Experimental determination of critical threshold in electron transport on Tore Supra - art. no. 125001

In Tore Supra plasmas with fast wave electron heating, a critical threshold in the electron temperature gradient (delT(e)) is clearly observed, i.e., a finite value of delT(e) for which the turbulent heat diffusivity vanishes . The radial profile of this critical gradient is experimentally determined from a set of discharges characterized by similar plasma parameters with f ast wave powers ranging from 0.75 to 7.4 MW. The dependence of the electron heat flux on the gradient length is found to be offset linearly. The offse t term increases linearly with the ratio of the local magnetic shear to the safety factor.