1
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Hidalgo-Salaverri J, Rueda-Rueda J, Galdon-Quiroga J, Cano-Megias P, Viezzer E, Garcia-Dominguez J, Silvagni D, Videla-Trevin M, Oyola P, Ayllon-Guerola J, Garcia-Munoz M, Happel T. First measurements of a scintillator-based fast-ion loss detector in reversed Ip/Bt at the ASDEX Upgrade tokamak. FUSION ENGINEERING AND DESIGN 2023. [DOI: 10.1016/j.fusengdes.2023.113661] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/07/2023]
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2
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Very High spatial Resolution IR thermography diagnostic positioning system upgrade in WEST Tokamak. FUSION ENGINEERING AND DESIGN 2023. [DOI: 10.1016/j.fusengdes.2023.113526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
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3
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Analytical expressions for thermophysical properties of solid and liquid beryllium relevant for fusion applications. NUCLEAR MATERIALS AND ENERGY 2022. [DOI: 10.1016/j.nme.2022.101195] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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4
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Hayashi Y, Kobayashi M, Mukai K, Masuzaki S, Murase T. Divertor heat load distribution measurements with infrared thermography in the LHD helical divertor. FUSION ENGINEERING AND DESIGN 2021. [DOI: 10.1016/j.fusengdes.2021.112235] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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5
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Faitsch M, Eich T, Harrer G, Wolfrum E, Brida D, David P, Griener M, Stroth U. Broadening of the power fall-off length in a high density, high confinement H-mode regime in ASDEX Upgrade. NUCLEAR MATERIALS AND ENERGY 2021. [DOI: 10.1016/j.nme.2020.100890] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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6
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Aumeunier MH, Gerardin J, Talatizi C, Le Bohec M, Ben Yaala M, Marot L, Loarer T, Mitteau R, Gaspar J, Rigollet F, Courtois X, Houry M, Herrmann A, Faitsch M. Infrared thermography in metallic environments of WEST and ASDEX Upgrade. NUCLEAR MATERIALS AND ENERGY 2021. [DOI: 10.1016/j.nme.2020.100879] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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7
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Zhang JY, Zhang B, Gong X, Chang J, Jia MN, Liu C, Liang RR, Chen WL, Wu CH, Feng S. Development of a new dynamic foveated imager on wide-angle infra-red thermography system to improve local spatial resolution in EAST. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2020; 91:116101. [PMID: 33261436 DOI: 10.1063/5.0013212] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2020] [Accepted: 10/14/2020] [Indexed: 06/12/2023]
Abstract
A new dynamic foveated imager has been developed and commissioned on the wide-angle infra-red thermography system in the Experimental Advanced Superconducting Tokamak. This technique improves the local spatial resolution by a factor of 2 while maintaining the wide-angle view to ensure safety operation. Taking advantage of the new foveated imager, heat flux splitting under the application of resonant magnetic perturbation (RMP) coils has been clearly observed. The results indicate that the toroidal asymmetric power load pattern is closely related to the perturbation field induced by the RMP coils.
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Affiliation(s)
- J Y Zhang
- Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - B Zhang
- Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - X Gong
- Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - J Chang
- School of Optics and Photonics, Beijing Institute of Technology, Zhongguancun Street, Beijing 100081, People's Republic of China
| | - M N Jia
- Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - C Liu
- School of Instrument Science and Opto-Electronics Engineering, Hefei University of Technology, Hefei 230009, People's Republic of China
| | - R R Liang
- Institute of Plasma Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, People's Republic of China
| | - W L Chen
- School of Optics and Photonics, Beijing Institute of Technology, Zhongguancun Street, Beijing 100081, People's Republic of China
| | - C H Wu
- School of Optics and Photonics, Beijing Institute of Technology, Zhongguancun Street, Beijing 100081, People's Republic of China
| | - S Feng
- School of Optics and Photonics, Beijing Institute of Technology, Zhongguancun Street, Beijing 100081, People's Republic of China
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8
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Yang Z, Wang Y, Zhang C, He P, Shu S, Zhang J, Tang B. Techniques Used for Registration and Reconditioning of Infrared Images of the Experimental Advanced Superconducting Tokamak (EAST) Divertor. JOURNAL OF FUSION ENERGY 2020. [DOI: 10.1007/s10894-020-00251-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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9
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Yang Z, He P, Yan H, Bin Z, Shuangbao S, Wang F, Chen M, Jia G, Gong X. The development of a three-dimensional finite element method code for the heat flux analysis of tungsten monoblock divertor on EAST. FUSION ENGINEERING AND DESIGN 2020. [DOI: 10.1016/j.fusengdes.2019.111448] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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10
