A Study on the Performance Improvement of an HTS Coil by the Outer Corner Modification

In designing an HTS coil, it is necessary to secure the large magnetic field and/or the stored energy with shorter tape length. From this point of view, the transport current performance of the HTS coil needs to be improved. The critical current and value depends on the magnitude and direction of the traversing magnetic field against the Bi-2223/Ag tapes. The critical current and value of the tape was measured with various magnitude and direction of the traversing magnetic field. From this, the fitting equations of the critical current and value for any magnitude and direction of the traversing magnetic field were obtained. Considering this anisotropic property of the tape, we considered the analytical model to obtain the coil critical current. As an initial coil shape, the minimum volume coil derived from the Fabry Factor constant curve is taken, which is often employed in low temperature superconducting coils. The electric field distribution within the coil cross-section was calculated to examine its effect on a current carrying capability. It was clear that high electric field portions appear at the coil edges due to the inclined magnetic flux against the tapes. In this study, the external corner portions of the coil are displaced under the condition that the total coil volume is kept constant. As a result of this, the coil critical current increased and the stored energy was improved by 20%.