Magnetic field and force evaluation in open boundary axisymmetric structures

This paper presents a method to obtain the magnetic field resulting from currents in coils and permanent magnets in structures with axial symmetry and open boundaries. The finite element method (FEM) is used inside a sphere containing the structures and a Legendre polynomial expansion is used to represent the field in the outside region. The polynomial expansion is truncated to an order equal to the number of grid nodes along the spherical boundary resulting from the FEM discretization. The polynomial coefficients are determined in order to guarantee the field continuity in those nodes. The method is then utilized to preview the interaction force between a samarium-cobalt (Sm-Co) magnet and solenoid.