Rapid assessment of REBCO CC angular critical current density J _c(B, T = 4.2 K, θ) using torque magnetometry up to at least 30 tesla

Abstract

Detailed design of REBCO-based magnets ideally relies on knowledge of the full angular and wide temperature range characterization of the critical current Ic of the REBCO coated conductors (CC) at high magnetic fields. In practice, however, obtaining Ic(B, T, θ) data by the commonly used electrical transport technique is expensive, tedious, and difficult, due to high critical current values that exceed 2000 A for B ‖ ab-plane (θ = 90 deg). The conductors are often damaged during angular transport measurements at angles approaching the ab-plane. Therefore, so far, REBCO magnets have been designed without full Ic(B, T, θ) data sets. Here, we present Jc(B, T, θ, ) results for more than twenty samples of CC all made to the same advanced pinning specification produced by SuperPower Inc. For this, we employed torque magnetometry, benchmarking the results to transport Ic measurements mostly made away from ab-plane, finding good agreement with scaling factors ≈ 1 − 1.3. What is striking is the huge variety of properties exhibited by the samples, even for CC made recently. Given the huge attention now being paid to the effects of screening currents and to the torques generated by offsets between the tape plane and the local magnetic field vector, our data set suggests some caution in detailed design of such magnets without having data of the type presented here.

HTS conductor coil by in-situ winding technology for large-scale high-field magnet

“…The magnetic field inside the copper tube is parallel to the surface direction of the tapes. The parallel magnetic field could not greatly decay the critical current at 4.2 K [41]. The central magnetic field was calculated by equation ( 7), and the central magnetic field was approximately 0.11 T. Estimations showed that the total critical current of the six-layer CORC conductor at 4.2 K was 35.6 kA and the single coil at 4.2 K could generate a central magnetic field of approximately 0.11 T. It can be noted that, for fusion magnets, the maximum magnetic field design of different coils is completely different, and the influence of external magnetic field on the critical current of the coil should be considered.…”