Design of an optics system for the short-HIBEAM beamline at the European Spallation Source

Sammanfattning

Dark matter remains a largely elusive phenomenon, particularly its composition. Several candidate particles have been proposed, including axions and axion-like particles (ALPs). Detection of axions and ALPs have been attempted but none so far have yielded positive results. The High Intensity Baryon Extraction and Measurement instrument (HIBEAM) at the European Spallation Source (ESS) will be used to attempt ALP detection using Ramsey interferometry with increased sensitivity by 2-3 orders of magnitude compared to current performance of other experiments. In order to maximize the sensitivity of the search, HIBEAM’s neutron guide must be optimized. The optimization of this guide is the subject of this thesis. The work was carried out using McStas, a neutron ray-tracing simulation framework that employs Monte Carlo sampling to model neutron transport through instrument components. The optimal guide specifications were determined to be a supermirror reflectivity of m = 4 , together with a selective collimation of the high-intensity region of the beam placed 15 m from the source to match the 10 cm diameter constraint of the polarizer at the end of the neutron guide section. These specifications were determined based on the maximization of a simplified figure of merit NT^2, where N is the neutron intensity and T is the time of flight in the neutron guide. By maximizing this quantity, the uncertainty in the Ramsey fringes is minimized.