Stability of multi-core MgB2/Ti/Cu/SS wires

Abstract

Stability of 19-filaments MgB 2 /Ti/Cu/SS wires carrying the transport currents has been examined. Properties of two identical wires annealed at 600 o C/2.5 h and 800 o C/0.5 h were compared. It was found that annealing conditions influence not only the current carrying capacity of MgB 2 filaments but also affect the inter-diffusion at Ti/Cu and Cu/SS interfaces, which is worsening the electrical and thermal conductivities of composite elements. Consequently, differences in wire's resistances and I-V quenches were measured, which are correlating well with experimentally estimated minimum quench energy and normal zone propagation velocity.

Quench Property of Twisted-Pair <inline-formula> <tex-math notation="TeX">$\hbox{MgB}_{2}$</tex-math></inline-formula> Superconducting Cables in Helium Gas

“…In both cases the MQE values are higher than has been reported for MgB 2 tapes without additional Cu stabilization i.e. less than 1 J per tape (less than 3 J for three tapes) [3]- [7]. Fig.…”

“…This suggests that the MQE at 23 K should be approximately 75% of the MQE at 31 K. However, as Fig. 7 shows we have measured a higher MQE at 23 K than at 31 K and, indeed, a general trend for MQE to decrease as temperature increases; a trend which is also seen in [6] and [7]. Further study is required to explain this phenomenon.…”

AC losses and transverse resistivity in filamentary MgB2 tape with Ti barriers

“…An increase of the copper resistivity q m may be caused by the diffusion of Ti into Cu [11]. To check this possibility we determined q m at 300 K and 4.2 K from measurements on samples 3 and 4.…”

“…Ti as a barrier material has several advantages: it is non-magnetic and nonsuperconducting above 4.2 K, it is very well formable and it has also positive effect on MgB 2 doped with SiC. On the other side, it was found that several inter-metallic layers Ti/Cu increasing the resistivity of copper are created between Ti and copper matrix during the annealing [11].…”

Calculated and measured normal state resistivity of 19-filament MgB2/Ti/Cu/stainless steel wire

“…The electrical resistivity decreased with increased heat treatment temperature in the row of materials used in the composite wire. Nevertheless, the total resistivity of the composite wire evidently increases with increasing heat treatment temperature [5]. It is assumed that the dominant factor in the resistivity development is the interface formed via diffusion interaction between the stabilizing Cu matrix and the surrounding metallic regions.…”