Abstract
The spin structure of the proton is one of the unsolved problems in physics. The Relativistic Heavy Ion Collider (RHIC) Spin Physics Program has been conducting research to investigate the spin structure by colliding high energy polarized proton beams. Maintaining high spin polarization while achieving high luminosity is critical for this program. Two of the challenges related to the program are to maintain spin polarization during spin flipping, a process designed to reduce systematic errors in spin asymmetry measurements, and during beam acceleration from the low energy source to the high energy collision experiment. Recently, a modification of the accelerator's magnet configuration (optics) was developed for reducing the spin tune spread. With the new optics implemented, higher spin flipping efficiency was achieved at both injection and top beam energies. The spin tune spread was also minimized during beam acceleration and the transmission efficiency of spin polarization was evaluated. In this report the modifications needed for minimizing the spin tune spread and their impact on the global beam optics are described.
Highlights
Preserving spin polarization during beam acceleration through the accelerator chain and during spin flipping in Relativistic Heavy Ion Collider (RHIC) are two substantial challenges for the RHIC Spin Physics Program [1,2]
A way to reduce the spin tune spread by matching the dispersion primes at the two Siberian snakes has been developed and implemented for RHIC
The γT quadrupoles, designed for crossing transition energy during beam acceleration, were repurposed to match the dispersion primes at the two Siberian snakes with minimal impact on the global optics
Summary
Preserving spin polarization during beam acceleration through the accelerator chain and during spin flipping in RHIC are two substantial challenges for the RHIC Spin Physics Program [1,2]. Despite upgrades of the spin flipper system [4,5,6,7,8] and improvement of the related closed orbit bump, spin polarization was not well preserved during spin flipping experiments until the optics was modified for reducing the spin tune spread. This article describes the optics modifications to reduce the spin tune spread including simulations and experimental results. This work demonstrated for the first time reduction of the spin tune spread by optics modification in RHIC.
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