Beam dynamics studies for high-intensity beams in the CERN proton synchrotron

Abstract

With the discovery of the Higgs boson, the existence of the last missing piece of the Standard Model of particle physics (SM) was confirmed. However, even though very elegant, this theory is unable to explain, for example, the generation of neutrino masses, nor does it account for dark energy or dark matter. To shed light on some of these open questions, research in fundamental particle physics pursues two complimentary approaches. On the one hand, particle colliders working at the high-energy frontier, such as the Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN), located in Geneva, Switzerland, are utilized to investigate the fundamental laws of nature. Alternatively, fixed target facilities require high-intensity beams to create a large flux of secondary particles to investigate, for example, rare particle decay processes, or to create neutrino beams. This thesis investigates limitations arising during the acceleration of high-intensity beams at the CERN Proton Synchrotron (PS). The studies presented are aimed at reducing beam loss occurring during the injection and extraction processes, which cause high radioactive activation of the PS ring. The minimization of beam loss is essential to allow maintenance, repair or exchange of crucial accelerator equipment, especially for the production of more intense proton beams, which will eventually be required by future experimental facilities. The first part of this thesis focuses on an intra-bunch oscillation phenomenon, which is observed immediately after injection of high-intensity beams and causes undesirable beam loss. The oscillations are experimentally characterized, detailed simulation studies are presented and the underlying mechanism, namely the interaction between the beam and the self-induced electromagnetic fields in the surrounding vacuum chamber, is explained. The second part of this thesis sets out the way to making the Multi-Turn Extraction (MTE), a novel scheme based on advanced concepts of non-linear beam dynamics, an operational replacement of the Continuous Transfer (CT) process. Experimental studies stressing the susceptibility of the MTE technique to fluctuations of the magnetic field are discussed, and the results of 6D time-dependent simulations are explained. Furthermore, a redesign of the extraction process itself is presented. The design of a new extraction bump, which is required by the installation of a passive absorber to protect the magnetic extraction septum, is set out. In addition, improved non-linear extraction optics are presented, which allow the reduction of beam loss at extraction to the expected design values of less than 2%. The entirety of the presented studies played a crucial role in concluding the MTE commissioning process. Since September 2015, the MTE scheme has successfully replaced the CT extraction, leading to a significant reduction of the activation of the PS ring.