Design and characterization of combined function multipole magnet for accelerators

This paper presents the design and analysis of a multipurpose combined function magnet for use in accelerators. This magnet consists of three corrector magnets: (i) skew quadrupole, (ii) horizontal dipole, and (iii) vertical dipole magnets, along with the main sextupole magnet. The strength of the corrector magnets is smaller than that of the main sextupole magnet. The strength of all the four magnets can be varied independently. The excitation strength required to produce skew quadrupole gradient and the presence of various multipole components in the magnet are estimated using first order perturbation theory. The experimental data for the variation of the sextupole strength and its higher order multipoles in the presence of skew quadrupole excitations are presented and compared to the theoretical predictions. Simulation using two-dimensional fine element code, Poisson, is also done. Results obtained from all the above three methods are found to be in good agreement with each other. The variations of skew quadrupole gradient for different sextupole excitations are also measured. The validity of this theory is also checked for various combinations of excitations including the case where magnet gets saturated. The excitation strengths required for producing the horizontal and vertical dipole fields are estimated analytically along with the presence of various multipoles. Theoretical predictions of permissible multipoles are compared to the results obtained from simulation.