Bulletin of the American Physical Society
62nd Annual Meeting of the APS Division of Plasma Physics
Volume 65, Number 11
Monday–Friday, November 9–13, 2020; Remote; Time Zone: Central Standard Time, USA
Session NP17: Poster Session: Magnetic Confinement: Superconducting Tokamaks (9:30am - 12:30pm)On Demand
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NP17.00001: Model Predictive Control Design for $q$-profile Shaping in EAST Zibo Wang, Hexiang Wang, Eugenio Schuster, Yao Huang, Zhengping Luo, Qiping Yuan, Bingjia Xiao, David Humphreys Extensive studies have shown that control capabilities for shaping the spatial profile of the toroidal current density, or equivalently the safety factor $q$ or the gradient of the poloidal magnetic flux, are essential for achieving advanced modes of operation, which are characterized by confinement improvement and possible steady-state operation. In this work, a model predictive control (MPC) design approach has been followed to further develop such control capabilities at EAST. A first-principles-driven, control-oriented model for the poloidal magnetic-flux profile evolution is used to design the MPC controller, which has the capability of simultaneously regulating the $q$ profile and the plasma stored energy $W$ by controlling the plasma current \textit{Ip} and the individual powers of four neutral beam injectors (NBI1L, NBI1R, NBI2L, NBI2R) and two lower hybrid wave sources (2.45 GHz, 4.60 GHz). Nonlinear simulations show that the controller can effectively regulate the $q$ profile and $W$. The proposed control law has been implemented in the recently developed Profile Control category in the EAST Plasma Control System (PCS) with the ultimate goal of testing them experimentally. Both simulation and experiment results will be reported to assess the effectiveness of the proposed control capability. [Preview Abstract] |
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NP17.00002: Investigation of LHCD Deposition Layer by Faraday-Effect Polarimetry on EAST Hui Lian, D.L. Brower, W.X. Ding, H.Q. Liu, Y.F. Wang, Y.Q. Chu, Y.X. Jie Weak or reversed magnetic shear plasma scenarios with internal transport barriers (ITB) are considered to be prime candidates for steady-state (or long-pulse) high-confinement plasma operation, which can be achieved using an optimized q profile by controlling the heating and current drive systems in tokamaks. Lower Hybrid Current Drive (LHCD) is one of the most effective ways to non-inductively drive the plasma current on EAST. Magnetic equilibrium reconstruction including multi-chord \textbf{PO}larimetry-\textbf{INT}erferometry (\textbf{POINT}) measurement constraints have been used to obtain the current density profile in previous experiments. However, stray light arising from multiple reflections in the optical path can negatively impact Faraday rotation measurements. In the EAST 2019 experiment campaign, a feedback loop between an optical lens and vacuum window was identified and reduced. With improved Faraday rotation measurements, position of LHCD deposition was investigated in detail. Initial results show the LHCD deposition position is around $\rangle =$0.5 (normalized poloidal flux), which is consistent with the simulation results. [Preview Abstract] |
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NP17.00003: Investigation of lower hybrid wave polarization in WEST G.M. Wallace, S.G. Baek, J.C. Wright, N. Bertelli, M. Ono, S. Shiraiwa, A. Ekedahl, M. Goniche, J. Hillairet, Y. Peysson, C.C. Klepper, C. Lau, E.H. Martin Theoretical studies identified the potential for $k_\perp$ rotation to impact lower hybrid (LH) wave propagation and absorption, and recent experimental analysis showed consistency between experimental LH current drive observations and modeling including $k_\perp$ rotation for Alcator C-Mod. Investigations on C-Mod indicate that rotation of $k_\perp$ may be due to scattering of the LH waves from density fluctuations. Conventional ray-tracing of LH waves assumes $k_\perp$ to be normal to the flux surface at the starting point of the ray. The DSELF diagnostic on WEST measures the LH wave electric field components ($E_R$, $E_Z$, $E_\phi$) near the antenna via dynamic Stark effect spectroscopy, which then constrains the angle of $k_\perp$ rotation used at the launch point of rays in the model ($\sim \arctan(E_Z/E_R)$). This rotation of $k_\perp$ impacts the up/down-shifts of $k_{||}$ as well as the ray trajectory itself, leading to broader or more peaked absorption depending on the direction of rotation. Ray-tracing/Fokker-Planck simulations including $k_\perp$ rotation for WEST are presented in this work and compared with experimental data. [Preview Abstract] |
