Density peaking in low collisionality ELMy H-mode in JET

Low collisionality, low particle source, ELMy H-modes (type-III) with sawteeth are produced in JET in order to address the question of density profile evolution in the reference q 95 = 3 ITER scenario. The paper focuses on particle transport in the core zone around the mid-radius. The pedestal region including ELMs and the region affected by sawteeth are not considered. By replacing a significant part of the neutral beam heating by RF power the beam particle flux at mid-radius has been reduced to Γ Beam / n e = 0.07 m s −1 . The additional flux due to wall neutrals is estimated as Γ Wall / n e ⩽ 0.12 m s −1 . Density profiles are found to be modestly peaked under these conditions with a relative density difference of Δ n /⟨ n ⟩ = 0.23 across the zone not affected by sawteeth and ELMs. In a region around the mid-radius the ratio of effective particle diffusivity to electron thermal diffusivity is found to be D e,eff /χ e ≈ 0.2, which might indicate an anomalous pinch provided the particle diffusivity D e is sufficiently large. The measured values of D e,eff /χ e are at the lower end of the range used in ITER models.