QSL Squasher: A Fast Quasi-Separatrix Layer Map Calculator

TL;DR

QSL Squasher is an open-source GPU-accelerated tool that rapidly computes 2D and 3D Quasi-Separatrix Layer maps in solar magnetic field models, significantly improving speed and efficiency over previous methods.

Contribution

The paper introduces QSL Squasher, a novel, optimized software that enables fast, high-resolution 3D QSL and FLEDGE map calculations using parallel processing and innovative boundary detection techniques.

Findings

QSL Squasher achieves an order-of-magnitude speed-up in QSL map calculations.

FLEDGE maps provide a quick alternative to QSL maps for identifying potential current sheet locations.

The tool enables constructing high-resolution 3D maps in minutes, previously taking much longer.

Abstract

Quasi-Separatrix Layers (QSLs) are a useful proxy for the locations where current sheets can develop in the solar corona, and give valuable information about the connectivity in complicated magnetic field configurations. However, calculating QSL maps even for 2-dimensional slices through 3-dimensional models of coronal magnetic fields is a non-trivial task as it usually involves tracing out millions of magnetic field lines with immense precision. Thus, extending QSL calculations to three dimensions has rarely been done until now. In order to address this challenge, we present QSL Squasher -- a public, open-source code, which is optimized for calculating QSL maps in both two and three dimensions on GPUs. The code achieves large processing speeds for three reasons, each of which results in an order-of-magnitude speed-up. 1) The code is parallelized using OpenCL. 2) The precision requirements for the QSL calculation are drastically reduced by using perturbation theory. 3) A new boundary detection criterion between quasi-connectivity domains is used, which quickly identifies possible QSL locations which need to be finely sampled by the code. That boundary detection criterion relies on finding the locations of abrupt field-line length changes, which we do by introducing a new Field-line Length Edge (FLEDGE) map. We find FLEDGE maps useful on their own as a quick-and-dirty substitute for QSL maps. QSL Squasher allows constructing high-resolution 3D FLEDGE maps in a matter of minutes, which is two orders of magnitude faster than calculating the corresponding 3D QSL maps. We include a sample of calculations done using QSL Squasher to demonstrate its capabilities as a QSL calculator, as well as to compare QSL and FLEDGE maps.