Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Plasma Physics
Volume 64, Number 11
Monday–Friday, October 21–25, 2019; Fort Lauderdale, Florida
Session CO6: MF: KSTAR |
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Chair: Raffi Nazikian, PPPL Room: Grand D |
Monday, October 21, 2019 2:00PM - 2:12PM |
CO6.00001: Overview of KSTAR experimental results in 2018 campaign S. W. Yoon, W. C. Kim, J. G. Kwak, J. I. Chung, H. Park Based on the refined control logics and detailed measurement capabilities, the KSTAR team has made significant contributions in 2018 campaign both in extending plasma performance as well as in physics understanding. KSTAR extended the pulse length of H-mode upto 90 seconds based on the previous high poloidal-beta discharges and issues for long-pulse is also investigated in terms of magnetic drift, effect of plasma shape and impurity accumulation. The fine tuning of the q-profile is also available from early diverting scheme and low/high qmin scenarios are successfully developed. The essential role of Alfven Eigen-modes in these discharges is also verified on the fast ion confinement using TRANSP, MEGA and kick-model simulations. For the ELM-crash suppression, using ECE 2-D imaging, changes of turbulent transport were observed at the transition into and out of ELM-crash suppression and the fluctuations were enhanced in the edge toward the ELM-crash suppression and at the same time, the rapid changes in perpendicular flow are synchronized. 3-D characteristics of the turbulent transport and flow near magnetic island was measured with imaging diagnostics and the fluctuation was localized near the magnetic island X-point and well reproduced with XGC1 and gKPSP gyrokinetic simulations. In addition, NTV offset toroidal rotation profile is measured with high resolution CES and compared with intrinsic rotation, and significantly greater co-Ip direction at the plasma boundary region was identified. [1] S. W. Yoon, Nucl. Fusion 51 (2011) 113009 (9pp) [Preview Abstract] |
Monday, October 21, 2019 2:12PM - 2:24PM |
CO6.00002: Characteristics of confinement enhancement in KSTAR hybrid scenarios Yong-Su Na, Y.H. Lee, M.S. Park, S.K. Kim, C.Y. Lee, C.S. Byeon, S.M. Yang, Y.M. Jeon, H.S. Kim, M.H. Woo, J.W. Juhn, J.H. Kim, W.H. Ko, S.W. Yoon, J.S. Kang, Raffi Nazikian Hybrid scenarios are being developed in KSTAR which exhibit H89 \textgreater 2.0, betaN \textgreater 2.4 sustained more than 5*tauE at q95 \textless 6.5 without or mild sawtooth. The origin of the confinement enhancement is studied in a slow transition phase where the interplay between core and edge pedestal appears. The power balance, the dominant core turbulence characteristics, and the edge pedestal is analyzed. The power balance analysis is done by the 1.5D transport code, ASTRA. The turbulence property is investigated by the linear gyro-kinetic simulations using GKW. The linear pedestal MHD stability is analzsed with MISHKA and EPED. The analyses show that the finite beta stabilization effect plays a role in the core turbulence and the diamagnetic flow and Shafranov shift contribute enhancement of the pedestal stability. \newline [Preview Abstract] |
Monday, October 21, 2019 2:24PM - 2:36PM |
CO6.00003: Upgrade of KSTAR MSE with background polychrometers Jinseok Ko, Steve Scott, Fred Levinton The 25-sightline Motional Stark Effect (MSE) diagnostic system equipped with the background polychrometer (BP) detectors have been installed to the KSTAR tokamak to simultaneously measure and subtract out the polarized background light in the MSE signals. A series of calibration activities performed for both the conventional (single-detector) MSE and the new MSE-BP systems include the in-vessel absolute polarization angle calibrations, beam-into-gas calibrations, and plasma-sweeping calibrations. Reliable magnetic equilbrium reconstructions with low systematic errors and quantitative estimates on the effect of polarized background noises in the carbon wall are expected from operating both MSE systems. A new real-time MSE data analysis technique under development will be discussed. [Preview Abstract] |
Monday, October 21, 2019 2:36PM - 2:48PM |
