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Magnetic resonance imaging (MRI), as well as some volume selected spectroscopy methods, use pulsed magnetic field gradients which induce multi-exponentially decaying eddy currents in all nonlaminated conductive parts of the superconducting magnets. This paper presents the analysis of the z gradient field distorsion due to the induced eddy currents and the corresponding correction in a 4 T / 30 c m bore superferric self-shielded magnet.

The paper presents a numerical procedure based on the finite element method to determine the performance of ferrite-type permanent magnet DC motors. Magnetic saturation, armature's displacement and temperature's effect were considered in the computation Qf the torque's variation with respect t o angular position. and coercivity [l]:The risk of demagnetization is bigger at low temperatures, where the remanent induction B,,, is high and the coercive force H,,,, is low. The B -H loop changes are reversible and linear over a limited range (0 -120)' C.Correspondingly, a linear approximation was used to determine the temperature coefficients for both remanence .

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