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 ${\mathcal{E}}_{\mathrm{FS}}$ gave very large deviations from the $^{*}\mathcal{E}_{Bdl}$ obtained from each rf magnet's $\ensuremath{\int}{B}_{rms}dl$. We recently varied an rf dipole's frequency sweep range $\ensuremath{\Delta}f$, and the momentum spread $\ensuremath{\Delta}p/p$ and betatron tune ${\ensuremath{\nu}}_{y}$ of stored $1.85\text{ }\text{ }\mathrm{GeV}/c$ polarized deuterons. We found a sharp constructive interference when ${\ensuremath{\nu}}_{y}$ was near an intrinsic spin resonance. Moreover, over large $\ensuremath{\Delta}f$ and $\ensuremath{\Delta}p/p$ ranges, ${\mathcal{E}}_{\mathrm{FS}}$ was about 7 times smaller than the predicted $^{*}\mathcal{E}_{Bdl}$.

Unexpected reduction of rf spin resonance strength for stored deuteron beams

The unpolarised differential cross section and the two deuteron tensor analysing powers Axx and Ayy of the � dp →{ pp}sn charge-exchange reaction have been measured with the ANKE spectrometer at the COSY storage ring. Using deuteron beams with energies 1.2, 1.6, 1.8, and 2.27 GeV, data were obtained for small momentum transfers to a {pp}s system with low excitation energy. The results at the three lower energies are consistent with impulse approximation predictions based upon the current knowledge of the neutron-proton amplitudes. However, at 2.27 GeV, where these amplitudes are far more uncertain, agreement requires a reduction in the overall double-spin-flip contribution, with an especially significant effect in the longitudinal direction. These conclusions are supported by measurements of the deuteron-proton spin-correlation parameters Cx,x and Cy,y that were carried out in the � dp →{ pp}sn reaction at 1.2 and 2.27 GeV. The values obtained for the proton analysing power A p also suggest the need for a radical re-evaluation of the neutron-proton elastic scattering amplitudes at the higher energy. It is therefore clear that such measurements can provide a valuable addition to the neutron-proton database in the charge-exchange region.

/pdf/the-neutron-proton-charge-exchange-amplitudes-measured-in-2gxfvjlotw.pdf

The neutron-proton charge-exchange amplitudes measured in the dp → ppn reaction

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 $\ensuremath{\int}Bdl$ and the weak energy dependence of its spin resonance strength $\mathcal{E}$ 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 $2.1\text{ }\text{ }\mathrm{GeV}/c$ polarized proton beam stored in COSY. We found no dependence of $\mathcal{E}$ on beam size, but we did find almost 100-fold enhancements when the rf spin resonance was near an intrinsic spin resonance.

Unexpected enhancements and reductions of rf spin resonance strengths

Prompted by recent, conflicting calculations, we have carried out a measurement of the spin flip cross section in low-energy electron-proton scattering. The experiment uses the cooling electron beam at COSY as an electron target. A reanalysis of the data leeds to a reduced statistical errors resulting in a factor of 4 reduced upper limit for the spin flip cross section. The measured cross sections are too small for making spin flip a viable tool in polarizing a stored beam.

https://iopscience.iop.org/article/10.1088/1742-6596/295/1/012133/pdf

Polarizing a stored proton beam by spin flip? – A high statistic reanalysis

High-density ion beams obtained by electron cooling will be used for medical and other applications at HIMAC. Cool-stacking injection was carried out with Ar 18 + ions at 6 MeV / u to increase the intensity to a limit, which was determined by instabilities and by the ion lifetime. The maximum ion stack intensity was 2 emA , above which fast-ion losses occurred simultaneously with vertical coherent oscillations. The instability depends on the working point, the ion stack density and secondary ions trapped in the cooler. The instability was damped by reducing the stacked ion density with transverse RF-excitation, and/or by clearing the secondary particles.

Cool-stacking injection and damping of a transverse ion-beam instability at the HIMAC synchrotron

COSY electronic cooling is used after charge-exchange injection of H– or D– to produce the required emittance and momentum spread in the beam after the beam is accelerated. The cooled and accelerated beam is then used for experimental applications, such as, fast or slow extraction for experiments onto an external target. Methods for setting up the electronic-cooling system and limiting the ion-beam intensity are discussed.

Current Status of the COSY Electron Cooler (Jülich, Germany)

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Current Status of the COSY Electron Cooler (Jülich, Germany)