Description
A Negative Triangularity (NT) Fusion Power Plant (FPP) can be considered as a valuable alternative to the standard Positive Triangularity (PT) H-mode design. It is has been experimentally proven that NT plasmas can close access to H-mode [1, 2], creating a robust ELM-free scenario, while achieving the same fusion performance as an H-mode through a strong reduction of turbulence [3–6]. We have reached a point of understanding of NT plasmas, where one of the main questions is how we can optimize even further the effect of shaping on turbulence and which are the factors that control this beneficial effect.
In this work, we answer this question with a comparative gyrokinetic study using the GENE code [7] of NT experiments carried out on TCV, DIII-D, AUG and JET. These experiments are characterized by different shapes, different turbulent regimes and thus different performance. By studying these scenarios and scanning over other important geometrical quantities, we were able to further validate and extend our physical picture of the impact of plasma shaping on turbulent regimes dominated by ITG, TEM and MTM [8, 9]. We will demonstrate that this model, primarily based on the impact of shaping on the magnetic drift velocity and Finite Larmor Radius (FLR) effects, allowed us to explain how shaping can reduce or enhance turbulent transport. In particular, it allows us to extend our understanding beyond the simple experimental definition of triangularity
and develop metrics that are capable of predicting qualitatively the reduction of turbulence from the full plasma shape. Such subtle distinctions in the plasma shape are important in understanding the AUG results, in particular, and are essential for designing future experiments and a future reactor.
To this end, we will present preliminary results of a study on the feasibility of NT scenarios on JT-60SA and a study on the feasibility of a NT DEMO and how it compares to the PT H-mode reference scenario. We will show that the reference PT scenario is too optimistic, while the NT one reaches satisfactory performance, with a much reduced level of uncertainty and no ELMs.
References
[1] A. O. Nelson et al., “Characterization of the ELM-free negative triangularity edge on DIII-D”, Plasma Physics and Controlled Fusion 66, 105014 (2024).
[2] A. Merle et al., “Pedestal properties of H-modes with negative triangularity using the EPED-CH model”, Plasma Physics and Controlled Fusion 59, 104001 (2017).
[3] S. Coda et al., “Enhanced confinement in diverted negative-triangularity L-mode plasmas in TCV”, Plasma Physics and Controlled Fusion 64, 014004 (2021).
[4] K. E. Thome et al., “Overview of results from the 2023 DIII-D negative triangularity campaign”, Plasma Physics and Controlled Fusion 66, 105018 (2024).
[5] A. Balestri et al., “Experiments and gyrokinetic simulations of TCV plasmas with negative triangularity in view of DTT operations”, Plasma Physics and Controlled Fusion 66, 065031 (2024).
[6] L. Aucone et al., “Experiments and modelling of negative triangularity asdex upgrade plasmas in view of DTT scenarios”, Plasma Physics and Controlled Fusion 66, 075013 (2024).
[7] F. Jenko et al., Physics of plasmas 7, 1904–1910 (2000).
[8] A. Balestri et al., “Physical insights from the aspect ratio dependence of turbulence in negative triangularity plasmas”, Plasma Physics and Controlled Fusion 66, 075012 (2024).
[9] A. Balestri et al., “On the interplay between plasma triangularity and micro-tearing turbulence”, Plasma Physics and Controlled Fusion 67, 105025 (2025).