Abstract
The Accelerator Test Facility 2 (ATF2) commissioning group aims to demonstrate the feasibility of the beam delivery system of the next linear colliders (ILC and CLIC) as well as to define and to test the tuning methods. As the design vertical beam sizes of the linear colliders are about few nanometers, the stability of the trajectory as well as the control of the aberrations are very critical. ATF2 commissioning started in December 2008, and thanks to submicron resolution beam position monitors (BPMs), it has been possible to measure the beam position fluctuation along the final focus of ATF2 during the 2009 runs. The optics was not the nominal one yet, with a lower focusing to make the tuning easier. In this paper, a method to measure the noise of each BPM every pulse, in a model-independent way, will be presented. A method to reconstruct the trajectory's fluctuations is developed which uses the previously determined BPM resolution. As this reconstruction provides a measurement of the beam energy fluctuations, it was also possible to measure the horizontal and vertical dispersion function at each BPMs parasitically. The spatial and angular dispersions can be fitted from these measurements with uncertainties comparable with usual measurements.
Highlights
The future linear collider projects (ILC [1] and CLIC [2]), to have a high luminosity, must collide beams with few nanometers vertical size
It was built to demonstrate the feasibility of the beam delivery system of a future linear collider, to implement and test the instrumentation and tuning procedures involved to obtain the nanometer scale transverse beam size necessary for a high luminosity
Thanks to precise cavity beam position monitors (BPMs), it is possible to reconstruct all the incident parameters of the beam pulse by pulse
Summary
The future linear collider projects (ILC [1] and CLIC [2]), to have a high luminosity, must collide beams with few nanometers vertical size It requires to create small emittance beams and to focus them to nanometers. The two main goals of ATF2 are to first demonstrate the ability to tune the beam down to 40 nm vertical beam size at the IP and later to control the pulse to pulse beam jitter to be lower than 4 nm at the IP Both of these goals require the use of feedback to reduce the incoming beam jitter. Thanks to precise cavity beam position monitors (BPMs) (with submicron resolution), it is possible to reconstruct all the incident parameters of the beam pulse by pulse This allows reconstructing beam fluctuations for the purpose of stability analysis and feedback, and measuring the dispersion functions in a noninvasive way.
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