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Description
A new testing facility employing a 15-T transverse field to evaluate the full-service-field characteristics of superconducting materials is now under development in China. A key objective is the development of a large bore, 15-T dipole magnet to provide the transverse magnetic field load. In this study, we designed and constructed a compact high-temperature superconducting (HTS) dipole magnet insert, consisting of six block-type no-insulation double pancakes (DP) wound with REBCO tapes. The insert features a 34-mm user bore and is designed to generate a 5-T field at 4.2 K with an operating current ($J_{\rm op}$) of 278 A, within a 10-T LTS background dipole magnet. Each DP coil incorporates hard bending at both ends with a bending diameter of 1 m. To suppress the electromagnetic stress under high background fields, circumferential confinement structures were installed around the REBCO coil group. Numerical simulations indicate that the maximum strain within the coils is less than 0.3%, while the maximum von-Mises stress within the supporting structure remains below 700 MPa, assuming uniform current within the coils. Considering the screening current, the maximum current operating point, defined as the maximum ratio of $J_{\rm op}$/$J_{\rm c}$ across the magnet, is 0.583. The magnet was tested independently at 4.2 K. Over three charging cycles, small voltage spikes were observed during current ramping, most of which disappeared in subsequent charging sequences. However, a large voltage spike above 3 mV occurred at $I_{\rm op}$=232 A with the central field of 3.91 T, prompting the current to be reduced to 210 A. No damage was detected afterward. Future tests at 4.2 K within a 6-T LTS dipole magnet are planned. This work provides valuable validation of the design methodology and fabrication techniques for block-type HTS dipole magnets with hard bending.
This work was supported by the Special Fund for Basic Research on Major Scientific Instruments of National Natural Science Foundation of China under Grant No. 12327901, and the National Natural Science Foundation of China under Grant No. 52277026.
