Macroparticle simulation studies of a proton beam halo experiment

We report macroparticle simulations for comparison with measured results from a proton beam halo experiment in a 52-quadrupole periodic-focusing channel. An important issue is that the input phase-space distribution is not experimentally known. Three different initial distributions with different shapes predict different beam profiles in the transport system. Simulations have been fairly successful in reproducing the core of the measured matched-beam profiles and the trend of emittance growth as a function of the mismatch factor, but underestimate the growth rate of halo and emittance for mismatched beams. In this study, we find that knowledge of the Courant-Snyder parameters and emittances of the input beam is not sufficient for reliable prediction of the halo. Input distributions with greater population in the tails produce larger rates of emittance growth, a result that is qualitatively consistent with the particle-core model of halo formation in mismatched beams.