Speaker
Description
Future fusion reactors require integrated operating scenarios that simultaneously address divertor power exhaust, tungsten impurity control, and good core confinement. In recent JET campaigns, dedicated “JET-ITER baseline” experiments with neon impurity seeding were conducted in D and D-T plasmas [1], developed at high input power (30-35 MW), high plasma current (2.5-3.2 MA), high density ($f_{GW}$ ≈ 0.7-0.8), and within an ITER-like configuration characterized by high triangularity and vertical divertor targets. In these discharges, simultaneous achievement of partial divertor detachment, small or no ELMs, low tungsten concentration ($C_W$ < 7×10⁻⁵), and reasonable confinement ($H_{98}$ ≈ 0.85-1.0) was demonstrated, highlighting attractive features for future device operation. Neon impurity seeding reduced divertor heat flux and tungsten sources while enhancing core confinement through improved pedestal pressure relative to unseeded plasmas.
Comprehensive modeling was carried out to interpret these experiments and to prepare for extrapolation to future devices. SOLPS-ITER simulations with drifts, using input power profiles from TRANSP, successfully reproduced key experimental measurements, including mid-plane electron and neon density and temperature profiles, divertor target conditions, and line-of-sight–resolved radiated power using exactly experimental gas fueling and seeding rates. The effects of drifts, D-Ne charge exchange, Lyman-opacity, neutral–neutral collisions, and sub-divertor structures, as well as transport assumptions—such as poloidal inhomogeneity associated with ballooning and divertor broadening, and differences between main ions and impurity species—are studied in detail to assess how they influence and contribute to reproducing experimental measurements. Comparisons between seeded and unseeded simulations, without altering transport assumptions, quantitatively reproduced the measured separatrix density drop, attributed to reduced ionization sources, while the underestimation of the pedestal density drop implies additional transport changes in that region. JINTRAC simulations [2] showed consistency with SOLPS-ITER in the separatrix region (e.g. neutral particle fluxes) and confirmed that the density reduction arises from decreased ionization sources or increased pedestal diffusivity.
Reference:
[1] C. Giroud et al., 30th IAEA FEC, Chengdu, China, Oct. 13-18, 2025.
[2] V.K. Zotta, et al., 51st EPS, Vilnius, Lithuania, Jul. 7-11, 2025.