Magnetic lenses for neutron beams
Purpose - To provide information on magnetic lens design principles for neutron beam focussing and to characterize the efficiency of these devices. Design/methodology/approach - Magnetostatic and neutron optical computations are presented for permanent magnet and electromagnetic hexapole lenses for neutron beam focusing. The numerical results are verified by magnetic and neutron beam measurements. Findings - Neutron lenses built from brick-shaped permanent magnets approximating the six-pole Halbach structure yield relatively high field constant for a relatively small useful diameter. Electromagnets are weaker, but allow field constant adjustment. Research limitations/implications - The main limitation of both presented solutions resides in the difficulty of obtaining high magnetic flux densities. Superconducting coils in hexapole configuration can overcome this limitation. Practical implications - The magnetic lenses can be used for beam focusing in scattering neutron instruments. The focused beam is also polarized. Originality/value - Analytical formulae are supplied for the neutron path calculation in a six-pole magnetic field. An electromagnet design with permanent magnet flux enforcement is provided.
magnetic devices numerical analysis optical instruments