Neoclassical flows in deuterium-helium plasma density pedestals

• Published in: Plasma physics and controlled fusion Vol. 59; no. 5; pp. 55019 - 55031
• Main Authors: Buller, S, Pusztai, I, Newton, S L, Omotani, J T
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01.05.2017
• Subjects: deuterium; flows; fusion; helium; Neoclassical transport; pedestal; radially global; tokamak
• ISSN: 0741-3335; 1361-6587; 1361-6587
• DOI: 10.1088/1361-6587/aa658a

In tokamak transport barriers, the radial scale of profile variations can be comparable to a typical ion orbit width, which makes the coupling of the distribution function across flux surfaces important in the collisional dynamics. We use the radially global steady-state neoclassical δ f code Perfect (Landreman et al 2014 Plasma Phys. Control. Fusion 56 045005) to calculate poloidal and toroidal flows, and radial fluxes, in the pedestal. In particular, we have studied the changes in these quantities as the plasma composition is changed from a deuterium bulk species with a helium impurity to a helium bulk with a deuterium impurity, under specific profile similarity assumptions. In the presence of sharp profile variations, the poloidally resolved radial fluxes are important for the total fluxes to be divergence-free, which leads to the appearance of poloidal return-flows. These flows exhibit a complex radial-poloidal structure that extends several orbit widths into the core and is sensitive to abrupt radial changes in the ion temperature gradient. We find that a sizable neoclassical toroidal angular momentum transport can arise in the radially global theory, in contrast to the local.