Depolarizing resonances occur at certain energies in all circular proton accelerators, whenever the frequency of proton spin precession equals the frequency with which the protons encounter depolarizing magnetic fields. At these depolarizing resonances, the horizontal fields icteract coherently with each spin and rapidly depolarize the beam.' The imperfection depolarizing resonances are due to imperfection horizontal fields or magnet misalignments. The intrinsic depolarizing resonances are due

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... o the horizont a1 focusing fields. The successful acceleration of polarized proton beams at the ZGS, Saturne, the AGS,2 and KEK required much hardware and difficult tuning to individually correct these resonances. The Siberian snake technique3 should correct all such depolarizing resonances without individually tuning through each resonance; a "full-strength" snake does this by rotating the spin of each proton by exactly 180" about a horizontal axis on each turn around the ring. The depolarizing fields should then cancel each other on two turns around the ring. Our earlier experiments at the IUCF Cooler Ring demonstrated that a Siberian snake could easily overcome imperfection4 and intrinsic5 depolarizing resonances. We also found and overcame other types of depolarizing resonances such as the synchrotron depolarizing resonance^,^ and the RF-induced depolarizing resonance^.^ We also studied partial Siberian