Non-linear neoclassical model for poloidal asymmetries in tokamak pedestals: diamagnetic and radial effects included

TL;DR

This paper introduces a self-consistent non-linear neoclassical model that includes impurity diamagnetic and radial effects to better explain poloidal asymmetries in tokamak pedestals, aligning theory with experimental observations.

Contribution

It is the first model to self-consistently incorporate impurity diamagnetic flow and its two-dimensional effects in tokamak pedestal analysis.

Findings

Successfully explains impurity density asymmetries

Aligns theoretical predictions with experimental measurements

Supports turbulence reduction in H-mode pedestals

Abstract

Stronger impurity density in-out poloidal asymmetries than predicted by the most comprehensive neoclassical models have been measured in several tokamaks around the world during the last decade, calling into question the reduction of turbulence by sheared radial electric fields in H-mode tokamak pedestals. However, these pioneering theories neglect the impurity diamagnetic drift, or fail to retain it self-consistently; while recent measurements indicate that it can be of the same order as the ExB drift. We have developed the first self-consistent theoretical model retaining the impurity diamagnetic flow and the two-dimensional features it implies due to its associated non-negligible radial flow divergence. It successfully explains collisionally the experimental impurity density, temperature and radial electric field in-out asymmetries; thus making them consistent with H-mode pedestal turbulence reduction.