Methods for Obtaining Polarized Beams

Abstract

Methods for obtaining high-energy polarized beams are strongly different for different particles. The problem of obtaining polarized proton beams is most complicated. In this case, it is necessary to create high-current sources of hydrogen ions with a high polarization degree and to guide such a beam through a long chain of accelerating units for reaching the final energy. It is particularly difficult to guide beams through strong-focusing accelerators, where a high-accuracy device, so-called “Siberian snake,” should be used to preserve polarization during the acceleration of the protons. This device will be described later. The polarimetry of high-energy proton beams is also difficult. The problem of obtaining polarized electron beams in circular accelerator is somewhat easier. This problem is simplified with the use of ring accelerators/colliders due to the effect of the synchrotron-radiation-induced self-polarization of electrons (so-called Sokolov–Ternov (ST) effect), which will be discussed in the section devoted to polarized electron/positron beams. The problem of obtaining polarized electron beams in linear accelerators is somewhat more complicated. In this case, it is necessary to create high-current sources of polarized electrons. It is particularly easy to obtain polarized muon beams. Muons appear being already polarized in the weak decay of pions. For this reason, many difficulties inherent in the production of polarized proton and even electron (linac) beams are absent in this case. These aspects will be discussed in more details later.