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Lee JE, Seo PH, Bak JG, Yun GS. A machine learning approach to identify the universality of solitary perturbations accompanying boundary bursts in magnetized toroidal plasmas. Sci Rep 2021; 11:3662. [PMID: 33574460 PMCID: PMC7878480 DOI: 10.1038/s41598-021-83192-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2020] [Accepted: 01/28/2021] [Indexed: 11/09/2022] Open
Abstract
Experimental observations assisted by 2-D imaging diagnostics on the KSTAR tokamak show that a solitary perturbation (SP) emerges prior to a boundary burst of magnetized toroidal plasmas, which puts forward SP as a potential candidate for the burst trigger. We have constructed a machine learning (ML) model based on a convolutional deep neural network architecture for a statistical study to identify the SP as a boundary burst trigger. The ML model takes sequential signals detected from 19 toroidal Mirnov coils as input and predicts whether each temporal frame corresponds to an SP. We trained the network in a supervised manner on a training set consisting of real signals with manually annotated SP locations and synthetic burst signals. The trained model achieves high performances in various metrics on a test data set. We also demonstrated the reliability of the model by visualizing the discriminative parts of the input signals that the model recognizes. Finally, we applied the trained model to new data from KSTAR experiments, which were never seen during training, and confirmed that the large burst at the plasma boundary that can fatally damage the fusion device always involves the emergence of SP. This result suggests that the SP is a key to understanding and controlling of the boundary burst in magnetized toroidal plasmas.
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Affiliation(s)
- J E Lee
- Pohang University of Science and Technology, Pohang, 37673, Korea
| | - P H Seo
- Pohang University of Science and Technology, Pohang, 37673, Korea
| | - J G Bak
- National Fusion Research Institute, Daejeon, 34133, Korea
| | - G S Yun
- Pohang University of Science and Technology, Pohang, 37673, Korea.
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Nam YB, Park HK, Lee W, Yun GS, Kim M, Sabot R, Elbeze D, Lotte P, Shen J. Compact ECEI system with in-vessel reflective optics for WEST. Rev Sci Instrum 2016; 87:11E135. [PMID: 27910691 DOI: 10.1063/1.4962941] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
An electron cyclotron emission imaging (ECEI) diagnostic system for WEST (W Environment for Steady state Tokamak) is under development to study the MHD instabilities affected by tungsten impurities. The system will provide 2-D Te fluctuation images (width × height = ∼18 cm × ∼ 34 cm at low field side and ∼13 cm × ∼ 39 cm at high field side) from a poloidal cross section with high spatial (≤1.7 cm) and temporal (≤2 μs) resolutions. While the key concept and electronic structure are similar to that of prior ECEI systems on other tokamak devices such as KSTAR, DIII-D, or ASDEX-U, part of the imaging optics have to be placed inside the vacuum vessel in order to resolve issues on limited installation space and longer beam path to the detector position. The in-vessel optics consisting of two large curvature-radius mirrors are expected to withstand the extreme heating on long-pulse operation scenario (∼1000 s). The out-vessel optical housing is constructed as compact as possible to remove easily from the installation site in case of necessity. Commissioning of the system is scheduled on the second experimental WEST campaign end of 2017.
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Affiliation(s)
- Y B Nam
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, South Korea
| | - H K Park
- Ulsan National Institute of Science and Technology, Ulsan 44919, South Korea
| | - W Lee
- Ulsan National Institute of Science and Technology, Ulsan 44919, South Korea
| | - G S Yun
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, South Korea
| | - M Kim
- Ulsan National Institute of Science and Technology, Ulsan 44919, South Korea
| | - R Sabot
- CEA, IRFM, F-13108 Saint Paul lez Durance, France
| | - D Elbeze
- CEA, IRFM, F-13108 Saint Paul lez Durance, France
| | - P Lotte
- CEA, IRFM, F-13108 Saint Paul lez Durance, France
| | - J Shen
- CEA, IRFM, F-13108 Saint Paul lez Durance, France
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Lee W, Leem J, Yun GS, Park HK, Ko SH, Wang WX, Budny RV, Luhmann NC, Kim KW. Ion gyroscale fluctuation measurement with microwave imaging reflectometer on KSTAR. Rev Sci Instrum 2016; 87:11E134. [PMID: 27910475 DOI: 10.1063/1.4963152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Ion gyroscale turbulent fluctuations with the poloidal wavenumber kθ ∼ 3 cm-1 have been measured in the core region of the neutral beam (NB) injected low confinement (L-mode) plasmas on Korea superconducting tokamak advanced research. The turbulence poloidal wavenumbers are deduced from the frequencies and poloidal rotation velocities in the laboratory frame, measured by the multichannel microwave imaging reflectometer. Linear and nonlinear gyrokinetic simulations also predict the unstable modes with the normalized wavenumber kθρs ∼ 0.4, consistent with the measurement. Comparison of the measured frequencies with the intrinsic mode frequencies from the linear simulations indicates that the measured ones are primarily due to the E × B flow velocity in the NB-injected fast rotating plasmas.
