Enhanced pedestal transport driven by edge collisionality on Alcator C-Mod and its role in regulating H-mode pedestal gradients
Experimental measurements of plasma and neutral profiles across the pedestal are used in conjunction with 2D edge modeling to examine pedestal stiffness in Alcator C-Mod H-mode plasmas. Enhanced D _α experiments on Alcator C-Mod observed pedestal degradation and loss in confinement below a critical...
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| Format: | Article |
| Language: | English |
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IOP Publishing
2025-01-01
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| Series: | Nuclear Fusion |
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| Online Access: | https://doi.org/10.1088/1741-4326/ada1e3 |
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| author | M.A. Miller J.W. Hughes A.M. Rosenthal S. Mordijck R. Reksoatmodjo M. Wigram J. Dunsmore F. Sciortino R.S. Wilcox T. Odstrčil |
| author_facet | M.A. Miller J.W. Hughes A.M. Rosenthal S. Mordijck R. Reksoatmodjo M. Wigram J. Dunsmore F. Sciortino R.S. Wilcox T. Odstrčil |
| author_sort | M.A. Miller |
| collection | DOAJ |
| description | Experimental measurements of plasma and neutral profiles across the pedestal are used in conjunction with 2D edge modeling to examine pedestal stiffness in Alcator C-Mod H-mode plasmas. Enhanced D _α experiments on Alcator C-Mod observed pedestal degradation and loss in confinement below a critical value of net power crossing the separatrix, $P_\mathrm{net} = P_\mathrm{net}^\mathrm{crit} \approx 2.3$ MW, in the absence of any external fueling. New analysis of ionization and particle flux profiles reveal saturation of the pedestal electron density, $n_{e}^\mathrm{ped}$ , despite continuous increases in ionization throughout the pedestal, inversely related to $P_\mathrm{net}$ . A limit to the pedestal $\nabla n_{e}$ emerges as the particle flux, $\Gamma_{D}$ , continues to grow, implying increases in the effective particle diffusivity, $D_\mathrm{eff}$ . This is well-correlated with the separatrix collisionality, $\nu^{*}_\mathrm{sep}$ and a turbulence control parameter, α _t , implying a possible transition in type of turbulence. The transition is well correlated with the experimentally observed value of $P_\mathrm{net}^\mathrm{crit}$ . SOLPS-ITER modeling is performed for select discharges from the power scan, constrained with experimental electron and neutral densities, measured at the outer midplane. The modeling confirms general growth in $D_\mathrm{eff}$ , consistent with experimental findings, and additionally suggests even larger growth in χ _e at the same $P_\mathrm{net}^\mathrm{crit}$ . |
| format | Article |
| id | doaj-art-3ca86af533d54db584f6038033751dad |
| institution | Kabale University |
| issn | 0029-5515 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | Nuclear Fusion |
| spelling | doaj-art-3ca86af533d54db584f6038033751dad2025-01-06T09:09:57ZengIOP PublishingNuclear Fusion0029-55152025-01-0165202602910.1088/1741-4326/ada1e3Enhanced pedestal transport driven by edge collisionality on Alcator C-Mod and its role in regulating H-mode pedestal gradientsM.A. Miller0https://orcid.org/0000-0002-6540-6533J.W. Hughes1https://orcid.org/0000-0003-4802-4944A.M. Rosenthal2https://orcid.org/0000-0002-6149-1136S. Mordijck3R. Reksoatmodjo4M. Wigram5J. Dunsmore6https://orcid.org/0009-0009-3975-0814F. Sciortino7https://orcid.org/0000-0002-5159-1889R.S. Wilcox8https://orcid.org/0000-0003-1369-1739T. Odstrčil9https://orcid.org/0000-0003-4173-4230MIT Plasma Science and Fusion Center , Cambridge, MA 02139, United States of AmericaMIT Plasma Science and Fusion Center , Cambridge, MA 02139, United States of AmericaCommonwealth Fusion Systems , Devens, MA 01434, United States of AmericaWilliam & Mary , Williamsburg, VA 23188, United States of AmericaLawrence Livermore National Laboratory , Livermore, CA 94550, United States of AmericaMIT Plasma Science and Fusion Center , Cambridge, MA 02139, United States of AmericaMIT Plasma Science and Fusion Center , Cambridge, MA 02139, United States of AmericaProxima Fusion , 81671 München, GermanyOak Ridge National Laboratory , Oak Ridge, TN 37831, United States of AmericaGeneral Atomics , San Diego, CA 92186, United States of AmericaExperimental measurements of plasma and neutral profiles across the pedestal are used in conjunction with 2D edge modeling to examine pedestal stiffness in Alcator C-Mod H-mode plasmas. Enhanced D _α experiments on Alcator C-Mod observed pedestal degradation and loss in confinement below a critical value of net power crossing the separatrix, $P_\mathrm{net} = P_\mathrm{net}^\mathrm{crit} \approx 2.3$ MW, in the absence of any external fueling. New analysis of ionization and particle flux profiles reveal saturation of the pedestal electron density, $n_{e}^\mathrm{ped}$ , despite continuous increases in ionization throughout the pedestal, inversely related to $P_\mathrm{net}$ . A limit to the pedestal $\nabla n_{e}$ emerges as the particle flux, $\Gamma_{D}$ , continues to grow, implying increases in the effective particle diffusivity, $D_\mathrm{eff}$ . This is well-correlated with the separatrix collisionality, $\nu^{*}_\mathrm{sep}$ and a turbulence control parameter, α _t , implying a possible transition in type of turbulence. The transition is well correlated with the experimentally observed value of $P_\mathrm{net}^\mathrm{crit}$ . SOLPS-ITER modeling is performed for select discharges from the power scan, constrained with experimental electron and neutral densities, measured at the outer midplane. The modeling confirms general growth in $D_\mathrm{eff}$ , consistent with experimental findings, and additionally suggests even larger growth in χ _e at the same $P_\mathrm{net}^\mathrm{crit}$ .https://doi.org/10.1088/1741-4326/ada1e3pedestal transportseparatrix collisionalityneutral fuelingboundary modeling |
| spellingShingle | M.A. Miller J.W. Hughes A.M. Rosenthal S. Mordijck R. Reksoatmodjo M. Wigram J. Dunsmore F. Sciortino R.S. Wilcox T. Odstrčil Enhanced pedestal transport driven by edge collisionality on Alcator C-Mod and its role in regulating H-mode pedestal gradients Nuclear Fusion pedestal transport separatrix collisionality neutral fueling boundary modeling |
| title | Enhanced pedestal transport driven by edge collisionality on Alcator C-Mod and its role in regulating H-mode pedestal gradients |
| title_full | Enhanced pedestal transport driven by edge collisionality on Alcator C-Mod and its role in regulating H-mode pedestal gradients |
| title_fullStr | Enhanced pedestal transport driven by edge collisionality on Alcator C-Mod and its role in regulating H-mode pedestal gradients |
| title_full_unstemmed | Enhanced pedestal transport driven by edge collisionality on Alcator C-Mod and its role in regulating H-mode pedestal gradients |
| title_short | Enhanced pedestal transport driven by edge collisionality on Alcator C-Mod and its role in regulating H-mode pedestal gradients |
| title_sort | enhanced pedestal transport driven by edge collisionality on alcator c mod and its role in regulating h mode pedestal gradients |
| topic | pedestal transport separatrix collisionality neutral fueling boundary modeling |
| url | https://doi.org/10.1088/1741-4326/ada1e3 |
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