Commissioning results of the BNL Alternating Gradient Synchrotron booster AC dipole

Abstract

An AC dipole has been installed in the AGS booster as part of polarized beam developments for the future Electron Ion Collider (EIC). This will allow preserving helion beam polarization through two intrinsic resonances during acceleration to an energy corresponding to |Gγ| = 10.5. AC dipoles can preserve polarization by forcing the beam to undergo large amplitude vertical betatron oscillations. These coherent oscillations cause all particles to sample the strong horizontal fields of quadrupoles, and result in a full spin flip. In preparation for the AC dipole being used for polarized helions, it was first commissioned with polarized protons. The proton extraction energy was raised to allow protons to cross Gγ=0+νy = 4.8087. As an artifact of the experiment using polarized protons, the booster settings for bunch extraction interfered with the coherent oscillations and limited the maximum coherent amplitude. This interference will be well separated in the case of polarized helions. Polarized protons crossed the Gγ=0+νy intrinsic resonance with a full spin flip through use of the AC dipole. Simulations of the resonance crossing using Zgoubi accurately predict the polarization relative to the coherent amplitude.