Electron transport and the critical temperature gradient

Tore Supra electron thermal fluxes, analyzed over a range of heating powers and plasma densities, are shown to vary parametrically according to the small-scale electron temperature gradient (ETG) model, rather than the ion inertial scale electrostatic gyro-Bohm model. Steady-state power balance analysis and time-varying interpretative transport simulations, performed on the Tore Supra Fast Wave Electron Heating database, validate the ETG thermal flux-versus-gradient relation and the existence of a critical electron temperature gradient. The critical gradient length R/Lc and the parametric dependence of the thermal flux, qe(ne,Te,∇Te,q,s), agree well with the ETG model.