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Affiliation(s)
- W Lee
- National Fusion Research Institute, Daejeon 34133, South Korea
| | - J Leem
- Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, South Korea
| | - G S Yun
- Pohang University of Science and Technology, Pohang, Gyeongbuk 37673, South Korea
| | - H K Park
- National Fusion Research Institute, Daejeon 34133, South Korea
| | - S H Ko
- National Fusion Research Institute, Daejeon 34133, South Korea
| | - W X Wang
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - R V Budny
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
| | - N C Luhmann
- University of California at Davis, Davis, California 95616, USA
| | - K W Kim
- Kyungpook National University, Daegu 41566, South Korea
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Nam YB, Lee DJ, Lee J, Kim C, Yun GS, Lee W, Park HK. New compact and efficient local oscillator optic system for the KSTAR electron cyclotron emission imaging system. Rev Sci Instrum 2016; 87:11E130. [PMID: 27910535 DOI: 10.1063/1.4961290] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Electron cyclotron emission imaging (ECEI) diagnostic on Korean Superconducting Tokamak Advanced Research utilizes quasi-optical heterodyne-detection method to measure 2D (vertical and radial) Te fluctuations from two toroidally separated poloidal cross section of the plasma. A cylindrical lens local oscillator (LO) optics with optical path length (OPL) 2-2.5 m has been used in the current ECEI system to couple the LO source to the 24 vertically aligned array of ECE detectors. For efficient and compact LO optics employing the Powell lens is proposed so that the OPL of the LO source is significantly reduced from ∼2.0 m to 0.4 m with new optics. The coupling efficiency of the LO source is expected to be improved especially at the edge channels. Results from the optical simulation together with the laboratory test of the prototype optics will be discussed in this paper.
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Affiliation(s)
- Y B Nam
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, South Korea
| | - D J Lee
- Ulsan National Institute of Science and Technology, Ulsan 44919, South Korea
| | - J Lee
- Ulsan National Institute of Science and Technology, Ulsan 44919, South Korea
| | - C Kim
- Pennsylvania State University, Old Main, State College, Pennsylvania 16801, USA
| | - G S Yun
- Department of Physics, Pohang University of Science and Technology, Pohang 37673, South Korea
| | - W Lee
- Ulsan National Institute of Science and Technology, Ulsan 44919, South Korea
| | - H K Park
- Ulsan National Institute of Science and Technology, Ulsan 44919, South Korea
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Choi MJ, Park HK, Yun GS, Nam YB, Choe GH, Lee W, Jardin S. Post calibration of the two-dimensional electron cyclotron emission imaging instrument with electron temperature characteristics of the magnetohydrodynamic instabilities. Rev Sci Instrum 2016; 87:013506. [PMID: 26827320 DOI: 10.1063/1.4940030] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/04/2015] [Accepted: 01/05/2016] [Indexed: 06/05/2023]
Abstract
The electron cyclotron emission imaging (ECEI) instrument is widely used to study the local electron temperature (Te) fluctuations by measuring the ECE intensity IECE ∝ Te in tokamak plasmas. The ECEI measurement is often processed in a normalized fluctuation quantity against the time averaged value due to complication in absolute calibration. In this paper, the ECEI channels are relatively calibrated using the flat Te assumption of the sawtooth crash or the tearing mode island and a proper extrapolation. The 2-D relatively calibrated electron temperature (Te,rel) images are reconstructed and the displacement amplitude of the magnetohydrodynamic modes can be measured for the accurate quantitative growth analysis.
