1
|
Samuell CM, Mclean AG, Johnson CA, Glass F, Jaervinen AE. Measuring the electron temperature and identifying plasma detachment using machine learning and spectroscopy. Rev Sci Instrum 2021; 92:043520. [PMID: 34243436 DOI: 10.1063/5.0034552] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [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
|
2
|
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. Phys Rev Lett 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] [What about the content of this article? (0)] [Affiliation(s)] [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
|
3
|
Jaervinen AE, Allen SL, Eldon D, Fenstermacher ME, Groth M, Hill DN, Leonard AW, McLean AG, Porter GD, Rognlien TD, Samuell CM, Wang HQ. E×B Flux Driven Detachment Bifurcation in the DIII-D Tokamak. Phys Rev Lett 2018; 121:075001. [PMID: 30169054 DOI: 10.1103/physrevlett.121.075001] [Citation(s) in RCA: 5] [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] [Received: 12/05/2017] [Revised: 06/21/2018] [Indexed: 06/08/2023]
Abstract
A bifurcative step transition from low-density, high-temperature, attached divertor conditions to high-density, low-temperature, detached divertor conditions is experimentally observed in DIII-D tokamak plasmas as density is increased. The step transition is only observed in the high confinement mode and only when the B×∇B drift is directed towards the divertor. This work reports for the first time a theoretical explanation and numerical simulations that qualitatively reproduce this bifurcation and its dependence on the toroidal field direction. According to the model, the bifurcation is primarily driven by the interdependence of the E×B-drift fluxes, divertor electric potential structure, and divertor conditions. In the attached conditions, strong potential gradients in the low field side (LFS) divertor drive E×B-drift flux towards the high field side divertor, reinforcing low density, high temperature conditions in the LFS divertor leg. At the onset of detachment, reduction in the potential gradients in the LFS divertor leg reduce the E×B-drift flux as well, such that the divertor plasma evolves nonlinearly to high density, strongly detached conditions. Experimental estimates of the E×B-drift fluxes, based on divertor Thomson scattering measurements, and their dependence on the divertor conditions are qualitatively consistent with the numerical predictions. The implications for divertor power exhaust and detachment control in the next step fusion devices are discussed.
Collapse
Affiliation(s)
- A E Jaervinen
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - S L Allen
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - D Eldon
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - M E Fenstermacher
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - M Groth
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - D N Hill
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - A W Leonard
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - A G McLean
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - G D Porter
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - T D Rognlien
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - C M Samuell
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| | - H Q Wang
- Lawrence Livermore National Laboratory, Livermore, California 94550, USA
| |
Collapse
|