An automated focal point positioning and emittance measurement procedure for the interaction point of the SLC

Abstract

To achieve maximum luminosity at the SLC, both the electron and positron beams must reach their minimum transverse size within 1 mm of the longitudinal location where the two bunches collide. This paper describes an automated procedure for positioning the focal point of each beam at this collision point. The technique is based on measurements of the beam size utilizing either secondary emission or bremsstrahlung signals from carbon fibers a few microns in diameter. We have achieved simultaneous and reproducible measurements of the angular spread (~ 200 [mu] rad) and of the optimum beam spot size ~ [omega]m), which when combined yield measurements of the beam emittance consistent with those obtained using conventional profile monitor techniques.