Nuclear spin-polarized He-3 gas at pressures on the order of 100 kPa (1 bar
) are required for several applications, such as neutron spin filters and m
agnetic resonance imaging. The metastability-exchange optical pumping (MEOP
) method for polarizing He-3 gas can rapidly produce highly polarized gas,
but the best results are obtained at much lower pressure (similar to0.1 kPa
). We describe a compact compression apparatus for polarized gas that is ba
sed on a modified commercial diaphragm pump. The gas is polarized by MEOP a
t a typical pressure of 0.25 kPa (2.5 mbar), and compressed into a storage
cell at a typical pressure of 100 kPa. In the storage cell, we have obtaine
d 20% to 35% He-3 polarization using pure He-3 gas and 35% to 50% He-3 pola
rization Using He-3-He-4 mixtures. By maintaining the storage cell at liqui
d nitrogen temperature during compression, the density has been increased b
y a factor of four.