Magnetic Field Requirements for the CLAS12 Polarized Target

Abstract

Upcoming spin structure experiments in Hall B at Jefferson Lab will employ a new dynamically polarized target inside the CLAS12 detector system. Protons and deuterons in irradiated NH 3 and ND 3 will be polarized at 1 K using the 5 T field of the CLAS12 solenoidal magnet. For optimum polarization, the field uniformity requirements are around 100 ppm over the volume of the target sample. I will discuss methods to improve field uniformity utilizing thin superconducting shim coils integrated within the 1 K refrigerator. I will also demonstrate that this method to adjust the 5 T field also enables the simultaneous opposite polarization of two adjacent target cells.

First Use of a Longitudinally Polarized Target with CLAS12

“…For optimum deuteron polarization, the CLAS12 solenoid is designed to provide a field uniformity of 100 ppm over the volume of the polarized target sample, but field mapping measurements indicate the uniformity is perhaps closer to 300 mm. We have therefore included four small, superconducting shim coils inside the target cryostat to improve the uniformity to ≤ 100 ppm [6].…”