DECOUPLING THE EFFECTS OF PLASMA CURRENT AND PLASMA-DENSITY ON DIII-DH-MODE ENERGY CONFINEMENT

Experiments that decoupled H mode plasma current and plasma density ha ve been performed for the first time on the DIII-D tokamak by the appl ication of divertor cryopumping. Deuterium ELMing H mode discharges we re operated in the single null configuration with 6 MW of neutral beam injection. These steady state discharges were operated at 1.5 and 0.7 5 MA with density ranges of(4.0-8.3) x 10(19) and (2.7-4.0) x 10(19) m (-3), respectively. Therefore, for the first time in a steady state DI II-D H mode, a factor of 2 range in I-p (n(e)) has been obtained at fi xed n(e) (I-p). A power law dependence of ELMing thermal confinement w as assumed, with the result that for a given magnetic field and a fixe d power dependence, tau(th) = 0.18I(P) (0.91+/-0.08)n(e)(0.18+/-0.09)P (L)(-0.5). If a linear dependence of tau(th) on internal inductance is assumed the density dependence disappears. A local power balance anal ysis employing the 1 1/2-D ONETWO transport code found that the one fl uid effective diffusivity did not change with a factor of 2 change in density and was strongly reduced with increasing current. The reductio n with increasing current occurs most dramatically for rho > 0.5. Util izing ONETWO for particle transport analysis demonstrated that the cor e particle transport was more rapid at lower density.