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    [Show abstract] [Hide abstract] ABSTRACT: Success of the puff-and-pump radiating divertor approach depends sensitively on both the divertor magnetic geometry and the ion B x 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 x 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 x B drift direction. The argon density in the main plasma during puff-and-pump operation fell by a factor of three for dRsep +0.4 cm when the ion B x 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 x B drift direction than to divertor closure in DIII-D.
    Full-text · Article · Jan 2008