A spin refrigerator polarized target for nuclear physics experiments

A cryogenic polarized proton target has been developed for use in nuclear physics experiments. This target makes use of the “spin refrigerator” mechanism to produce the polarization, instead of the microwave pumping used in conventional polarized targets. The design, operating procedures and experience are discussed. While the polarization is low, typically 40% during actual experiments, other advantages make the target useful for certain applications. These include low development and operating costs, magnetic fields as low as 590 G during data acquisition, open geometry, the possibility of large-area targets, and the ability to change the polarization direction on a 10 min time scale.