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, Bz, and its uniformity, ΔBz, was analyzed. The magnetic orientation of individual segments and the aspect-ratio of the solenoid have a significant effect on Bz and ΔBz. Two-layered configurations assembled with trapezoidal or arc segments result in a more uniform Bz 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%.