Rønnow, Henrik MoodyssonZanini, LucaAkhyani, Mina2024-06-042024-06-042024-06-04202410.5075/epfl-thesis-10567https://infoscience.epfl.ch/handle/20.500.14299/208221Conducting neutron scattering experiments in the presence of high pulsed magnetic fields, namely above 40 T, provides valuable information about the magnetic structures of materials. However, these experiments are challenging and time-consuming because the neutron count is typically low, due to the asynchronization between the neutron pulses with 14-60Hz at available spallation sources and magnetic pulses with a repetition rate of about 5 minutes. In this thesis, we investigate the idea of having an optimized dedicated source. The focus of this design diverged from traditional spallation sources in two crucial aspects. Firstly, this source is designed to serve a single instrument exclusively. Secondly, the frequency of the proton pulses on the target is low, which dramatically reduces the average heat load. These factors enable the utilization of an existing high-power accelerator facility, such as the one at the European Spallation Source (ESS), without disrupting experiments at the main station. Furthermore, by positioning the guides closer to the source, it becomes feasible to optimize the Target-Moderator-Reflector assembly specifically for the requirements of the single instrument. Two calculation approaches, analytical and Monte Carlo (MC) simulations, were employed to determine the gain factor over ESS performance. The Figure-of-Merit chosen for this evaluation is the source brightness. The analytical approach with the assumption of ESS geometry and 2-dimensional phase space, revealed a maximum gain factors of around 2 to 4. MC simulations using various geometries showed a brightness gain factor of 4 to 4.5 for the optimized Sandwiched Flat geometry in 1~cm$^2$ area and 1-degree divergence. This is in reasonable agreement with the analytical findings, considering the assumptions behind the analytical approach. To overcome the limitations of conventional methods in brightness calculations, we introduced a novel methodology named "Brightify". This approach offers unparalleled flexibility in pinpointing the optimal location and direction of brightness, addressing the constraints of traditional methods. With the envisaged dedicated source serving as a potential second target station at ESS, a feasibility study for a transfer line from ESS proton linear accelerator to the target station is conducted to transfer the beam to the target with minimal dispersion and a beam size close to the optimal value. A supplementary focus within the broader scope of this thesis involved a developmental effort towards enhancing the functionality of ESS. As part of the HighNESS collaboration, a He-II based ultracold neutron source was designed for the large beam port at ESS. This design is based on the constraints imposed, such as confined space of the beam port and the heat load on the He-II vessel. An innovative approach was adopted, involving the utilization of single crystalline bismuth as an advanced gamma shield. Additionally, by integrating MgH$_2$ as a cold reflector, it became possible to boost UCN production rates while addressing engineering design losses and ensuring the heat load below 60 W. The presented work confirms a minimum gain factor of 4 for this dedicated source. Further enhancements are possible through the implementation of fissile layers and improvements in neutron moderation. In conclusion, the promising results of this study indicate that exploring the feasibility of constructing such a dedicated source merits consideration.enTarget-Moderator-Reflector AssemblyMonte Carlo SimulationBrightifyBrightnessPara-hydrogen moderatorHe-II UCN sourceEGO.thesis::doctoral thesis