This paper presents a numerical method, based on the partial element equivalent circuit (PEEC) technique, for spatially-distributed and time-varying simulation to analyze nonlinear ‘defect-irrelevant’ behaviors of a no-insulation (NI) high temperature superconductor (HTS) coil. We suggest a resistivity parameterization approach in combination of the PEEC method to replicate electromagnetic dynamics of an NI HTS coil containing multiple ‘defects.’ The proposed method is adopted to investigate ‘defect-irrelevant’ behaviors of an NI single pancake coil having lap joints as a form of artificial defects. To validate our approach, electromagnetic characteristics of the NI test coil are measured in a bath of liquid nitrogen at 77 K and compared with four key simulation results: (a) local voltages; (b) current distribution; (c) magnetic field;
and (d) Joule heating distribution. Experimental measurements of local voltages and the magnetic field are compared to the simulation results to validate our numerical method.
We report that the field homogeneity of a large-scale metal-clad no-insulation all-ReBa 2 Cu 3 O 7−x magnet is reproducible after occasional operating conditions, in this case the current ramp down/ up and magnet warm-up/cool-down conditions. First, we shimmed the magnet by cylindrically arraying ferromagnetic shims on the wall of the room-temperature bore of the magnet to improve the spatial field homogeneity. As a result, the field homogeneity of the magnet was improved from 557.7 to 14.1 ppm in a 10 mm diameter spherical volume. The resultant acquisition of field homogeneity tremendously enhanced from an inhomogeneous state greatly degraded by screening currents qualified us to study the temporal stability of the field homogeneity. We used a magnet-energizing protocol with the field drift minimized to shrink a nuclear magnetic resonance (NMR) lineshape into a much narrower super-imposable lineshape. We demonstrate the technique by NMR experiments, showing excellent reproducibility in every case, presenting strong evidence of recovery to certain time-unvarying field gradients and to a state of homogeneity. These findings suggest a new route for high-resolution high-temperature superconducting NMR and magnetic-resonance-imaging magnet technology.
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