Noise in Proton Accelerators

A high energy proton-electron-positron colliding beam system (PEP) will be described elsewhere in an invited paper. It is necessary that the proton beam be stored, tightly bunched in longitudinal space, for many hours. Since there is almost no damping of synchrotron oscillations (for protons), noise which can couple to this motion may cause the protons to diffuse so as to increase the synchrotron amplitude and destroy the tight bunches. This paper describes experiments performed on the Bevatron and attempts to correlate the results with theory. Initial theoretical studies of the effect of noise in the rf system are described in Ref. 1. The theory is extended to include the presence of a feedback control of the rf frequency. Although a properly designed feedback system can suppress coherent synchrotron oscillations of a bunched beam, it is found that the diffusion of particles within the bucket may be unaffected. An obvious source of noise is the rf voltage necessary to maintain the bunched structure. Other noise sources, such as collisions with residual gas, are included.