Performance of an over-pressure processed Bi-2223/Ag/SUS tape and a small layer-winding coil

Abstract

We have successfully demonstrated the utility and potential of Bi-2223/Ag tapes fabricated by a CT-OP (controlled-overpressure) process. In this paper, we report the Ic–B–T performance of a short tape with stainless steel lamination and energizing-test results of a small layer-winding coil in an external magnetic field ranging from 0 to 12 T and at temperatures ranging from 4.2 to 90 K. The coil is a solenoid layer-winding of a 135 m piece of Bi-2223/Ag tape with stainless steel lamination on both sides. The dimensions of the conductor are 2.7 mm in width and 0.25 mm in thickness, including a 0.02 mm thick stainless steel lamination on both sides. A short sample cut from the same tape has critical currents exceeding 76 A, 307 A and 438 A at 77 K, 30 K and 4.2 K, respectively, in self-field. The winding was performed using a ‘react & wind’ technique and the resultant coil had 597 turns and dimensions of 65 mm (inner diameter), 83 mm (outer diameter) and 60 mm (winding height). In 12 T, 4.2 K, the coil-Ic is 191 A, which adds 1.42 T to the external field. In the present coil, the coil-Ic is controlled by the field component in the coil’s radial direction generated by the coil itself. The Ic values of the coil agree very well with those estimated from the short sample’s performance and field distribution. The results indicate that the homogeneity of the Bi-2223 conductor is very good throughout its whole 135 m length.

$I_{\rm c}$– $B$–$T$ Evaluation for High-$T_{\rm c}$ Superconductors in Pressurized/Depressurized Liquid Nitrogen

“…n-value decreases monotonically with increasing magnetic field for B ⊥ tape, whereas there are plateaus for B tape, although the plateau region is small. The wide range characterization provided that n-value depends on temperature and magnetic field in a temperature range higher than 30 K [4]. Although the temperature dependence is not clear because of the narrow temperature range, the magnetic field dependence is consistent with the previous result.…”

“…Specifications are shown in Table I. A 60-mm long specimens were prepared for each superconductor. The specimen was set on the sample holder, which was described in [4] and [5]. Both ends were mechanically pressed onto the current terminals using copper blocks.…”

High field Ic characterizations of commercial HTS conductors

“…The hysteretic I c -B with magnetic field ramping up and down is a well-known behaviour considered to be related to the weakly coupled grain boundaries [30]. The anisotropy, I c (B k )/I c (B \ ), is less than 2 at 2 T and decreases with field to 1.5 at 17 T, similarly to the reported behaviour of Bi-based filamentary tapes [31,32]. The measurements in high fields beyond 24 T were affected by the anomalous behaviour discussed in [33,34] while ramping down the field, that we could not determine I c definitively on the ramp down leg.…”

A feasibility study of high-strength Bi-2223 conductor for high-field solenoids

“…Similar to Bi-2212, the brittle superconducting grains are embedded in a mechanically-weak Ag/Ag-alloy matrix. In Bi-2223, however, the mechanical properties are substantially improved [34, 35] (while retaining performance [45]) by soldering pre-tensioned stainless-steel (SS) or copper alloys (CA) onto the reacted tape. This lamination process was pioneered at American Superconductor Corporation [46, 47] and further optimized and commercialized by SEI.…”