Development and application of a $^3$He Neutron Spin Filter at J-PARC

TL;DR

This paper reports on the development and successful application of a polarized $^3$He neutron spin filter at J-PARC, enabling improved neutron scattering experiments through high polarization and practical system design.

Contribution

It introduces a new $^3$He spin filter system with high polarization and demonstrates its effective use in neutron scattering experiments at J-PARC.

Findings

Achieved 85% $^3$He polarization at a neutron beamline.

Constructed a $^3$He gas-filling station and developed compact pumping systems.

First user experiment utilizing the $^3$He spin filter was successfully conducted.

Abstract

We are developing a neutron polarizer with polarized $^3$He gas, referred to as a $^3$He spin filter, based on the Spin Exchange Optical Pumping (SEOP) for polarized neutron scattering experiments at Materials and Life Science Experimental Facility (MLF) of Japan Proton Accelerator Research Complex (J-PARC). A $^3$He gas-filling station was constructed at J-PARC, and several $^3$He cells with long spin relaxation times have been fabricated using the gas-filling station. A laboratory has been prepared in the MLF beam hall for polarizing $^3$He cells, and compact pumping systems with laser powers of 30~W and 110~W, which can be installed onto a neutron beamline, have been developed. A $^3$He polarization of 85% was achieved at a neutron beamline by using the pumping system with the 110~W laser. Recently, the first user experiment utilizing the $^3$He spin filter was conducted, and there have been several more since then. The development and utilization of $^3$He spin filters at MLF of J-PARC are reported.