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Affiliation(s)
- M J Choi
- National Fusion Research Institute, Daejeon 34133, South Korea
| | - H K Park
- National Fusion Research Institute, Daejeon 34133, South Korea
| | - G S Yun
- Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784, South Korea
| | - Y B Nam
- Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784, South Korea
| | - G H Choe
- Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784, South Korea
| | - W Lee
- Ulsan National Institute of Science and Technology, Ulsan 689-798, South Korea
| | - S Jardin
- Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
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Yun GS, Lee W, Choi MJ, Lee J, Kim M, Leem J, Nam Y, Choe GH, Park HK, Park H, Woo DS, Kim KW, Domier CW, Luhmann NC, Ito N, Mase A, Lee SG. Quasi 3D ECE imaging system for study of MHD instabilities in KSTAR. Rev Sci Instrum 2014; 85:11D820. [PMID: 25430233 DOI: 10.1063/1.4890401] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
A second electron cyclotron emission imaging (ECEI) system has been installed on the KSTAR tokamak, toroidally separated by 1/16th of the torus from the first ECEI system. For the first time, the dynamical evolutions of MHD instabilities from the plasma core to the edge have been visualized in quasi-3D for a wide range of the KSTAR operation (B0 = 1.7∼3.5 T). This flexible diagnostic capability has been realized by substantial improvements in large-aperture quasi-optical microwave components including the development of broad-band polarization rotators for imaging of the fundamental ordinary ECE as well as the usual 2nd harmonic extraordinary ECE.
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Affiliation(s)
- G S Yun
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - W Lee
- Ulsan National Institute of Science and Technology, Ulsan 689-798, Korea
| | - M J Choi
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - J Lee
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - M Kim
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - J Leem
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - Y Nam
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - G H Choe
- Department of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
| | - H K Park
- Ulsan National Institute of Science and Technology, Ulsan 689-798, Korea
| | - H Park
- School of Electrical Engineering, Kyungpook National University, Daegu 702-701, Korea
| | - D S Woo
- School of Electrical Engineering, Kyungpook National University, Daegu 702-701, Korea
| | - K W Kim
- School of Electrical Engineering, Kyungpook National University, Daegu 702-701, Korea
| | - C W Domier
- Department of Electrical and Computer Engineering, University of California, Davis, California 95616, USA
| | - N C Luhmann
- Department of Electrical and Computer Engineering, University of California, Davis, California 95616, USA
| | - N Ito
- KASTEC, Kyushu University, Kasuga-shi, Fukuoka 812-8581, Japan
| | - A Mase
- Ube National College of Technology, Ube-shi, Yamaguchi 755-8555, Japan
| | - S G Lee
- National Fusion Research Institute, Daejeon 305-333, Korea
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Lee J, Yun GS, Lee JE, Kim M, Choi MJ, Lee W, Park HK, Domier CW, Luhmann NC, Sabbagh SA, Park YS, Lee SG, Bak JG. Toroidal mode number estimation of the edge-localized modes using the KSTAR 3-D electron cyclotron emission imaging system. Rev Sci Instrum 2014; 85:063505. [PMID: 24985817 DOI: 10.1063/1.4883180] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
A new and more accurate technique is presented for determining the toroidal mode number n of edge-localized modes (ELMs) using two independent electron cyclotron emission imaging (ECEI) systems in the Korea Superconducting Tokamak Advanced Research (KSTAR) device. The technique involves the measurement of the poloidal spacing between adjacent ELM filaments, and of the pitch angle α* of filaments at the plasma outboard midplane. Equilibrium reconstruction verifies that α* is nearly constant and thus well-defined at the midplane edge. Estimates of n obtained using two ECEI systems agree well with n measured by the conventional technique employing an array of Mirnov coils.
