonhomme, Marie Farge, Pascale Monier-Garbet Images acquired by cameras installed in tokamaks are difficult to interpret because the three-dimensional structure of the plasma is flattened in a non-trivial way. Nevertheless, taking advantage of the slow variation of the fluctuations along magnetic field lines, the optical transformation may be approximated by a generalized Abel transform, for which we proposed in Nguyen van yen et al., Nucl. Fus., 52 (2012) 013005, an inversion technique based on the wavelet-vaguelette decomposition. After validation of the new method using an academic test case and numerical data obtained with the Tokam 2D code, we present an application to an experimental movie obtained in the tokamak Tore Supra. A comparison with a classical regularization technique for ill-posed inverse problems, the singular value decomposition, allows us to assess the efficiency. The superiority of the wavelet-vaguelette technique is reflected in preserving local features, such as blobs and fronts, in the denoised emissivity map. [Preview Abstract] |
Thursday, November 1, 2012 11:42AM - 11:54AM |
TO6.00012: Development of an Interferometer Diagnostic for the Spheromak Turbulent Physics Experiment (STPX) Jerry Clark, J. Titus, A.B. Alexander, E.D. Mezonlin Laser interferometry is a proven method for measuring electron density in fusion plasmas. Typically, far-infrared interferometers are used because of the large phase shift due to the change in the index of refraction of the plasma and their relative insensitivity to vibrations. A two-color (CO$_{2}$: $\lambda $=10.6 $\mu $m, HeNe: $\lambda $=633 nm) interferometer has been designed for installation on STPX. The interferometer is a Mach-Zehnder configuration with a single-chord, double pass probe beam. The laser beams copropagate along a 10-meter path for vibration subtraction along with frequency modulation for heterodyne detection. Detection is carried out using a HgCdTe photoconductor for the CO$_{2}$ and a Si APD for the HeNe. The capabilities and challenges with the installation of the interferometer on STPX will be discussed. [Preview Abstract] |
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