Stimulated longitudinal emittance growth in the Main Ring

The authors describe efforts to upgrade the Main Ring bunch spreaders in anticipation of even greater intensity requirements (2-3×10¹⁰ protons/bunch) in the coming fixed target run. During fixed target operations beam intensity is limited by coherent instabilities in both the Main Ring and Tevatron. The growth rates for instabilities are generally inversely proportional to the proton bunch length. Since fixed target operations are insensitive to the longitudinal emittance of the beams, bunch spreaders are employed to increase the emittance, and hence the bunch length. Emittance growth is stimulated by injecting noise onto either the RF phase or amplitude control voltages. Test results of the efficiency of various stimulation schemes are reported. The design of a 10-kHz bandwidth bunch length monitor, used to measure the effect of the bunch spreader, is also presented. Tests show that 50% bunch length growths are possible with tolerable beam loss