Siberian Snake Experiments at the Iucf Cooler Ring

Recent polarized proton beam experiments in the IUCF Cooler Ring found an evidence for a second-order snake depolarizing resonance, when the vertical betatron tune was inadvertently set near a quarter-integer. We have also studied the possibility of spin-flipping the beam polarization in the presence of a full Siberian snake using an rf solenoid. By varying the rf solenoid’s ramp time and frequency range, we reached a spin-flip efficiency of about 97%. 1 SECOND-ORDER SNAKE DEPOLARIZING RESONANCE One must overcome many spin depolarizing resonances to accelerate a polarized proton beam to high energy. Earlier IUCF experiments [1] suggest that the Siberian snake technique [2] could universally overcome all intrinsic and imperfection depolarizing resonances even at high energy. However, another type of depolarizing resonances called “snake” resonances could occur at certain values of the vertical betatron tune even in the presence of a full Siberian snake in a ring. Using a 104 MeV stored polarized proton beam and a full Siberian snake, we recently found evidence for a second-order “snake” depolarizing resonance. In any circular accelerator or storage ring, each proton’s spin precesses around the vertical fields of the ring’s dipole magnets. The spin tune νs, which is the number of spin precessions during one turn around the ring, is proportional to the proton’s energy