Philipp Brumund | Searcharxiv

arXiv2022

Beam focus modifications by cropping partially coherent X-ray beams

We simulate the focusing of a partially-coherent X-ray beam emitted by an undulator in a fourth-generation storage ring performing coherent mode decomposition and wave optics propagation. The focus position is shifted, and its size is enlarged when an entrance slit crops the beam. This is the usual case when a slit is used to select the coherent fraction. The pairing of two focusing elements (mirrors, lenses or transfocators) to ensure a fixed focal position is also analyzed. Our results show that the image of a partially coherent source, such an undulator in a low-emittance storage ring, is a non-trivial function of the aperture used to control the coherence fraction.

physics.optics↗

arXiv2021

A fast and light tool for partially-coherent beamline simulations in fourth generation storage rings based on coherent mode decomposition

A new algorithm to perform coherent mode decomposition of the undulator radiation is proposed. It is based in separating the horizontal and vertical directions, reducing the problem by working with one-dimension wavefronts. The validity conditions of this approximation are discussed. Simulations require low computer resources, and run interactively in a laptop. We study the focusing with lenses of the radiation emitted by an undulator in a fourth-generation storage ring (EBS-ESRF). Results are compared against multiple optics packages implementing a variety of methods for dealing with partial coherence: full 2D coherent mode decomposition, Monte-Carlo combination of wavefronts from electrons entering the undulator with different initial conditions, and hybrid ray-tracing correcting geometrical optics with wave optics.

physics.acc-ph↗