A polarimeter for GeV protons of recirculating synchrotron beams

A polarimeter for use in recirculating beams of proton synchrotrons with energies from 300 MeV up to several GeV has been developed. The polarimetry is based on the asymmetry measurement of elastic p→p scattering on an internal CH2 fiber target. The forward going protons are detected with two scintillator systems on either side of the beam pipe close to the angle Θf of maximum analyzing power AN. Each one operates in coincidence with a broad (ΔΘb=21.4°), segmented detector system for the recoil proton of kinematically varying direction Θb; this position resolution is also used for a concurrent measurement of the p→C and nonelastic p→p background. The CH2 fiber can be replaced by a carbon fiber for detailed background studies; “false” asymmetries are accounted for with a rotation of the polarimeter around the beam axis. Polarimetry has been performed in the internal beam of the Cooler Synchrotron COSY at fixed energies as well as during proton acceleration across depolarizing or spin flipping resonances. With luminosities in the order of 1030 cm−2 s−1, count rates allow precise polarimetry within 10 min (6–10 h) at fixed energies (over the whole acceleration ramp).