Abstract
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.
Highlights
The performance of the future Compact Linear Collider (CLIC) [1] relies heavily on efficient preservation of emittance throughout the machine
Several previous CLIC studies have shown that a trajectory feedback system can be used to prevent the emittance growth caused by ground motion [4,5]
By summing the emittance growth caused by ground motion, feedback with imperfect beam position monitors (BPMs), and jitter, a complete emittance growth expression is obtained: Quadrupole jitter (q )
Summary
The performance of the future Compact Linear Collider (CLIC) [1] relies heavily on efficient preservation of emittance throughout the machine Both static and dynamic imperfections influence the emittance and cause severe emittance growth if not mitigated. By using beam position monitor (BPM) readings, the trajectory feedbacks resteer the beam locally to the ideal trajectory Without such feedbacks, dynamic misalignments would cause increasing deviations from the ideal trajectory and the emittance would quickly become unacceptable. An efficient way of simulating dynamic imperfections will be described This method will be shown to facilitate an analytic determination of the emittance growth caused by jitter and ground motion while using a feedback system with imperfect BPMs. The analytic expressions are confirmed by comparisons to full simulations. It will be described how the feedback system can be optimized for the optics of a certain machine and the particular ground motion spectrum of the site
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