Charge dependence of neoclassical and turbulent transport of light impurities on MAST

TL;DR

This study investigates how charge state affects the transport of light impurities like carbon, nitrogen, and helium in MAST, revealing weak screening for carbon and nitrogen and peaked helium profiles, enhancing understanding of impurity behavior in spherical tokamaks.

Contribution

The paper provides a comparative analysis of impurity transport coefficients for multiple light impurities on MAST, highlighting charge dependence and poloidal asymmetry effects.

Findings

Weak screening of carbon and nitrogen impurities in the core

Helium impurity density profile is peaked across the plasma

Transport coefficients vary with impurity charge state

Abstract

Carbon and nitrogen impurity transport coefficients are determined from gas puff experiments carried out during repeat L-mode discharges on the Mega-Amp Spherical Tokamak (MAST) and compared against a previous analysis of helium impurity transport on MAST. The impurity density profiles are measured on the low-field side of the plasma, therefore this paper focuses on light impurities where the impact of poloidal asymmetries on impurity transport is predicted to be negligible. A weak screening of carbon and nitrogen is found in the plasma core, whereas the helium density profile is peaked over the entire plasma radius.