High critical current STAR^® wires with REBCO tapes by advanced MOCVD

Abstract

RE-Ba-Cu-O (REBCO, RE=rare earth) Symmetric Tape Round (STAR®) wires of 1.5 – 2.5 mm in diameter have been fabricated with 4 – 12 strands of symmetric REBCO tapes made by Advanced Metal Organic Chemical Vapor Deposition (MOCVD). 1.5 mm diameter STAR® wires made with just four Advanced MOCVD tape strands are able to sustain nearly the same critical current (Ic ) as 2.5 mm diameter STAR® wires made with 12 commercial-grade tape strands. An Ic of 1070 A, corresponding to an engineering current density (Je ) of 597 A/mm2, has been demonstrated at 4.2 K, 30 T in 1.5 mm diameter, 4-strand STAR® wire at a bend radius of 15 mm. This Ic value exactly matches the Ic expected from the lift factor of the tape strands used in the wire. The 2.5 mm diameter STAR® wires made with 12 Advanced MOCVD tape strands exhibit an Ic of 1,075 A at 77 K, self-field and sustained currents of 2,500 to 2,750 A at 4.2 K, 30 T before burnout, corresponding to a Je greater than 500 A/mm2. These results show that the cost of STAR® wires can be substantially reduced using fewer tape strands of high-performance Advanced MOCVD tapes and that the superior bend performance of STAR® wires can be maintained even using 12 strands of Advanced MOCVD tapes with 4-µm-thick REBCO films.

A 6-around-1 cable using high-temperature superconducting STAR ® wires for magnet applications

“…We used computed tomography (CT) scans to evaluate the solder distribution inside a flute-type termination [33]. Figure 16 shows two micro-CT scan images of a 30 mm long segment of a prototype termination.…”

“…The early voltage rise itself in Cable 1c does not necessarily mean that Wire 0 degraded. The wire had rebco tapes of different widths and critical currents [33,34]. Due to the non-uniform critical current among the rebco tapes, one tape can reach its critical current before other tapes, leading to an early voltage rise across the wire and a deviation from the power-law relationship between the voltage and sample current [36,37].…”

“…Cable 6a had a relatively low J e of 56 A mm −2 at 77 K, self-field. AMPeers recently reported a star ® wire containing four rebco tapes manufactured by the advanced mocvd process [33]. The wire has a diameter of 1.51 mm and a critical current of 420 A at 77 K, self-field and 1070 A, 4.2 K and 30 T, both at a bend radius of 15 mm.…”

“…The mechanical strength of the 6-around-1 cable should be measured, including the tensile strength and the strength against the transverse compressive stress. An effective impregnation approach to support individual rebco tapes in star ® wires against the electromagnetic forces needs to be developed [33].…”