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

We are developing a neutron polarizer with polarized He-3 gas, referred to as a He-3 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 He-3 gas-filling station was constructed at J-PARC, and several He-3 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 He-3 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 He-3 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 He-3 spin filter was conducted, and there have been several more since then. The development and utilization of He-3 spin filters at MLF of J-PARC are reported.