QSL Squasher：一个快速的准分界线图层计算器
QSL Squasher: A Fast Quasi-Separatrix Layer Map Calculator
摘要：
准分界线层（Quasi-Separatrix Layers，QSL）是日冕中电流片形成位置的一个有用的替代物，并提供了有关复杂磁场配置中连通性的有价值的信息。然而，通过三维模型的日冕磁场计算QSL地图，即使是二维切片也是一个不平凡的任务，因为它通常涉及以极高的精度追踪数百万条磁场线。因此，到目前为止，很少将QSL计算扩展到三维。为了应对这一挑战，我们提出了QSL Squasher-一个公共的开源代码，它被优化用于在GPU上计算二维和三维的QSL映射。代码实现大的处理速度有三个原因，其中每一个都导致一个数量级的加速。1)代码使用OpenCL并行化。2)利用微扰理论大大降低了QSL计算的精度要求。3)一个新的准连通域之间的边界检测标准，它可以快速识别可能的QSL位置，需要精细采样的代码。该边界检测标准依赖于找到突然的场线长度变化的位置，我们通过引入新的场线长度边缘（FLEDGE）图来实现。我们发现FLEDGE地图本身很有用，可以作为QSL地图的快速而肮脏的替代品。QSL Squasher允许在几分钟内构建高分辨率的3D FLEDGE地图，这比计算相应的3D QSL地图快两个数量级。我们包括一个使用QSL Squasher完成的计算示例，以展示其作为QSL计算器的功能，以及比较QSL和FLEDGE地图。
英文摘要：
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.
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