Predicting core transport in ITER baseline discharges with neon injections

TL;DR

This paper tackles the challenge of achieving self-consistent core transport and divertor power exhaust predictions for ITER under neon-seeded divertor conditions. It introduces an integrated modeling approach using the OMFIT STEP workflow to compute self-consistent core profiles with TGYRO, constrained by SOLPS-ITER edge solutions, and derives the separatrix power flux $P_{ m sep}$ for a controlled $Z_{ m eff}$ scan. The study finds a narrow compatibility window around $Z_{ m eff} \,\approx\,1.6$–$1.75$ and $f_{P_{ m aux}}\approx0.75$–1.0 where core performance and edge power exhaust align with divertor protection targets, with $P_{ m sep}\approx100$ MW when matched to SOLPS-ITER. It also shows that intrinsic rotation variations produce modest changes (\lesssim 20\%) in $P_{ m sep}$ and that charge-exchange radiation inside the separatrix is negligible under predicted neutral densities. The work provides a practical framework for impurity-control and auxiliary-heating scheduling in early ITER operation and sets the stage for future whole-device scenario optimization and pedestal–core coupling validation.

Abstract

Achieving self-consistent performance predictions for ITER requires integrated modeling of core transport and divertor power exhaust under realistic impurity conditions. We present results from the first systematic power-flow and impurity-content study for the ITER 15 MA baseline scenario constrained directly by existing SOLPS-ITER neon-seeded divertor solutions. Using the OMFIT STEP workflow, stationary temperature and density profiles are predicted with TGYRO for $1.5 \le Z_{\rm eff} \le 2.5$, and the corresponding power crossing the separatrix $P_{\rm sep}$ is evaluated. We find that $P_{\rm sep}$ varies by more than a factor of 1.7 across this scan and matches the $\sim 100$~MW SOLPS-ITER prediction when $Z_{\rm eff} \simeq 1.6$ or when auxiliary heating is reduced to $\sim 75\%$ of nominal. Rotation-sensitivity studies show that plausible variations in toroidal flow magnitude modify $P_{\rm sep}$ by $\lesssim 20\%$, while AURORA modeling confirms that charge-exchange radiation inside the separatrix is dynamically negligible under predicted ITER neutral densities. These results identify a restricted compatibility window, $Z_{\rm eff} \approx 1.6$--1.75 and $0.75 \lesssim f_{P_{\rm aux}} \le 1.0$, in which core transport predictions remain aligned with neon-seeded divertor protection targets. This self-consistent, model-constrained framework provides actionable guidance for impurity control and auxiliary-heating scheduling in early ITER operation and supports future whole-device scenario optimization.

Figures (9)

• Figure 1: Baseline ITER 15 MA single-null equilibrium and initial kinetic profiles used as the starting point for all simulations in this study. From left to right: magnetic geometry with the separatrix indicated; electron pressure profile; and safety-factor profile $q(r)$, characterized by a broad region of flat $q$ ($q_0 < 1$) typical of the ITER baseline scenario.
• Figure 2: Initial core density profiles for deuterium, tritium, helium, and neon for the $Z_{\rm eff}$ scan in PRO-CREATE.
• Figure 3: Stationary temperature and density profiles predicted by TGYRO for the $Z_{\rm eff}$ scan. Rising $Z_{\rm eff}$ leads to increased electron collisionality and correspondingly lower core temperatures, while ion heating becomes relatively more efficient.
• Figure 4: SOLPS-ITER simulation of the neon-seeded ITER divertor scenario used to constrain the edge impurity content in this work. Left: two-dimensional distribution of $Z_{\rm eff}$ in the SOLPS-ITER domain, including the scrape-off layer and a narrow band of closed flux surfaces. While the open-field-line region exhibits strong poloidal variation in impurity concentration, the closed-field-line region is nearly uniform, justifying the use of a radially flat $Z_{\rm eff}$ in the core-transport modeling Lore_2022. Right: poloidally averaged radial profile of the effective charge $Z_{\rm eff}$ just inside the last closed flux surface, plotted versus outer mid-plane distance from the separatrix $dR^{\rm OMP}_{\rm sep}$. The profile rapidly flattens to $Z_{\rm eff}\simeq 1.6$ in the confined region.
• Figure 5: Radial power-flow profiles predicted by TGYRO for five values of $Z_{\rm eff}$. The extracted power crossing the separatrix decreases monotonically with increasing impurity concentration, and matches the SOLPS-ITER target condition of ${\sim}100\,\mathrm{MW}$ for $Z_{\rm eff} \approx 1.75$.