Density profile peaking on DIII-D and JET – fuelling versus transport

Dimensionless collisionality (ν*) scans with fixed density in H-mode plasmas on DIII-D and JET together with modelling have shown that the NBI fuelling plays a more important role in density peaking than found in earlier multi-machine datasets where the increased peaking at low collisionality has been primarily ascribed to turbulent effects. Perturbative gas puff modulations are performed to disentangle the fuelling and the transport effects. On DIII-D, we find that, at the lowest ν*, the pinch is directed outward and the diffusion coefficients are larger compared to higher ν* cases. With increasing ν*, the pinch becomes inward outside the mid-radius, while remaining outward inside the mid-radius. At the same time, a strong increase in ion-scale density fluctuations with reduced ν* is observed with BES and predicted with TGLF. On JET, perturbative transport analysis, predictive integrated modelling with JINTRAC+TGLF and non-linear and linear GENE runs all show that NBI fuelling provides an important contribution to density peaking. These results indicate that the density profiles on ITER, where NBI fuelling is very small, may be less peaked than previously thought.