Prediction of temperature barriers in weakly collisional plasmas by a Lagrangian Coherent Structures computational tool

TL;DR

This paper introduces a novel computational tool based on Lagrangian Coherent Structures to analyze magnetic field line paths and predict temperature barriers in chaotic magnetized plasmas, aligning simulations with experimental observations.

Contribution

We developed a general numerical tool for detecting LCSs in dynamical systems, applied it to magnetic field analysis, and demonstrated its effectiveness in predicting temperature gradients in plasmas.

Findings

The tool matches existing techniques like connection length analysis.

Simulations reproduce temperature profiles observed in RFP experiments.

Hidden LCS patterns correlate with high temperature gradients.

Abstract

Analysis of Lagrangian Coherent Structures (LCSs) has been showed to be a valid mathematical approach to explain the formation of transport barriers in magnetized plasmas. Such LCSs, borrowed from fluid dynamics theory, can be considered as the hidden skeleton of the system and can be used for studying a wide spectrum of transport mechanisms even in plasmas. In this paper, we demonstrate that such structures can be particularly useful for underlying the hidden paths governing the motion of magnetic field lines in chaotic magnetic fields. To perform such an analysis, we developed a numerical tool able to detect LCSs for a general dynamical system. The tool is able to deal with general coordinate systems and it is shown to match with other techniques already used to analyse chaotic magnetic fields, e.g. connection length. After the description of the computational tool, we focus on the heat transport equation and the comparison between temperature profile and topology of the LCSs. We provide evidence that numerical simulations are able to reproduce the temperature profiles similar to those observed in RFP experiments and that our tool successfully predicts the location of temperature gradients. The results suggest that, inside the chaotic region, the field-lines motion is far from stochastic and that the presence of hidden patterns allows the development of high temperature gradients.