Description
This contribution will first review the history of tokamak plasma physics research related to
negative triangularity (NT), starting by explaining why it was disregarded early on, based on
ideal MHD considerations [1]. Nevertheless, leveraging on the pioneering work on TCV, NT
studies have been extended to larger tokamaks among which DIII-D, AUG and even JET on its
last day of plasma operation, and significant progress was made. For the three main pillars
considered to design a reactor (plasma confinement, heat exhaust and integrated design), no
showstopper is identified so far. While the baseline scenario for ITER and next step devices
relies on the H-mode confinement regime, and its harmful edge localized modes, the promise
of NT is that plasma confinement is as good as H-mode PT (positive triangularity) but in Lmode
[see papers in 2 and refs therein]. This benefit alleviates the problem of ELM suppression
but also the request to ensure a certain level of power crossing the separatrix to maintain the Hmode.
The H-mode avoidance for NT shapes is explained by a closed path to the second stability
region for ballooning modes, hence the benefit of “bad” ideal stability, and allows robust
predictions. The example of JET experiments will be used to illustrate these aspects. Another
breakthrough is that operation at much larger densities than the “density limit” in tokamaks has
been demonstrated in DIII-D. Here also, theoretical advancements are supporting the
experimental findings. Prospects for an optimized DEMO-NT will be explained.
[1] A. Marinoni, S. Coda and O. Sauter, Reviews of Modern Plasma Physics 5 (2021) 6
[2] S. Coda, T. Happel, M. Kikuchi, C. Paz-Soldan, Special Issue on Advances in the Physics Basis of Negative Triangularity Tokamaks, https://iopscience.iop.org/collections/ppcf-231109-
412
a B.P. Duval et al 2024 Nucl. Fusion 64 112023
b K E Thome et al 2024 Plasma Phys. Control. Fusion 66 105018
c H. Zohm et al 2024 Nucl. Fusion 64 112001
d C.F. Maggi et al 2024 Nucl. Fusion 64 112012
e E. Joffrin et al 2024 Nucl. Fusion 64 112019