First global gyrokinetic profile predictions of ITER burning plasma

TL;DR

This work delivers the first radially global, self-consistent gyrokinetic predictions for the ITER baseline (15 MA) using the GENE-Tango framework in fully electromagnetic mode. By coupling global GENE simulations with a transport solver, the study reveals that electromagnetic turbulence, including MTMs, low-$k_y$ EM modes, and AITG/KBMs, strongly shapes core transport and density peaking, while a flat safety-factor core can drastically degrade confinement. The results show a fusion gain of $Q=12.2$ and a density profile compatible with empirical scalings, with rotation playing a minor role in transport and ETG turbulence being quenched by zonal flows at low collisionality. Comparisons with reduced models (QuaLiKiz, TGLF) indicate general agreement in several regimes, underscoring the value of global simulations for validating and guiding fast predictive tools. These findings advance first-principles predictions for ITER, informing profile control strategies and future investigations of alpha-particle effects and impurities.

Abstract

In this work, we present the first global gyrokinetic simulations of the ITER baseline scenario operating at 15 MA using GENE-Tango electrostatic and electromagnetic simulations. The modeled radial region spans close to the magnetic axis up to rho_tor = 0.6. Our results show a pronounced density peaking, moderated by electromagnetic fluctuations. The predicted fusion gain for this scenario is Q = 12.2, aligning well with ITER's mission objectives. We further characterize the turbulence spectra and find that electromagnetic modes, such as microtearing modes, kinetic ballooning modes, and Alfvenic ion temperature gradient modes at low binormal wave numbers, play a critical role in the core transport of this ITER scenario, necessitating high numerical resolution for accurate modeling. Local flux-tube simulations qualitatively reproduce the key features observed in the global gyrokinetic simulations but exhibit a much higher sensitivity to profile gradients, reflecting increased stiffness, likely due to the linearization of the equilibrium profiles and safety factor. Our study also reveals that the imposed external toroidal rotation profiles have a negligible impact on turbulent transport, as their magnitudes are substantially lower than the dominant linear growth rates. Furthermore, we demonstrate that the safety factor profile is of paramount importance: scenarios featuring flat q profiles with near-zero magnetic shear lead to the destabilization of kinetic ballooning modes in the plasma core, significantly enhancing turbulent transport and potentially degrading confinement. Finally, although electron temperature gradient turbulence initially appears large, sometimes exceeding ion-scale transport levels, it is ultimately quenched over long timescales by secular evolution of zonal flows, which are weakly damped under the very low collisionality conditions expected in ITER.

Figures (22)

• Figure 1: Radial profiles of the initial (a) thermal ion temperature (50-50 deuterium-tritium mixture), (b) electron temperature, and (c) density for the ITER 15MA baseline scenario, as computed by QuaLiKiz-HFPS and used as initial conditions for the GENE-Tango simulations. The vertical dotted black lines denote the radial domain covered by the GENE-Tango simulations.
• Figure 2: Radial profiles of (a) ion heating, (b) electron heating, and (c) particle sources for the ITER 15MA baseline scenario, as computed by QuaLiKiz-HFPS and held fixed throughout the GENE-Tango simulations. Alpha particle heating, collisional energy exchange, and radiative power losses are computed self-consistently by GENE-Tango at each iteration.
• Figure 3: Radial profiles of (a) $Zeff$, (b) safety factor $q$ and (c) toroidal rotation $vtor$ for the ITER 15MA baseline scenario, as computed by QuaLiKiz-HFPS and kept fixed throughout the GENE-Tango simulations.
• Figure 4: Contours of constant poloidal flux from magnetic equilibria computed using CHEASE, based on the initial profiles from QuaLiKiz-HFPS (blue) and the final profiles from the GENE-Tango electromagnetic simulation (red).
• Figure 5: Time-averaged radial profile of the (a) ion, (b) electron heat fluxes in MW and (c) particle flux in $1/s$ corresponding to the averaged last five GENE–Tango iterations (red) in the electrostatic GENE-Tango simulation. The shaded gray areas denote the buffer regions and the black circles the volume integral of the injected particle and heat sources. The shaded red areas represent the variations of the GENE turbulent fluxes in the last five GENE-Tango iterations.