Equilibrium reconstruction for Single Helical Axis reversed field pinch plasmas

TL;DR

This paper introduces a new equilibrium reconstruction method for Single Helical Axis RFP plasmas, combining measurements with a superposition approach, validated through mapping temperature, density, and emission data.

Contribution

The paper presents a novel equilibrium reconstruction technique for SHAx RFP plasmas using a superposition of axisymmetric and helical components in the force-free approximation.

Findings

Successful mapping of temperature, density, and emission data onto reconstructed surfaces

Validation of the equilibrium through consistency with Ohm's law

Application of the method to evaluate thermal conductivity profiles

Abstract

Single Helical Axis (SHAx) configurations are emerging as the natural state for high current reversed field pinch (RFP) plasmas. These states feature the presence of transport barriers in the core plasma. Here we present a method for computing the equilibrium magnetic surfaces for these states in the force-free approximation, which has been implemented in the SHEq code. The method is based on the superposition of a zeroth order axisymmetric equilibrium and of a first order helical perturbation computed according to Newcomb's equation supplemented with edge magnetic field measurements. The mapping of the measured electron temperature profiles, soft X-ray emission and interferometric density measurements on the computed magnetic surfaces demonstrates the quality of the equilibrium reconstruction. The procedure for computing flux surface averages is illustrated, and applied to the evaluation of the thermal conductivity profile. The consistency of the evaluated equilibria with Ohm's law is also discussed.