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.Comment: 36 pages, 13 figure
