Electron thermal transport in enhanced core confinement regimes

The cause of the anomalous electron thermal transport in a region of suppressed ion thermal transport is investigated using a comprehensive gyrokinetic stability code. Analysis of a DIII-D negative central shear discharge with additional fastwave electron heating is presented. It is found that the electron heating excites the electron temperature gradient mode (ETG). The enhanced electron thermal transport from power balance analysis is consistent with the increased growth rate for the ETG mode. The ion thermal transport barrier is observed to retreat towards the plasma center during the fastwave heating (FW). Transport modeling with self-consistent E x B velocity shear reproduces this effect for on-axis electron heating. The same transport model predicts that off-axis electron heating can extend the region of reduced transport outward