The beam-beam interaction in electron storage rings: A study of the weak/strong case

The beam-beam interaction is a major factor limiting the luminosity performance of high energy e+e- storage rings. CESR (Cornell Electron Storage Ring) is no exception. In an effort to gain insight into the beam-beam interaction the author studied the weak/strong colliding-beam case both with machine experiment in CESR and by particle tracking simulations. The essential features of the study were the following: Methods were developed for measuring, as accurately as possible, the entire vertical distribution of the weak beam and all machine conditions which produced the particular distribution. These methods were used to make many measurements, near the normal CESR operating point, over a multi-dimensional parameter space. Particle tracking simulations were performed with input parameters as close as possible to those observed during experimental measurements. Results of simulation and experiment were compared. Development of both the experimental techniques and simulation were continued until agreement was good or disagreements between the results were understood. The simulation was then used to study the particle distribution in a more controlled way than was possible in experiment. These final simulations were designed to help achieve a better understanding of the dynamics leading to beam blowup and observed particle losses. The study focused on how the resultant vertical beam distributions are obtained and maintained. Particular emphasis is placed upon the study of large amplitude particles within the distribution. Explorations centered about large increases in both the vertical beam size and particle loss rate seen in both experiment and simulation near the normal CESR operating point. The synchrobetatron resonance 2Qx - 2Qy = Qs was determined to be the cause and was seen to dominate this region of the tune plane