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Affiliation(s)
- J Lee
- Pohang University of Science and Technology, Pohang 790-784, South Korea
| | - G S Yun
- Pohang University of Science and Technology, Pohang 790-784, South Korea
| | - J E Lee
- Pohang University of Science and Technology, Pohang 790-784, South Korea
| | - M Kim
- Pohang University of Science and Technology, Pohang 790-784, South Korea
| | - M J Choi
- Pohang University of Science and Technology, Pohang 790-784, South Korea
| | - W Lee
- Pohang University of Science and Technology, Pohang 790-784, South Korea
| | - H K Park
- Ulsan National Institute of Science and Technology, Ulsan 689-798, South Korea
| | - C W Domier
- University of California at Davis, Davis, California 95616, USA
| | - N C Luhmann
- University of California at Davis, Davis, California 95616, USA
| | - S A Sabbagh
- Columbia University, New York, New York 10027, USA
| | - Y S Park
- Columbia University, New York, New York 10027, USA
| | - S G Lee
- National Fusion Research Institute, Daejeon 305-333, South Korea
| | - J G Bak
- National Fusion Research Institute, Daejeon 305-333, South Korea
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Seol J, Lee SG, Park BH, Lee HH, Terzolo L, Shaing KC, You KI, Yun GS, Kim CC, Lee KD, Ko WH, Kwak JG, Kim WC, Oh YK, Kim JY, Kim SS, Ida K. Effects of electron-cyclotron-resonance-heating-induced internal kink mode on the toroidal rotation in the KSTAR Tokamak. Phys Rev Lett 2012; 109:195003. [PMID: 23215391 DOI: 10.1103/physrevlett.109.195003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2012] [Indexed: 06/01/2023]
Abstract
It is observed that the magnitude of the toroidal rotation speed is reduced by the central electron cyclotron resonance heating (ECRH) regardless of the direction of the toroidal rotation. The magnetohydrodynamics activities generally appear with the rotation change due to ECRH. It is shown that the internal kink mode is induced by the central ECRH and breaks the toroidal symmetry. When the magnetohydrodynamics activities are present, the toroidal plasma viscosity is not negligible. The observed effects of ECRH on the toroidal plasma rotation are explained by the neoclassical toroidal viscosity in this Letter. It is found that the neoclassical toroidal viscosity torque caused by the internal kink mode damps the toroidal rotation.
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Affiliation(s)
- J Seol
- National Fusion Research Institute, Gwahangno 113, Yuseong-gu, Daejeon 305-333, Korea
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Yun GS, Park HK, Lee W, Choi MJ, Choe GH, Park S, Bae YS, Lee KD, Yoon SW, Jeon YM, Domier CW, Luhmann NC, Tobias B, Donné AJH. Appearance and dynamics of helical flux tubes under electron cyclotron resonance heating in the core of KSTAR plasmas. Phys Rev Lett 2012; 109:145003. [PMID: 23083252 DOI: 10.1103/physrevlett.109.145003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2011] [Indexed: 06/01/2023]
Abstract
Dual (or sometimes multiple) flux tubes (DFTs) have been observed in the core of sawtoothing KSTAR tokamak plasmas with electron cyclotron resonance heating. The time evolution of the flux tubes visualized by a 2D electron cyclotron emission imaging diagnostic typically consists of four distinctive phases: (1) growth of one flux tube out of multiple small flux tubes during the initial buildup period following a sawtooth crash, resulting in a single dominant flux tube along the m/n=1/1 helical magnetic field lines, (2) sudden rapid growth of another flux tube via a fast heat transfer from the first one, resulting in approximately identical DFTs, (3) coalescence of the two flux tubes into a single m/n=1/1 flux tube resembling the internal kink mode in the normal sawteeth, which is explained by a model of two current-carrying wires confined on a flux surface, and (4) fast localized crash of the merged flux tube similar to the standard sawtooth crash. The dynamics of the DFTs implies that the internal kink mode is not a unique prerequisite to the sawtooth crash, providing a new insight on the control of the sawtooth.
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Affiliation(s)
- G S Yun
- POSTECH, Pohang 790-784, Korea.
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Nam Y, Lee W, Yun GS, Park HK, Elbeze D, Segui JL, Sabot R, Chenevoix JP. Design of the reflective optics for Tore Supra ECEI system. Rev Sci Instrum 2012; 83:10E318. [PMID: 23126976 DOI: 10.1063/1.4732852] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
A 2D electron cyclotron emission (ECE) imaging system for Tore Supra is under design for studying the MHD physics of the magnetically confined plasma such as sawteeth, tearing modes, and turbulent fluctuations. Complex beam path due to the tight access in Tore Supra led to the design of reflective optics made of 6 or more large cylindrical∕flat mirrors. The total path length of the ECE beam is about 11 m, including almost 4 m inside the vacuum vessel. The imaging property of the optics has been estimated using the Gaussian beam simulation and ray transfer analysis. The possible setups for the optical alignment of the diagnostic and the operation scenarios with single- or dual-array measurement system are discussed.
