Impurities in a nonaxisymmetric plasma. Transport and effect on bootstrap current
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 driftkinetic solver, the SFINCS code (the Stellarator FokkerPlanck Iterative Neoclassical Conservative Solver) [M. Landreman et al., Phys. Plasmas 21 (2014) 042503] which employs the full linearized FokkerPlanckLandau operator, to calculate neoclassical impurity transport coefficients for a Wendelstein 7X (W7X) magnetic configuration. We compare SFINCS calculations with theoretical asymptotes in the high collisionality limit. We observe and explain a 1/nuscaling of the interspecies radial transport coefficient at low collisionality, arising due to the field term in the interspecies 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 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 Z _{eff} of order unity can affect the bootstrap current enough to cause a deviation in the divertor strike point locations.
 Authors:

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^{[2]}
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^{[3]}
 Chalmers Univ. of Technology, Goteborg (Sweden); MaxPlanckInstitut fur Plasmaphysik, Greifswald (Germany)
 Univ. of Maryland, College Park, MD (United States)
 MaxPlanckInstitut fur Plasmaphysik, Greifswald (Germany)
 MaxPlanckInstitut fur Plasmaphysik, Greifswald (Germany); Institute of Engineering Thermodynamics, Stuttgart (Germany)
 Publication Date:
 Grant/Contract Number:
 FG0293ER54197; AC0205CH11231; DEFC0208ER54964; DEFG0293ER54197
 Type:
 Accepted Manuscript
 Journal Name:
 Physics of Plasmas
 Additional Journal Information:
 Journal Volume: 22; Journal Issue: 11; Journal ID: ISSN 1070664X
 Publisher:
 American Institute of Physics (AIP)
 Research Org:
 Univ. of Maryland, College Park, MD (United States)
 Sponsoring Org:
 USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC24)
 Country of Publication:
 United States
 Language:
 English
 Subject:
 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Stellarators; impurities; neoclassical transport; electric fields; plasma impurities; Fokker Planck equation; plasma transport properties
 OSTI Identifier:
 1227103
 Alternate Identifier(s):
 OSTI ID: 1226677
Mollén, A., Landreman, M., Smith, H. M., Braun, S., and Helander, P.. Impurities in a nonaxisymmetric plasma. Transport and effect on bootstrap current. United States: N. p.,
Web. doi:10.1063/1.4935901.
Mollén, A., Landreman, M., Smith, H. M., Braun, S., & Helander, P.. Impurities in a nonaxisymmetric plasma. Transport and effect on bootstrap current. United States. doi:10.1063/1.4935901.
Mollén, A., Landreman, M., Smith, H. M., Braun, S., and Helander, P.. 2015.
"Impurities in a nonaxisymmetric plasma. Transport and effect on bootstrap current". United States.
doi:10.1063/1.4935901. https://www.osti.gov/servlets/purl/1227103.
@article{osti_1227103,
title = {Impurities in a nonaxisymmetric plasma. Transport and effect on bootstrap current},
author = {Mollén, A. and Landreman, M. and Smith, H. M. and Braun, S. and Helander, P.},
abstractNote = {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 driftkinetic solver, the SFINCS code (the Stellarator FokkerPlanck Iterative Neoclassical Conservative Solver) [M. Landreman et al., Phys. Plasmas 21 (2014) 042503] which employs the full linearized FokkerPlanckLandau operator, to calculate neoclassical impurity transport coefficients for a Wendelstein 7X (W7X) magnetic configuration. We compare SFINCS calculations with theoretical asymptotes in the high collisionality limit. We observe and explain a 1/nuscaling of the interspecies radial transport coefficient at low collisionality, arising due to the field term in the interspecies 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 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.},
doi = {10.1063/1.4935901},
journal = {Physics of Plasmas},
number = 11,
volume = 22,
place = {United States},
year = {2015},
month = {11}
}