Halbach arrays are an appealing magnet design for low field MRI due to their low weight and cost typically suffer from relatively high B0 inhomogeneity. In this work we show a new approach to shimming Halbach arrays using higher order Halbach inserts which can be designed to target specific spherical harmonic terms. We demonstrate the principle by correcting for the x2-y2 spherical harmonic, improving B0 homogeneity of a 31cm diameter bore Halbach array by 50% and show that in simulations homogeneities of 280 ppm can be achieved over a 20 cm sphere by correcting up to 5th order spherical harmonics.
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