Polarized 3He ion source based on the 23S1 metastables: Status Report

The 23S1 state of helium is metastable but very long lived and allows the utilisation of atomic beam techniques in order to produce a beam of polarized 3He ions. An intense metastable beam (6×1015 p.s−1 sr−1) at energies between 0.07 and 0.1 eV is generated using a cold cathode discharge. The multipole selection and focussing of Zeeman components ‖F=3/2, mF=3/2〉 and ‖F=1/2, mF=1/2〉 produces an atomic beam with high vector polarization. An adiabatic transition of +mF to −mF allows to produce a beam with (theoretical) 100% nuclear polarization in a strong magnetic field (B∼0.2T). Ionization is effected with an electron bombardment ionizer. Bench tests have produced 100 nA of 3He+ from the polarized atomic beam. Installation of the source in the HV terminal of a 7.5 MV CN Van de Graaff is underway.