Improvement of electromechanical properties of an ITER internal tin Nb3Sn wire

Abstract

The critical current of an internal tin Nb 3 Sn wire developed by Oxford Instruments, Superconducting Technology for International Thermonuclear Experimental Reactor ͑ITER͒ ͑OST type-I, billet No. 7567͒ has been studied under axial strain at fields between 12 and 19 T at 4.2 K. Simulating the situation in a cable in conduit, where thermally induced compressive strain is important, a single wire ͑strand͒ was jacketed with AISI 316L stainless steel. The reinforced wire shows an important increase in m , the applied strain where I c reaches its maximum, from 0.25% to 0.57%. In addition the irreversibility limit, irr , is improved from 0.50% applied strain to Ͼ1.10%. It could also be shown that the I c at zero intrinsic strain is almost identical. This demonstrates that jacketing does not influence the physical parameters of the original wire. Experimental data of the bare wire has been well fitted by different strain functions. However, it was not possible to model the data of the jacketed wire. There are indications that only models which take into account the multidimensional character of strain are able to describe the behavior but further development is required.

Progresses and challenges in the development of high-field solenoidal magnets based on RE123 coated conductors

“…This behavior is dissimilar to that observed in Nb 3 Sn wires, where the effects of applied strain on the critical current become more pronounced when B/B c2 increases [53]. The difference is attributed to the stronger strain dependence of the superconducting parameters B c2 and T c in Nb 3 Sn compared with that in the biaxially textured RE123 layer.…”

Reduced strain sensitivity of the critical current of Nb3Sn multifilamentary wires

“…The slightly higher strain value for the maximum of I c may be explained that filaments are not all parallel to the wire axis due to the twist pitch of about 15 mm. 12 The situation is similar for the stainless steel jacketed wire [Fig. 1(b)].…”

“…Because qualitative results of these wires are similar, emphasis is given to the "OST type-I" wire where detailed data of critical current vs strain are available. 12 Note that in a cable-in-conduit conductor (CICC), the differential thermal contraction between the steel jacket and the Nb 3 Sn wire bundles (cable) causes a uniaxial compression of the superconductor during cooling from the temperature of the reaction heat treatment to the operating temperature. In addition, the cable is periodically bent.…”

“…The critical current, I c , was measured at 19 T and 4.2 K as a function of strain in an independent experiment. 12 Note that the variation of the critical current follows the distortion of the cubic Nb 3 Sn lattice. The maximum current is observed at a strain of 0.25%.…”

Simulation of transport properties in Nb3Sn strand under bending

“…The critical current density J c of Nb 3 Sn strand depends on the magnet field, temperature and strain, which can be formulated via alternatives of the scaling laws [25][26][27][28][29] and direct fits of experimental data [21]. The exponent n has the similar dependence [30], but in this paper we just consider it as a constant, which is obtained from the uniaxial loading test for a specific strand [6].…”