Correction of Intensity-Dependent Beam Loss in the NAL Booster Synchrotron

At beam currents above 1.5 × 1011 protons/ pulse in the 8-GeV booster synchrotron, part of the beam is lost during a time interval of 2 to 4 msec just before transition. Particles are lost from several of the 84 rf beam bunches while the number of particles in the other bunches does not change. Electromagnetic coupling between the betatron motion and the magnet laminations which are not shielded from the beam by a vacuum chamber may induce the head-to-tail effect and cause the loss. This effect is sensitive to the chromaticity, ξ = (Δν/ν)/(Δp/p). Changing the chromaticity with dc sextupole magnets at three locations in the ring has eliminated the loss for beam currents as high as 4.5 × 1011 protons/pulse.