The density evolution during the transient phase just after the L–H transition is investigated using theoretical transport models. Cases characterized by core densities which evolve in longer timescales than the edge densities, leading to hollow density profiles () are modelled. This density evolution is particularly interesting because it has been shown to be beneficial in the view of the access to burning plasma conditions in ITER (Loarte et al 2013 Nucl. Fusion53 083031). Self-consistent simulations of the JET discharge 79676 of the density-only, and of the density and the temperatures are carried out using a quasilinear gyrokinetic code, QuaLiKiz (Bourdelle et al 2007 Phys. Plasmas14 112501), coupled with a transport code CRONOS (Artaud et al 2010 Nucl. Fusion50 043001). The slow evolution of the hollow density, associated with the self-consistently calculated hollow NBI particle deposition, is well reproduced in the plasma core. Indeed, QuaLiKiz is shown to reproduce nonlinear gyrokinetic heat and particle fluxes well for both positive and negative . That gives a theoretical and general basis for the persistence of the hollowness, laying the groundwork for the extrapolation to ITER.
Collisional drift instability in hollow and coaxial plasmas