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Ali A, Niemann H, Jakubowski M, Pedersen TS, Neu R, Corre Y, Drewelow P, Sitjes AP, Wurden G, Pisano F, Cannas B, Gao Y, Ślęczka M. Initial results from the hotspot detection scheme for protection of plasma facing components in Wendelstein 7-X. NUCLEAR MATERIALS AND ENERGY 2019. [DOI: 10.1016/j.nme.2019.03.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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11
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Effect of magnetic perturbation fields on power decay length in EMC3-EIRENE simulations and comparison to experiment in ASDEX upgrade. NUCLEAR MATERIALS AND ENERGY 2019. [DOI: 10.1016/j.nme.2019.02.020] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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12
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Assessment of particle and heat loads to the upper open divertor in ASDEX Upgrade in favourable and unfavourable toroidal magnetic field directions. NUCLEAR MATERIALS AND ENERGY 2019. [DOI: 10.1016/j.nme.2019.03.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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13
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Happel T, Griener M, Silvagni D, Freethy S, Hennequin P, Janky F, Manz P, Prisiazhniuk D, Ryter F, Bernert M, Brida D, Eich T, Faitsch M, Gil L, Guimarais L, Merle A, Nille D, Pinzón J, Sieglin B, Stroth U, Viezzer E. Stationarity of I-mode operation and I-mode divertor heat fluxes on the ASDEX Upgrade tokamak. NUCLEAR MATERIALS AND ENERGY 2019. [DOI: 10.1016/j.nme.2018.12.022] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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14
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Pisano F, Cannas B, Jakubowski MW, Niemann H, Puig Sitjes A, Wurden GA. Towards a new image processing system at Wendelstein 7-X: From spatial calibration to characterization of thermal events. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:123503. [PMID: 30599560 DOI: 10.1063/1.5045560] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2018] [Accepted: 11/25/2018] [Indexed: 06/09/2023]
Abstract
Wendelstein 7-X (W7-X) is the most advanced fusion experiment in the stellarator line and is aimed at proving that the stellarator concept is suitable for a fusion reactor. One of the most important issues for fusion reactors is the monitoring of plasma facing components when exposed to very high heat loads, through the use of visible and infrared (IR) cameras. In this paper, a new image processing system for the analysis of the strike lines on the inboard limiters from the first W7-X experimental campaign is presented. This system builds a model of the IR cameras through the use of spatial calibration techniques, helping to characterize the strike lines by using the information given by real spatial coordinates of each pixel. The characterization of the strike lines is made in terms of position, size, and shape, after projecting the camera image in a 2D grid which tries to preserve the curvilinear surface distances between points. The description of the strike-line shape is made by means of the Fourier Descriptors.
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Affiliation(s)
- F Pisano
- Department of Electrical and Electronic Engineering, University of Cagliari, Via Marengo 2, Cagliari 09123, Italy
| | - B Cannas
- Department of Electrical and Electronic Engineering, University of Cagliari, Via Marengo 2, Cagliari 09123, Italy
| | - M W Jakubowski
- Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Wendelsteinstraße 1, Greifswald D-17491, Germany
| | - H Niemann
- Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Wendelsteinstraße 1, Greifswald D-17491, Germany
| | - A Puig Sitjes
- Max-Planck-Institut für Plasmaphysik, Teilinstitut Greifswald, Wendelsteinstraße 1, Greifswald D-17491, Germany
| | - G A Wurden
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
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15
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Jakubowski M, Drewelow P, Fellinger J, Puig Sitjes A, Wurden G, Ali A, Biedermann C, Cannas B, Chauvin D, Gamradt M, Greve H, Gao Y, Hathiramani D, König R, Lorenz A, Moncada V, Niemann H, Ngo TT, Pisano F, Sunn Pedersen T. Infrared imaging systems for wall protection in the W7-X stellarator (invited). THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:10E116. [PMID: 30399980 DOI: 10.1063/1.5038634] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 06/13/2018] [Indexed: 06/08/2023]
Abstract
Wendelstein 7-X aims at quasi-steady state operation with up to 10 MW of heating power for 30 min. Power exhaust will be handled predominantly via 10 actively water cooled CFC (carbon-fiber-reinforced carbon) based divertor units designed to withstand power loads of 10 MW/m2 locally in steady state. If local loads exceed this value, a risk of local delamination of the CFC and failure of entire divertor modules arises. Infrared endoscopes to monitor all main plasma facing components are being prepared, and near real time software tools are under development to identify areas of excessive temperature rise, to distinguish them from non-critical events, and to trigger alarms. Tests with different cameras were made in the recent campaign. Long pulse operation enforces additional diagnostic design constraints: for example, the optics need to be thermally decoupled from the endoscope housing. In the upcoming experimental campaign, a graphite scraper element, in front of the island divertor throat, will be tested as a possible means to protect the divertor pumping gap edges during the transient discharge evolution.
