Setting and Measuring the Longitudinal Optics in CEBAF Injector*

The CEBAF injector is designed to produce three cw polarized beams to be simultaneously accelerated and delivered to three experimental halls. These beams have independent current controls that can be as low as few hundred pico-amperes or as high as 200 microamperes. The beams are created in a photocathode gun using 3 separate rf gain switched lasers each operating at 499 MHz which together make up 1497 MHz, the CEBAF fundamental frequency. At the gun, the beams have the same time structure as the lasers with about 55 picoseconds bunch length at 499 MHz. Through the injector, this bunch length is then adiabatically reduced to less than 1 pico-seconds. The main requirement is that the beams have short stable bunch lengths at the end of the injector. In this paper we discuss the longitudinal bunching process for the JLAB injector. We also describe how the bunch length is measured at various places along the injector and how the measurement results are used to set relative phases of the three lasers and the phases and amplitudes of various rf cavities with high precision.