Electron thermal transport in NSTX and Tore Supra

A transport analysis of Tore Supra (TS) and NSTX discharges with centrally deposited fast wave electron heating is performed, and electron thermal fluxes are derived from power balance. Measurements of the electron temperature and density profiles, combined with ray tracing computation of the power deposition, allow detailed interpretation of the thermal flux versus temperature gradient. Evidence supporting the occurrence of electron temperature gradient (ETG) turbulent transport in the two confinement devices is found. Evidence for this mechanism includes: (1) a consistent scaling in density and temperature in both the profiles and radial heat flux, (2) a clear analytical and fundamental thermodynamic origin for the critical temperature gradient and its dependence on magnetic shear, (3) insensitivity of the turbulence to the mixture of trapped and passing electrons, (4) self-consistent turbulent generation of a magnetic flutter component from the parallel electron currents, and (5) good agreement between the thermal flux formulas used in radial transport codes with auxiliary heating and the profiles measured both in radius and time. Finally, internal transport barriers created in certain TS and NSTX discharges are argued to be a universal feature of transport equations in the presence of a (partially broken) invariant torus that is generic to nonmonotonic rotational transforms in dynamical systems. Weakly reversed magnetic shear discharges in NSTX show improved confinement in L-mode discharges. (author)