A compact in-situ polarized ³He system for neutron scattering

The performance of a new compact (55 cm × 56 cm × 48 cm) in-situ spin-exchange optical pumping (SEOP) ³He-neutron spin filter (NSF) system developed at the China Spallation Neutron Source (CSNS) is presented. The enclosed NSF cell, filled with 2.53 bar ³He, was born with a ³He polarization of around 60%. After subsequent improvements to the magnetic field and heating system, this in-situ system is able to achieve 75.66%±0.09% ³He polarization, resulting in a 96.30% neutron polarization at 2 Å. This highly compact in-situ system is equipped with self-supportive features, pre-pumping capabilities, polarization maintenance, and low-noise Nuclear Magnetic Resonance (NMR) system. These advantages significantly reduce the preparation time and simplify the processes in polarized neutron experiments, allowing it to be adopted on various neutron beamlines in China, especially those with limited sample space. These characteristics establish it as a quasi-standardized system, playing a vital role in polarized neutron experiments including polarized neutron imaging, neutron reflection, the performance calibration of polarized neutron instruments, Neutron Optics Parity and Time Reversal EXperiment (NOPTREX).