Analysis of local heat flux in JET

The total heat flux q arising in steady state from Ohmic and neutral beam heating is calculated for a series of power scan experiments on JET. A radial resolution of q at selected radii is made to examine the dependence of q upon local plasma parameters such as density n e , temperature T e , current I and their gradients. Non-linear regression analysis techniques are applied to fit the data on q to empirical expressions q fit , involving the local plasma parameters. The most plausible fit emerging from the analysis is q fit = − (C/I)n e ∇T e − q pinch , in which C is a constant, I the current enclosed by a plasma surface and q pinch a constant so-called heat pinch. The net heat diffusivity inferred from this relationship agrees with estimates from heat pulse propagation measurements and it leads to a scaling law for the incremental energy confinement time which agrees with the one determined experimentally. There is a substantial amount of scatter in the data due to approximations made in the analysis and due to uncertainties in the experimental measurements.