Low-cost, infinite-length 2G strand for cable-in-conduit fusion magnets
This Phase I SBIR project aims to develop a new HTS wire architecture that is tolerant to current blocking defects. Our technical approach is based on using a proprietary process of exfoliation and laser slicing of YBCO tape that is currently under development at BTG. The major thrust of the project is the development of a cabling technology that forgoes the handling of long, thin filaments by automating the slicing, layering, and other cabling steps. In addition, in this new 2G wire architecture, YBCO layers are continuously electrically coupled via a conducting layer which allows for current flow normal to the face of the filament, thus making the cable defect-tolerant. The defect tolerance of the cable would enable manufacturers to guarantee the performance of 2G-based superconducting devices. During Phase I, the team de-risked the slice-less cable concept by identifying the optimum cable-fusion technology that delivered contact resistance < 200 nΩ cm2. After trying tree techniques, such as laser fusion, solder bath dipping, it was concluded that hot air-blade fusion is the most suitable method. Hot air reliably and locally fused the cable without damaging the coliform and the insulation. In this embodiment, a narrow stream of pre-heated air was directed onto a winding stack. The airstream fused the filaments, thus enabling good electric contact. To prove the feasibility of defect-tolerant cable, we manufactured a test coil comprised of 5 meters of 4-filament SuperPower cable, sliced into 2 mm filaments using a fiber nanosecond laser. Each of the four filaments in the coil winding was intentionally cut and mechanically spliced. The splice provided only a mechanical connection between the filaments. The coil was tested before and after the fusion step. Before the fusion step, the coil demonstrated resistive behavior. A simple analysis shows that resistivity between the filaments is on the order of 10 μΩ cm2, which is not nearly sufficient for a reliable current sharing and defect tolerance. The experiment confirmed that a simple mechanical connection between cable filaments would not result in a defect-tolerant cable. After the fusion step, the winding exhibited a distinctly superconducting response with a well-defined Ic and n-value of 10. The coil was thoroughly tested at the BTG facility and handed over to Brookhaven National Lab (BNL) team for in-field and low-temperature, 4.2 K tests. Test at BNL Superconducting Magnet Division showed that the coil retained superconducting behavior in the external field up to 1 Tesla, 77 K. Measurements of dissipation at nano-volt level placed the total winding resistance below 0.5 nΩ, at 77 K, limited by the system noise. The liquid Helium experiments tested the coil performance up to 1,600 A, or 1,200 A/mm2. The winding voltage stayed well below 1 μV up to 900 A. The coil exhibited a well-defined transition to a normal state without quenching or over-heating. The maximum 0.27 T magnetic field was recorded during these experiments. These experiments confirmed the feasibility of a defect-tolerant 2G cable up to the current density of 1,200 A/mm2. We conclude that a cable with distributed splices spaced > 5 meters apart would be electrically identical to a cable with intact filaments.
- Research Organization:
- Brookhaven Technology Group
- Sponsoring Organization:
- USDOE Office of Science (SC), Fusion Energy Sciences (FES)
- DOE Contract Number:
- SC0020832
- OSTI ID:
- 1810748
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- DOE-BTG-0020832
- Country of Publication:
- United States
- Language:
- English
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