CO6.00004: Stability Research of High Beta and High Non-inductive Fraction Plasmas on KSTAR S.A. Sabbagh, Y.S. Park, J. Berkery, J.H. Ahn, Y. Jiang, J.D. Riquezes, J.G. Bak, S.H. Hahn, H.S. Han, Y. Jeon, J. Kim, H.S. Kim, J.S. Kang, J. Ko, W.H. Ko, J. Lee, B. Park, S.W. Yoon, A.H. Glasser, N. Ferraro, Z. Wang KSTAR has exceeded the ideal $n \quad =$ 1 no-wall MHD stability limit, has transiently exceeded $\beta_{\mathrm{N}} \quad =$ 4, and research now turns to sustainment. TRANSP analysis shows plasma non-inductive current fraction has reached 75 percent. Kinetic equilibrium reconstructions with MSE data for local magnetic field pitch angle constraint are used to evaluate ideal and resistive stability. Tearing modes are observed to limit $\beta _{\mathrm{N}}$. The linear stability of $m$/$n \quad =$ 2/1 modes is computed using resistive DCON and M3D-C$^{\mathrm{1}}$ and are linearly unstable with positive $\Delta \prime $ throughout the long pulse duration. The bootstrap current contribution to neoclassical tearing mode stability is computed using TRANSP. Predictive TRANSP is used to analyze the impact of the new second NBI system. At usual energy confinement quality and Greenwald density fraction, 100 percent non-inductive plasmas are found in the range $\beta_{\mathrm{N}} \quad =$ 3.5--5.0. The Generalized NTV Offset rotation produced record values of co-I$_{\mathrm{p}}$ plasma rotation by this 3D field effect reaching 40 km/s, or 2.8 kHz (8.9 times faster than ITER modeling in the pedestal region) and is envisioned as a disruption avoidance tool. An RWM active control system has been completed for use including required sensor compensation of the applied and induced AC fields from the passive stabilizers. [Preview Abstract] |
Monday, October 21, 2019 2:48PM - 3:00PM |
CO6.00005: \textbf{`Predict-first' transport and stability analyses of KSTAR plasmas supporting disruption event characterization and forecasting} J.-H. Ahn, S. A. Sabbagh, Y. S. Park, Y. Jiang, M. D. Boyer, Z. R. Wang, J. S. Kang, L. Terzolo, A. H. Glasser KSTAR plasmas have reached high stability parameters with normalized beta $\beta_{\mathrm{N}}$ reaching 4.3 at relatively low plasma internal inductance l$_{\mathrm{i}}$ ($\beta_{\mathrm{N}}$/l$_{\mathrm{i\thinspace }}$\textgreater 6), including operation at high $\beta_{\mathrm{N}}$ \textgreater $\beta_{\mathrm{N}}^{\mathrm{no-wall}}$ [1]. Transport analyses are conducted to best understand a disruption-free path toward the KSTAR design target of $\beta_{\mathrm{N}}=$ 5 while aiming to maximize the non-inductive current fraction f$_{\mathrm{NI}}$. Interpretive TRANSP code analyses indicate that f$_{\mathrm{NI}}$ in existing high-performance KSTAR plasmas have reached up to 75{\%}. The predictive capability of TRANSP is used to investigate the effects of the second NBI system recently installed on KSTAR. Extrapolations based on past KSTAR plasma global energy confinement quality (H98y2) and the Greenwald density fraction reveal possible scenarios of fully non-inductive plasmas (f$_{\mathrm{NI}}$\textasciitilde 100{\%}) in the range $\beta _{\mathrm{N}}=$ 3--5 with varied NBI source usage These `predict-first' analyses are used to design high-$\beta $ scenario development experiments for the 2019 run campaign. Ideal and resistive stability of MHD modes in these plasmas are evaluated using the DCON code including the effect of passive stabilizing structure in the device supporting disruption forecasting [1] Y.S. Park, S.A. Sabbagh, et al., Phys. Plasmas \textbf{24} (2017) 012512. [Preview Abstract] |
Monday, October 21, 2019 3:00PM - 3:12PM |
CO6.00006: Model-based control development for KSTAR enabled by TRANSP Mark Boyer, Xingqiu Yuan, Francesca Poli, Hyun-Seok Kim, Sang-hee Hahn, Eugenio Schuster, Shira Morosohk, Steve Sabbagh, Jae-heon Ahn, William Wehner Model-based control and scenario development will be critical for reaching the highest possible performance of KSTAR and future fusion devices like ITER. Key to the model-based approach is the development of a hierarchy of models of varying fidelity, execution speed, and complexity, suited to different roles in the design process. These approaches are being actively developed for KSTAR to enable reaching many of the scientific goals of the device, including ramp-up optimization, non-inductive scenario optimization, and rotation and current profile control. For this work, both analytic and data-driven reduction methods have been used, with the TRANSP integrated modeling code serving as the foundation of the modeling hierarchy. Initial control algorithms and design tools have been developed that will enable accelerated offline and real-time model-based decision making in future experimental campaigns. The reduced models and TRANSP have been integrated with the control design software Simulink. This enables a hierarchy of models to be used to validate control algorithms prior to experiments, which will accelerate the commissioning process. Several recent results in these areas will be covered along with plans for future development and applications. [Preview Abstract] |
