Radiative polarization in high-energy storage rings

Electron and positron beams circulating in high-energy storage rings become spontaneously polarized by the emission of synchrotron radiation. The asymptotic degree of polarization that can be attained is strongly affected by depolarizing resonances. Detailed experimental measurements of the polarization were made at Stanford Positron Electron Asymmetric Ring (SPEAR) about ten years ago, but due to the lack of a suitable theory only a limited theoretical fit to the data has so far been achieved. The author presents a general formalism for calculating depolarizing resonances, which has been coded into a computer program called SMILE, and uses it to fit the SPEAR data. By using suitable approximations, the author is able to fit both higher order and nonlinear resonances, and thereby to interpret many hitherto unexplained features in the data as well as to resolve a puzzle concerning the asymmetry of certain resonance widths seen in the data