MEASUREMENT OF SMALL ELECTRON-BEAM SPOTS¹

Measurements of transverse beam size are tremendously important to the performance of e⁺e⁻ linear colliders. In this paper we review the traditional technologies used to make such measurements, such as profile monitors and wire scanners, and their limitations. We introduce a new technique for electron beam-size measurement: Compton-scattered laser light, which may be used as an unbreakable “wire” or in the form of an interferometer beam-size monitor (BSM). We describe the use of such an interferometer BSM, noting both the general issues related to its design and operation and the specific experiences with such an interferometer at the Final Focus Test Beam at SLAC. We conclude by considering the ultimate limitations of the laser-interferometer BSM.