Interlaboratory comparison on high-temperature superconductor critical-current measurements

Abstract

An extensive interlaboratory comparison was conducted on high temperature superconductor (HTS) critical-current measurements. This study was part of an international cooperative effort through the Versailles Project on Advanced Materials and Standards (VAMAS). The study involved six U.S. laboratories that are recognized leaders in the field of HTS. This paper includes the complete results from this comparison of critical-current measurements on Ag-sheathed Bi2Sr2Ca2Cu3O10–x (2223) tapes. The effects of sample characteristics, specimen mounting, measurement technique, and specimen damage were studied. The future development of a standard HTS measurement method is also discussed. Most of the evolution of this emerging technology has occurred in improvement of the performance of the conductors. The successful completion of this interlaboratory comparison is an important milestone in the evolution of HTS technology and marks a level of maturity that the technology has reached.

Characterisation of the Transport Critical Current Density for Conductor Applications

“…Low temperature solder such as In0.52Sn0.48 (M.P. ~ 118 °C) can be used to minimise thermal shock [51,115]. It should also be noted that standard PbSn solder (m.p.…”

“…Because it is often not possible to wind high temperature superconducting tapes into small coils for measurements in small bore magnets without generating a large strain, most interlaboratory comparison measurements on high 𝑇 " tapes use the short straight geometry [115]. Some BiSCCO conductors are not fully dense.…”

“…For the Ag-sheathed BiSCCO tapes and wires, it was observed that the thermal expansion was dependent on thermal cycling, which was attributed to yielding due to an internal stress between the Ag-sheath and the BiSCCO(2223) filaments [39]. Since cryogenic liquid can seep into the conductor during measurements, it is essential to warm the samples slowly after measurement so the cryogen can escape without blistering the silver matrix [115]. Equally the RE-123 samples can delaminate.…”

“…Variable strain can also be parametersied using 𝛼(𝑇, 𝜀) = 𝛼(𝑇) OE1 − 𝑐(𝑇)'𝜀 − 𝜀 f (𝑇)" µ • as demonstrated from fits to variable strain 𝐽 " data from Sunwong [81] and Sugano [165]. In round robin testing, the coefficient of variation for a BiSCCO sample premounted by a central laboratory (NIST) were 4.4% (77 K) and 3.2% (4.2 K) [115]. The IEC/TC90 has developed a d.c. critical current test method for Ag-sheathed BiSCCO conductors [6] and a public database of critical current data of HTS conductors is now available for magnet designers [166].…”