Low-emittance tuning at the Cornell Electron Storage Ring

TL;DR

This paper presents a rapid low-emittance tuning method developed at CESR, achieving around 10 pm vertical emittance, which is crucial for future large-scale damping rings like those in the ILC.

Contribution

The paper introduces a fast, scalable beam-based tuning technique for low-emittance conditions, with detailed analysis of uncertainties and systematics involved.

Findings

Achieved vertical emittance of approximately 10 pm at 2.085 GeV.

Tuning iteration takes about 10 minutes.

Residual emittance dominated by measurement systematics and other non-optics errors.

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.