R. A. Phelps

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 solenoids ramp time and frequency range, we reached a spin-flip efficiency of about 97%.

First test of a partial Siberian snake for acceleration of polarized protons

We recently studied the first acceleration of a spin‐polarized proton beam through a depolarizing resonance using a partial Siberian snake. We accelerated polarized protons from 95 to 140 MeV with a constant 10% partial Siberian snake obtained using rampable solenoids. The 10% partial snake suppressed all observable depolarization during acceleration due to the Gγ=2 imperfection depolarizing resonance which occurred near 108 MeV. However, 20% and 30% partial Siberian snakes apparently moved an intrinsic depolarizing resonance, normally near 177 MeV, into our energy range; this caused some interesting, although not‐yet‐fully understood, depolarization.

Spin flipping a stored vertically polarized proton beam with an RF solenoid

A recent experiment in the IUCF cooler ring studied the spin flip of a stored vertically polarized 139 MeV proton beam. This spin flip was accomplished by using an RF solenoid to induce an artificial depolarizing resonance in the ring, and then varying the solenoid’s frequency through this resonance value to induce spin flip. We found a polarization loss after multiple spin flips of about 0.00±0.05% per flip and also losses for very long flip times. This device will be useful for reducing systematic errors in polarized beam‐internal target scattering asymmetry experiments by enabling experimenters to perform frequent beam polarization reversals in the course of the experiment.

Energy change of a depolarizing resonance due to a type-3 Siberian snake

The authors measured the photon beam polarization in the IUCF (Indiana University Cyclotron Facility) Cooler Ring at five energies. They found that the G/sub lambda /=2 imperfection depolarizing resonance occurred about 1.9 MeV below the expected resonance energy of 108.4 MeV. This energy shift could be due to a shift of about +0.0036 in the spin time, nu /sub s/, which is the number of spin rotations in each turn around the ring. It was then demonstrated that this spin tune shift is consistent with the cooler ring containing a partial type-3 Siberian snake, which is apparently caused by the magnets that confine the electron and proton beams in the cooling region.<<ETX>>