INSTALLATION OF AN ONLINE LAMB SHIFT SPIN-FILTER POLARIMETER IN THE TRIANGLE UNIVERSITIES NUCLEAR LABORATORY ATOMIC-BEAM POLARIZED ION-SOURCE

An atomic beam polarized ion source, used heavily since 1989 for produ cing, polarized H-+/- and D-+/- beams for experiments between 25 keV a nd 20 MeV, has been modified to accept a Lamb shift, spin-filter polar imeter. In this source, polarized ground-state H or D atoms enter an e lectron cyclotron resonance ionizer where they are stripped to produce an outgoing positive polarized ion beam. When negative ions are desir ed, cesium vapor is introduced into a downstream charge-exchange canal . The polarimeter, based on an atomic physics concept first developed to produce nuclear-spin-polarized beams at Los Alamos, is designed to monitor the polarization of 2S(1/2) metastable H or D atoms emerging f rom the cesium canal. Metastable 2S(1/2) atoms created by electron pic kup in a collision with cesium are ''filtered'' by the polarimeter acc ording to magnetic substate, as the magnetic field imposed on the pola rimeter cavity is tuned between 53 and 61 mT. Photons produced by subs equent quenching of these filtered atoms to their ground state are mon itored downstream by a phototube to reveal the magnetic substate popul ation of the incident positive beam. To install the polarimeter cavity and phototube assembly, the existing polarized ion source was lengthe ned by 30 cm. Installation is complete, and comparisons with calibrate d nuclear polarimeters have shown agreement to better than 0.023. Prin ciples of operation, a description of the hardware, measurements for c ross calibration, and impressions gained from its use are all presente d. (C) 1996 American Institute of Physics.