Experimental validation for the compensation method of nonlinearities in periodic magnets

Abstract

Nonlinearities from any periodic magnet in accelerators may strongly degrade the dynamics of the beams. This may be especially critical for magnets where the beam excursions are comparable to the good field region, as for example in wigglers, since the beam trajectory can be of the order of the pole width. A general method based on alternately shifting the magnetic axis of each pole to compensate this effect was proposed and applied to the $\mathrm{DA}\mathrm{\ensuremath{\Phi}}\mathrm{NE}$ wigglers, where an important integrated octupole was measured. This approach has been optimized by multipolar analyses and the effect on the beam dynamics verified by tracking studies. In this paper we report about the experimental validation of the magnetic model and the verification of the method by beam based measurements. The latter were performed after all the wigglers in the $\mathrm{DA}\mathrm{\ensuremath{\Phi}}\mathrm{NE}$ main rings had been modified according to the optimal configuration. These measurements were in agreement with the expectations and allowed experimentally proving the method.