DESIGN STUDY FOR AN ANTIPROTON POLARIZER RING (APR)

In the framework of the FAIR [1] project, the PAX collaboration (Polarized Antiproton eXperiments) has suggested new experiments using polarized antiprotons [2], in particular the study of the transverse spin structure of the proton. In order to reach a high degree of polarization of the antiprotons, the spin filtering method is proposed using an optimally designed dedicated Antiproton Polarizer Ring (APR). In this contribution the design of such a storage ring is described. The basic parameters follow from the requirements to have a large ring acceptance at an energy, where the spin-dependence of the antiproton-proton interaction leads to a large antiproton beam polarization: This suggests to operate the APR at an antiproton beam energy of 250 MeV with an emittance in both planes of 250 pi mm mrad. The APR consists of two 180 degree arcs and two straight sections. One straight section houses the elements needed for injection and extraction, and the polarized internal target. In the other straight section, the electron cooler and a Siberian snake are located. Different optical conditions have to be fulfilled in the straight sections: (1) The target cell requires a beta function of less than 0.3 m. (2) The beam has to be circular and upright in the phase space ellipse at the target, at the electron cooler, and at the snake. (3) The antiproton beam should have a size of 10 mm for an emittance of 250 pi mm mrad at the target. (4) The momentum dispersion has to be zero in both straight sections.