Simple-stacking (non-twisting) of ReBCO tapes is explored to make a large-current High Temperature Superconducting (HTS) cable for fusion magnet applications [1, 2], to be used especially in DC operation. The simple-stacking approach helps mechanical robustness, simplifies the manufacturing process, and reduces the overall cost of the conductor.

There is experimental evidence that a straight and short (length: 1.3 m) simple-stacked HTS cable can operate stably, under a worst-case non-uniform current distribution feeding [3, 4]. Still, for long-length cables, internal current redistribution and non-uniform current formation (due to inductance variability across the HTS tapes) are concerns for a coil shape, since they may disrupt the stable operation.

An experiment is proposed to explore these features, for a simple-stacked HTS cable wound as a solenoid, including uniform current and worst-case non-uniform current inputs. It considers a conduit with bolts, to vary the mechanical pressure among the HTS tapes, controlling the contact resistance and current redistribution. Manufacture and assembly of the solenoid are in process, and the experimental data is to be compared with a numerical calculation.

Due to the high cryogenic stability of HTS materials and previous experimental results, it is expected that the solenoid can achieve stable operation despite inductance variation. Then, notions of stable operating ranges can be obtained for HTS coil shapes, based on the simple-stacking approach.

[1] N. Yanagi et al. “Magnet design with 100-kA HTS STARS conductors for the helical fusion reactor”. Cryogenics 80 (2016).
[2] Y. Narushima et al. “Test of 10 kA-Class HTS WISE Conductor in High Magnetic Field Facility”. Plasma and Fusion Research 17 (2022).
[3] T. A. J. Meulenbroeks et al. “Observation of a non-uniform current distribution in stacked high temperature superconducting tapes”. Journal of Physics Conference Series 1293 (2019).
[4] D. Garfias-Dávalos et al. “Simulation of non-uniform current distribution in stacked HTS tapes”. Plasma and Fusion Research 17 (2022).

Keywords: HTS, ReBCO, current distribution, fusion magnets