Correlation of the L-mode density limit with edge collisionality
The ‘density limit’ is one of the fundamental bounds on tokamak operating space, and is commonly estimated via the empirical Greenwald scaling. This limit has garnered renewed interest in recent years as it has become clear that ITER and many tokamak pilot plant concepts must operate near or above t...
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| Language: | English |
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IOP Publishing
2024-01-01
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| Series: | Nuclear Fusion |
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| Online Access: | https://doi.org/10.1088/1741-4326/ad90f0 |
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| author | A.D. Maris C. Rea A. Pau W. Hu B. Xiao R. Granetz E. Marmar the EUROfusion Tokamak Exploitation team the Alcator C-Mod team the ASDEX Upgrade team the DIII-D Team the EAST Team and the TCV team |
| author_facet | A.D. Maris C. Rea A. Pau W. Hu B. Xiao R. Granetz E. Marmar the EUROfusion Tokamak Exploitation team the Alcator C-Mod team the ASDEX Upgrade team the DIII-D Team the EAST Team and the TCV team |
| author_sort | A.D. Maris |
| collection | DOAJ |
| description | The ‘density limit’ is one of the fundamental bounds on tokamak operating space, and is commonly estimated via the empirical Greenwald scaling. This limit has garnered renewed interest in recent years as it has become clear that ITER and many tokamak pilot plant concepts must operate near or above the Greenwald limit to achieve their objectives. Evidence has also grown that the Greenwald scaling—in its remarkable simplicity—may not capture the full complexity of the density limit. In this study, we assemble a multi-machine database to quantify the effectiveness of the Greenwald limit as a predictor of the L-mode density limit and compare it with data-driven approaches. We find that a boundary in the plasma edge involving dimensionless collisionality and pressure, $\nu_{*, \mathrm{edge}}^\text{limit} = 3.5 \beta_{T,\text{edge}}^{-0.40}$ , achieves significantly higher accuracy (false positive rate (FPR) of 2.3% at a true positive rate (TPR) of 95%) of predicting density limit disruptions than the Greenwald limit (FPR of 13.4% at a TPR of 95%) across a multi-machine dataset including metal- and carbon-wall tokamaks (AUG, C-Mod, DIII-D, and TCV). This two-parameter boundary succeeds at predicting L-mode density limits by robustly identifying the radiative state preceding the terminal MHD instability. This boundary can be applied for density limit avoidance in current devices and in ITER, where it can be measured and responded to in real time. |
| format | Article |
| id | doaj-art-38de6b1b70cd46feb367d1b7b5377288 |
| institution | OA Journals |
| issn | 0029-5515 |
| language | English |
| publishDate | 2024-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | Nuclear Fusion |
| spelling | doaj-art-38de6b1b70cd46feb367d1b7b53772882025-08-20T02:33:44ZengIOP PublishingNuclear Fusion0029-55152024-01-0165101605110.1088/1741-4326/ad90f0Correlation of the L-mode density limit with edge collisionalityA.D. Maris0https://orcid.org/0000-0001-9457-8927C. Rea1https://orcid.org/0000-0002-9948-2649A. Pau2https://orcid.org/0000-0002-7122-3346W. Hu3https://orcid.org/0000-0003-3420-2607B. Xiao4R. Granetz5E. Marmar6the EUROfusion Tokamak Exploitation teamthe Alcator C-Mod teamthe ASDEX Upgrade teamthe DIII-D Teamthe EAST Teamand the TCV teamPlasma Science and Fusion Center, Massachusetts Institute of Technology , Cambridge, MA 02139, United States of AmericaPlasma Science and Fusion Center, Massachusetts Institute of Technology , Cambridge, MA 02139, United States of AmericaÉcole Polytechnique Fédérale de Lausanne (EPFL), Swiss Plasma Center (SPC) , CH-1015 Lausanne, SwitzerlandInstitute of Plasma Physics , Chinese Academy of Sciences, Hefei 230031, ChinaInstitute of Plasma Physics , Chinese Academy of Sciences, Hefei 230031, ChinaPlasma Science and Fusion Center, Massachusetts Institute of Technology , Cambridge, MA 02139, United States of AmericaPlasma Science and Fusion Center, Massachusetts Institute of Technology , Cambridge, MA 02139, United States of AmericaThe ‘density limit’ is one of the fundamental bounds on tokamak operating space, and is commonly estimated via the empirical Greenwald scaling. This limit has garnered renewed interest in recent years as it has become clear that ITER and many tokamak pilot plant concepts must operate near or above the Greenwald limit to achieve their objectives. Evidence has also grown that the Greenwald scaling—in its remarkable simplicity—may not capture the full complexity of the density limit. In this study, we assemble a multi-machine database to quantify the effectiveness of the Greenwald limit as a predictor of the L-mode density limit and compare it with data-driven approaches. We find that a boundary in the plasma edge involving dimensionless collisionality and pressure, $\nu_{*, \mathrm{edge}}^\text{limit} = 3.5 \beta_{T,\text{edge}}^{-0.40}$ , achieves significantly higher accuracy (false positive rate (FPR) of 2.3% at a true positive rate (TPR) of 95%) of predicting density limit disruptions than the Greenwald limit (FPR of 13.4% at a TPR of 95%) across a multi-machine dataset including metal- and carbon-wall tokamaks (AUG, C-Mod, DIII-D, and TCV). This two-parameter boundary succeeds at predicting L-mode density limits by robustly identifying the radiative state preceding the terminal MHD instability. This boundary can be applied for density limit avoidance in current devices and in ITER, where it can be measured and responded to in real time.https://doi.org/10.1088/1741-4326/ad90f0tokamakdensity limitmachine learningGreenwald limit |
| spellingShingle | A.D. Maris C. Rea A. Pau W. Hu B. Xiao R. Granetz E. Marmar the EUROfusion Tokamak Exploitation team the Alcator C-Mod team the ASDEX Upgrade team the DIII-D Team the EAST Team and the TCV team Correlation of the L-mode density limit with edge collisionality Nuclear Fusion tokamak density limit machine learning Greenwald limit |
| title | Correlation of the L-mode density limit with edge collisionality |
| title_full | Correlation of the L-mode density limit with edge collisionality |
| title_fullStr | Correlation of the L-mode density limit with edge collisionality |
| title_full_unstemmed | Correlation of the L-mode density limit with edge collisionality |
| title_short | Correlation of the L-mode density limit with edge collisionality |
| title_sort | correlation of the l mode density limit with edge collisionality |
| topic | tokamak density limit machine learning Greenwald limit |
| url | https://doi.org/10.1088/1741-4326/ad90f0 |
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