Optically Pumped Polarized $^3$He$^{++}$ Ion Source Development for RHIC/EIC

TL;DR

This paper presents a new technique for producing high-intensity polarized $^3$He$^{++}$ ion beams for RHIC/EIC, involving innovative gas handling, optical pumping, and polarization measurement methods.

Contribution

It introduces a novel approach combining cryogenic purification, gas injection, and optical pumping to achieve high polarization and intensity of $^3$He$^{++}$ ions.

Findings

Achieved 80-85% polarization of $^3$He in an open cell configuration.

Developed a cryogenic purification technique for high-purity $^3$He gas.

Demonstrated long polarization relaxation times of about 30 minutes.

Abstract

The proposed polarized $^3$He$^{++}$ acceleration in RHIC and the future Electron-Ion Collider will require about $2\times10^{11}$ ions in the source pulse. A new technique had been proposed for production of high intensity polarized $^3$He$^{++}$ ion beams. It is based on ionization and accumulation of the $^3$He gas (polarized by metastability-exchange optical pumping and in the 5 T high magnetic field) in the existing Electron Beam Ion Source (EBIS). A novel $^3$He cryogenic purification and storage technique was developed to provide the required gas purity. An original gas refill and polarized $^3$He gas injection to the EBIS long drift tubes, (which serves as the storage cell) were developed to ensure polarization preservation. An infrared laser system for optical pumping and polarization measurements in the high 3--5 T field has been developed. The $^3$He polarization 80--85\% (and sufficiently long $\sim30$ min relaxation time) was obtained in the \lq\lq{open}\rq\rq\ cell configuration with refilling valve tube inlet and isolation valve closed. The development of the spin-rotator and $^3$He $^4$He absolute nuclear polarimeter at 6 MeV $^3$He$^{++}$ beam energy is also presented.