Fusion environments present extreme operating conditions for HTS cables: modern high-field compact tokamak designs reach peak magnetic fields of over 20 T in the central solenoid (CS) coils, at temperatures of around 20 K. Of the various HTS cable designs proposed for fusion applications, the Cable-in-Conduit Conductor (CICC) family has emerged as a popular option, with the Vacuum Pressure Impregnated, Insulated, Partially transposed, Extruded, and Roll-formed (VIPER) cable developed by Commonwealth Fusion Systems (CFS) being a prominent example. A critical design consideration for these cables is AC loss resulting from exposure to external time varying magnetic fields. Although AC loss in twisted tapes and stacks—including VIPER cables—has been the subject of increasing research, many studies focus on lower fields and higher temperatures outside the range applicable to fusion. There remains a need for a detailed and more fundamental examination of magnetization loss in VIPER cables under conditions relevant to fusion applications.
In this work, we will investigate the magnetization loss of a VIPER-style cable and its constituents, starting with individual VIPER strands, then single stacks, and finally full four-stack cables. For the purposes of this study, the copper former and jacket will not be included. We will conduct 3D finite element method (FEM) simulations using H-Φ formulation implemented in COMSOL Multiphysics. Simulated temperatures will include 20, 40 and 77 K, under applied magnetic fields of up to 8 T. The field-angle dependence of critical current and n-value will be accounted for, based on measured data from 4 mm SuperOx tape. The influence of temperature, pitch length, applied field strength, and tape number on magnetization loss will be investigated. In addition, we will compare these losses with simulated results in flat and twisted tapes and stacks, focusing on differences such as the average effective penetration field.
This work was supported by NZ Royal Society Marsden under Grant MFP-VUW2205.
Keywords: Magnetization loss; VIPER cables; Fusion; H-Φ formulation