Comparison of ETG model for the electron pedestal temperature profile across isotope mix and gas fuelling rate scans in JET-ILW H-mode plasmas

• A R Field
• L Frassinetti
• B Chapman-Oplopiou
• C M Roach
• S Saarelma
• L Petru-Turica
• JET contributors

Predictions of the pedestal temperature profile calculated using a model for ETG turbulent electron heat transport [A R Field et al 2023 Phil. Trans. Royal Soc. A 381 (2242) 20210228] are compared with the pedestal structure of JET-ILW (‘ITER-like wall’) H-mode plasmas over scans of the deuterium-tritium (D:T) isotope mix and hydrogenic gas fuelling rate [L Frassinetti et al 2023 Nucl. Fusion 63 112009]. The model predictions for the electron temperature at the location of the density pedestal top T_e(ψ^ne,top_N) are found to agree well with the measured values over both scans across the full range of D:T ratio. However, the pedestal top temperature T_e,ped, which is typically located somewhat inside the density pedestal top, is under predicted by as much as a factor ∼ 2. This discrepancy implies that the ETG heat flux scaling, on which the model is based, appropriate for the steep-density gradient region is not applicable where the density gradient is weak. This difference might be attributed to a difference between the physics of the ETG turbulence in regimes where the density gradient either strong or weak, which are thought to be dominated by either the ‘slab’ or ‘toroidal’ branches of ETG turbulence. Other branches of turbulence might also play a role in the electron heat transport, particularly in the weak density gradient region at the pedestal top. As in the experiment, the predicted T_e across the pedestal is found to decrease with the ratio of separatrix to pedestal density n_e,sep/n_e,ped, which increases with the gas fuelling rate. Results from three models combining the ETG heat flux model with the EPED pedestal model [P B Snyder et al 2009 Phys. Plasmas 16 056118] are also presented, including one which also incorporates the density pedestal prediction mode of Saarelma et al [S Saarelma et al 2023 Nucl. Fusion 63 052002], providing a complete prediction of the pedestal profiles.