Homogeneous performance and strain tolerance of long Bi-2223 HTS conductors under hoop stress

Abstract

Two types of high-strength industrial Bi-2223 conductor, one laminated by copper alloy and the other laminated by stainless steel, have been tested to examine the effect of hoop stress on the transport property. The specimens (∼2 m long) were prepared by winding one layer around a GFRP mandrel and the measurements were made in a liquid helium bath with the hoop stress calculated from the BJR product applied by external magnetic field. A careful measurement wire configuration was necessary to cancel the noise pick-up from the environment for more accurate determination of I c and n-value. We show for the first time that both conductors showed homogeneous voltage-current characteristics over a long length and degradations with hoop stress occurred uniformly, which is crucial information for the development of HTS magnet technology. The onset of degradation occurred at 200 MPa and 220 MPa, with additional bending stress present from the winding diameter of 108 mm, for copper alloy laminated and stainless steel laminated conductors, respectively. After considering the effect of bending strain, our result agrees well with the previously measured data.

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

“…A critical current of I c =193 A is measured before application of an external load, which is in good agreement with the I c =194 A value that is reported in [19]. In Fig.…”

High field Ic characterizations of commercial HTS conductors

“…8) is comparable to the previously measured I c -B of HT-CA and HT-SS conductors with 90 mm probe [29]. 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].…”

Hoop stress test on new high strength alloy laminated Bi-2223 conductor

“…Seeing the requirement of mechanical robustness for magnet applications, laminated conductors with copper alloy (HT-CA) and stainless steel (HT-SS) have been developed with nominal tensile strength at 77 K of 250 MPa and 270 MPa for HT-CA (50 μm Cu alloy laminations) and HT-SS (20 μm stainless steel laminations), respectively [7]. We have previously observed that these laminated conductors degrade homogeneously under a homogeneous hoop stress loading [8], which is crucial in avoiding degradations due to local strain concentrations. Those laminated conductors have been instrumental in realizing the 3 T MRI magnet with 137 MPa maximum hoop stress [9], the upgrading of the 18 T cryogenfree magnet to 20 T with 212 MPa maximum hoop stress [10], and, most recently, the successful operation of a 24.2 T/ 1.03 GHz NMR magnet with a Bi-2223 insert with the expected hoop stress of ∼200 MPa [11].…”