Absorbed dose and fluence measurements and simulations at EuXFEL undulator systems

by Olga Ewa Falowska-Pietrzak (Stockholm University)

Thursday 23 Mar 2023, 13:00 → 15:00 Europe/Stockholm

AlbaNova B4:1059 - Instrumenteringsfysik/Admin (AlbaNova Main Building)

The European X-Ray Free Electron Laser generates X-ray pulses as GeV
electrons progress in the beam pipe through periodic arrangements of magnets
called undulators. An undesired scattered radiation (stray radiation) is also
present outside the beam pipe. It may damage not only undulator magnets,
but also diagnostic and correction equipment located near undulators. It results
in decreased performance of the EuXFEL. As the severity of magnet damage
differs for different particles and energies, it is of great importance to properly
characterize the stray radiation field in the vicinity of the undulators.
In this thesis, results of Gafchromic film dose measurements near EuXFEL
undulators are presented. Films were placed at the entrance of the undulator
segments, along the undulator permanent magnets and at the front of phase
shifters located in the intersections separating two undulator segments. In addition,
Monte Carlo simulations of absorbed dose and fluence were performed
with Geant4 toolkit to characterize the composition and energy spectra of the
radiation field near undulators.
Comparison of film measurements and simulations show that the radiation
field near the upstream undulator cells may be a result of high-energy electrons
interactions with the beam pipe. Almost 99 % of the dose absorbed to the
permanent magnets comes from electrons and positrons created through photon
interactions with matter. However, the majority of particles are photons. In
addition, simulations show that neutrons are also presented within the magnets.
Significant doses were measured further away from the permanent magnets, close
to phase shifters installed in the intersections.