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Affiliation(s)
- Y Nam
- Department of Physics, POSTECH, Pohang, Gyeongbuk 790-784, South Korea
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Jeon YM, Park JK, Yoon SW, Ko WH, Lee SG, Lee KD, Yun GS, Nam YU, Kim WC, Kwak JG, Lee KS, Kim HK, Yang HL. Suppression of edge localized modes in high-confinement KSTAR plasmas by nonaxisymmetric magnetic perturbations. Phys Rev Lett 2012; 109:035004. [PMID: 22861864 DOI: 10.1103/physrevlett.109.035004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2011] [Indexed: 06/01/2023]
Abstract
Edge localized modes (ELMs) in high-confinement mode plasmas were completely suppressed in KSTAR by applying n=1 nonaxisymmetric magnetic perturbations. Initially, the ELMs were intensified with a reduction of frequency, but completely suppressed later. The electron density had an initial 10% decrease followed by a gradual increase as ELMs were suppressed. Interesting phenomena such as a saturated evolution of edge T(e) and broadband changes of magnetic fluctuations were observed, suggesting the change of edge transport by the applied magnetic perturbations.
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Affiliation(s)
- Y M Jeon
- National Fusion Research Institute, Daejeon, Korea.
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Yun GS, Lee W, Choi MJ, Lee J, Park HK, Tobias B, Domier CW, Luhmann NC, Donné AJH, Lee JH. Two-dimensional visualization of growth and burst of the edge-localized filaments in KSTAR H-mode plasmas. Phys Rev Lett 2011; 107:045004. [PMID: 21867016 DOI: 10.1103/physrevlett.107.045004] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2011] [Indexed: 05/31/2023]
Abstract
The filamentary nature and dynamics of edge-localized modes (ELMs) in the KSTAR high-confinement mode plasmas have been visualized in 2D via electron cyclotron emission imaging. The ELM filaments rotating with a net poloidal velocity are observed to evolve in three distinctive stages: initial linear growth, interim quasisteady state, and final crash. The crash is initiated by a narrow fingerlike perturbation growing radially from a poloidally elongated filament. The filament bursts through this finger, leading to fast and collective heat convection from the edge region into the scrape-off layer, i.e., ELM crash.
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Affiliation(s)
- G S Yun
- POSTECH, Pohang, Republic of Korea
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Yun GS, Bac LH, Kim JS, Kwon YS, Choi HS, Kim JC. Effect of synthetic temperature on the dispersion stability of gold nanocolloid produced via electrical explosion of wire. J Nanosci Nanotechnol 2011; 11:6429-6432. [PMID: 22121729 DOI: 10.1166/jnn.2011.4394] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
In this study, gold nanocolloid was produced via the electrical explosion of wire in water, for the purpose of medical treatment. Thus, the use of other additives was avoided to stabilize the gold nanocolloid. The temperature of the water that was to be used for explosion was changed, and its effect on the stability of the gold nanocolloid was investigated. The synthetic temperature was varied from ice temperature to 80 degrees C. The morphology and particle size were studied using a transmission electron microscope. The UV-Vis spectra confirmed the formation of gold nanoparticles in the water. The stability of the gold nanocolloid was estimated using the zeta-potential and Turbiscan methods. The results showed that the synthetic temperature affected the stability of the gold nanocolloid. The TEM images of the gold nanoparticles prepared at low temperatures (0 and 20 degrees C) have several big particles. But, when the synthetic temperature was increased to 80 degrees C, most of the nanoparticles formed a spherical shape, without neck connection. Better stability was obtained in the gold nanocolloid sample prepared at a higher temperature. The gold nanocolloid that was synthesized at 80 degrees C was stable for more than three months, with small sedimentation.
