Influence of Coil Size and Ramping Rate on Ramping Behaviors of Parallel-Wound No-Insulation HTS Coils

The Parallel-wound No-insulation (PWNI) high temperature superconducting (HTS) coil is a potential choice for high magnetic field fusion applications, which has been used in the development of spherical tokamak magnets. Previous works have analyzed electromagnetic behaviors of experimental-size coils during ramping process, while that of large-scale PWNI coils have not been studied so far, which is crucial to the development of large-scale PWNI magnets. This study is to analyze the influence of the coil geometry on the ramping behaviors as well as the charging delay of large-scale PWNI coils. A multi-physics model coupling the equivalent circuit network model and an improved T-A FEM model is used in this study. Results show that the charging time dramatically increases with the inner diameter, while it slightly increases with the number of turns. For a large-scale PWNI HTS coil (inner diameter of 2 m), results show that the PWNI technique can significantly reduce the inductance as well as charging delay of NI coil wound by single tape, and the non-uniform current redistribution on stacked tapes to some extent further accelerates the charging process. These results will serve as theoretical basis for the R&D of large-scale PWNI HTS high-field magnets.