# A cryostat to hold frozen-spin polarized HD targets in CLAS: HDice-II

## TL;DR

This paper presents a cryostat system designed to maintain frozen-spin polarized HD targets at ultra-low temperatures and high magnetic fields, enabling long polarization lifetimes during experiments at Jefferson Lab.

## Contribution

It introduces a novel cryostat and magnet system capable of sustaining polarized HD targets for extended periods under experimental conditions.

## Key findings

- Achieved a base temperature of 50 mK and a 1 Tesla holding field.
- Maintained polarization lifetimes of several months.
- Proton polarization up to 50% and deuteron up to 27%.

## Abstract

The design, fabrication, operation, and performance of a helium-3/4 dilution refrigerator and superconducting magnet system for holding a frozen-spin polarized hydrogen deuteride target in the Jefferson Laboratory CLAS detector during photon beam running is reported. The device operates both vertically (for target loading) and horizontally (for target bombardment). The device proves capable of maintaining a base temperature of 50 mK and a holding field of 1 Tesla for extended periods. These characteristics enabled multi-month polarization lifetimes for frozen spin HD targets having proton polarization of up to 50% and deuteron up to 27%.