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Affiliation(s)
- G S Yun
- School of Materials Science and Engineering, University of Ulsan, Daehak-ro 102, Nam-gu, Ulsan 680-749, South Korea
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Bac LH, Yun GS, Kim JS, Choi HS, Kim JC. Preparation and stability of gold colloid by electrical explosion of wire in various media. J Nanosci Nanotechnol 2011; 11:1730-1733. [PMID: 21456278 DOI: 10.1166/jnn.2011.3345] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Gold colloids were prepared by electrical explosion of wire in various media: cold water (0 degrees C), room temperature water (25 degrees C), hot water (80 degrees C), 0.01 M polysorbate surfactant 20 (TW 20) solution, mixture of 0.01 M TW 20 and 0.01 M ascorbic acid. The size distribution of nanoparticles measured by transmission electron microscope was found to shift to a smaller size with a decrease of temperature and a presence of TW 20 surfactant. The multiple light scattering results showed that medium temperature and ambient medium of explosion process is much influence on the stability of colloid. The gold colloid prepared in cold water is unstable in comparison with one prepared in warm and hot water. The best stability of gold colloid obtained with explosion medium of TW 20 and ascorbic acid solution.
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Affiliation(s)
- L H Bac
- School of Materials Science and Engineering, University of Ulsan, San-29, Mugeo-2Dong, Nam-Ku, Ulsan 680-749, Korea
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Lee W, Yun GS, Nam Y, Hong I, Kim JB, Park HK, Tobias B, Liang T, Domier CW, Luhmann NC. Comparative study between the reflective optics and lens based system for microwave imaging system on KSTAR. Rev Sci Instrum 2010; 81:10D932. [PMID: 21033960 DOI: 10.1063/1.3491189] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Recently, two-dimensional microwave imaging diagnostics such as the electron cyclotron emission imaging (ECEI) system and microwave imaging reflectometry (MIR) have been developed to study magnetohydrodynamics instabilities and turbulence in magnetically confined plasmas. These imaging systems utilize large optics to collect passive emission or reflected radiation. The design of this optics can be classified into two different types: reflective or refractive optical systems. For instance, an ECEI/MIR system on the TEXTOR tokamak [Park et al., Rev. Sci. Instrum. 75, 3787 (2004)] employed the reflective optics which consisted of two large mirrors, while the TEXTOR ECEI upgrade [B. Tobias et al., Rev. Sci. Instrum. 80, 093502 (2009)] and systems on DIII-D, ASDEX-U, and KSTAR adopted refractive systems. Each system has advantages and disadvantages in the standing wave problem and optical aberrations. In this paper, a comparative study between the two optical systems has been performed in order to design a MIR system for KSTAR.
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Affiliation(s)
- W Lee
- POSTECH, Pohang, Gyeongbuk 790-784, Republic of Korea.
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Park HK, Hong I, Kim M, Yun GS, Lee W, Kim J, Tobias B, Domier CW, Luhmann NC, Kim KW. Microwave imaging reflectometry studies for turbulence diagnostics on KSTAR. Rev Sci Instrum 2010; 81:10D933. [PMID: 21033961 DOI: 10.1063/1.3499606] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The first prototype microwave imaging reflectometry (MIR) system [H. Park et al., Rev. Sci. Instrum. 74, 4239 (2004)] clearly demonstrated the shortcomings of conventional reflectometry when the probe beam encountered a large amplitude and/or high fluctuation wavenumber at the reflection layer in laboratory tests, the distinctive advantages shown in these tests were not fully realized in the plasma operation. To understand the discrepancies, the MIR system performance has been thoroughly investigated at POSTECH. In this paper, a possible cause of the MIR performance degradation on TEXTOR will be presented together with a concept of multifrequency MIR system design that will be developed for KSTAR.
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Affiliation(s)
- H K Park
- Pohang University of Science and Technology, Pohang, Gyeongbuk 790-784, Korea.
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17
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Choi MJ, Yun GS, Park HK, Jeon YM, Jeong SH. Relatively scaled ECE temperature profiles of KSTAR plasmas. Rev Sci Instrum 2010; 81:10D934. [PMID: 21033962 DOI: 10.1063/1.3479005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
A scheme to obtain relatively scaled profiles of electron cyclotron emission (ECE) temperature directly from uncalibrated raw radiometer data is proposed and has been tested for the 2009 campaign KSTAR plasmas. The proposed method utilizes a position controlled system to move the plasma adiabatically and compares ECE radiometer channels at the same relative radial positions assuming the profile consistency during the adiabatic change. This scaling method is an alternative solution when an absolute calibration is unreliable or too time consuming. The application to the two dimensional ECE imaging data, wherein calibration is extremely difficult, may also prove to be useful.
