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In this paper, we briefly review our recent progress on development of core technologies for 2G HTS NMR/MRI magnets at Korea University. To outperform the current state-of-art NMR/MRI magnet systems, we have developed the following technologies: 1) a REBCO-REBCO superconducting joint for operation of persistent current mode; 2) partial and grease-insulation winding techniques for self-protection of the HTS magnets; 3) pre-shimming to reduce the screening-current-induced-field; and 4) optimization of multi-width winding to minimize conductor consumption and volume of the HTS magnets. The test results demonstrated the feasibility of employing the developed techniques to achieve ultra-high-field and LHe-free 2G NMR/MRI magnets possessing self-protecting feature.

This paper reports the optimization procedure for a no-insulation (NI) multi-width (MW) REBCO magnet, which enables the fabrication of a highly compact and competitively priced superconducting magnet. In order to identify the design considerations for the NI-MW magnet, the electromagnetic performances of 3 different magnets were investigated using the finite element method (FEM). Based on the comparison results, it was verified that the critical current distribution-factor (CCD-factor), which is the ratio of the highest pancake critical current (Ic) to the lowest pancake Ic within the magnet, should be close to 1.00 for the MW configuration to be most effective. In the optimized MW magnet, the center Bz (7.54 T) remarkably exhibited an ∼ 51% increase compared to the 4-mm single width magnet (5.00 T). Furthermore, the CCD-factor of the optimized MW magnet was 1.04, which is quite close to 1.00, sufficiently demonstrating the validity of the optimization process and result.

In this study, sudden discharge tests were performed on partially-insulated (PI) GdBCO coated conductor single-pancake coils to investigate the effects of a PI winding scheme on the discharge characteristics. Three sets of PI coils were constructed with insulation at 3 different intervals: every 2nd, 4th, and 8th turn. Each set included coils with 4 different insulation-angles: 90°, 180°, 270°, and 360°. Discharge delay of the PI coils was alleviated by increasing the insulation-interval or insulation-angle due to increased insulated area, which partially hinders radial current flow. The results of the sudden discharge test were in fairly good agreement with simulations of the PI coils using an equivalent circuit model consisting of a single RL circuit in parallel. The characteristic resistance of the PI coils was reasonably estimated through the numerical approach with contact surface resistance and compensation for the current-bottleneck effect, which enables the PI coils to be utilized in practical superconducting magnet applications.