Abstract
In 2008 the Cornell Electron/Positron Storage Ring (CESR) was reconfigured from an electron/positron collider to serve as a testbed for the International Linear Collider (ILC) damping rings. One of the primary goals of the CESR Test Accelerator (CesrTA) project is to develop a fast low-emittance tuning method which scales well to large rings such as the ILC damping rings, and routinely achieves a vertical emittance of order 10 pm at 2.085 GeV. This paper discusses the tuning methods developed at CesrTA to achieve low-emittance conditions. One iteration of beam-based measurement and correction requires about 10 minutes. A minimum vertical emittance of 10.3 +3.2/-3.4(sys) +/-0.2(stat) pm has been achieved at 2.085 GeV. In various configurations and beam energies the correction technique routinely achieves vertical emittance around 10 pm after correction, with RMS coupling < 0.5%. The measured vertical dispersion is dominated by beam position monitor systematics. The propagation of uncertainties in the emittance measurement is described in detail. Simulations modeling the effects of magnet misalignments, BPM errors, and emittance correction algorithm suggest the residual vertical emittance measured at the conclusion of the tuning procedure is dominated by sources other than optics errors and misalignments.
Highlights
In 2008 the Cornell Electron Storage Ring (CESR) was reconfigured from an electron/positron collider to the CESR Test Accelerator (CesrTA) [1,2,3], a test bed for the International Linear Collider (ILC) damping rings [4]
This paper describes the optics correction procedure developed at CesrTA that meets these requirements
The low-emittance tuning procedure developed at CesrTA takes advantage of the fact that all magnets are independently powered, and all beam position monitor (BPM) are capable of betatron phase and coupling measurements through turn-by-turn acquisition
Summary
In 2008 the Cornell Electron Storage Ring (CESR) was reconfigured from an electron/positron collider to the CESR Test Accelerator (CesrTA) [1,2,3], a test bed for the International Linear Collider (ILC) damping rings [4]. One of the primary objectives of the CesrTA program is to develop low-emittance tuning methods for the ILC damping rings. The time required for measuring the response matrix scales linearly with the number of correctors. The tuning algorithm developed for CesrTA was required to be fast, and scale well to large rings such as the ILC damping rings. Betatron phase measurements are significantly faster than traditional response matrix analyses, allowing for less time to be spent on optics correction. The measurements may be performed using a witness bunch, exciting and measuring only a single bunch in a fully loaded machine Measurements such as betatron phase and coupling, which utilize resonant excitation, do not require changing the machine conditions and minimize hysteresis in corrector magnets. Discussed are simulations of the correction procedure, which have been essential to understanding measurement systematics and recognizing that the residual vertical emittance is dominated by sources other than optics errors and misalignments
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