Magnetic Design Method of Non-Axisymmetric Yoke Shapes for MRI Magnets

This paper presents a magnetic design method of non-axisymmetric yoke shapes for reducing the magnetic stray field and yoke weight. A new variant of the differential evolution for multi-objective functions is implemented to search for the optimal yoke dimensions. This new algorithm has two characteristics: 1) the yoke weight, which is treated as an objective function, is always evaluated before the magnetic stray field, which is treated as a constraint function and 2) among the generated solution candidates, only the worst solution candidate is chosen to be updated. After giving a detailed description of this algorithm, results of the application of the design method to a magnetic resonance imaging magnet are shown.