Transfer of a polarized proton beam from AGS to RHIC

As part of the RHIC project, the RHIC machine will also be able to accelerate polarized proton beam bunches. The bunches will be extracted from the AGS machine, with kinetic energy T=25 GeV, and transferred into RHIC via the AtR transfer line. When the RHIC machine accelerates polarized protons, it will operate with two full snakes, which define the stable spin direction of a polarized proton beam circulating in each ring, along the vertical. Therefore a polarized proton beam should be injected into the RHIC machine with the stable spin direction along the vertical in order to match that of the RHIC machine. The layout of the dipole magnets of the AtR line creates a dependance, on the injection energy, of the stable spin direction of a polarized proton beam injected into the RHIC machine. In this paper, the study of the stable spin direction (at the RHIC injection point) of a polarized proton beam as a function of the injection energy is presented. A modification of the AtR transfer line, which eliminates this energy dependance (within the range of proton injection energies) of the stable spin direction is also presented