C-AD Accelerator Physics Seminar

As part of the investigation of the feasibility of a storage ring search for an electric dipole moment (EDM), the Cooler Synchrotron (COSY) at the Forschungszentrum-Jülich has been used along with a polarized deuteron beam and the EDDA scintillation detector array to study storage ring polarimetry and, more recently, spin coherence time in the horizontal or ring plane. The EDDA detector, first developed for precise angle measurements in nucleon-nucleon scattering, was used in a mode that emphasized the detection of elastic-like scattering from a carbon target. That target was made 15 mm thick and placed at the edge of the beam where the beam could be slowly extracted onto the target’s front face. This resulted in a very high efficiency for making continuous measurements of the polarization of the beam, one requirement for an EDM search. Studies completed in 2009 showed that it is possible to expand the cross ratio, or square root, formula for polarization measurements to contain correction terms that remove systematic geometric or rate errors to the level of one part per million, thus satisfying another EDM requirement. This polarimeter arrangement now makes possible a new class of studies of the time coherence of beams polarized in the horizontal plane. A first run was made in January studying the RF-solenoid spin resonance with the intention of investigating the contribution of momentum spread and emittance to the resonance width since these mechanisms also contribute to the decoherence of the polarization. The most important phenomena observed during the run was, however, the interplay between synchrotron oscillations in the bunched beam and the RF solenoid oscillating field. These effects can be described in a simple, no-lattice treatment of the spin properties of the ring and RF-solenoid. The plans for the future of this study will be described.