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DIII-D discharges that transition to H-mode solely with off-axis electroncyclotron heating (ECH) often exhibit strong off-axis peaking of electrontemperature profiles at the heating location. Electron heat transportproperties near these off-axis temperature peaks have been studied usingmodulated ECH. The Fourier analyzed electron temperature data have been used toinfer electron thermal diffusivity. Comparisons with numerical solutions of thetime-dependent electron thermal equation find that the data are consistent witha narrow region with electron diffusivity $\chi_e$ an order of magnitude lowerthan the average value across the plasma, suggesting an electron internaltransport barrier (ITB) near the ECH heating location. Detailed profileanalysis and equilibrium reconstructions suggest that the formation of theseITBs are correlated with off-axis values of the safety factor $q$ being near 1.Furthermore, the ECH driven H-mode discharges demonstrate more rapid electronheating rate near the ECH deposition location than L-mode discharges withhigher auxiliary ECH heating power. Additional modeling attributes thisdifference to the modification of electron heat transport in the core at theL-H transition, which also sustains the off-axis electron temperature peaks.

Investigation of Core Transport Barriers in DIII-D Discharges with off-axis Te Profile Peaks