Global effects on neoclassical transport in the pedestal with impurities
Abstract
We present a numerical study of collisional transport in a tokamak pedestal in the presence of non-trace impurities, using the radially global neoclassical solver PERFECT [M. Landreman et al. 2014 Plasma Phys. Control. Fusion 56 045005]. It is known that in a tokamak core with non-trace impurities present the radial impurity flux opposes the bulk ion flux to provide an ambipolar particle transport, with the electron transport being negligibly small. However, in a sharp density pedestal with sub-sonic ion flows the electron transport can be comparable to the ion and impurity flows. Furthermore, the neoclassical particle transport is not intrinsically ambipolar, and the non-ambipolarity of the fluxes extends outside the pedestal region by the radial coupling of the perturbations. The neoclassical momentum transport, which is finite in the presence of ion orbit-width scale profile variations, is significantly enhanced when impurities are present in non-trace quantities, even if the total parallel mass flow is dominated by the bulk ions.
Keywords
Cite
@article{arxiv.1603.00688,
title = {Global effects on neoclassical transport in the pedestal with impurities},
author = {I. Pusztai and S. Buller and M. Landreman},
journal= {arXiv preprint arXiv:1603.00688},
year = {2016}
}