Intense polarized electron beams from chemi-ionization reactions with optically pumpedHe(2S3)

An optically pumped flowing helium afterglow is evaluated as a potential source of polarized electrons. Spin angular momentum conservation in chemi-ionization reactions involving optically oriented $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ atoms has been exploited to yield microampere electron beams with 30% polarization and energy spread ≤ 0.5 eV. The beam emittance is on the order of 10 mrad cm at 500 V extraction potential. This source appears well-suited for most spin-dependent scattering experiments that have been proposed.