Wide Aperture Multipole Magnets of Separator Combas

The high-resolving wide aperture separator COMBAS has been designed and commissioned at the FLNR JINR. The magneto-optical structure of the separator is based on the strong focusing principle, which is realized on the basis of multipole magnets M1-M8. The magnetic fields of the four main analysing magnets, M1, M2, M7, M8, contain powerful quadrupole components of alternating sign, which provide horizontal and vertical beam focusing. Besides, all the magnets contain sextupole and octupole field components, which minimizes the 2^nd and 3^rd order aberrations at the intermediate and final foci. All this allowed one to decrease the total number of magnet elements and the total channel length, to increase their apertures and to effectively form a beam of the required longitudinal profile and transverse sizes at both the foci. Such implementation of wide aperture magnets with combined functions is unique for fragment-separation technology. The basic principles of the separator and magnet design, as well as the manufacturing steps, are presented. Comprehensive magnetic measurements of all the magnets had been performed and became the basis of the field quality analysis. Procedures to estimate the magnet field errors and to correct them are presented. The measured data allow reconstructing the 3D-distributions of the fields in all the magnets. 3D-maps are supposed to be used for particle trajectory simulations throughout the entire separator. The investigations have been performed at the Flerov Laboratory of Nuclear Reactions, JINR.