Monday, October 21, 2019 3:12PM - 3:24PM |
CO6.00007: Impact of Alfv\'{e}nic activities to the KSTAR advanced scenario operation Jisung Kang, Junghee Kim, Tongneyol Rhee, Mario Podestà , Raffi Nazikian, Sanghee Hahn, Jinil Chung, Youngmu Jeon, J. M. Park, Y.-S. Na, Jaemin Kwon, Siwoo Yoon This study reports the results of fast-ion transport induced by Alfv\'{e}nic activities, which is one of the key to achieving KSTAR high-performance scenario and forming various q-profiles. Over the past several years, KSTAR has successfully performed the high beta experiments with suppressed high frequency MHD mode in various toroidal magnetic field and q95 regimes. It is found that the plasma performance degradation and corresponding beta loss are often accompanied by high-frequency Alfv\'{e}nic activities. Mode control experiments have also been carried out several times to recover the plasma stored energy as the Alfv\'{e}nic mode disappears utilizing control knobs such as ECH. Furthermore, a high minimum safety factor scenario has been developed by manipulating plasma current ramp-up rate and heating/shaping timing. It has been found that fast-ion transport occurring in the safety factor profile of minimum q over 2 plays a major role. Numerical investigation with NOVA / Kick-model performed, so that the strong impact of the mode was intensively analyzed. Finally, the outlook for the future advanced operation scenario of KSTAR is discussed. [Preview Abstract] |
Monday, October 21, 2019 3:24PM - 3:36PM |
CO6.00008: Search for Alfv\'{e}n Sound Eigenmodes in high beta KSTAR plasmas M. Podesta, C. Z. Cheng, G. J. Kramer, R. Nazikian, J. S. Kang, J. Kim, T. Rhee At finite plasma beta, MHD theory predicts that mixed Alfv\'{e}n/Sound Eigenmodes (ASE) can exist in frequency gaps produced by the coupling between Alfv\'{e}nic and acoustic branches. Energetic ions from Neutral Beam (NB) injection can potentially drive ASE unstable. In turn, ASE with sufficiently large amplitude can affect transport properties and confinement of NB ions, thus resulting in degraded plasma performance. ASE destabilization is explored in NB heated, high-beta KSTAR discharges aimed at long-pulse scenario optimization, in which Alfv\'{e}nic modes and other instabilities are observed to degrade fast ion confinement. The NOVA/NOVA-K codes are used in this study to identify and characterize potential instabilities in the ASE range of frequency for typical KSTAR high-beta parameters. Numerical results are compared with observations in terms of measured mode frequency, mode number spectrum and mode localization. Initial studies through the `kick model' implemented in TRANSP are then discussed to explore the potential impact of ASE on fast ion confinement, in order to identify candidate AE mitigation/suppression strategies for high performance, long-pulse KSTAR scenarios. [Preview Abstract] |
Monday, October 21, 2019 3:36PM - 3:48PM |
CO6.00009: Radiation Measurements with InfraRed imaging Video Bolometer and Filtered AXUV Arrays in KSTAR Juhyeok Jang, Byron Peterson, Seungtae Oh, Inwoo Song, Jae-Sun Park, Kiyofumi Mukai, Wonho Choe, Jayhyun Kim, Junghee Kim, Matthew Reinke, Byung-Ho Park The radiated power from the plasmas is a crucial parameter in fusion plasma study. In KSTAR, an InfraRed imaging Video Bolometers (IRVB) has been used for radiation measurement. The IRVB has advantages such as a flat sensitivity and a wide field of view. The FLIR SC7600 camera is used as a detector. The spatial and temporal resolutions are 10 ms and 9 cm, respectively. Tomographic reconstruction code provides 2-D cross-sectional radiation profiles and the total radiated power of plasmas. The KSTAR IRVB plays an important role in impurity seeding and plasma-divertor detachment experiments. In the krypton seeding experiment, ELM mitigation, suppression and ITB formation are achieved with increasing Kr radiation. IRVB also shows the poloidally asymmetric distribution of tungsten. Besides, AXUV-based fast bolometers are developed for shattered pellet injection (SPI) experiments. Poloidal and toroidal filtered AXUV arrays are designed to assess the cross sectional images and the toroidal peaking factor of SPI radiation, respectively. [Preview Abstract] |
