Magnetic Measurements of the First Short Models of Twin Aperture Magnets for FCC-ee

Abstract

We report on the results of magnetic measurements of the first short models of twin aperture magnets for the FCC-ee arcs. To date, we have built and tested three 1-m long bending magnets, using different materials for the ferromagnetic yoke and a 1-turn vs. a multi-turn excitation. Besides the interest in checking the unusual I-layout, the focus is also on the behavior at low field, down to about 15 mT in the gap, and its impact on field quality (in particular, on the gradient term). In parallel, we have also built a 1-m long quadrupole model, to test the peculiar twin configuration and assess the multipole field errors as a function of the excitation current, checking especially the dipole and sextupole terms. The results presented can be the basis of further developments for this kind of magnets.