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Affiliation(s)
- M J Choi
- Department of Physics, Pohang University of Science and Technology, Pohang, Gyungbuk 790-784, South Korea
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Liang T, Tobias B, Kong X, Domier CW, Luhmann NC, Lee W, Yun GS, Park HK. Innovations in optical coupling of the KSTAR electron cyclotron emission imaging diagnostic. Rev Sci Instrum 2010; 81:10D909. [PMID: 21033941 DOI: 10.1063/1.3478637] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The installation of a new electron cyclotron emission imaging diagnostic for the Korea Superconducting Tokamak Advanced Research (KSTAR) is underway, making use of a unique optical port cassette design, which allows placement of refractive elements inside the cryostat region without adverse effects. The result is unprecedented window access for the implementation of a state of the art imaging diagnostic. A dual-array optical design has been developed, capable of simultaneously imaging the high and low field sides of the plasma with independent features of focal plane translation, vertical zoom, and radial channel spacing. The number of translating optics has been minimized by making use of a zoom lens triplet and parabolic plasma facing lens for maximum channel uniformity over a continuous vertical zoom range of 3:1. The simulated performance of this design is presented along with preliminary laboratory characterization data.
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Affiliation(s)
- T Liang
- University of California at Davis, Davis, California 95616, USA.
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Kim JB, Lee W, Yun GS, Park HK, Domier CW, Luhmann NC. Data acquisition and processing system of the electron cyclotron emission imaging system of the KSTAR tokamak. Rev Sci Instrum 2010; 81:10D931. [PMID: 21033959 DOI: 10.1063/1.3479023] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
A new innovative electron cyclotron emission imaging (ECEI) diagnostic system for the Korean Superconducting Tokamak Advanced Research (KSTAR) produces a large amount of data. The design of the data acquisition and processing system of the ECEI diagnostic system should consider covering the large data production and flow. The system design is based on the layered structure scalable to the future extension to accommodate increasing data demands. Software architecture that allows a web-based monitoring of the operation status, remote experiment, and data analysis is discussed. The operating software will help machine operators and users validate the acquired data promptly, prepare next discharge, and enhance the experiment performance and data analysis in a distributed environment.
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Affiliation(s)
- J B Kim
- Department of Physics, POSTECH, San-31, Hyoja-dong, Nam-gu, Pohang, Kyungbuk 790-784, South Korea.
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20
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Yun GS, Lee W, Choi MJ, Kim JB, Park HK, Domier CW, Tobias B, Liang T, Kong X, Luhmann NC, Donné AJH. Development of KSTAR ECE imaging system for measurement of temperature fluctuations and edge density fluctuations. Rev Sci Instrum 2010; 81:10D930. [PMID: 21033958 DOI: 10.1063/1.3483209] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The ECE imaging (ECEI) diagnostic tested on the TEXTOR tokamak revealed the sawtooth reconnection physics in unprecedented detail, including the first observation of high-field-side crash and collective heat transport [H. K. Park, N. C. Luhmann, Jr., A. J. H. Donné et al., Phys. Rev. Lett. 96, 195003 (2006)]. An improved ECEI system capable of visualizing both high- and low-field sides simultaneously with considerably better spatial coverage has been developed for the KSTAR tokamak in order to capture the full picture of core MHD dynamics. Direct 2D imaging of other MHD phenomena such as tearing modes, edge localized modes, and even Alfvén eigenmodes is expected to be feasible. Use of ECE images of the optically thin edge region to recover 2D electron density changes during L/H mode transitions is also envisioned, providing powerful information about the underlying physics. The influence of density fluctuations on optically thin ECE is discussed.
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Affiliation(s)
- G S Yun
- Pohang University of Science and Technology, Pohang, Gyungbuk 790-784, South Korea.
