Beam transport insensitive electron spin rotators for nuclear physics applications

Spin polarized particle beams play a critical role in experimental physics and materials science, and are utilized in accelerators ranging in scale from tabletop electron microscopes to large scale accelerators such as the Continuous Electron Beam Accelerator Facility (CEBAF) at Jefferson National Laboratory (JLAB), which has serviced parity-violation (PV) experiments for roughly two decades. Spin-polarized beams also feature prominently in important future nuclear physics experiments such as the Electron Ion Collider (EIC) being built at Brookhaven National Lab, the world's first polarized electron-proton collider, which will probe the quark and gluon contributions to the proton's spin using polarized proton and electron beams. In addition to the EIC, the planned MOLLER (Measurement of the Lepton-Lepton Electroweak Reaction) experiment will scatter longitudinally polarized electrons with unpolarized electrons using the upgraded 11 GeV beam in Hall A JLAB and is designed to discover new dynamics beyond the Standard Model of electroweak interactions. This experiment represents the most ambitious PV experiment to date, and several upgrades to the CEBAF facility have been completed or are planned in anticipation of beam delivery to the experiment beginning in 2025. The most relevant to this work is the desire to install a new spin rotator in the 6 MeV portion of the CEBAF injector system, as an alternative to using existing low energy rotator device. This new spin rotator could then be used to provide automated feedback for zeroing the transverse polarization used to minimize helicity-correlated beam asymmetries. Furthermore, the inclusion of additional focusing elements to compensate changes to the downstream beam optics induced by operation of the new spin manipulator further increases the attractiveness of this option. The team at Xelera Research LLC has many decades of combined expertise in the generation of and manipulation of polarized beams for particle accelerators and microscopes. In this SBIR project we aim to develop an optimized solution for the requested spin parameters such that the electron beam exiting the device experiences minimal disruption as the spin direction is changed, a critical metric for the complex nuclear physics experiments. In Phase 2, Xelera would build the device and then carry out beam tests at a national lab facility to verify its performance. Xelera Research LLC is uniquely experienced in the design and construction of novel optics, detectors, particle beam sources, injectors, beam transport systems, and beam dumps, and has pioneered work with using modern optimization techniques for applications of interest to the Department of Energy. This project also has commercial applications, and Xelera will be pursuing commercial sales to industrial users in addition to supporting important nuclear physics experiments.