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Optimization of flux-surface density variation in stellarator plasmas with respect to the transport of collisional impurities

Authors :
Buller, Stefan
Smith, Håkan M.
Mollén, Albert
Newton, Sarah Louise
Pusztai, Istvan
Publication Year :
2018

Abstract

Avoiding impurity accumulation is a requirement for steady-state stellarator operation. The accumulation of impurities can be heavily affected by variations in their density on the flux-surface. Using recently derived semi-analytic expressions for the transport of a collisional impurity species with high-$Z$ and flux-surface density-variation in the presence of a low-collisionality bulk ion species, we numerically optimize the impurity density-variation on the flux-surface to minimize the radial peaking factor of the impurities. These optimized density-variations can reduce the core impurity density by $0.75^Z$ (with $Z$ the impurity charge number) in the Large Helical Device case considered here, and by $0.89^Z$ in a Wendelstein 7-X standard configuration case. On the other hand, when the same procedure is used to find density-variations that maximize the peaking factor, it is notably increased compared to the case with no density-variation. This highlights the potential importance of measuring and controlling these variations in experiments.<br />Comment: 19 figures, 17 pages. Accepted into Nuclear Fusion

Subjects

Subjects :
Physics - Plasma Physics

Details

Database :
arXiv
Publication Type :
Report
Accession number :
edsarx.1812.09194
Document Type :
Working Paper
Full Text :
https://doi.org/10.1088/1741-4326/ab12a7