Impurities in a non-axisymmetric plasma: Transport and effect on bootstrap current
Journal article, 2015

Impurities cause radiation losses and plasma dilution, and in stellarator plasmas the neoclassical ambipolar radial electric field is often unfavorable for avoiding strong impurity peaking. In this work we use a new continuum drift-kinetic solver, the SFINCS code (the Stellarator Fokker-Planck Iterative Neoclassical Conservative Solver) [M. Landreman et al., Phys. Plasmas 21 (2014) 042503] which employs the full linearized Fokker-Planck-Landau operator, to calculate neoclassical impurity transport coefficients for a Wendelstein 7-X (W7-X) magnetic configuration. We compare SFINCS calculations with theoretical asymptotes in the high collisionality limit. We observe and explain a 1/nu-scaling of the inter-species radial transport coefficient at low collisionality, arising due to the field term in the inter-species collision operator, and which is not found with simplified collision models even when momentum correction is applied. However, this type of scaling disappears if a radial electric field is present. We also use SFINCS to analyze how the impurity content affects the neoclassical impurity dynamics and the bootstrap current. We show that a change in plasma effective charge Zeff of order unity can affect the bootstrap current enough to cause a deviation in the divertor strike point locations.

bootstrap current


plasma impurities



Albert Mollén

Chalmers, Applied Physics, Nuclear Engineering

Matt Landreman

University of Maryland

Håkan Smith

Max Planck Institute

Stefanie Braun

German Aerospace Center (DLR)

Max Planck Institute

Per Helander

Max Planck Institute

Physics of Plasmas

1070-664X (ISSN) 1089-7674 (eISSN)

Vol. 22 11 112508- 112508

Driving Forces

Sustainable development

Areas of Advance



Basic sciences

Subject Categories

Fusion, Plasma and Space Physics



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