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. These H-mode experiments were conducted in a diverted deuterium plasma with values of current I(p) = 0.65 MA, magnetic field B(T) = 2 T, density [n(e)] = 4.5 x 10(19) m-3, aspect ratio R/a = 1.83/0.48 = 3.8, and elongation K = 1.5. Off-axis heating was accomplished by vertically displacing the plasma by 0.30 m; 85% of the auxiliary heat was deposited outside the normalized minor radius of rho = 0.4. 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 1 1/2-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.