Numerical analysis on characteristic resistance of no-insulation and partial-insulation NbTi solenoids

This paper presents a numerical approach for calculation of the characteristic resistance, i.e., R_C, of no-insulation (NI) and partial-insulation (PI) low-temperature superconductor solenoid coils, based on a contact resistance matrix model implementing 'Hertzian contact.' The proposed method was applied to both NI and PI NbTi solenoid coils, for which test results have been reported. To consider the Hertzian contact effect, the stresses within the coil were quantitatively identified using a force balance equation. The stresses calculated in the axial and radial directions were 104 and 16 MPa, respectively, which consequently enabled estimation of the R_C values of 36.2 and 203 μΩ for the NI and PI solenoid coils, respectively. The R_C ratio of PI to NI coil was 5.6, implying that the estimated charge/discharge delay time of the NI coil was 5.6 times larger than that of the PI coil. The simulated R_C ratio of PI to NI coil was in reasonable agreement with the experimental value, demonstrating the validity of the proposed approach in this paper.