Validation of geometric proxies using negative and positive triangularity plasmas with varying elongation on TCV and multi-machine gyrokinetic simulations
Abstract
Negative Triangularity (NT) tokamak plasmas can achieve H-mode-like confinement while avoiding Edge Localized Modes, making them an attractive reactor scenario. Predicting in which configuration this benefit occurs requires understanding how magnetic geometry controls turbulent transport. Using a set of geometric proxies based on the poloidally averaged magnetic drift velocity, its poloidal variation, and Finite Larmor Radius (FLR) effects, this work validates their predictive power against gyrokinetic simulations and experiments. First, the proxies are used to predict how the relative benefit of NT over Positive Triangularity (PT) evolves with elongation κ, forecasting a detrimental effect of NT below κ∼0.75--$0.8$. This prediction is confirmed by linear and nonlinear GENE simulations in both ITG- and TEM-dominated regimes. Additionally, a dedicated experimental elongation scan on TCV shows that NT plasmas at κLCFS=1.5 have βN and H98y2 roughly 1.5 times larger than PT counterparts, while no difference is observed at κLCFS=0.95. The analysis is then extended to realistic ITG-dominated scenarios from DIII-D, AUG, and JET, including up-down asymmetric equilibria where conventional triangularity-based descriptions break down. In all three devices, simulations of NT equilibria exhibit substantially reduced nonlinear heat fluxes relative to PT (factors of 1.8, 1.6, and 2.1, respectively). A systematic swap of geometric coefficients between NT and PT equilibria shows that magnetic drifts and FLR effects are the dominant stabilizing mechanisms across all machines, with parallel dynamics playing a secondary role. These results establish the geometric proxies as reliable, computationally inexpensive predictors of NT transport benefits across diverse shapes and turbulence regimes.
Related
- Predicting Negative Triangularity Edge Confinement with a Neutral-Coupled Full-f Gyrokinetic Model
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- Accelerating high-fidelity gyrokinetic fusion simulations with iGENE
- Global Gyrokinetic Simulations of Electromagnetic Turbulence in STEP
BibTeX
@misc{balestri2026validation,
title = {{Validation of geometric proxies using negative and positive triangularity plasmas with varying elongation on TCV and multi-machine gyrokinetic simulations}},
author = {Alessandro Balestri and Justin Ball and Stefano Coda and Olivier Sauter and Paola Mantica and Alberto Mariani and Benoit Labit and Branka Vanovac and Joerg Hobirk and the TCV team},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.17974},
eprint = {2610.17974},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.17974},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Validation of geometric proxies using negative and positive triangularity plasmas with varying elongation on TCV and multi-machine gyrokinetic simulations
AU - Alessandro Balestri
AU - Justin Ball
AU - Stefano Coda
AU - Olivier Sauter
AU - Paola Mantica
AU - Alberto Mariani
AU - Benoit Labit
AU - Branka Vanovac
AU - Joerg Hobirk
AU - the TCV team
PY - 2026
DA - 2026/10/13
PB - arXiv
DO - 10.48550/arxiv.2610.17974
UR - https://arxiv.org/abs/2610.17974
AB - Negative Triangularity (NT) tokamak plasmas can achieve H-mode-like confinement while avoiding Edge Localized Modes, making them an attractive reactor scenario. Predicting in which configuration this benefit occurs requires understanding how magnetic geometry controls turbulent transport. Using a set of geometric proxies based on the poloidally averaged magnetic drift velocity, its poloidal variation, and Finite Larmor Radius (FLR) effects, this work validates their predictive power against gyrokinetic simulations and experiments. First, the proxies are used to predict how the relative benefit of NT over Positive Triangularity (PT) evolves with elongation κ, forecasting a detrimental effect of NT below κ∼0.75--$0.8$. This prediction is confirmed by linear and nonlinear GENE simulations in both ITG- and TEM-dominated regimes. Additionally, a dedicated experimental elongation scan on TCV shows that NT plasmas at κ^LCFS=1.5 have β_N and H_98y2 roughly 1.5 times larger than PT counterparts, while no difference is observed at κ^LCFS=0.95. The analysis is then extended to realistic ITG-dominated scenarios from DIII-D, AUG, and JET, including up-down asymmetric equilibria where conventional triangularity-based descriptions break down. In all three devices, simulations of NT equilibria exhibit substantially reduced nonlinear heat fluxes relative to PT (factors of 1.8, 1.6, and 2.1, respectively). A systematic swap of geometric coefficients between NT and PT equilibria shows that magnetic drifts and FLR effects are the dominant stabilizing mechanisms across all machines, with parallel dynamics playing a secondary role. These results establish the geometric proxies as reliable, computationally inexpensive predictors of NT transport benefits across diverse shapes and turbulence regimes.
ER -