Proton beam polarization at SATURNE II in the vicinity of the first depolarizing resonance

A polarized proton beam in any ring-type accelerator passes through the first depolarizing resonance γG = 2 at 108.4 MeV. It is crossed using the correctors, whereas for all other resonances of the same kind the spin flip is usually applied. A possible loss of the beam polarization was studied at SATURNE II energies in a vicinity of this resonance. An optimal crossing is important for acceleration procedure and may strongly affect the proton beam polarization at high energies. For this purpose the proton-carbon asymmetry was measured in small energy steps between 80 and 130 MeV using a modified beam polarimeter. A narrow width of the resonance crossed with correctors was observed, providing ∼3% loss of the beam polarization above the resonant energy. This loss was completely compensated by a new tuning of the correctors. When the correctors are not applied, a “bad spin flip”, followed by a fast decrease of the absolute beam polarization value with increasing energy occurs. During a cross of the resonance without correctors we observe a spin precession into the longitudinal direction. Present measurements also provide new inclusive p-C analyzing power data at energies below the pion production threshold. They are in excellent agreement with the existing data for one outgoing charged particle.