Scaling of density peaking in JET H-modes and implications for ITER

Results from an extensive profile database analysis of JET density profiles in H-mode show that the density peaking factor n e0 / < n e > in JET H-modes increases as the effective collisionality drops from ∼1 at mid-radius to below 0.1 as expected for ITER. Density peaking is also strongly correlated with the Greenwald number N G , the particle outward flux Γ from the neutral beam source and T i / T e . The correlations with l i , q 95 , β N , ρ*, L Te , L Ti , the toroidal Mach number and its shear are weak or insignificant. H- modes heated only by ICRH are, on average, only slightly less peaked than H-modes dominated by NBI, demonstrating that neutral beam fuelling can only explain a modest part (∼20%) of the peaking. Scaling expressions involving ν eff , N G , R Γ/( n e χ) and T i / T e suggest that n e0 /< n e > may exceed 1.5 in ITER, providing a boost of fusion power of more than 30% for fixed β and average density with respect to the usual assumption of a flat density profile.