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Mitigating ab-Plane Critical Current Density Inhomogeneity in Bulk HTS Rings for the Generation of NMR-Grade Magnetic Fields

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(RE)-Ba-Cu-O ring bulks, used as trapped field magnets, show great promise as a compact and lightweight source for generating the magnetic fields required for nuclear magnetic resonance (NMR). The inhomogeneities introduced by the growth pro-cess of such bulks pose a challenge to the required field uniformity for NMR. In this study, we model a stack of ring bulks with varying ab-plane inhomogeneity and orientation to investigate the impact on the trapped field profile following field cooled magnetization. For a pair of rings, by offsetting the growth sector boundaries (GSBs), the inhomogeneity of the circumferential field at the mid-plane can be reduced by up to 65% compared with aligned GSBs, for less than 0.4% reduction in the central trapped field strength. Using two pairs of rings allows for the generation of a larger homogeneous region at the center of the bore, with a lower peak-peak variation across the measuring volume. The relative harmonic weighting of the field moves to higher orders, requiring more complex shimming coils to correct the residual field.



Harmonic analysis, High-temperature superconductors, Superconducting magnets, Nuclear magnetic resonance, Power system harmonics, Nonhomogeneous media, Magnetic field measurement, Bulk superconducting rings, field homogeneity, growth sector boundary, high-temperature superconductors, HTS modelling, nuclear magnetic resonance, numerical modelling

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IEEE Transactions on Applied Superconductivity

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Institute of Electrical and Electronics Engineers (IEEE)
Engineering and Physical Sciences Research Council (EP/P020313/1)
W.D. Armstrong Studentship in the Application of Engineering in Medicine; EPSRC Early Career Fellowship, EP/P020313/1
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