Determination of local transport coefficients by heat flux analysis and comparisons with theoretical models

The energy confinement properties of different regimes of JET plasmas are investigated. The results of local transport analysis in both L- and H-mode regimes are discussed and the properties of H-mode plasmas produced by neutral beam injection (NBI) and/or ion cyclotron resonance heating (ICRH) are compared. Two aspects of transport analysis are addressed. Firstly, the relative importance of the electron and ion heat conductivities χe and χi and a comparison with the effective particle diffusivity D since this determines the nature of the turbulence responsible for the degradation in confinement. The second issue is whether the present theoretical models adequately describe the radial dependence of the measured heat flux. Several theoretical models are considered: the ion temperature gradient driven turbulence model, the Rebut-Lallia critical temperature gradient model, the dissipative and collisionless trapped electron drift wave mode, the Carreras-Diamond resistive ballooning model and the neoclassical pressure gradient driven turbulence model. None of these give a completely good fit to the radial behaviour of the measured heat flux in all of the pulses. (author)