Dynamic radiation effects induced by short-pulsed U-ion beams in metallic targets
Creators: name: Notari, Lorenzo
Publisher: name: Zenodo
Year: 2022
Subjects: beam window
vacuum window
particle accelerator
spallation neutron source
accelerator-driven system
heavy ion irradiation
beam-induced damage
radiation damage
Aluminium alloy
Titanium alloy
Steel T91
Inconel 718
particle transport analysis
thermomechanics

description: Master Thesis Rome, “La Sapienza” University of Rome, Master Degree in Energy and Nuclear Engineering, 2022 The aim of this thesis is to research and identify innovative materials to be adopted for beam windows, one of the most critical components of accelerator facilities. The work behind this thesis has been carried out at CERN, in Geneva, and has been promoted by the I.FAST project in view of developing promising accelerator equipment and components capable of enhancing the performance of next-generation accelerator facilities. A beam window is any type of thin interface of separation traversed by particle beams which is located between the accelerator vacuum beamline and an external environment at higher pressure. The increasingly high energies of the new generations of accelerator facilities and the development of innovative high-power proton beam applications, such as Spallation Neutron Sources and Accelerator-driven systems, require a detailed investigation of the materials of these components in terms of dynamic response to severe and quasi-instantaneous thermal loads. In the first two chapters of this thesis, an extensive bibliographical research focused on materials adopted for beam-windows applications in accelerator facilities and nuclear research centres worldwide is reported. This research has led to a broad selection of materials considered attractive which have undergone a series of initial analytical studies and preliminary considerations with appropriate figures of merit. As a result, a shortlist of four materials deemed interesting for further testing has been derived. In particular, such materials have been chosen to be exposed to short-pulsed U-ion beam irradiation at the M3-branch beamline of the GSI <em>Helmholtzzentrum für Schwerionenforschung</em> in Darmstadt. The description and the outcomes of the irradiation experiment are discussed in the third chapter. The exposition of the selected materials to beams of high-energy heavy ions gives the opportunity to mimic, with a reasonable time, the particularly high radiation levels and the high strain rate loads to which the beam-window materials could be subjected in the future high-power and high-energy accelerators and, consequently, to predict the deterioration of thermophysical and mechanical properties of these materials. Disc-shaped samples of four materials (Steel T91, Inconel 718, Al-6082-T6 and Titanium Grade 23) were thus irradiated with U-ion pulses with GeV kinetic energy. Beam-induced heating of the samples was controlled with a thermal camera, while the dynamic response of the targets was monitored by recording the surface velocity signal of the samples using Laser Doppler Vibrometry. The mechanical properties of the specimens have been explored through post-irradiation examinations, including measurements of microindentation and SEM spectroscopy. In the fourth chapter of the thesis, the experimental findings have been investigated and compared with the results of analytical and numerical analyses. The SRIM-2013 Monte Carlo simulation-based software has been used to assess relevant parameters for the transport of ions in targets, including the range, the stopping power and the displacements-per-atom (dpa), the most common quantity to predict the operating lifetime of materials in radiation environments. ANSYS Workbench was used to numerically benchmark the experimental data acquired from the LDV, the Thermal Camera and the microindentation measurements by implementing appropriate thermo-mechanical models. The last chapter summarises the main conclusions of this work, describes the thesis' key findings and makes suggestions for potential future directions of the work performed.