Dependence of the density shape on the heat flux profile in ASDEX Upgrade high density H modes

For high density H modes with constant gas puff on ASDEX Upgrade a slow evo lution of the density profile is observed with a time constant much larger than T-E. While the edge density remains constant the central density incre ases as does the stored energy until sawteeth are lost and impurity influx sets in. This peaking process is only observed with NBI heating. Substituti ng half of the heating by central ICRH leads to completely flat profiles ev en though half of the original NBI particle fuelling remains. This behaviou r, as well as the slow timescale of the peaking process with pure NBI heati ng, is successfully modelled with a pinch of the order of the neoclassical Ware pinch and a proportionality between the particle diffusion coefficient D and the heat conductivity X. Such an assumption links D to the heat flux profile (qheat), since the temperature profile is observed to be stiff. Su ch a model implies flat density profiles for a centrally heated fusion reac tor.