Emittance preservation and luminosity tuning in future linear colliders

• Main Author: Eliasson, Peder
• Format: Doctoral Thesis
• Language: English
• Published: Uppsala universitet, Institutionen för fysik och astronomi 2008
• Subjects: linear colliders; CLIC; ILC; emittance preservation; luminosity tuning; beam-based alignment; dispersion free steering; tuning bumps; trajectory feedback; static imperfections; dynamic imperfections; jitter; ground motion; ATL model; multi-pulse emittance; curved tunnel; Elementary particle physics; Elementarpartikelfysik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-8576; http://nbn-resolving.de/urn:isbn:978-91-554-7130-9

The future International Linear Collider (ILC) and Compact Linear Collider (CLIC) are intended for precision measurements of phenomena discovered at the Large Hadron Collider (LHC) and also for the discovery of new physics. In order to offer optimal conditions for such experiments, the new colliders must produce very-high-luminosity collisions at energies in the TeV regime. Emittance growth caused by imperfections in the main linacs is one of the factors limiting the luminosity of CLIC and ILC. In this thesis, various emittance preservation and luminosity tuning techniques have been tested and developed in order to meet the challenging luminosity requirements. Beam-based alignment was shown to be insufficient for reduction of emittance growth. Emittance tuning bumps provide an additional powerful preservation tool. After initial studies of tuning bumps designed to treat certain imperfections, a general strategy for design of optimised bumps was developed. The new bumps are optimal both in terms of emittance reduction performance and convergence speed. They were clearly faster than previous bumps and reduced emittance growth by nearly two orders of magnitude both for CLIC and ILC. Time-dependent imperfections such as ground motion and magnet vibrations also limit the performance of the colliders. This type of imperfections was studied in detail, and a new feedback system for optimal reduction of emittance growth was developed and shown to be approximately ten times more efficient than standard trajectory feedbacks. The emittance tuning bumps require fast and accurate diagnostics. The possibility of measuring emittance using a wide laserwire was introduced and simulated with promising results. While luminosity cannot be directly measured fast enough, it was shown that a beamstrahlung tuning signal could be used for efficient optimisation of a number of collision parameters using tuning bumps in the Final Focus System. Complete simulations of CLIC emittance tuning bumps, including static and dynamic imperfections and realistic tuning and emittance measurement procedures, showed that an emittance growth six times lower than that required may be obtained using these methods.