Optimizing Polarization with an Improved Integer Resonance Correction Scheme at Elsa∗

The Electron Stretcher Facility ELSA of Bonn University provides a polarized electron beam of up to 3.2GeV. In the stretcher ring various depolarizing resonances are crossed during the fast energy ramp of 6GeV/s. The high polarization degree of up to 70% can only be conserved by taking several appropriate countermeasures. Concerning integer resonances, additional harmonic horizontal fields are applied by orbit correction magnets around the ring to compensate the resonance driving fields. The correction field has to be adjusted by empirical optimization of polarization. Recent developments enhance this optimization process, especially at high energies: A new magnet system allows for higher correction amplitudes and shorter rising times. Furthermore, a modified correction scheme was implemented. It takes into account the additional fields of the quadrupole magnets, arising from the orbit response of the correction magnets.