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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, 042503 (2014)] 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/ν-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 Z{sub eff} of order unity can affect the bootstrap current enough to cause a deviation in the divertor strike point locations.
Authors:
 [1] ;  [2] ;  [3] ; ;  [4] ;  [4] ;  [2]
  1. Department of Applied Physics, Chalmers University of Technology, Göteborg (Sweden)
  2. (Germany)
  3. Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, Maryland 20742 (United States)
  4. Max-Planck-Institut für Plasmaphysik, 17491 Greifswald (Germany)
Publication Date:
OSTI Identifier:
22489842
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 11; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AXIAL SYMMETRY; BOOTSTRAP CURRENT; DILUTION; DIVERTORS; EFFECTIVE CHARGE; ELECTRIC FIELDS; ENERGY LOSSES; FOKKER-PLANCK EQUATION; NEOCLASSICAL TRANSPORT THEORY; PLASMA; PLASMA IMPURITIES; STELLARATORS