Examination of heat transport during off-axis neutral beam injection in DIII-D

Off-axis heating experiments have been conducted in DIII-D using 75 keV neutral beam injection as the auxiliary power source. The application of 7.5 MW of deuterium neutral beam power resulted in the plasma transiting into the high density H-mode confinement regime with equal electron and ion temperatures. The global thermal energy confinement was not affected by changing the heating location. A power balance analysis employing the 11/2-D ONETWO transport code and assuming purely diffusive heat transport found that the one-fluid effective diffusivity changed dramatically between the two cases. These results indicate the possibility that the local diffusivity is a function of some quantity other than the density, temperature and their gradients. An alternative explanation is that the diffusivity remains unchanged and that there is an inward non-diffusive heat flow to balance the power flow