J.A. Crittenden

Observations and predictions at CesrTA, and outlook for ILC

In this paper, we will describe some of the recent experimental measurements [1, 2, 3] performed at CESRTA [4], and the supporting simulations, which probe the interaction of the electron cloud with the stored beam. These experiments have been done over a wide range of beam energies, emittances, bunch currents, and fill patterns, to gather sufficient information to be able to fully characterize the beam-electron-cloud interaction and validate the simulation programs. The range of beam conditions is chosen to be as close as possible to those of the ILC damping ring, so that the validated simulation programs can be used to predict the performance of these rings with regard to electroncloud- related phenomena. Using the new simulation code Synrad3D to simulate the synchrotron radiation environment, a vacuum chamber design has been developed for the ILC damping ring which achieves the required level of photoelectron suppression. To determine the expected electron cloud density in the ring, EC buildup simulations have been done based on the simulated radiation environment and on the expected performance of the ILC damping ring chamber mitigation prescriptions. The expected density has been compared with analytical estimates of the instability threshold, to verify that the ILC damping ring vacuum chamber design is adequate to suppress the electron cloud single-bunch head-tail instability.

A Study of the Effect of Beam-Beam Interactions on CESR Optics

The CESR storage ring facility has begun operation in an energy region which allows high-statistics investigation of charm-quark bound states. Experience during the first two years has shown that the effects of parasitic crossings in the pretzel orbits present an important factor in injection efficiency, in the beam lifetime and in the stored current limits. We compare the results of beam dynamics and tracking calculations which quantify the effects of these parasitic crossings on optics and dynamic aperture for the injected and stored trajectories to observations of beam behavior.