Dynamic Imperfections in the Compact Linear Collider

The Compact Linear Collider (CLIC) is a proposed TeV-scale electron-positron collider under development at the European Organization for Nuclear Research (CERN). CLIC adopts a staged approach with three centre-of-mass energies: 380 GeV, 1.5 TeV and 3 TeV. This work focuses on the first stage, which has been optimised for studies of the Higgs boson and top-quark physics. A high luminosity is achieved by targeting ultra-small beam sizes at the collision point. Realising these beam sizes relies on the production and transport of ultra-low emittance beams. The preservation of emittance is important in three sections: the Ring to Main Linac (RTML), the Main Linac (ML) and the Beam Delivery System (BDS). Typically, each section is studied individually. In this work, they are integrated into a single simulation, referred to as an ‘integrated simulation'. In an integrated simulation, particles are tracked through the RTML, ML and BDS to reach the collision point. The luminosity is calculated with a full simulation of the collision including beam-beam effects. Imperfections lead to emittance growth and degrade luminosity. Integrated simulations are performed to evaluate the impact of static and dynamic imperfections. The impact of static imperfections is mitigated with well known beam-based tuning procedures. This work focuses on the impact of dynamic imperfections and their mitigation. A well studied dynamic imperfection is ground motion. Integrated simulations in this work show ground motion can be mitigated with a feedback system that corrects the beam trajectory and a stabilisation system for quadrupole magnets. Much of this work is devoted to a newly considered dynamic imperfection, that is stray magnetic fields (SFs). CLIC is sensitive to sub-nT SFs. The typical amplitude of SFs found in an accelerator environment is several orders of magnitude larger than this. Therefore, SFs are a serious consideration in the design and operation of CLIC. %This work examines particular SF sources: natural sources, such as the Earth's magnetic field; environmental sources, such as electrical power infrastructure and technical sources, such as magnets, power cables, ventilation systems, etc. A dedicated mitigation system is needed to ensure SFs do not significantly impact luminosity. A passive shielding technique is investigated. Measurements of the shielding provided by mu-metal for small-amplitude external magnetic fields are performed. With these measurements, a magnetic shielding model is validated. The proposed mitigation strategy for CLIC is to surround sensitive regions of the beamline with a 1 mm mu-metal layer. SFs at two accelerator facilities at CERN are surveyed. With these measurements, a model for SFs is developed. Integrated simulations including SFs are performed and show luminosity loss is effectively mitigated with a beam trajectory feedback system and mu-metal shield.