Multifilamentary Round Wires of REBCO Coated Conductors for High Field Accelerators (Final Report)
A specific objective of the project was to demonstrate multifilamentary, ultra-small-diameter round RE-Ba-Cu-O (REBCO, RE = rare earth) high temperature superconductor (HTS) wires with a high engineering current density (Je) in high magnetic fields at 4.2 K. The primary goal of the Phase II project was to scale up the round, multifilamentary ultra-small diameter REBCO wire technology demonstrated in meter lengths in Phase I to manufacturing of 50-meter lengths with a Je of 250 A/mm2 at 4.2 K, 20 T. The round REBCO wires were made by a) fabrication of ultrathin REBCO tapes of total 25 µm thickness consisting of a 18 - 22 µm thick Hastelloy substrate, b) creation of symmetric REBCO tapes by electroplating of the copper stabilizer primarily on the REBCO film side to position the film near the neutral plane, c) winding of symmetric tapes on copper wire formers of 0.64 – 1 mm in diameter. These round wires are called Symmetric Tape Round (STAR) wires. We successfully scaled up fabrication of ultra-thin REBCO tapes up to 97 m lengths with uniform thickness and no dropouts in critical current (Ic) more than 10%. Multiple batches of 50 m and ≥ 80 m long, 18-25 μm thick substrate REBCO tapes were fabricated with no more than 10% Ic dropout. Next, we scaled up fully stabilized, symmetric REBCO tapes to 80 meters. The long ultra-thin REBCO tapes were slit to different widths (1.4 - 2.6 mm) using a reel-to-reel laser slitting process. Cracks that typically occur in mechanically-slit samples were not observed. A 43 m long, 50 μm thick (including copper thickness), 2.5 mm wide symmetric REBCO tape exhibited an average critical current of 95 A at 77 K, with a uniformity of 4.5%. A 95 m long 2.5 mm wide, 55 μm thick (including copper thickness) symmetric REBCO tape with an average Ic of 89 A and a standard deviation of 3.1% was also fabricated. STAR wires were fabricated with symmetric REBCO tapes with thinner substrates and narrower widths wound in the inner layers of the wire, and tapes with progressively increasing thickness and widths in the outer layers. A 10.48 m long STAR wire was fabricated by winding 7 layers of 2.4 – 2.6 mm wide symmetric tape on 1.02 mm (18 AWG) diameter Cu former. A minimum Ic of 436 A (77 K, self-field) was measured. For subsequent long-length STAR wires, we used a Cu/NbTi composite former instead of a copper former. A hybrid STAR wire exhibited a Je of 572 A/mm2 at 4.2 K, 20 T and another hybrid STAR wire showed a Je of 739 A/mm2 at 4.2 K, 15 T and an extrapolated Je of 600 A/mm2 at 4.2 K, 20 T. We successfully demonstrated a 23 m long, 8 layer, 1.95 mm diameter hybrid STAR wire with an average Ic of 482 A and a standard deviation of 2.5%. Finally, we demonstrated a 61.5 m long, 7-layer, 1.84 mm diameter hybrid STAR wire with an average Ic of 368 A, and a standard deviation of just 1%. We also demonstrated short STAR wires with symmetric REBCO tapes made by Advanced Metal Organic Chemical Vapor Deposition (A-MOCVD) at the University of Houston. Tapes made by A-MOCVD has been shown to exhibit 5x the Ic of commercial REBCO tapes. A STAR wire made with symmetric REBCO tapes made by A-MOCVD showed a Ic of 431 A in a straight form and an Ic of 416 A at 30 mm bend diameter which corresponds to a 96.5% retention. We also conducted Manufacturing Scale-up Analysis of STAR wire fabrication. Cost and manufacturing volume projections were developed for the next five years and a roadmap to achieve these targets was prepared. Given the remarkably high engineering current density of REBCO coated conductors in high magnetic fields at 4.2 K, REBCO STAR wires of ultra-small diameters (~ 1 – 2 mm) show great promise for the development of high-field compact REBCO accelerator magnets operating in fields above 20 T.
- Research Organization:
- AMPeers LLC, Houston, TX (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP)
- DOE Contract Number:
- SC0015983
- OSTI ID:
- 1787719
- Type / Phase:
- SBIR (Phase II)
- Report Number(s):
- DOE-AMPeers-0002
- Country of Publication:
- United States
- Language:
- English
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