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arXiv · 2001.06984

Stepped pressure equilibrium with relaxed flow and applications in reversed-field pinch plasmas

Z. S. Qu·R. L. Dewar·F. Ebrahimi·J. K. Anderson·S. R. Hudson·M. J. Hole
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Abstract

The Multi-region Relaxed MHD (MRxMHD) has been successful in the construction of equilibria in three-dimensional (3D) configurations. In MRxMHD, the plasma is sliced into sub-volumes separated by ideal interfaces, each undergoing relaxation, allowing the formation of islands and chaos. The resulting equilibrium has a stepped pressure profile across sub-volumes. The Stepped Pressure Equilibrium Code (SPEC) [S.R. Hudson et al., Phys. Plasmas 19, 112502 (2012)] was developed to calculate MRxMHD equilibria numerically. In this work, we have extended the SPEC code to compute MRxMHD equilibria with field-aligned flow and rotation, following the theoretical development to incorporate cross-helicity and angular momentum constraints. The code has been verified for convergence and compared to a Grad-Shafranov solver in 2D. We apply our new tool to study the flow profile change before and after the sawtooth crash of a reversed-field pinch discharge, in which data of the parallel flow is available. We find the promising result that under the constraints of cross-helicity and angular momentum, the parallel flow profile in post-crash SPEC equilibrium is flat in the plasma core and the amplitude of the flow matches experimental observations. Finally, we provide an example equilibrium with a 3D helical field structure as the favoured lower energy state. This will be the first 3D numerical equilibrium in which the flow effects are self-consistently calculated.

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Z. S. Qu, R. L. Dewar, F. Ebrahimi, J. K. Anderson, S. R. Hudson, M. J. Hole. 2020-01-20. Stepped pressure equilibrium with relaxed flow and applications in reversed-field pinch plasmas. https://doi.org/10.1088/1361-6587/ab7fc5

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