ANALYSIS OF BEAM PROFILE BROADENING AT HIGH INTENSITY IN THE PSR ACCUMULATOR RING

Beam profile measurements taken after extraction from the Proton Storage Ring (PSR) at Los Alamos National Laboratory show significant broadening in the vertical direction at high intensities for bare tunes near 14 . 2 = y ν . Careful simulations of the injection, accumulation, and extraction yield good agreement with the measured beam profiles. In both experiment and simulations, raising the bare tunes even slightly reduces the profile broadening. Simulations show that the addition of second harmonic RF focusing reduces the transverse beam broadening. When second harmonic RF focusing is combined with raised bare tunes in the simulations, the beam profile broadening is negligible. Analysis shows that the vertical broadening is a result of the beam envelope in resonance with the lattice at precisely four envelope oscillations per turn. These results suggest that high-intensity beams can be well contained in accumulator rings through a proper choice of operating tunes, injection scheme, and RF focusing.