Resonant beam response in the PSR accumulator ring

Observed beam profile broadening at high intensity in the Proton Storage Ring (PSR) at Los Alamos National Laboratory motivates this analysis of resonant beam response using a particle core model. Previous numerical PIC code simulations gave good agreement with the measured beam profiles, and analysis of those simulations suggested that the profile broadening at high beam intensities is related to the half integer resonance at Q_y = 2 (the bare tune was Q_y = 2.14). The physics of half integer resonances has been studied analytically using the envelope equations. We now carry out particle core model calculations for the PSR lattice under the same conditions as the previous PIC calculations. We show that the resonant behavior of the envelope equations is consistent with the previous PIC and experimental findings and with the theoretical envelope equations analysis for half integer resonances. These results provide further support for the half integer resonance at Q_y = 2 as the cause of the beam broadening.