Monday, October 21, 2019 3:48PM - 4:00PM |
CO6.00010: Gyrokinetic Simulation Study for Global Structures of Flows in KSTAR Jae-Min Kwon To predict the performance of fusion machine such as tokamak, it is critical to understand the physics of plasma turbulence and flow. In this presentation, we report recent progresses in theoretical and experimental studies of plasma flows in KSTAR tokamak. Firstly, we present gyrokinetic simulation studies for the effects of external magnetic fields on plasma flow in a KSTAR L-mode discharge. It is shown that a (2,1) magnetic field induced by the external fields changes the structures of poloidal plasma flows and these changes affect the ambient plasma fluctuations and resulting transports. Along with these simulations, we also present 2D ECEI measured electron temperature fluctuations in the corresponding KSTAR L-mode discharge, which reveals the structures of plasma flows around the (2,1) magnetic island. It is found that the flow structures from the gyrokinetic simulations are consistent with the experimental ones. Secondly, we report 2D ECEI measurement of electron temperature fluctuations in a MHD-free KSTAR L-mode plasma, which reveals quasi-static corrugations in the electron temperature profile and also hints the existence of zonal flow shearing layers corresponding to the corrugations. Very interestingly, it is found that global gyrokinetic simulations employing the experimental condition also show similar corrugation patterns and zonal flow shearing layers. More detailed results and implications of them will be discussed in the presentation. [Preview Abstract] |
Monday, October 21, 2019 4:00PM - 4:12PM |
CO6.00011: Numerical modeling of helicon wave coupling optimization and possible parasitic excitation of slow waves in KSTAR Eun-Hwa Kim, Masayuki Ono, Nicola Bertelli, Syunichi Shiraiwa, Sonjong Wang, Hyeon Park Helicon waves are being considered for plasma heating and current drive in KSTAR. While slow mode has a low cutoff density and can propagate from the antenna to the higher magnetic field/density region, helicon waves can have an evanescent layer between the antenna and the edge plasma. Therefore, both helicon and slow waves should be considered in the modeling of the KSTAR helicon experiment. We first perform wave simulations by adopting a time-dependent 1D fluid wave code to examine helicon and slow wave excitation from the antenna and subsequent propagation to the plasma core for various values of angle between normal antenna current and static magnetic field. We then examine 2D simulations of fast and slow waves using Petra-M (Physics equation translator for MFEM) developed by the RF SciDAC center (Center for Integrated Simulation of Fusion Relevant RF Actuators), which is an open source finite element analysis platform. The optimized plasma conditions for helicon wave coupling to the plasma core in KSTAR is also discussed. [Preview Abstract] |
Monday, October 21, 2019 4:12PM - 4:24PM |
CO6.00012: RMP-driven, ELM-crash-suppression on KSTAR for ITER Yongkyoon In, Alberto Loarte, Yueqiang Liu, Kimin Kim, Hyungho Lee, Sanghee Han KSTAR has made significant progress in resonant magnetic perturbation (RMP)-driven, edge-localized-mode (ELM)-crash-suppression in support of ITER. Utilizing the unique capability to realize ITER-like 3-row RMP configurations, a set of intentionally misaligned configurations (IMC) have been confirmed to be not only compatible with ELM-crash-suppression, but also effective in broadening the divertor heat fluxes with minimal electromagnetic loads [1]. In contrast, since no or little broadening was found in 2-row, IMC-driven ELM-crash-suppression, the origin of the divertor heat flux broadening is being investigated. Although ideal MHD-based field line tracing was not accompanied by any broadening feature, the inclusion of plasma rotation appears quite promising. The presence of the 3$^{\mathrm{rd}}$ row in IMC might have led to the additional deformation on magnetic topology that would have been helically structured by dominantly resonant components from 2 rows. Based on newly established ITER similar shape (ISS) plasmas, an initial attempt of n$=$1 RMP on q$_{\mathrm{95\thinspace }}$\textasciitilde 3.2 was frequently challenged by mode-locking without ELM-suppression yet. The application of n$=$2 RMP is considered more favorable not only for ELM-crash-suppression but also for ITER-like detached plasmas. [1] Y. In et al, IAEA-FEC (2018) [Preview Abstract] |
