Correction of the spin chromaticity in RHIC

Abstract

The independence of the spin tune of the momentum is a critical requirement for a full spin flip using the RHIC spin flipper. We show how the spin chromaticity can be corrected with a minimum impact on the RHIC optics and how the correction improves the spin flip.

RHIC Spin flipper, fast-sweep efficiency simulations

“…The principles of this spin flipper and its installation in RHIC are detailed and discussed in Refs. [1]- [5]. The 4 "spin rotator" dipoles are DC, they yield spin y-rotation angles +/ − / − / + ×φ 0 respectively, with…”

“…Fields in ACD 2 and 4 are 180 o + φ 0 distant in phase. This configuration induces spin resonance at Q osc = Q s while eliminating the image resonance at 1 − Q s , therefore ensuring single resonance crossing during Q osc sweep through Q s ≈ 1 2 and allowing full spin flip (isolated resonance crossing in the presence of image resonance instead, would otherwise require Q s to be away enough from 1 2 and Q osc excursion accordingly small). The strength of this spin-resonance system is…”

“…"D' lattice" optics are aimed at overcoming that effect, by ensuring minimized ∆D ′ during the ACD frequency sweep. They require dedicated, possibly lengthy, tunings based on the use of gamma transition quads [1].…”

“…, and D' lattice (right) using the gamma transition patch translated from RHIC MADX model. ∆D ′ can easily be changed by tweaking a sensitive one of the γ tr quadrupole families [1] -this is done here regardless of possible δβ/β betatron modulation however that tweak is small. Separation bumps at all IPs have been zeroed in the simulations, the orbit is flat.…”

“…These simulations have had two significant outcomes : (i) increasing the AC dipole frequency sweep rate, by a substantial amount compared to the value initially used during the experiments, appears to improve the spin flip efficiency, (ii) in the conditions of the simulations (e.g., defect-free ring ; ideal snakes : 180 o spin rotation at ±45 o from the longitudinal axis ; 180 o orbit angle between the two snakes opposing in RHIC diameter ; perfect spin flipper setting including absence of image resonance, etc. ), the difference in the dispersion derivative at the two snakes as a source of spin tune spread via the chromatic orbit angles at the snakes [1], subject to dedicated RHIC optics settings during Run 17 spin flipper experiment, does not seem of very stringent importance.…”