Dynamically polarized target for the g2p and GEp experiments at Jefferson Lab

TL;DR

This paper details a dynamically polarized target system used in Jefferson Lab's electron scattering experiments, highlighting its design, performance, and operational flexibility in achieving high proton polarization.

Contribution

Introduction of a new polarized target system with high cooling power and rapid rotation capability for improved experimental performance at Jefferson Lab.

Findings

Achieved maximum proton polarizations of 28% and 95%.

Demonstrated rapid rotation of the magnet between angles in minutes.

Validated the target's performance under high beam currents and magnetic fields.

Abstract

We describe a dynamically polarized target that has been utilized for two electron scattering experiments in Hall A at Jefferson Lab. The primary components of the target are a new, high cooling power 4He evaporation refrigerator, and a re-purposed, superconducting split-coil magnet. It has been used to polarize protons in irradiated NH3 at a temperature of 1 K and at fields of 2.5 and 5.0 Tesla. The performance of the target material in the electron beam under these conditions will be discussed. Maximum polarizations of 28% and 95% were obtained at those fields, respectively. To satisfy the requirements of both experiments, the magnet had to be routinely rotated between angles of 0, 6, and 90 degrees with respect to the incident electron beam. This was accomplished using a new rotating vacuum seal which permits rotations to be performed in only a few minutes.