Global and local energy confinement properties of simple transport coefficients of the Bohm type

Global and local energy transport analysis of experimental results in TFTR and JET indicate that transport models of the Bohm type allow a better representation of experimental data than models of the gyro-Bohm type. Hence a Bohm-like model has been developed by allowing a dependence on a few dimensionless parameters so as to reproduce the main features of global L-mode thermal confinement scaling laws in tokamaks and to obtain bowl-shaped thermal diffusivity profiles. The electron temperature profiles predicted by this model are shown to be in agreement with measured ones in a variety of steady-state and time-dependent JET L-mode discharges.