Design and Prototyping of a Step-Like Field Magnet

Many applications using accelerator beams require a nearly uniform beam distribution at the target. A nested structure magnet producing a step-like magnet field has been proposed to transform an originally Gaussian or even irregular distribution into a more-or-less uniform one at targets. In this paper, the prototyping of a step-like field magnet is presented, which is based on the application in the China Spallation Neutron Source where the magnets are used to obtain a uniform beam profile from an initially irregular distribution at the spallation target. It includes the magnet design, 3D magnetic field calculation, prototype fabrication and field measurement. The prototyping confirms the technical feasibility of the magnet structure and the magnetic field quality consistent with the field calculations. The design improvements are discussed from the prototyping experience.