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Affiliation(s)
| | - Peter Drewelow
- Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
| | - Joris Fellinger
- Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
| | | | - Glen Wurden
- Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA
| | - Adnan Ali
- Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
| | | | | | - Didier Chauvin
- Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
| | - Marc Gamradt
- Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
| | - Henry Greve
- Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
| | - Yu Gao
- Forschungszentrum Jülich GmbH, IEK-4, 52428 Jülich, Germany
| | - Dag Hathiramani
- Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
| | - Ralf König
- Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
| | - Axel Lorenz
- Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
| | | | - Holger Niemann
- Max-Planck-Institut für Plasmaphysik, 17491 Greifswald, Germany
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16
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Zoletnik S, Biedermann C, Cseh G, Kocsis G, König R, Szabolics T, Szepesi T. First results of the multi-purpose real-time processing video camera system on the Wendelstein 7-X stellarator and implications for future devices. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2018; 89:013502. [PMID: 29390718 DOI: 10.1063/1.4995947] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
A special video camera has been developed for the 10-camera overview video system of the Wendelstein 7-X (W7-X) stellarator considering multiple application needs and limitations resulting from this complex long-pulse superconducting stellarator experiment. The event detection intelligent camera (EDICAM) uses a special 1.3 Mpixel CMOS sensor with non-destructive read capability which enables fast monitoring of smaller Regions of Interest (ROIs) even during long exposures. The camera can perform simple data evaluation algorithms (minimum/maximum, mean comparison to levels) on the ROI data which can dynamically change the readout process and generate output signals. Multiple EDICAM cameras were operated in the first campaign of W7-X and capabilities were explored in the real environment. Data prove that the camera can be used for taking long exposure (10-100 ms) overview images of the plasma while sub-ms monitoring and even multi-camera correlated edge plasma turbulence measurements of smaller areas can be done in parallel. These latter revealed that filamentary turbulence structures extend between neighboring modules of the stellarator. Considerations emerging for future upgrades of this system and similar setups on future long-pulse fusion experiments such as ITER are discussed.
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Affiliation(s)
- S Zoletnik
- Wigner Research Centre for Physics, P.O. Box 49, H-1525 Budapest, Hungary
| | - C Biedermann
- Max Planck Institute for Plasma Physics, 17491 Greifswald, Germany
| | - G Cseh
- Wigner Research Centre for Physics, P.O. Box 49, H-1525 Budapest, Hungary
| | - G Kocsis
- Wigner Research Centre for Physics, P.O. Box 49, H-1525 Budapest, Hungary
| | - R König
- Max Planck Institute for Plasma Physics, 17491 Greifswald, Germany
| | - T Szabolics
- Wigner Research Centre for Physics, P.O. Box 49, H-1525 Budapest, Hungary
| | - T Szepesi
- Wigner Research Centre for Physics, P.O. Box 49, H-1525 Budapest, Hungary
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17
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Iglesias D, Bunting P, Esquembri S, Hollocombe J, Silburn S, Vitton-Mea L, Balboa I, Huber A, Matthews G, Riccardo V, Rimini F, Valcarcel D. Digital twin applications for the JET divertor. FUSION ENGINEERING AND DESIGN 2017. [DOI: 10.1016/j.fusengdes.2017.10.012] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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18
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Zammuto I, Giannone L, Herrmann A, Houben A, Kallenbach A, Schuhbeck K, Sieglin B, Vorbrugg S. Implementation of ferritic steel as in vessel wall: Lessons learnt and follow up. FUSION ENGINEERING AND DESIGN 2017. [DOI: 10.1016/j.fusengdes.2017.04.016] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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19
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20
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Brida D, Lunt T, Wischmeier M, Birkenmeier G, Cahyna P, Carralero D, Faitsch M, Feng Y, Kurzan B, Schubert M, Sieglin B, Suttrop W, Wolfrum E. Determination of the stochastic layer properties induced by magnetic perturbations via heat pulse experiments at ASDEX upgrade. NUCLEAR MATERIALS AND ENERGY 2017. [DOI: 10.1016/j.nme.2017.03.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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21
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Density dependence of SOL power width in ASDEX upgrade L-Mode. NUCLEAR MATERIALS AND ENERGY 2017. [DOI: 10.1016/j.nme.2016.11.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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22
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Faitsch M, Sieglin B, Eich T, Herrmann A, Suttrop W. 2D heat flux in ASDEX Upgrade L-Mode with magnetic perturbation. NUCLEAR MATERIALS AND ENERGY 2017. [DOI: 10.1016/j.nme.2017.03.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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23
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Kang CS, Lee HH, Oh S, Lee SG, Wi HM, Kim YS, Kim HS. Study on the heat flux reconstruction with the infrared thermography for the divertor target plates in the KSTAR tokamak. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:083508. [PMID: 27587124 DOI: 10.1063/1.4961030] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
An infrared (IR) thermography is the preferred diagnostic that can quantify heat flux by measuring the surface temperature distributions of the divertor plates. The IR thermography is successfully instrumented on Korea Superconducting Tokamak Advanced Research (KSTAR). In this study, finite volume method is considered to solve the heat conduction equations. 1D-, 2D-, and 3D models are developed and compared with various calculation algorithms, such as Duhamel's theorem and THEODOR. These comparisons show good agreement. In order to acquire more efficient and reliable calculation results, we consider two numerical analysis schemes, influence of temperature on thermal properties and image stabilization. Recently, this reconstruction code is successfully applied to the KSTAR IR thermography.
