Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
The Cornell Electron Storage Ring operations group is planning a major upgrade of the storage ring performance as an X-ray user facility. The principal modification foresees replacing the former e−e+ interaction region with six double-bend achromats, reducing the emittance by a factor of four. The beam energy will increase from 5.3 to 6.0 GeV and single-beam operation will replace the present two-beam e−e+ operation. The initial phase of the project will operate a single positron beam, so electron cloud buildup may contribute to performance limitations. This work describes a synchrotron radiation analysis of the new ring, and employs its results to provide ring-wide estimates of cloud buildup and consequences for the lattice optics.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
We report on measurements of electron cloud (EC) induced tune shifts and emittance growth at the Cornell Electron-Positron Storage Ring Test Accelerator (CesrTA) with comparison to tracking simulation predictions. Experiments were performed with 2.1 GeV positrons in a 30 bunch train with 14 ns bunch spacing and 9 mm bunch length, plus a witness bunch at varying distance from the train to probe the cloud as it decays. Complementary data with an electron beam were obtained to distinguish EC effects from other sources of tune shifts and emittance growth. High resolution electric field maps are computed with EC buildup simulation codes (ECLOUD) in the small region around the beam as the bunch passes through the cloud. These time-sliced field maps are input to a tracking simulation based on a weak-strong model of the interaction of the positron beam (weak) with the electron cloud (strong). Tracking through the full lattice over multiple radiation damping times with electron cloud elements in the dipole and field-free regions predict vertical emittance growth, and tune shifts in agreement with the measurements.
