A forward-angle large-acceptance magnetic spectrometer

TL;DR

This paper describes the design, construction, and features of a large-acceptance magnetic spectrometer at Jefferson Lab, enabling high-luminosity forward scattering experiments with a broad solid angle coverage.

Contribution

It introduces a novel spectrometer design with a horizontal slit opening, magnetic shielding, and correction magnets for improved performance in high-luminosity experiments.

Findings

Achieved 70 msr solid angle acceptance.

Implemented effective magnetic shielding to reduce residual fields.

Ensured mechanical stability of the large dipole magnet near the target.

Abstract

A large solid angle magnetic spectrometer for high luminosity and forward scattering angles was constructed at the Thomas Jefferson National Accelerator Facility. A number of physics experiments have used this spectrometer, and a significant physics program of future experiments has already been approved. A key feature of the spectrometer concept is a horizontal slit opening that allows the beamline to pass through the yoke of the spectrometer magnet. This design enables a short distance between the target and spectrometer, resulting in a 70~msr solid angle acceptance. The residual magnetic-field on the beamline inside the slit is reduced by a two-layer magnetic shielding system, with the external layer comprising a set of iron rings. Two correcting magnets, before and after the dipole, were used to compensate for the transverse component of the fringe field outside of the dipole yoke. The mechanical stability of the tall dipole magnet in close proximity to the target was provided by means of a heavy counterweight.