A flowing afterglow as a polarized electron source

A source of polarized electrons based on a helium flowing afterglow has been developed at Orsay. The different parts of the device are described. The results about the polarization of the metastable He atoms, the electron current and polarization and optical properties of the output electron beam are given. They reveal electron polarizations in the range 70–82% for currents up to 30 μA, about 60% for 100 μA, an average emittance of 0.5π mm mrad and an energy spread of 0.25 eV.