Enhancement of the critical current density in Chevrel phase superconducting wires

Abstract

The critical current densities J c of Chevrel phase wires with niobium as an antidiffusion barrier were measured in magnetic fields up to 24 T. At 20 T and 1.9 K, Jc reaches 5.4 X 108 A/m2 and decreases slightly down to 3.IX 108 A/m2 at 24 T. A wire with a 20% superconducting cross section has been successfully drawn and its overall critical current density 7°v exceeds 100 A/mm2 at 1.9 K up to a magnetic field slightly above 20 T. This demonstrates the ability of Chevrel phase wires to be used in high magnetic field applications. Moreover, some parts of the coil have certainly higher J c , since J c is very often limited by a thermal excursion of the entire coil. The effective upper critical field Mo^c2 > deduced from the magnetic field dependence of J c, is too low compared to the expected bulk value, indicating that superconducting properties at the grain boundaries are still degraded. If the bulk fi0H C 2 can be restored at the grain surfaces, should be higher than 100 A/mm2 up to at least 30 T. © 1997 American Institute of Physics. [S0021-8979(97) 00409-X]

Irreversibility line and granularity in Chevrel phase superconducting wires

“…In Fig. 3, the irreversibility line, deduced from Kramer plots, is compared to results on the same wire HIPed at 900°C for 0.5 h. 3,14 The slope dB irr /dTϷϪ4.7 T/K. Similar to the high temperature superconductors, the improvement of B irr is criterion dependent.…”

“…Full details of the wire fabrication can be found elsewhere. 3,14 A wire sample 70 cm long was wound on a thin walled stainless steel sample holder. After the HIP cycle, the wire together with the sample holder were electroplated with cop- per and soldered together.…”

“…1 Chevrel phase superconductors ͑Pb,Sn͒Mo 6 S 8 ͑PSMS͒ are also a possibility since B c2 of this material is about 55 T at 4.2 K. 2 Very recently, a new benchmark for the overall critical current density of Chevrel phase wires of 105 and 60 A/mm 2 at 20 and 24 T at 1.9 K has been set. 3 In spite of these high values, the irreversibility line ͓B irr (T)͔ of these wires lies far below the B c2 (T) curve. 4,5 Nevertheless, magnetic measurements on bulk samples have shown that Chevrel phase materials may not be intrinsically granular despite their short coherence length.…”

Chevrel Phases: Genesis and Developments

“…Whatever the route used, the critical current density was in the range 1-2 10 8 A/m 2 at 200 kG and 4.2 K[55]. Values of 5.and 3.1 10 8 A/m2 were further reached at 1.9 K for fields as high as 200 kG and 240 kG, respectively[56].Figure 11 shows that CP wires over-passed any technical superconductors above 170 kG [57]. Thin-films are the ideal form for some physical measurements, such as critical current density and the development of superconducting junctions.…”