Dipartimento di Fisica, Università degli Studi di Milano, INFN Sezione di Milano, and CIMAINA, via G. Celoria 16, 20133 Milan, Italy.
European XFEL, Holzkoppel 4, 22869 Schenefeld, Germany.
J Synchrotron Radiat. 2023 Jan 1;30(Pt 1):217-226. doi: 10.1107/S1600577522010748.
FOCUS (Fast Monte CarlO approach to Coherence of Undulator Sources) is a new GPU-based simulation code to compute the transverse coherence of undulator radiation from ultra-relativistic electrons. The core structure of the code, which is written in the language C++ accelerated with CUDA, combines an analytical description of the emitted electric fields and massively parallel computations on GPUs. The combination is rigorously justified by a statistical description of synchrotron radiation based on a Fourier optics approach. FOCUS is validated by direct comparison with multi-electron Synchrotron Radiation Workshop (SRW) simulations, evidencing a reduction in computation times by up to five orders of magnitude on a consumer laptop. FOCUS is then applied to systematically study the transverse coherence in typical third- and fourth-generation facilities, highlighting peculiar features of undulator sources close to the diffraction limit. FOCUS is aimed at fast evaluation of the transverse coherence of undulator radiation as a function of the electron beam parameters, to support and help prepare more advanced and detailed numerical simulations with traditional codes like SRW.
FOCUS（Fast Monte CarlO approach to Coherence of Undulator Sources）是一个新的基于 GPU 的模拟代码，用于计算超相对论电子的波荡器辐射的横向相干性。该代码的核心结构是用 C++语言编写的，并使用 CUDA 进行加速，它结合了对发射电场的分析描述和 GPU 上的大规模并行计算。这种组合是通过基于傅里叶光学方法的同步加速器辐射的统计描述严格证明的。FOCUS 通过与多电子同步加速器辐射研讨会（SRW）模拟的直接比较得到验证，在消费级笔记本电脑上的计算时间减少了多达五个数量级。然后，FOCUS 被应用于系统地研究典型的第三代和第四代设施中的横向相干性，突出了接近衍射极限的波荡器源的特殊特征。FOCUS 的目的是快速评估波荡器辐射的横向相干性作为电子束参数的函数，以支持和帮助准备更先进和详细的数值模拟，如 SRW 等传统代码。
