Second Generation Superconducting Cable with Exfoliated YBCO Filaments
In this Phase II SBIR Brookhaven Technology Group (BTG) started a pilot production of a novel superconducting cable, ExoCable, using a technology based on exfoliation of YBCO layer from the substrate. Currently, second generation (2G) wire is the most promising conductor for high-field magnets such as accelerator dipoles and compact fusion devices. The key element of the wire is a thin HTS layer deposited on a flexible substrate. The substrate, which becomes incorporated in the 2G conductor, reduces electrical and mechanical performance of the wire, thus preventing the 2G wire technology from reaching larger markets. BTG technology eliminates these shortcomings by exfoliating the YBa2Cu3O7 (YBCO) layer from the substrate. In the Phase II work, the technology for reel-to-reel exfoliation of wide YBCO tape was refined. We demonstrated exfoliation on over 100 m long coupon of YBCO tape. Retention of over 90% of the original Ic is demonstrated over a 50 m length of tape. During Phase II a system for laser reel-to-reel slicing of exfoliated filaments was designed, assembled and implemented. A 200 W CO2 laser was used to slice the tape into narrow filaments. The focus of the laser slicing operation was to minimize the edge damage caused by the laser heat load. The optimum cutting regime has the right balance of cooling gas flow and laser power, delivering a 2 mm wide filament that retained over 85% of the original Ic. The cabling machine designed and built during Phase II is capable of stacking, wrapping and twisting up to 10 filaments. Five, 3” test coils were wound and tested at 77 K and 25 K in conduction cooled mode. The filaments are coupled electrically through a re-flow process, which results in enhanced electrical connectivity between the adjacent layers. The coils were tested at 77 K (up to 500 A) in liquid nitrogen and at 25 K (up to 1,300 A) in conduction cooled mode. The cable carries 500 A critical current at 77 K. A six-layer coil wound from 10.5 m of the cable, the largest coil created in the study, demonstrates critical current of 280 A at 77 K at 0.4 T magnetic field on the winding. The coil was tested at 1,300 A at 25 K and demonstrated 0.7 T central field. The coils were fully impregnated with Stycast 1266 and Henkel W19 low-viscosity epoxies. Repeated thermal cycling, to 77 K and 22 K, does not degrade the coil’s performance. The cable AC loss and the coil winding magnetization are compared with the traditional 2G wide tape pancake geometry at 77 K. We observe a 5x reduction of the winding magnetization when the 12 mm tape is replaced by 2.4 mm cable, which is explained by the smaller magnetic moment of the cable winding. The field hysteresis profiles recorded at 22 K and 77 K are presented to demonstrate the effect of the operation temperature on the winding magnetization. A finite element analysis of the winding magnetization shows a good agreement between the experimentally measured trapped field value, and the critical state model prediction. We conclude that ExoCable™ technology demonstrated is a robust solution for a conduction-cooled HTS magnets.
- Research Organization:
- Brookhaven Technology Group
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP)
- Contributing Organization:
- American Superconductor Corporation, National High magnetic Field Laboratory, Fermi National Accelerator Facility, Write Patterson Air Force Base
- DOE Contract Number:
- SC0013856
- OSTI ID:
- 1560873
- Type / Phase:
- SBIR (Phase II)
- Report Number(s):
- DOE-BTG-SC-0013856; 6318165189
- Country of Publication:
- United States
- Language:
- English
Similar Records
Low-cost, infinite-length 2G strand for cable-in-conduit fusion magnets
Performance of layer wound epoxy-impregnated coils made from a multifilamentary cable of exfoliated YBCO