Polarization

Electron beam polarization has provided energy calibration for LEP, HERA etc. High energy beam experiments with spin has provided useful information on standard model, and spin structure of quarks in nucleons. Our present understanding of beam dynamics issues on beam polarization is listed as follows:

Polarized proton sources can be obtained from ABS, or OPPIS with 80% polarization and a few mA of H-minus high brightness sources. Polarized deuteron source has also made much progress in recent years.

In electron storage rings, beam polarization can be obtained by the Sokolov-Ternov effect. On the other hand, polarized electron source is needed in linear collider and in CEBAF facility. At SLC, polarized electrons are produced by the strained Ga-As photocathode. attaining a polarization of 80--90%. This  has enabled SLC to achieve very accurate measurement of the left-right asymmetry parameter for the Z production. Electron polarized sources with a high quantum efficiency will continue to play important roles in future linear colliders. In the near future, possible polarized positron source may be generated from the pair production of circular polarized photons. The result of this research effort can provide polarization for future linear colliders.

The equation of spin motion in accelerator obeys the Thomas-BMT equation, while the dynamics of particle motion obeys the Lorentz force law. Understanding of the physics of beam polarization in accelerators has produced many innovative spin manipulation methods, e.g. the spin rotator and/or snake, spin transparent insert, rf dipole kicker, tune jump, spin matching, etc.

High energy polarized beams in ZGS, AGS, SPEAR, HERA, LEP, etc., has been fruitful in many nuclear and particle physics experiments. In the near future, high energy polarized beam experiments will be available in RHIC and HERA for both polarized proton, polarized deuteron, and polarized electrons.

In the future, polarized beam experiments in high energy colliders may be possible. However, it is important to design polarized beam experiments at the design stage of a collider.

Polarized antiproton beams are difficult to come by, thus it is difficult to design a polarized proton-antiproton collider. On the other hand, high energy polarized proton-proton collider in the VLHC can be implemented with a small initial cost adjustment. Experience in the polarized beam experience at the RHIC will serve important guidance for this effort.

Polarized e+/e- collider in the VLHC tunnel may be difficult. The spin chromaicity has been shown to limit the polarization of polarized beams in the LEP to a maximum energy of 60 GeV. Unfortunately, the spin matching effort for the  final LEP polarized beam experiment was limited only to two harmonics. It would be of great value to carry out controlled experiments with a large spin chromaticity and more extendsive spin matching corrections. The inclusion of snakes and polarization wigglers  deserves careful analysis as well.

Besides these efforts, topics not fully understood are polarization lifetime, dynamics of multi-snake accelerators, spin diffusion in high energy colliders, etc.