IMPROVED CONFINEMENT WITH PEAKED DENSITY PROFILES CAUSED BY TE PROFILE INVARIANCE

The origin of the better energy and particle transport with peaked density profiles observed in Ohmic plasmas and auxiliary heated plasmas is investigated. It is found that this property results from a reduction of the nonlocal component of the electron heat diffusivity chi-e caused by T(e) profile invariance in the outer half of the plasma. Density profile peaking diminishes the net electron heating power and the conductive electron heat flux which forces chi-e to adjust in such a way that the T(e) profile shape is conserved. Owing to the coupling with chi-e, the diffusion coefficient D is also reduced, which improves the particle confinement time and leads to the density profile peaking.