Equilibrium reconstruction for single helical axis reversed field pinch plasmas

Abstract

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