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Affiliation(s)
- C S Kang
- National Fusion Research Institute, Daejeon 305-806, South Korea
| | - H H Lee
- National Fusion Research Institute, Daejeon 305-806, South Korea
| | - S Oh
- National Fusion Research Institute, Daejeon 305-806, South Korea
| | - S G Lee
- National Fusion Research Institute, Daejeon 305-806, South Korea
| | - H M Wi
- National Fusion Research Institute, Daejeon 305-806, South Korea
| | - Y S Kim
- National Fusion Research Institute, Daejeon 305-806, South Korea
| | - H S Kim
- National Fusion Research Institute, Daejeon 305-806, South Korea
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24
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Sieglin B, Faitsch M, Herrmann A, Martinov S, Eich T, Team ASDEXU. Real-Time Infrared Thermography at ASDEX Upgrade. FUSION SCIENCE AND TECHNOLOGY 2016. [DOI: 10.13182/fst15-183] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- B Sieglin
- Max Planck Institute for Plasma Physics, Boltzmannstr. 2, Garching 85748, Germany
| | - M Faitsch
- Max Planck Institute for Plasma Physics, Boltzmannstr. 2, Garching 85748, Germany
| | - A Herrmann
- Max Planck Institute for Plasma Physics, Boltzmannstr. 2, Garching 85748, Germany
| | - S Martinov
- Max Planck Institute for Plasma Physics, Boltzmannstr. 2, Garching 85748, Germany
| | - T Eich
- Max Planck Institute for Plasma Physics, Boltzmannstr. 2, Garching 85748, Germany
| | - ASDEX Upgrad Team
- Max Planck Institute for Plasma Physics, Boltzmannstr. 2, Garching 85748, Germany
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25
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Brunner D, Burke W, Kuang AQ, LaBombard B, Lipschultz B, Wolfe S. Feedback system for divertor impurity seeding based on real-time measurements of surface heat flux in the Alcator C-Mod tokamak. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2016; 87:023504. [PMID: 26931846 DOI: 10.1063/1.4941047] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/18/2015] [Accepted: 01/16/2016] [Indexed: 06/05/2023]
Abstract
Mitigation of the intense heat flux to the divertor is one of the outstanding problems in fusion energy. One technique that has shown promise is impurity seeding, i.e., the injection of low-Z gaseous impurities (typically N2 or Ne) to radiate and dissipate the power before it arrives to the divertor target plate. To this end, the Alcator C-Mod team has created a first-of-its-kind feedback system to control the injection of seed gas based on real-time surface heat flux measurements. Surface thermocouples provide real-time measurements of the surface temperature response to the plasma heat flux. The surface temperature measurements are inputted into an analog computer that "solves" the 1-D heat transport equation to deliver accurate, real-time signals of the surface heat flux. The surface heat flux signals are sent to the C-Mod digital plasma control system, which uses a proportional-integral-derivative (PID) algorithm to control the duty cycle demand to a pulse width modulated piezo valve, which in turn controls the injection of gas into the private flux region of the C-Mod divertor. This paper presents the design and implementation of this new feedback system as well as initial results using it to control divertor heat flux.
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Affiliation(s)
- D Brunner
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - W Burke
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - A Q Kuang
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - B LaBombard
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
| | - B Lipschultz
- Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom
| | - S Wolfe
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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