  A burning fusion plasma has a large inwards flux of fuel and outwards flux of
ash. Existing impurity transport theories do not account for a steady-state
environment of such large fluxes. In this paper, we extend classical transport
theory to account for a background of such fluxes. In a mainly two-ion species
magnetized plasma, with oppositely directed density gradients maintained by
oppositely directed sources of the two species, trace impurity ions are shown
to align with the larger mass ions. This unexpected behavior is derived
analytically and simulated numerically using the MITNS (Multiple-Ion Transport
Numerical Solver) code. The result suggests a potential advantage of
edge-fueled p-B11 fusion in extracting high-Z impurities, and possible
applications in plasma-based separation methods.
