Flat Beams in the SLC*

The Stanford Linear Collider was designed to operate with round beams [ 11; horizontal and vertical emittance made equal hi the damping rings. The main motivation was to facilitate the optical matching through beam lines with strong coupling elements like the solenoid spin rotator magnets and the SLC ales. Tests in 1992 showed that ‘flat’ beams with a vertical to horizontal emittance ratio of around l/10 can be successfully delivered to the end of the linac [2]. Techniques developed to measure and control the coupling of the SLC arcs [ 31 allow these beams to be transported to the Interaction Point (IP). Before flat beams could be used for collisions with polarized electror+s, a new -method of rotating the electron spin orientation with vertical arc orbit bumps [4] had to be developed Early in the 1993 run, the SLC was switched to ‘flat’ beam opetaf&%n.~ Within a short time the peak luminosity of the previous running cycle was reached and then surpassed. The average daily luminosity is now a factor of about two higher than the best achieved last year. In the following we present an overview of the problems encountered and their solutions for different parts of the SLC. I. FLAT BEAMS IN THE DAMPING RINGS The SLC was designed to operate with ‘round’ beams where horizontal and vertical beam emittance are equal (~3~). Electron/positron storage rings naturally produce ‘flat’ beams where E~>x,,. Round beams had to be produced by operating the SLC damping rings on the linear coupling difference resonanCe: