Stability and transport of gyrokinetic critical pedestals

Journal Article · 26 June 2024 · Nuclear Fusion

DOI: https://doi.org/10.1088/1741-4326/ad4d02 · OSTI ID:2377463

Parisi, J. F. ; Nelson, A. O. ; Guttenfelder, W. ; Gaur, R. ; Berkery, J. W. ; Kaye, S. M. ; Barada, K.; Clauser, C. ; Diallo, A. ; Hatch, D. R. ; Kleiner, A. ; Lampert, M.; Macwan, T. ; Menard, J. E.

Abstract A gyrokinetic threshold model for pedestal width–height scaling prediction is applied to multiple devices. A shaping and aspect ratio scan is performed on National Spherical Torus Experiment (NSTX) equilibria, finding ${\mathrm{\Delta }}_{\mathrm{ped}}=0.92A^{1.04}{\kappa }^{-1.24}{0.38}^{\delta }{\beta }_{\theta ,\mathrm{ped}}^{1.05}$ for the wide-pedestal branch with pedestal width ${\mathrm{\Delta }}_{\mathrm{ped}}$ , aspect ratio A , elongation κ , triangularity δ , and normalized pedestal height ${\beta }_{\theta ,\mathrm{ped}}$ . The width–transport scaling is found to vary significantly if the pedestal height is varied either with a fixed density or fixed temperature, showing how fueling and heating sources affect the pedestal density and temperature profiles for the kinetic-ballooning-mode (KBM) limited profiles. For an NSTX equilibrium, at fixed density, the wide branch is ${\mathrm{\Delta }}_{\mathrm{ped}}=0.028{(q_{\text{e}}/{\mathrm{\Gamma }}_{\text{e}}-1.7)}^{1.5}\sim {\eta }_{\text{e}}^{1.5}$ and at fixed temperature ${\mathrm{\Delta }}_{\mathrm{ped}}=0.31{(q_{\text{e}}/{\mathrm{\Gamma }}_{\text{e}}-4.7)}^{0.85}$ $\sim {\eta }_{\text{e}}^{0.85}$ , where $q_{\text{e}}$ and ${\mathrm{\Gamma }}_{\text{e}}$ are turbulent electron heat and particle fluxes and ${\eta }_{\text{e}}=\mathrm{\nabla }\ln T_{\text{e}}/\mathrm{\nabla }\ln n_{\text{e}}$ for an electron temperature $T_{\text{e}}$ and density $n_{\text{e}}$ . Pedestals close to the KBM limit are shown to have modified turbulent transport coefficients compared to the strongly driven KBMs. The role of flow shear is studied as a width–height scaling constraint and pedestal saturation mechanism for a standard and lithiated wide pedestal discharge. Finally, the stability, transport, and flow shear constraints are combined and examined for an NSTX experiment.

• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: AC02-09CH11466
• OSTI ID: 2377463
• Journal Information: Nuclear Fusion, Journal Name: Nuclear Fusion Journal Issue: 8 Vol. 64; ISSN 0029-5515
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: IAEA
• Language: English