Effects beyond ideal MHD on stability of wide and enhanced pedestal regimes in NSTX

Pankin, Alexei; Ebrahimi, Fatima; King, Jacob; Kleiner, Andreas; Dominguez-Palacios, Jesus

doi:10.1088/1361-6587/ae049c

Effects beyond ideal MHD on stability of wide and enhanced pedestal regimes in NSTX

Journal Article · Wed Sep 17 00:00:00 EDT 2025 · Plasma Physics and Controlled Fusion

DOI:https://doi.org/10.1088/1361-6587/ae049c· OSTI ID:2589446

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Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)
FiatLux, Lafayette, CO (United States)

Stability of edge-localized modes (ELMs) in spherical tokamaks is explored using the extended MHD model. Linear NIMROD simulations have been performed for three NSTX discharges 132543, 132588, and 141133, to investigate the role of resistivity, diffusivity, and shear flows on the onset of ELMs. The first discharge represents the wide pedestal regime and the later two discharges represent ELM-free enhanced pedestal H-mode. We first present the effect of toroidal rotation shear and find a flow shear destabilizing effect in these NSTX discharges. Simulations are also extended to include the two-fluid and ion gyroviscosity effects. Simulations show that the flow shear can shift the mode spectrum and alter the critical condition of ELM onset. We also uncover that ELM onset prediction in spherical tokamaks requires effects beyond MHD, in particular gyroviscosity and diamagnetic terms could stabilize Peeling-Ballooning modes consistent with the experimental observation of ELM-free regimes in NSTX. The findings give new insight into the nature of the interplay between resistivity, flows, and diamagnetic stabilization in ELM suppression and have potential applications to ELM control schemes in NSTX-U and next-generation spherical tokamaks. This study identifies the essential physical effects that must be included in future predictive and validation simulations.

View Accepted Manuscript (DOE)

Research Organization:: Princeton Plasma Physics Laboratory (PPPL), Princeton, NJ (United States)

Sponsoring Organization:: USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF); National Energy Research Scientific Computing (NERSC)

Grant/Contract Number:: AC02-09CH11466; AC02-05CH11231

OSTI ID:: 2589446

Journal Information:: Plasma Physics and Controlled Fusion, Journal Name: Plasma Physics and Controlled Fusion Journal Issue: 9 Vol. 67; ISSN 0741-3335; ISSN 1361-6587

Publisher:: IOP PublishingCopyright Statement

Country of Publication:: United States

Language:: English

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