Wide aperture permanent magnet solenoid

Various configurations of rare earth permanent magnet solenoids with a large bore were simulated using finite element computer modeling. The configuration effect on the axial field, B_z, and its uniformity, ΔB_z, was analyzed. The magnetic orientation of individual segments and the aspect-ratio of the solenoid have a significant effect on B_z and ΔB_z. Two-layered configurations assembled with trapezoidal or arc segments result in a more uniform B_z compared to configurations assembled with five-faced polyhedrons. The two-layered configuration also has the advantage of easier fabrication. A permanent magnet solenoid prototype, based on the two-layered arc segment configuration and built using Nd-Fe-B magnets, was experimentally tested. The solenoid was designed to have a length to inner diameter ratio of approximately 5:3 and a peak axial field magnitude of 1.8 kGauss. Experimental measurements agree with simulation predictions to within < 5%.