Equilibrium analysis of current profiles in tokamaks

TLDR

The authors present an efficient, self‑consistent method for reconstructing tokamak current profiles and magnetic topology from MHD equilibrium constraints using external magnetic, kinetic, internal poloidal magnetic, and soft‑X‑ray data, illustrated on DIII‑D H‑mode divertor discharges, and also describe an alternative approach that incorporates an edge‑pressure‑gradient constraint. Comparative reconstructions demonstrate that including internal poloidal magnetic measurements alongside external magnetic, kinetic, and SXR data improves the accuracy of the axial safety factor q(0).

Abstract

An efficient method is given for self-consistent reconstruction of the tokamak current profiles and their associated magnetic topology using the magnetohydrodynamic (MHD) equilibrium constraint from external magnetic measurements, kinetic profile measurements, internal poloidal magnetic field measurements, and topological information from soft X-ray (SXR) measurements. Illustrative examples for beam heated H-mode divertor discharges in the DIII-D tokamak are presented, using the experimentally measured kinetic profile information and external magnetic data from the existing diagnostics. Comparative reconstructions of the current profile using various combinations of diagnostics are given. Also presented is an alternative magnetic analysis method in which the MHD equilibrium is reconstructed using external magnetic data and a constraint on the edge pressure gradient. The results of a sensitivity study are given which show that the axial safety factor q(0) can be more accurately determined when additional information from internal poloidal magnetic measurements is used in conjunction with the external magnetic, kinetic and SXR topological data.