Density distributions of tune shifts from space charge or beam-beam interactions in Gaussian bunches

Abstract: The amplitude dependent tune shifts from either space charge or beam-beam interactions are calculated analytically with the inclusion of synchrotron oscillations and multiple interactions around the ring. Simpler formulae are derived under limits of bunches longer than the transverse sizes, equal and unequal transverse sizes etc. This is used to derive semi-analytical forms for the density distribution of the tune shifts. The tune spread and the density distribution are needed to understand beam decoherence or Landau damping with either interaction. The tune footprints due to space charge in IOTA are simulated using pyorbit and found to be in good agreement with the theoretical predictions.