Energy Vernier System for CEBAF

The beam energy of CEBAF must be accurately controlled for precise physics experiments. In order to achieve a relative energy spread better than sigma{sub E}/E = 2.5 x 10{sup -5}, a feedback system is needed to stabilize the energy against phase and amplitude fluctuations in the individual cavities. In the energy vernier system, the energy deviation of the beam is measured at a location with high dispersion. The error signal controls the accelerating gradient of selected vernier cavities. The methods used to correct the energy will be discussed, as well as the noise sources in the system. The results of beam tests at the CEBAF north linac will also be reported