Monday, October 21, 2019 4:24PM - 4:36PM |
CO6.00013: Pedestal parameter dependences of $n$ = 1, RMP-driven, ELM-crash control on KSTAR M. Kim, W.H. Ko, Y.M. Jeon, J. Lee, S.-H. Hahn, G.Y. Park, Y. In, W. Suttrop RMP ELM-crash control is expected to be unified soon in terms of the accessibility conditions among multiple devices, helping us to predict the performance in ITER and beyond. Utilizing the improved Thomson scattering profiles in KSTAR, we have launched a rigorous edge parameter scan, focusing on a few key edge parameters, such as edge plasma rotation and collisionality ($\nu^*_e$). Based on a typical $n$=1 RMP-driven, ELM-crash-suppression condition at $q_{95}\sim$5, both parameters have been explored using a controlled divertor gas puff under $P_{NBI}$=2.85 MW, where $\nu^*_e$ varied from $\sim$0.2 to $\sim$1.0 (at $Z_{eff}$=2). The ELM-crash-suppression was observed at $0.4<\nu^{*}_e<0.7$ with $I_{RMP}$=1.7 kA/turn. Interestingly the ELM-suppression window was slightly expanded to $0.3<\nu^*_e<0.8$ by applying more $I_{RMP}$ of 2.1 kA/turn. To quantify the uncertainties of the prior estimates, a set of qualified data in previous run-campaigns are reprocessed. So far, both parameters remain in a similar range, despite more diversified conditions; $P_{NBI}=2.8-3.4$, and $q_{95}\sim5.1-5.5$. But, to ascertain whether the limits of $\nu^*_e$ exist, along with an edge rotation threshold for ITER-like low-torque plasma, additional scans are planned in KSTAR as ITPA-PEP activity. [Preview Abstract] |
Monday, October 21, 2019 4:36PM - 4:48PM |
CO6.00014: ELM Suppression and Recycling Control with Boron Nitride and Boron Powder Injection in KSTAR ELMy H-modes E. P. Gilson, H. H. Lee, A. Bortolon, W. H. Cho, A. Diallo, S. H. Hong, R. Maingi, D. K. Mansfield, A. Nagy, S. H. Park, I. W. Song, S. W. Yoon, R. Nazikian Experiments using an Impurity Powder Dropper (IPD) to introduce precise, controllable amounts of B and BN into ELMy H-Mode KSTAR discharges showed the mitigation of ELMs and reduction of recycling when B powder is dropped. ELMs are eliminated and edge fluctuations are altered when BN powder is dropped. The results indicate that the IPD can be used for intra-shot wall conditioning and ELM control. The IPD consists of four powder reservoirs that drop powder onto troughs that, when vibrated by piezoelectric actuators, drop the powder into a common drop tube and into the plasma. Powders were dropped into ~15 s duration, 1.5 MW, 500 kA plasmas. A 10 mg dose of B caused a disruption, but may have enabled ELM-free phases in several subsequent shots, likely due to reduced recycling. Several 2.5 mg doses of B during a single discharge reduced recycling as evidenced by the reduced baseline D$_\alpha$ level during the following shot. A series of 2.5 mg doses of BN, delivered in 0.1 bursts, was observed to transiently eliminate ELMs for up to 5 s, without changing the stored energy or plasma density. A continuous BN dose of 2.5 mg/s for ten seconds reduced the ELM amplitude. [Preview Abstract] |
Monday, October 21, 2019 4:48PM - 5:00PM |
CO6.00015: Non-normal fluid mode and its explosive burst in H-mode plasma boundary Gunsu Yun, Jien Lee, Minho Kim, Minuk Lee, Jaehyun Lee, Jeong-Young Ji The steep pressure boundary of H-mode tokamak plasma is dynamically unstable with a strong imprint of edge localized mode (ELM) instabilities and the related fast loss of edge confinement called ELM crash. On the KSTAR tokamak, distinct features of the ELM dynamics have been uncovered by the mm-wave imaging diagnostics and high-resolution RF spectroscopy system: quasi-steady filaments with eigenmode structure, transitions between quasi-steady states, and abrupt transition to non-modal solitary flux tube of low toroidal mode number, and finally the burst of the solitary tube. The changes of the fluid modes are accompanied by changes in turbulence and emissions of ion cyclotron harmonic waves, which can be attributed to time-varying perpendicular flow shear as the key parameter controlling the dynamical states. The burst of the solitary tube involves strong whistler-range emissions implying a localized magnetic reconnection. A model of collisionless fast reconnection incorporating both finite viscosity and radiative loss is proposed to explain the burst time scale of the solitary tube. [Preview Abstract] |
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