Understanding of the physics mechanisms that determine plasma fuelling and core particle transport is required to predict both the plasma density profiles and fuelling requirements for burning plasmas in next step devices, the access to burning plasma conditions and its possible control requirements. The evolution of the plasma density following the H-mode transition is particularly relevant for ITER because it affects the temporal evolution of the alpha heating power level build-up from L-mode conditions, as well as the edge power flow which is required to maintain the H-mode confinement itself. For the alpha heating evolution, the behaviour of the central plasma density and temperature (from where most of the alpha power is produced) in conditions with very low central fuelling (as expected in ITER with Negative Neutral Beam Injection) is of particular interest.