[Séminaire] - sotope-dependent 𝐸 × 𝐵 shear effect on turbulence heat flux in JET-ILW edge plasma conditions and integrated modeling using ASTRA-TGLF of high-𝝱 H-mode discharges

The high confinement mode (H-mode) is foreseen for deuterium-tritium (DT) stationary operation in tokamak fusion reactors. A major challenge is the low-to-high confinement (L–H) transition, which is not fully understood and is difficult to predict. Recent DT experiments in JET-ILW (ITER-Like Wall) have
provided new ITER-relevant observations. In previously dedicated JET-ILW experiments1, the heating power required to reach H-mode (PLH) was found to be proportional to the effective conductivity Ꭓeff of the plasma and inversely proportional to the effective mass Aeff of the hydrogenic species used.
Experiments were conducted at fixed magnetic configuration (𝐵!"#$%&'=1.91 T, 1.65 MA, q95=3.65) with a favourable lower single-null geometry for H-mode access. These experiments showed that a pure deuterium plasma requires less power to reach H-mode than a 50% hydrogen + 50% tritium plasma
(𝑃() * = 1.68𝑀𝑊 < 𝑃() )+, = 2.98𝑀𝑊), despite having a similar effective mass $A_{eff}=2$. A similar observation is made at Aeff=2.5 where a 25% hydrogen + 75% tritium plasma requires more power than a 50% deuterium + 50% tritium plasma to reach H-mode (𝑃()*+, = 1.66𝑀𝑊 < 𝑃())+, = 2.42𝑀𝑊). 

Via high-fidelity local gyrokinetic simulations (GENE2,3) and local reduced transport models (TLGF4) at 𝜌!"# = 0.95 using JET-ILW experimental conditions1, we observed similar heat flux levels at the same effective mass, close to experimental levels (2-3 MW)5. Turbulence is found to be of electron drift-wave nature, regardless of the isotope species. Including a non-negligible radial electric field shear allows different heat flux levels at the same effective mass between isotopic mixtures (H+T, D+T) and singular isotopes5 (D and synthetic Aeff=2.5). The heat flux in simulations is higher for the H+T cases compared to their respective effective mass equivalents of either singular isotopes or D+T mixture. This difference increases with the shear amplitude. This difference correlates with a different response of the zonal flow energy, higher in the D+T and singular isotope cases than in the corresponding H+T cases. This suggests stronger zonal-flow–turbulence coupling in certain isotopic configurations, favouring D+T operation.
Other JET discharges from the JET DTE2-05 & 06 campaign6, with high ꞵ values were reached in the core using pure hydrogen, deuterium and tritium, are studied using GENE and the ASTRA-TGLF7 integrated modeling framework. Discharges match dimensionless profiles of collisionality, normalized Larmor radius, ꞵ, safety factor, magnetic configuration and heating scheme. We performed linear and non-linear GENE simulations at different radial position, with and without fast-ions, 𝐸 × 𝐵 shear and parallel velocity transport8. Integrated modelling runs using ASTRA coupled to TGLF were done to explore the impact of the aforementioned parameters on profile evolution and stored thermal energy.

[1] G. Birkenmeier et al., Nuclear Fusion, 2022
[2] F. Jenko et al., Physics of plasmas, 2000
[3] T. Goerler et al., J. Comput. Phys., 2011
[4] G. M. Staebler et al., Nucl. Fusion, 2021
[5] G. Lo-Cascio et al., Nuclear Fusion, 2025
[6] P.A. Schneider et al., Nucl. Fusion, 2023
[7] G. Tardini et al., Nucl. Fusion, 2021
[8] C. F. B. Zimmermann et al, Nucl. Fusion, 2023