Investigation of the origin of stray radiation at XFEL using FLUKA

• Main Author: Hellström, Terese
• Format: Others
• Language: English
• Published: Stockholms universitet, Fysikum 2019
• Subjects: Accelerator Physics and Instrumentation; Acceleratorfysik och instrumentering; Atom and Molecular Physics and Optics; Atom- och molekylfysik och optik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-183355

The European X-Ray Free-Electron Laser facility (XFEL) provides ultra-short x-ray pulsesof high peak brilliance that are used in research to analyse atomic or molecular structures.The facility accelerates electrons and moves them through an undulator system consistingof several undulator cells containing permanent magnet poles supplying an alternatingmagnetic field, which causes the electrons to emit x-ray pulses. A concern is raised overthe deterioration of the permanent magnets due to radiation damage originating from strayradiation in the undulator system. The stray radiation is believed to be released by the highenergy electrons interacting with the beam pipe wall. In this study particle simulations aremade using the Monte Carlo particle transport code FLUKA to compare to previous sim-ulations and measurements performed at XFEL. A beam line model was made in FLUKA,simulating electron beams interacting with the vacuum pipe at several points. The sim-ulated energy deposition distribution along the undulator segment surface was fitted tomeasurement data of the dose over the magnets in different undulator cells at XFEL. Thisway the probability of the stray radiation originating from different electron beam interac-tion points could be studied. For the undulator cells that were studied the radiation wasfound to originate from interactions mainly in the gap between undulator segments. Forcell 4 and 12 it was found that radiation also originates from electron interactions with thebeam pipe inside the undulator segments. It was concluded that improvements can bemade in the simulation technique by simulating electron beam interactions at more posi-tions along the vacuum pipe’s longitudinal axis and around its lateral cross section. Furtherresearch is needed to find the impact of the alternating magnetic field over the undulatorsegments as well as to find which particles contribute to the radiation damage at XFEL. Asthe undulator cells had different relative contributions to the damaging dose from differentelectron beam interaction points it could be of interest to use the same method for fittingsimulated dose distributions to measurements of other undulator cells at XFEL.