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NP17.00004: Disruption Event Characterization and Forecasting in Tokamaks and Expansion to Real-Time Application* S.A. Sabbagh, J.W. Berkery, Y.S. Park, J.H. Ahn, J. Bialek, Y. Jiang, J.D. Riquezes, J.G. Bak, S.H. Hahn, J. Kim, J. Ko, J. Lee, S.W. Yoon, C. Ham, A. Kirk, L. Kogan, D. Ryan, A. Thornton, M. Boyer, K. Erickson, Z. Wang, V. Klevarova, G. Pautasso Disruption prediction and avoidance is critical for ITER and reactor-scale tokamaks. Disruption event characterization and forecasting (DECAF) results are shown for multiple tokamaks including KSTAR, MAST, NSTX, and AUG. Automated analysis of rotating MHD modes allows identification of disruption event chains including coupling, bifurcation, locking, and triggering by other MHD activity. DECAF analysis of a \textasciitilde 10$^{\mathrm{4}}$ plasma database predicts disruptions with over 91{\%} true positives and 8.7{\%} false negatives. DECAF provides an early disruption forecast (on transport timescales) for disruption avoidance through profile control. Significant new hardware and software for real-time data acquisition and analysis are being designed/written and installed on KSTAR including magnetics, plasma velocity and T$_{\mathrm{e}}$ profiles, pitch angle and magnetic fluctuation profiles, and 2D internal T$_{\mathrm{e}}$ fluctuations. Real-time magnetics data processed off-line shows excellent agreement with offline data/analysis. TRANSP predictive analyses computes plasmas at $\beta_{N}$ \textgreater 3.5 with 100{\%} non-inductive current drive: a novel operating regime for disruption prediction studies. Resistive stability including calculation of $\Delta $' by DCON is evaluated with comparison to experiment. *US DOE grants DE-SC0016614, DE-SC0018623. [Preview Abstract] |
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NP17.00005: Kinetic equilibrium reconstruction, ideal and resistive stability analyses supporting Disruption Event Characterization and Forecasting on KSTAR* Y. Jiang, S.A. Sabbagh, Y.S. Park, J.W. Berkery, J.H. Ahn, J.D. Riquezes, J. Ko, J.H. Lee, S.W. Yoon, A.H. Glasser, z. Wang Disruption prediction and avoidance are critical research elements for modern superconducting tokamak devices such as Korea Superconducting Tokamak Advanced Research (KSTAR) facility to reliably sustain long pulse and high performance plasmas. High fidelity equilibrium reconstruction is an essential requirement for accurate determination of the plasma stability and disruption prediction analyses to support the goal of continuous, disruption-free operation. Kinetic equilibrium reconstructions with excellent convergence error (from 10$^{\mathrm{-10}}$ to 10$^{\mathrm{-13}})$ are generated by using Thomson scattering, charge exchange spectroscopy data, motional Stark effect data, and all available magnetic sensors, in addition of vacuum vessel and passive plate currents following an approach used in NSTX [1]. Ideal global magnetohydrodynamic (MHD) and resistive MHD stability are studied for KSTAR plasmas to provide input to plasma disruption forecasting analysis, with the Resistive DCON code being used for these studies. Time-evolving stability analysis comparing mode activity and rational surface evolution shows the possible relation between key surfaces such as $q=$ 2 and observed plasma modes. *Supported by U.S. DOE Grant DE-SC0016614. [1] S.A. Sabbagh, A.C. Sontag, J.M. Bialek, et al., Nucl. Fusion 46 (2006) 635. [Preview Abstract] |
