Search Results (14 total)

The Chao matrix formalism allows analytic calculations of a beam’s polarization behavior inside a spin resonance. We recently tested its prediction of polarization oscillations occurring in a stored beam of polarized particles near a spin resonance. Using a 1.85  GeV/c polarized deuteron beam stored in the COoler SYnchrotron, we swept a new rf solenoid’s frequency rather rapidly through 400 Hz during 100 ms, while varying the distance between the sweep’s end frequency and the central frequency of an rf-induced spin resonance. Our measurements of the deuteron’s polarization near and inside the resonance agree with the Chao formalism’s predicted oscillations.

Stored beams of polarized protons, electrons, or deuterons can be spin flipped by sweeping an rf dipole’s or solenoid’s frequency through an rf spin resonance. Fitting such data to the modified Froissart-Stora equation’s spin resonance strength E_FS gave very large deviations from the ^*E_Bdl obtained from each rf magnet’s ∫B_rmsdl. We recently varied an rf dipole’s frequency sweep range Δf, and the momentum spread Δp/p and betatron tune ν_y of stored 1.85  GeV/c polarized deuterons. We found a sharp constructive interference when ν_y was near an intrinsic spin resonance. Moreover, over large Δf and Δp/p ranges, E_FS was about 7 times smaller than the predicted ^*E_Bdl.

We recently started testing Chao’s proposed new matrix formalism for describing the spin dynamics due to a single spin resonance. The Chao formalism is probably the first fundamental improvement of the Froissart-Stora equation in that it allows analytic calculations of the beam polarization’s behavior inside a resonance. We tested the Chao formalism using a 1.85  GeV/c polarized deuteron beam stored in COSY, by sweeping an rf dipole’s frequency through 200 Hz, while varying the distance from the sweep’s end frequency to an rf-induced spin resonance’s central frequency. Since the Froissart-Stora equation itself can make no prediction inside a resonance, we compared our experimental data with the predictions of the Chao formalism and those of an empirical two-fluid model based on the Froissart-Stora equation. The data strongly favor the Chao formalism.

We recently analyzed all available data on spin-flipping stored beams of polarized protons, electrons, and deuterons. Fitting the modified Froissart-Stora equation to the measured polarization data after crossing an rf-induced spin resonance, we found 10–20-fold deviations from the depolarizing resonance strength equations used for many years. The polarization was typically manipulated by linearly sweeping the frequency of an rf dipole or rf solenoid through an rf-induced spin resonance; spin-flip efficiencies of up to 99.9% were obtained. The Lorentz invariance of an rf dipole’s transverse ∫Bdl and the weak energy dependence of its spin resonance strength E together imply that even a small rf dipole should allow efficient spin flipping in 100 GeV or even TeV storage rings; thus, it is important to understand these large deviations. Therefore, we recently studied the resonance strength deviations experimentally by varying the size and vertical betatron tune of a 2.1  GeV/c polarized proton beam stored in COSY. We found no dependence of E on beam size, but we did find almost 100-fold enhancements when the rf spin resonance was near an intrinsic spin resonance.

We recently studied the spin manipulation of 1.85  GeV/c vertically polarized deuterons stored in the COSY cooler synchrotron. We adiabatically swept an rf dipole’s frequency through an rf-induced spin resonance and observed its effect on the deuterons’ vector and tensor polarizations. After optimizing the resonance crossing rate and maximizing the rf dipole’s voltage, we measured spin-flip efficiencies of 97±1% and 98.5±0.3% in two separate runs. We also confirmed at higher energy the striking behavior of the spin-1 tensor polarization recently found at IUCF.

We recently studied spin flipping of a 270 MeV vertically polarized deuteron beam stored in the Indiana University Cyclotron Facility Cooler Ring. We adiabatically swept an rf solenoid’s frequency through an rf-induced spin resonance and observed its effect on the deuterons’ vector and tensor polarizations. After optimizing the resonance crossing rate and maximizing the solenoid’s voltage, we measured a vector spin-flip efficiency of 94.2%±0.3%. We also found striking behavior of the spin-1 tensor polarization.

The time dependence of the vector and tensor polarization of a 270 MeV stored deuteron beam was measured near a depolarizing resonance, which was induced by an oscillating, longitudinal magnetic field. The distance to the resonance was varied by changing the oscillation frequency. The measured ratio of the polarization lifetimes is τ_vector/τ_tensor=1.9±0.2. Assuming that the effect of the resonance is to induce transitions between magnetic substates m_I, we find that the transition rate between neighboring states (+1 and 0 or -1 and 0) is four times higher than between the states with m_I=+1 and -1.

We recently used an rf dipole magnet to study the spin flipping of a 120 MeV horizontally polarized proton beam stored in the presence of a nearly full Siberian snake in the Indiana University Cyclotron Facility Cooler Ring. We flipped the spin by ramping the rf dipole's frequency through an rf-induced depolarizing resonance. After optimizing the frequency ramp parameters, we used multiple spin flips to measure a spin-flip efficiency of 86.5±0.5%. The spin-flip efficiency was apparently limited by the field strength in the rf dipole. This result indicates that spin flipping a stored polarized proton beam should be possible in high energy rings such as the Brookhaven Relativistic Heavy Ion Collider and HERA where Siberian snakes are certainly needed and only dipole rf-flipper magnets are practical.

We recently studied the spin flipping of a 202.7 MeV vertically polarized proton beam stored in the Indiana University Cyclotron Facility cooler ring during the first polarized run with its new cooler injector synchrotron and its new cooler injector polarized ion source. We first set the vertical betatron tune to avoid the measured ν_y value of the Gγ=7-ν_y intrinsic depolarizing resonance in the cooler ring. We then flipped the spin by ramping the frequency of an rf dipole through an rf-induced depolarizing resonance. After optimizing the rf dipole's frequency ramp parameters, we used multiple spin flips to measure a maximum spin-flip efficiency of 97.5±1%.

We recently created a snake depolarizing resonance using an rf solenoid magnet in a ring containing a nearly 100% Siberian snake. We found that the primary snake rf resonance also had two weaker synchrotron sidebands, which are second-order snake resonances; they were probably caused by the energy-dependent strength of the solenoid snake due to the Lorentz contraction of its longitudinal ∫Ḃ dl. This was the first observation of an rf synchrotron-sideband depolarizing resonance in the presence of a nearly full Siberian snake.

We have demonstrated for the first time spin flipping of a polarized proton beam stored in a ring containing a nearly 100% Siberian snake; we did this using a “snake” depolarizing resonance induced by an rf solenoid magnet. By varying the rf solenoid's ramp time, frequency range, and voltage, we reached a spin-flip efficiency of about 91%. This spin-flip efficiency was probably reduced because the horizontal stable spin direction was not perpendicular to the longitudinal field of the rf solenoid, and was possibly reduced by nearby synchrotron sideband resonances. The planned use of a vertical rf dipole may improve the spin-flip efficiency.

Using an rf solenoid magnet, we studied the depolarization of a stored 104.1 MeV vertically polarized proton beam. The two primary rf depolarizing resonances were properly centered around the protons’ circulation frequency f_c, at f_c(3-ν_s) and f_c(ν_s-1), where ν_s is the spin tune; moreover, each resonance was roughly consistent with the expected width of about 720 Hz. Each primary rf resonance had two synchrotron sideband resonances at the expected frequencies. The two ν_s-1 sidebands were deep dips while the two 3-ν_s sidebands were very shallow; this was not expected. Moreover, all four sideband resonances were unexpectedly wider than the two primary resonances.