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Title: Impurities in a non-axisymmetric 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 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 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.
ORCiD logo [1] ; ORCiD logo [2] ;  [3] ;  [4] ;  [3]
  1. Chalmers Univ. of Technology, Goteborg (Sweden); Max-Planck-Institut fur Plasmaphysik, Greifswald (Germany)
  2. Univ. of Maryland, College Park, MD (United States)
  3. Max-Planck-Institut fur Plasmaphysik, Greifswald (Germany)
  4. Max-Planck-Institut fur Plasmaphysik, Greifswald (Germany); Institute of Engineering Thermodynamics, Stuttgart (Germany)
Publication Date:
Grant/Contract Number:
FG02-93ER54197; AC02-05CH11231; DEFC0208ER54964; DEFG0293ER54197
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 22; Journal Issue: 11; Journal ID: ISSN 1070-664X
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) (SC-24)
Country of Publication:
United States
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Stellarators; impurities; neoclassical transport; electric fields; plasma impurities; Fokker Planck equation; plasma transport properties
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1226677