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arXiv · 2304.12736

Effect of triangularity on plasma turbulence and the SOL-width scaling in L-mode diverted tokamak configurations

Kyungtak Lim·Maurizio Giacomin·Paolo Ricci·António Coelho·Olivier Février·Davide Mancini·Davide Silvagni·Louis Stenger
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Abstract

The effect of triangularity on tokamak boundary plasma turbulence is investigated by using global, flux-driven, three-dimensional, two-fluid simulations. The simulations show that negative triangularity stabilizes boundary plasma turbulence, and linear investigations reveal that this is due to a reduction of the magnetic curvature drive of interchange instabilities, such as the resistive ballooning mode. As a consequence, the pressure decay length $L_p$, related to the SOL power fall-off length $\lambda_q$, is found to be affected by triangularity. Leveraging considerations on the effect of triangularity on the linear growth rate and nonlinear evolution of the resistive ballooning mode, the analytical theory-based scaling law for $L_p$ in L-mode plasmas, derived by Giacomin \textit{et al.} [{Nucl. Fusion}, \href{https://doi.org/10.1088/1741-4326/abf8f6}{\textbf{61} 076002} (2021)], is extended to include the effect of triangularity. The scaling is in agreement with nonlinear simulations and a multi-machine experimental database, which include recent TCV discharges dedicated to the study of the effect of triangularity in L-mode diverted discharges. Overall, the present results highlight that negative triangularity narrows the $L_p$ and considering the effect of triangularity is important for a reliable extrapolation of $\lambda_q$ from present experiments to larger devices.

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Kyungtak Lim, Maurizio Giacomin, Paolo Ricci, António Coelho, Olivier Février, Davide Mancini, Davide Silvagni, Louis Stenger. 2023-04-25. Effect of triangularity on plasma turbulence and the SOL-width scaling in L-mode diverted tokamak configurations. https://doi.org/10.1088/1361-6587%2Facdc52

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