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Dynamic imperfections and optimized feedback design in the Compact Linear Collider main linac
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
2008 (English)In: Physical Review Special Topics. Accelerators and Beams, ISSN 1098-4402, Vol. 11, no 5, 051003- p.Article in journal (Refereed) Published
Abstract [en]

The Compact Linear Collider (CLIC) main linac is sensitive to dynamic imperfections such as element jitter, injected beam jitter, and ground motion. These effects cause emittance growth that, in case of ground motion, has to be counteracted by a trajectory feedback system. The feedback system itself will, due to jitter effects and imperfect beam position monitors (BPMs), indirectly cause emittance growth. Fast and accurate simulations of both the direct and indirect effects are desirable, but due to the many elements of the CLIC main linac, simulations may become very time consuming. In this paper, an efficient way of simulating linear (or nearly linear) dynamic effects is described. The method is also shown to facilitate the analytic determination of emittance growth caused by the different dynamic imperfections while using a trajectory feedback system. Emittance growth expressions are derived for quadrupole, accelerating structure, and beam jitter, for ground motion, and for noise in the feedback BPMs. Finally, it is shown how the method can be used to design a feedback system that is optimized for the optics of the machine and the ground motion spectrum of the particular site. This feedback system gives an emittance growth rate that is approximately 10 times lower than that of traditional trajectory feedbacks. The robustness of the optimized feedback system is studied for a number of additional imperfections, e. g., dipole corrector imperfections and faulty knowledge about the machine optics, with promising results.

Place, publisher, year, edition, pages
2008. Vol. 11, no 5, 051003- p.
National Category
Physical Sciences
URN: urn:nbn:se:uu:diva-96901DOI: 10.1103/PhysRevSTAB.11.051003ISI: 000256500100008OAI: oai:DiVA.org:uu-96901DiVA: diva2:171632
Available from: 2008-03-20 Created: 2008-03-20 Last updated: 2009-11-03Bibliographically approved
In thesis
1. Emittance preservation and luminosity tuning in future linear colliders
Open this publication in new window or tab >>Emittance preservation and luminosity tuning in future linear colliders
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2008. 63 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 409
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
National Category
Subatomic Physics
urn:nbn:se:uu:diva-8576 (URN)978-91-554-7130-9 (ISBN)
Public defence
2008-04-11, Polhemsalen, Ångströmlaboratoriet, Box 516, SE-75120, Uppsala, Sweden, 13:15
Available from: 2008-03-20 Created: 2008-03-20Bibliographically approved

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