Impurity behaviour under puff-and-pump radiating divertor conditions

T. W. Petrie, G. D. Porter, N. H. Brooks, M. E. Fenstermacher, J. R. Ferron, M. Groth, A. W. Hyatt, R. J. La Haye, C. J. Lasnier, A. W. Leonard, T. C. Luce, P. A. Politzer, M. E. Rensink, M. J. Schaffer, M. R. Wade, J. G. Watkins, W. P. West

Research output: Contribution to journalArticleScientificpeer-review

21 Citations (Scopus)

Abstract

The effectiveness of the puff-and-pump technique to enrich a seeded impurity in the divertor relative to the core and, thereby, to maximize radiation in the divertor depends sensitively on both the magnetic geometry and the ion B × ∇B drift direction. In the puff-and-pump scenario used here, argon impurities injected into the private flux region are inhibited from accumulation in the core plasma by enhanced plasma flows to the divertor created by a combination of deuterium gas puffing upstream of the divertor targets and particle pumping near the divertor targets. Modelling of single-null, H-mode plasmas with the UEDGE fluid transport code indicates that particle drifts in the scrape-off layer and divertor strongly affect the locations where the argon seed impurity accumulates. It is also found in double-null cases that argon always shows a larger accumulation in the divertor out of which the ion B × ∇B drift is directed, regardless of the divertor into which the argon is injected. Experiments have shown that the degree to which the deuterium gas-puffing rate inhibits the escape of the seed impurity from the divertor(s) depends critically on the direction of the ion B × ∇B drift and on whether the plasma is single-null or double-null. The transition in behaviour from double-null to single-null character during puff-and-pump occurs for |dR = 0.4 cm when the ion B × ∇B drift was pointing away from the dominant divertor. The lowest argon density buildup in the main plasma of any of the configurations studied during puff-and-pump was achieved in single-null plasmas with the ion B × ∇B drift direction away from the divertor.

Original languageEnglish
Article number065013
Pages (from-to)1-8
Number of pages8
JournalNuclear Fusion
Volume49
Issue number6
DOIs
Publication statusPublished - 2009
MoE publication typeA1 Journal article-refereed

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