Enhanced pedestal transport driven by edge collisionality on Alcator C-Mod and its role in regulating H-mode pedestal gradients

Miller, M. A.; Hughes, J. W.; Rosenthal, A. M.; Mordijck, S.; Reksoatmodjo, R.; Wigram, M.; Dunsmore, J.; Sciortino, F.; Wilcox, R. S.; Odstrčil, T.

doi:10.1088/1741-4326/ada1e3

Enhanced pedestal transport driven by edge collisionality on Alcator C-Mod and its role in regulating H-mode pedestal gradients

Journal Article · Sun Jan 05 23:00:00 EST 2025 · Nuclear Fusion

DOI:https://doi.org/10.1088/1741-4326/ada1e3· OSTI ID:2496725

; ; ; Mordijck, S.; Reksoatmodjo, R.; Wigram, M.; ; ; ;

Abstract

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, $P_{net} = P_{net}^{crit} \approx 2.3$ MW, in the absence of any external fueling. New analysis of ionization and particle flux profiles reveal saturation of the pedestal electron density, $n_{e}^{ped}$ , despite continuous increases in ionization throughout the pedestal, inversely related to $P_{net}$ . A limit to the pedestal $\nabla n_{e}$ emerges as the particle flux, $Γ_{D}$ , continues to grow, implying increases in the effective particle diffusivity, $D_{eff}$ . This is well-correlated with the separatrix collisionality, $ν_{sep}^{*}$ 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 $P_{net}^{crit}$ . 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 $D_{eff}$ , consistent with experimental findings, and additionally suggests even larger growth in χ _e at the same $P_{net}^{crit}$ .

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Sponsoring Organization:: USDOE Office of Science (SC), Fusion Energy Sciences (FES)

Grant/Contract Number:: SC0007880

OSTI ID:: 2496725

Alternate ID(s):: OSTI ID: 2483366
OSTI ID: 2502164

Journal Information:: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 2 Vol. 65; ISSN 0029-5515

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: IAEA

Language:: English

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