Density peaking in low collisionality ELMy H-mode in JET

Abstract

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 q95 = 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 ΓBeam/ne = 0.07 m s−1. The additional flux due to wall neutrals is estimated as ΓWall/ne ⩽ 0.12 m s−1. Density profiles are found to be modestly peaked under these conditions with a relative density difference of Δn/⟨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 De,eff/χe ≈ 0.2, which might indicate an anomalous pinch provided the particle diffusivity De is sufficiently large. The measured values of De,eff/χe are at the lower end of the range used in ITER models.