1
|
Validation of EDGDE2D-EIRENE predicted 2D distributions of electron temperature and density against Divertor Thomson scattering measurements in the low-field side divertor leg in DIII-D. NUCLEAR MATERIALS AND ENERGY 2023. [DOI: 10.1016/j.nme.2023.101372] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
|
2
|
Kobayashi T, Kobayashi M, Narushima Y, Suzuki Y, Watanabe KY, Mukai K, Hayashi Y. Self-Sustained Divertor Oscillation Driven by Magnetic Island Dynamics in Torus Plasma. PHYSICAL REVIEW LETTERS 2022; 128:085001. [PMID: 35275668 DOI: 10.1103/physrevlett.128.085001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/21/2021] [Revised: 12/10/2021] [Accepted: 01/12/2022] [Indexed: 06/14/2023]
Abstract
A new type of self-sustained divertor oscillation is discovered in the Large Helical Device stellarator, where the peripheral plasma is detached from material diverters by means of externally applied perturbation fields. The divertor oscillation is found to be a self-regulation of an isolated magnetic field structure (the magnetic island) width induced by a drastic change in a poloidal inhomogeneity of the plasma radiation across the detachment-attachment transitions. A predator-prey model between the magnetic island width and a self-generated local plasma current (the bootstrap current) is introduced to describe the divertor oscillation, which successfully reproduces the experimental observations.
Collapse
Affiliation(s)
- T Kobayashi
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
- The Graduate University for Advanced Studies, SOKENDAI, Toki 509-5292, Japan
| | - M Kobayashi
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
- The Graduate University for Advanced Studies, SOKENDAI, Toki 509-5292, Japan
| | - Y Narushima
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
- The Graduate University for Advanced Studies, SOKENDAI, Toki 509-5292, Japan
| | - Y Suzuki
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
- The Graduate University for Advanced Studies, SOKENDAI, Toki 509-5292, Japan
- Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
| | - K Y Watanabe
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
- Nagoya University, Graduate School of Engineering, Nagoya 464-8603, Japan
| | - K Mukai
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
- The Graduate University for Advanced Studies, SOKENDAI, Toki 509-5292, Japan
| | - Y Hayashi
- National Institute for Fusion Science, National Institutes of Natural Sciences, Toki 509-5292, Japan
| |
Collapse
|
3
|
Samuell CM, Mclean AG, Johnson CA, Glass F, Jaervinen AE. Measuring the electron temperature and identifying plasma detachment using machine learning and spectroscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2021; 92:043520. [PMID: 34243436 DOI: 10.1063/5.0034552] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Accepted: 02/18/2021] [Indexed: 06/13/2023]
Abstract
A machine learning approach has been implemented to measure the electron temperature directly from the emission spectra of a tokamak plasma. This approach utilized a neural network (NN) trained on a dataset of 1865 time slices from operation of the DIII-D tokamak using extreme ultraviolet/vacuum ultraviolet emission spectroscopy matched with high-accuracy divertor Thomson scattering measurements of the electron temperature, Te. This NN is shown to be particularly good at predicting Te at low temperatures (Te < 10 eV) where the NN demonstrated a mean average error of less than 1 eV. Trained to detect plasma detachment in the tokamak divertor, a NN classifier was able to correctly identify detached states (Te < 5 eV) with a 99% accuracy (an F1 score of 0.96) at an acquisition rate 10× faster than the Thomson scattering measurement. The performance of the model is understood by examining a set of 4800 theoretical spectra generated using collisional radiative modeling that was also used to predict the performance of a low-cost spectrometer viewing nitrogen emission in the visible wavelengths. These results provide a proof-of-principle that low-cost spectrometers leveraged with machine learning can be used to boost the performance of more expensive diagnostics on fusion devices and be used independently as a fast and accurate Te measurement and detachment classifier.