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NP17.00006: ELM Detection Capability for Disruption Event Characterization and Forecasting J. Butt, S.A. Sabbagh, Y.S. Park, J.H. Ahn, J.W. Berkery, Y. Jiang, J.D. Riquezes Edge-Localized Modes (ELMs) can deposit high energy loads from the plasma onto tokamak walls, and pose serious constraints to the successful operation and lifetime of reactor-scale tokamaks such as ITER. Further, ELMs can trigger more detrimental plasma instabilities that can disrupt the plasma. ELM detection is therefore an important capability to determine the threat ELMs may pose in plasma termination. The initial implementation of an ELM-detection capability for the Disruption Event Characterization and Forecasting (DECAF) code is presented. A set of criteria based on relevant plasma signals (e.g. D$_{\mathrm{\alpha }}$ light, stored energy, energy confinement time) are used to make the detection. The detector works in conjunction with other DECAF "events", which characterize disruption-relevant instabilities and other phenomena, such as the L-mode-to-H-mode transition. The presented ELM-detection capability used a database of plasmas from KSTAR and NSTX for detection validation. The ELM-detection event is also currently being developed for the real-time DECAF code as part of active real-time disruption prediction and avoidance research on KSTAR. *US DoE grant DE-SC0016614. [Preview Abstract] |
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NP17.00007: ~Rotating MHD Mode Analysis Including Real-time data on KSTAR Supporting Disruption Event Characterization and Forecasting J.D. Riquezes, S.A. Sabbagh, J.W. Berkery, Y.S. Park, J.H. Ahn, Y. Jiang, J. Butt, E. Fredrickson, J.G. Bak A low ceiling in disruptivity (i.e. percentage of shots with major disruptions in a run campaign) for reactor scale, advanced tokamak operation at high performance highlights the need for accurate forecasting tools that can guide dynamic control of auxiliary systems meant for disruption avoidance, suppression, or mitigation. Survey studies of disruption databases have shown Neoclassical Tearing Modes (NTM) to be an important precursor to disruption events. The formation of saturated magnetic island chains on rational surfaces can lead to a plasma rotation drag in which the mode locks to the wall and subsequently disrupts the plasma. A characterization of the drag dynamics, primarily based on data taken from a toroidal array of Mirnov probes, has been developed and validated using NSTX/-U and KSTAR databases. A real-time causal counterpart to the offline analysis has also been advanced that employs a real-time Mirnov probe data acquisition system and Fourier decomposition recently being developed for the KSTAR Plasma Control System (PCS). A comparison of the two approaches is made and implications for successful NTM characterization and disruption forecasting is considered. *Supported by US DOE grants DE-SC0016614 and DE-FG02-99ER54524. [Preview Abstract] |
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NP17.00008: Investigation of Neoclassical Tearing Mode Stabilization by ECCD in KSTAR Y.S. Park, S.A. Sabbagh, J.H. Ahn, J.W. Berkery, Y. Jiang, B.H. Park, M.H. Woo, M.J. Choi, H.S. Kim, J.G. Bak In KSTAR, high performance plasma operation to date has been limited by the onset of strong $m$/$n=$ 2/1 neoclassical tearing modes (NTMs) that significantly reduce the plasma confinement. Recent experiments demonstrated active stabilization of 2/1 NTMs by the electron cyclotron current drive (ECCD). In the experiment, the 2/1 mode is destabilized by an extended duration of ECH at the initial phase of the discharge which is found to play a critical role in the mode destabilization. The 2/1 mode initially has a small amplitude then it increases to greater than 10 G due to a slow plasma current ramp-up. The pre-programmed ECCD deposition location is varied in steps around the $q=$ 2 surface inferred from the ECE imaging diagnostic. The mode amplitude is reduced by 80{\%} when the ECCD is deposited on the region closest to the $q=$ 2. Rather insufficient EC-power of 0.7 MW from a single gyrotron and the co-existing modes at higher $q$-surfaces presumably having a tearing parity with $n=$ 1 could explain the observed partial stabilization. The stabilization experiment using an increased EC-power from two gyrotrons to achieve a complete mode stabilization is scheduled to run in the 2020 KSTAR operation, and the result from the run will be reported. [Preview Abstract] |
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