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21
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Lei L, Tobias B, Domier CW, Luhmann NC, Kramer GJ, Valeo EJ, Lee W, Yun GS, Park HK. A synthetic diagnostic for the evaluation of new microwave imaging reflectometry diagnostics for DIII-D and KSTAR. Rev Sci Instrum 2010; 81:10D904. [PMID: 21033936 DOI: 10.1063/1.3464461] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The first microwave imaging reflectometry (MIR) system for characterization of fluctuating plasma density has been implemented for the TEXTOR tokamak [H. Park et al., Rev. Sci. Instrum. 75, 3787 (2004)]; an improved MIR system will be installed on DIII-D and KSTAR. The central issue remains in preserving phase information by addressing antenna coupling between the reflection layer and the detector array in the presence of plasma turbulence. A synthetic diagnostic making use of coupled full-wave diffractive codes has been developed in geometries and applied to a variety of optical arrangements. The effectiveness of each scheme is quantitatively compared with respect to the fluctuation levels accessible in the simulation.
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Affiliation(s)
- L Lei
- University of California at Davis, Davis, California 95616, USA
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22
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Tobias B, Domier CW, Liang T, Kong X, Yu L, Yun GS, Park HK, Classen IGJ, Boom JE, Donné AJH, Munsat T, Nazikian R, Van Zeeland M, Boivin RL, Luhmann NC. Commissioning of electron cyclotron emission imaging instrument on the DIII-D tokamak and first data. Rev Sci Instrum 2010; 81:10D928. [PMID: 21033956 DOI: 10.1063/1.3460456] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
A new electron cyclotron emission imaging diagnostic has been commissioned on the DIII-D tokamak. Dual detector arrays provide simultaneous two-dimensional images of T(e) fluctuations over radially distinct and reconfigurable regions, each with both vertical and radial zoom capability. A total of 320 (20 vertical×16 radial) channels are available. First data from this diagnostic demonstrate the acquisition of coherent electron temperature fluctuations as low as 0.1% with excellent clarity and spatial resolution. Details of the diagnostic features and capabilities are presented.
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Affiliation(s)
- B Tobias
- University of California at Davis, Davis, California 95616, USA.
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Bellan PM, Yun GS, Tripathi SKP, Stenson EV. Tendency of MHD Forces to Create Localized, Collimated Plasma-filled Flux Tubes & Ion Orbit Instability in a Flux Tube. J Fusion Energ 2007. [DOI: 10.1007/s10894-007-9111-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Tripathi SKP, Bellan PM, Yun GS. Observation of kinetic plasma jets in a coronal-loop simulation experiment. Phys Rev Lett 2007; 98:135002. [PMID: 17501208 DOI: 10.1103/physrevlett.98.135002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Revised: 06/03/2006] [Indexed: 05/15/2023]
Abstract
Under certain conditions an intense kinetic plasma jet is observed to emerge from the apex of laboratory simulations of coronal plasma loops. Analytic and numerical models show that these jets result from a particle orbit instability in a helical magnetic field whereby magnetic forces radially eject rather than confine ions with sufficiently large countercurrent axial velocity.
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Affiliation(s)
- S K P Tripathi
- Applied Physics, California Institute of Technology, Pasadena, CA 91125, USA
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Bellan PM, You S, Yun GS. Measurements of Plasma Jets and Collimated Flux Tubes that are the Precursors of Spheromak Self-organization. J Fusion Energ 2006. [DOI: 10.1007/s10894-006-9048-z] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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26
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You S, Yun GS, Bellan PM. Dynamic and stagnating plasma flow leading to magnetic-flux-tube collimation. Phys Rev Lett 2005; 95:045002. [PMID: 16090816 DOI: 10.1103/physrevlett.95.045002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2005] [Indexed: 05/03/2023]
Abstract
Highly collimated, plasma-filled magnetic-flux tubes are frequently observed on galactic, stellar, and laboratory scales. We propose that a single, universal magnetohydrodynamic pumping process explains why such collimated, plasma-filled magnetic-flux tubes are ubiquitous. Experimental evidence from carefully diagnosed laboratory simulations of astrophysical jets confirms this assertion and is reported here. The magnetohydrodynamic process pumps plasma into a magnetic-flux tube and the stagnation of the resulting flow causes this flux tube to become collimated.
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Affiliation(s)
- S You
- California Institute of Technology, Pasadena, 91125, USA
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