Optimization of flux-surface density variation in stellarator plasmas with respect to the transport of collisional impurities
Journal article, 2019

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.

fusion plasma

impurity transport


collisional transport


Stefan Buller

Chalmers, Physics, Subatomic and Plasma Physics

Håkan Smith

Max Planck Society

Albert Mollén

Chalmers, Physics, Subatomic and Plasma Physics

Sarah Newton

Chalmers, Physics, Subatomic and Plasma Physics

Istvan Pusztai

Chalmers, Physics, Subatomic and Plasma Physics

Nuclear Fusion

00295515 (ISSN) 17414326 (eISSN)

Vol. 59 6 066028

Implementation of activities described in the Roadmap to Fusion during Horizon 2020 through a Joint programme of the members of the EUROfusion consortium (EUROfusion)

European Commission (EC) (EC/H2020/633053), 2014-01-01 -- 2019-01-01.

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Fusion, Plasma and Space Physics



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