Collapse
Affiliation(s)
- C M Samuell
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - A G Mclean
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - C A Johnson
- Auburn University, Auburn, Alabama 36849, USA
| | - F Glass
- General Atomics, San Diego, California 92186, USA
| | - A E Jaervinen
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| |
Collapse
|
4
|
Ren J, Donovan D, Watkins J, Wang H, Thomas D, Boivin R. Experimental observation of heat flux mitigation during divertor detachment in the DIII-D small angle slot divertor. NUCLEAR MATERIALS AND ENERGY 2021. [DOI: 10.1016/j.nme.2020.100887] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
|
6
|
Wang HQ, Guo HY, Xu GS, Leonard AW, Wu XQ, Groth M, Jaervinen AE, Watkins JG, Osborne TH, Thomas DM, Eldon D, Stangeby PC, Turco F, Xu JC, Wang L, Wang YF, Liu JB. First Evidence of Local E×B Drift in the Divertor Influencing the Structure and Stability of Confined Plasma near the Edge of Fusion Devices. PHYSICAL REVIEW LETTERS 2020; 124:195002. [PMID: 32469565 DOI: 10.1103/physrevlett.124.195002] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2019] [Accepted: 04/17/2020] [Indexed: 06/11/2023]
Abstract
The structure of the edge plasma in a magnetic confinement system has a strong impact on the overall plasma performance. We uncover for the first time a magnetic-field-direction dependent density shelf, i.e., local flattening of the density radial profile near the magnetic separatrix, in high confinement plasmas with low edge collisionality in the DIII-D tokamak. The density shelf is correlated with a doubly peaked density profile near the divertor target plate, which tends to occur for operation with the ion B×∇B drift direction away from the X-point, as currently employed for DIII-D advanced tokamak scenarios. This double-peaked divertor plasma profile is connected via the E×B drifts, arising from a strong radial electric field induced by the radial electron temperature gradient near the divertor target. The drifts lead to the reversal of the poloidal flow above the divertor target, resulting in the formation of the density shelf. The edge density shelf can be further enhanced at higher heating power, preventing large, periodic bursts of the plasma, i.e., edge-localized modes, in the edge region, consistent with ideal magnetohydrodynamics calculations.
Collapse
Affiliation(s)
- H Q Wang
- General Atomics, Post Office Box 85608, San Diego, California 92186-5608, USA
| | - H Y Guo
- General Atomics, Post Office Box 85608, San Diego, California 92186-5608, USA
| | - G S Xu
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
| | - A W Leonard
- General Atomics, Post Office Box 85608, San Diego, California 92186-5608, USA
| | - X Q Wu
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
| | - M Groth
- Department of Applied Physics, Aalto University, FI-00076, Aalto, Finland
| | - A E Jaervinen
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - J G Watkins
- Sandia National Laboratories, Post Office Box 969, Livermore, California 94551, USA
| | - T H Osborne
- General Atomics, Post Office Box 85608, San Diego, California 92186-5608, USA
| | - D M Thomas
- General Atomics, Post Office Box 85608, San Diego, California 92186-5608, USA
| | - D Eldon
- General Atomics, Post Office Box 85608, San Diego, California 92186-5608, USA
| | - P C Stangeby
- University of Toronto Institute for Aerospace Studies, 4925 Dufferin St., Toronto M3H 5T6, Canada
| | - F Turco
- Columbia University, 500 West 120th St., New York, New York 10027, USA
| | - J C Xu
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
| | - L Wang
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
| | - Y F Wang
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
| | - J B Liu
- Institute of Plasma Physics, Chinese Academy of Sciences, Hefei 230031, China
| |
Collapse
|
8
|
Jaervinen A, Allen S, Eldon D, Fenstermacher M, Groth M, Hill D, Lasnier C, Leonard A, McLean A, Porter G, Rognlien T, Samuell C, Wang H, Watkins J. Impact of drifts on divertor power exhaust in DIII-D. NUCLEAR MATERIALS AND ENERGY 2019. [DOI: 10.1016/j.nme.2019.02.023] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
|
9
|
Campanell MD, Johnson GR. Thermionic Cooling of the Target Plasma to a Sub-eV Temperature. PHYSICAL REVIEW LETTERS 2019; 122:015003. [PMID: 31012647 DOI: 10.1103/physrevlett.122.015003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Revised: 11/27/2018] [Indexed: 06/09/2023]
Abstract
Contemporary models of bounded plasmas assume that the target plasma electron temperature far exceeds the temperature of the cold electrons emitted from the target, T_{emit}. We show that when the sheath facing a collisional plasma becomes inverted, the target plasma electron temperature has to equal T_{emit} even if the upstream plasma is hotter by orders of magnitude. This extreme cooling effect can alter the plasma properties and the heat transmission to thermionically emitting surfaces in many applications. It also opens a possibility of using thermionic divertor plates to induce detachment in tokamaks.
Collapse
Affiliation(s)
- M D Campanell
- Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA
| | - G R Johnson
- Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, California 94551, USA
| |
Collapse
|