EX/P4-21 The Effect of Magnetic Balance and Particle Drifts on Radiating Divertor Behavior in DIII-D

Success of the puff-and-pump radiating divertor approach depends sensitively on both the divertor magnetic geometry and the ion B B drift direction. In the puff-and-pump scenario used in this study, argon impurities were injected into the private flux region, while plasma flows into both the inner and outer divertors were enhanced by a combination of particle pumping near both divertor targets and deuterium gas puffing upstream of the divertor targets. For single-null (SN) configurations, argon accumulation was 2–3 times lower in the main plasma when the ion B B drift was directed away from the divertor. The puff-and-pump approach was much less effective in screening argon from the main plasma of double-null (DN) discharges than of SN discharges, such that argon impurities accumulated in the main plasma of DNs at a rate ~2–3 times higher than in corresponding SNs. Regardless of which divertor in DN had argon injection, argon accumulated in the divertor that was opposite the B B drift direction. The argon density in the main plasma during puff-andpump operation fell by a factor of three for dRsep +0.4 cm when the ion B B drift was directed away from the dominant divertor, and this represents the transition from DN to SN behavior during puff-and-pump application. Comparison of identically-prepared SN H-mode plasmas showed that core density control of deuterium and the argon was far more sensitive to the ion B B drift direction than to divertor closure in DIII-D.