Proton Compression for the Muon Collider Project

Sammanfattning

A muon collider is a promising future collider concept for particle physics. The International Muon Collider Collaboration (IMCC) and the Muon Collider Collaboration (MuCol) are currently conducting a design study to investigate the feasibility of such a facility. To produce muons, a high-intensity, short pulse proton beam produced in a proton complex is directed onto a target, where pions are produced, which subsequently decay into muons. This proton complex includes a compressor before final transport to the target. The collective repulsion between the protons, referred to as space-charge, is expected to be significant in the compressor, where proton bunches are to be compressed to pulse lengths below 2 ns. Previous studies of the compressor have modeled space-charge using 2.5D Particle-in-Cell (PIC) simulations in Xsuite, whose space-charge implementation employs a static mesh, i.e., the mesh does not adapt to an evolving beam size. However, 2.5D space-charge may not be sufficient to accurately describe the effects of space-charge in the compressor. In addition, a 3D model with a static mesh would be computationally inefficient due to the compression. In this thesis, an adaptive-mesh space-charge implementation has been developed for Xsuite. Using both static- and adaptive-mesh configurations, 2.5D and 3D space-charge models have been compared for the compressor. The results indicate that 3D modeling is required to capture important aspects of the compressor dynamics. A four-fold structure has been observed in the absence of space-charge, and its cause has been investigated. Further studies have been conducted using adaptive-mesh 3D modeling, including a convergence study and a tune scan, where the latter aided in the exploration of a new working point for the compressor. No fundamental obstacle to sub-2 ns compression was identified. However, it is not fully clear whether observed microbunching phenomena are numerical or physical in nature.