Stable, predictable and training-free operation of superconducting Bi-2212 Rutherford cable racetrack coils at the wire current density of 1000 A/mm2

Abstract

High-temperature superconductors (HTS) could enable high-field magnets stronger than is possible with Nb-Ti and Nb 3 Sn, but two challenges have so far been the low engineering critical current density J E , especially in high-current cables, and the danger of quenches. Most HTS magnets made so far have been made out of REBCO coated conductor. Here we demonstrate stable, reliable and training-quench-free performance of Bi-2212 racetrack coils wound with a Rutherford cable fabricated from wires made with a new precursor powder. These round multifilamentary wires exhibited a record J E up to 950 A/mm 2 at 30 T at 4.2 K. These coils carried up to 8.6 kA while generating 3.5 T at 4.2 K at a J E of 1020 A/mm 2 . Different from the unpredictable training performance of Nb-Ti and Nb 3 Sn magnets, these Bi-2212 magnets showed no training quenches and entered the flux flow state in a stable manner before thermal runaway and quench occurred. Also different from Nb-Ti, Nb 3 Sn, and REBCO magnets for which localized thermal runaways occur at unpredictable locations, the quenches of Bi-2212 magnets consistently occurred in the high field regions over a long conductor length. These characteristics make quench detection simple, enabling safe protection, and suggest a new paradigm of constructing quench-predictable superconducting magnets from Bi-2212.

A 1.2 T canted cosθ dipole magnet using high-temperature superconducting CORC® wires

“…Compared to NbTi and Nb 3 Sn conductors with orderof-magnitude lower minimum quench energy [51], we expect that REBCO accelerator magnets will be immune to training that has been a lasting issue for low-temperature superconducting (LTS) accelerator magnets [2]. A similar remarkable thermal stability was also demonstrated in Bi2212 racetrack coils [3,4].…”

“…To reach a dipole field of 20 T and beyond, high-temperature superconducting (HTS) materials such as Bi 2 Sr 2 CaCu 2 O 8+x (Bi-2212) and REBa 2 Cu 3 O x (REBCO, RE = rare earth elements) are required because of their superior current-carrying capability in a background field of 45 T or higher [1,2]. Recent progress in Bi-2212 magnets can be found in [3,4]. Here we focus on REBCO coated conductors with several unique features that can have significant impact on future accelerator magnet technology and its applications.…”

Dipole Magnets above 20 Tesla: Research Needs for a Path via High-Temperature Superconducting REBCO Conductors

“…Other cable configurations such as twisted-stack [32] and exfoliated REBCO cable [33] may also be viable for accelerator magnet applications. [35] 26 [8] 105 [8] 110 [36] Upper critical field at 20 K T 0 0 9 [8] 100 [36] Typical wire diameter mm 1.065 [24] 0.85 [27] 0.80 [28] 12×1.5 [37] 3.7 [38] 1.3 [34] J e at 16 T, 4.2 K a A mm −2 0 474 [39] 1300 [28] 964 b [40] 310 c [38] 695 d [34] J e at 20 T, 4.2 K A mm −2 0 123 [39] 1180 [28] 821 b [40] 267 c [38] [43] 30 [38] 15 [34] Effective filament diameter f µm 7 [24] 55 [27] 130 [44] 2-5500 g [22] 2000 g [38] 1400-2500 g [34] Magnetization at 4.2 K, 1 T h mT 10 i [45] 270 [46] 60 [47] 716 j [48] 502 [49] TBD Strand transposition -Full Full Partial Peak heat treatment temperature…”

“…The Nb-Ti data are from the LHC outer cable strand [72]. The Nb 3 Sn data are from the High Luminosity LHC conductor [39]. The Bi-2212 data are from [28,39].…”

“…The Nb 3 Sn data are from the High Luminosity LHC conductor [39]. The Bi-2212 data are from [28,39]. The data for the commercial SPI 2 mm wide tape (30 µm thick substrate) with the magnetic field perpendicular to the tape broad surface were measured by D. Abraimov and A. Francis at ASC/NHMFL/FSU and provided by D. van der Laan and J. Weiss at ACT.…”