Abstract
The high luminosity requirement for a future linear collider sets a demanding limit on the beam quality at the Interaction Point (IP). One potential source of luminosity loss is the motion of the ground itself. The resulting misalignments of the quadrupole magnets cause distortions to the beam orbit and hence an increase in the beam emittance. This paper describes a technique for compensating this orbit distortion by using seismometers to monitor the misalignment of the quadrupole magnets in real-time.The first demonstration of the technique was achieved at the Accelerator Test Facility (ATF) at KEK in Japan. The feed-forward system consisted of a seismometer-based quadrupole motion monitoring system, an FPGA-based feed-forward processor and a stripline kicker plus associated electronics. Through the application of a kick calculated from the position of a single quadruple, the system was able to remove about 80% of the component of the beam jitter that was correlated to the motion of the quadrupole. As a significant fraction of the orbit jitter in the ATF final focus is due to sources other than quadrupole misalignment, this amounted to an approximately 15% reduction in the absolute beam jitter.
Highlights
The dynamic misalignment of the beamline components of a future linear collider results in beam imperfections such as increased emittance [1] and position offsets at the Interaction Point (IP) [2]
For a single-pass machine this is the machine repetition rate, which corresponds to 5 Hz for the International Linear Collider (ILC) [4] and 50 Hz for the Compact Linear Collider (CLIC) [5]
This paper describes the quadrupole motion monitoring system deployed at the KEK Accelerator Test Facility (ATF), a test accelerator whose primary goal is the generation of very low emittance electron beams, and summarizes the results obtained with that system and what they said about the relationship between the position of the quadrupoles and the beam orbit in the final focus region of ATF
Summary
The dynamic misalignment of the beamline components of a future linear collider results in beam imperfections such as increased emittance [1] and position offsets at the Interaction Point (IP) [2]. The technique of beam orbit feedback [3] uses at least one beam position monitor (BPM) to track the position of the beam and one corrector magnet to restore it to its nominal orbit. Such systems are limited by the frequency at which the BPM data is generated. The novel technique of compensation of orbit distortion due to quadrupole motion using feed-forward control [11] is similar in concept to beam orbit feedback but the measured displacement of a quadrupole is used to determine the deflection to provide to the beam, instead of the position of the beam itself (Fig. 1).
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