Design of a Superconducting 32 T Magnet With REBCO High Field Coils

Abstract

The design and fabrication of a 32 T, 32 mm cold bore superconducting magnet with high field REBCO inner coils is underway at the NHMFL. In support of the design, conductor characterization measurements have been made including critical current as a function of field, field orientation, temperature, and strain on conductors and joints. Various conductor and turn insulation systems were examined. The selected coil fabrication method for the 32 T magnet is pancake wind, dry wind coils with sol-gel insulation on a stainless steel co-wind. Quench protection of the REBCO coils by distributed heaters is under development. Small REBCO coils have been made and tested in a 20 T background field to demonstrate performance of the technology. The design of the 32 T magnet is described, including coil configuration and conductor lengths, fraction of critical current, selection of conductor copper content for protection, and stress in the windings.Index Terms-High field superconducting magnets, insulation, quench protection, REBCO.

Comparison of Electromechanical Properties and Lattice Distortions of Different Cuprate High-Temperature Superconductors

“…Similar irreversible strain limits of SuperPower tapes have been reported elsewhere [33,34,35]. The irreversible axial tensile strain limit of the AMSC tape is with  irr-5% =1% the highest of all conductors studied here.…”

Strongly enhanced vortex pinning from 4 to 77 K in magnetic fields up to 31 T in 15 mol.% Zr-added (Gd, Y)-Ba-Cu-O superconducting tapes

“…We ascribe the excellent pinning performance at high temperatures to the high density (equivalent vortex matching field ∼7 T) of self-assembled BZO nanorods, while the low temperature pinning force is enhanced by large additional pinning which we ascribe to strain-induced point defects induced in the REBCO matrix by the BZO nanorods. Our results suggest even more room for further performance enhancement of commercial REBCO coated conductors and point the way to REBCO coil applications at liquid nitrogen temperatures since the critical current density J c (H//c) characteristic at 77 K are now almost identical to those of fully optimized Nb-Ti at 4 Thanks to its high critical temperature T c , high critical current density J c , high irreversibility field H irr , and moderate anisotropy parameter γ , REBa 2 Cu 3 O x (REBCO, where RE = rare earth) thin films grown on flexible and mechanically strong substrates can exceed the temperature and field application limits of the Nb-based low temperature superconductors, and enable superconducting applications in a broad temperature and magnetic field regime now exceeding 35 T at 4 K. [1][2][3] However, further J c and H irr enhancement and anisotropy reduction are strongly desirable for compelling, costeffective applications, and especially to enable multi-Tesla fields in a temperature regime of 30-77 K. [4][5][6] Enhanced vortex pinning is needed both to raise higher temperature irreversibility fields and to raise J c so that overall conductor current density J E can reach the required high values of the order of 500 A/mm 2 . Adding higher densities of nanoscale defects with strong vortex pinning properties is the most efficient strategy.…”

REBCO tape performance under high magnetic field

“…However, according to Section 2.2, only small angles are interesting for the HTS inserts. Hence, the decrease of 30% is a major concern to evaluate the critical current that will limit the performance of the coil [4].…”

“…As the calculated nominal current is 200 A, the final prototype is expected to work at 57% of its limiting critical current. In this case, the critical current is different than the limiting critical current because only the critical current values on a specific area of the winding are considered [4].…”

“…The outer LTS magnet generates 15 T and the HTS insert made of two coils generates 17 T [4]. A second magnet project at Tohoku University, Japan aims at delivering a fullsuperconducting magnet, expected to generate 20 T [5] with an 11.5 T HTS insert.…”