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Article
Title	FOCUS: fast Monte Carlo approach to coherence of undulator sources
Author(s)	Siano, M (Milan U. ; INFN, Milan) ; Geloni, G (European XFEL, Hamburg) ; Paroli, B (Milan U. ; INFN, Milan) ; Butti, D (CERN) ; Lefèvre, T (CERN) ; Mazzoni, S (CERN) ; Trad, G (CERN) ; Iriso, U (CELLS - ALBA, LLS) ; Nosych, A A (CELLS - ALBA, LLS) ; Torino, L (CELLS - ALBA, LLS) ; Potenza, M A C (Milan U. ; INFN, Milan)
Publication	2023
Number of pages	10
In:	J. Synchrotron Radiat. 30 (2023) 217-226
DOI	10.1107/s1600577522010748
Subject category	Accelerators and Storage Rings
Abstract	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.
Copyright/License	Publication: (License: CC-BY-4.0)

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