Development of a universal Lamb-shift polarimeter for polarized atomic-beam targets like at ANKE/COSY

Since 1994 a Lamb-shift polarimeter (LSP) for the fast and precise measurement of the polarization of an atomic beam was designed, built and tested at the Institut fuer Kernphysik of the Universitaet zu Koeln. This universal polarimeter can be used to develop a atomic beam polarized ion source (like for the Cologne SAPIS project) or to measure the polarization of atomic beam targets (jet or storage cell targets, e.g. at COSY-Juelich). This Lamb-shift polarimeter was tested with an unpolarized beam of protons and deuterons at Cologne and, since the beginning of 2001, at the Forschungszentrum (FZ) Juelich with the polarized atomic hydrogen and deuterium beams from the atomic beam source of the polarized gas target at ANKE (apparatus for nucleon and kaon ejectiles). This polarized internal storage-cell gas target will be used in the storage ring COSY (cooler synchrotron) in 2003. The polarimeter is based on measuring the ratios of Lyman-α transition intensities after Stark quenching of spinfilter selected Zeeman hyperfine states. The nuclear polarization of the atomic beam is deduced by applying the product of several correction factors calculated from known effects. The total correction amounts to between 1.1 and 1.2 depending on the occupation numbers of the hyperfine states. The nuclear polarization of atomic beams of hydrogen and deuterium is determined with an accuracy of ≤ 1% within a few seconds for beams of ∝ 3 . 1016 atoms/s in one hyperfine state. Its error is dominated by the systematic errors of the various correction factors and will be lowered to ∼ 0.5% using a recently developed new ionizer. The sensitivity of the polarimeter is such that even for a beam intensity reduced to 10% the polarization could be determined reliably. The new ionizer will lower this sensitivity limit to ≤ 3%. With this sensitivity it appears feasible to measure the polarization in the planned storage cell of ANKE by extracting a small fraction of the atoms. In addition to these studies of the (de)polarization in a storage cell plans are to study the polarization and fraction of recombined molecules H2 and especially D2 in such a cell (CELGAS project). At Cologne the LSP will be used to develop the atomic beam source for the SAPIS project (stored atoms pulsed ion source). The LSP offers itself as a very good instrument for all polarized gas target installations at storage rings. (orig.)