Conceptual design of the spin rotator for the SuperKEKB High Energy Ring

Abstract

This project focuses on the conceptual design of the spin rotator for a proposed electron polarization upgrade of the SuperKEKB. The goal is to achieve the longitudinal electron polarization at the interaction point (IP). In this design, four existing dipoles will be replaced with four rotator magnets on both sides of the IP. The rotator magnet structure consists of dipole-solenoid combined function magnets with skew-quadrupoles installed on top to decouple the x-y plane. The advantage of this design is that the original machine geometry is maintained, and the original machine can be recovered by turning off the solenoid-quadrupole in the rotator magnet. With Bmad, a powerful lattice simulation tool applied to perform the optimizations for this design, the longitudinal spin alignment at the IP reaches a significantly high level, greater than 99.99%. Furthermore, the influence of the installation of the spin rotator on the original machine dynamics is minimized to an acceptable level.