The effect of transverse loads up to 300 MPa on the critical currents of Nb/sub 3/Sn cables (for LHC)

Abstract

In the framework of the development of an experimental 10 T Nb3Sn dipole coil for the LHC at CERN the effects of transverse stress on Rutherford type of Nb3Sn cables have been investigated. For this purpose a special facility was designed and taken into operation in which the voltage-current behaviour of short pieces of Nb3Sn cables can be investigated in a background field up to 11 T and an applied stress of 300 MPa. The repulsive Lorentz force of 250 kN, generated by a set of superconduct9g coils, is used to impress the cable over an area of 20x42 mm maximum, in presence of a transport current up to 40 kA. In this paper the testing equipment is described and the fiist results of the observed critical current degradation of two Nb3Sn cables are discussed. It was found, that current reduction starts immediately upon loading and that already at transverse compressive stress of 100 MPa the critical current at 11 T is reduced by more than 20 % for one cable and even about 60 % for the other one. Furthermore, it seems, that the edges of the Rutherford type of cable are much more sensitive to the applied force than the cross-over points of the strands.

Conceptual Design of a New Sample Holder for the FRESCA Cable Test Station

“…Finally Fig. 8 shows the correlation between the pressure measured by the gages in the middle of the aluminum bar (3,4) and the stress measured in the corresponding gages on the shell (05, 07). From the test results one can conclude that at 77 K the pressure on the cable stack can be monitored to an accuracy of 10 MPa through the gages on the shell.…”

Superconducting Materials and Conductors: Fabrication and Limiting Parameters

“…The behavior of superconductors under stress and strain is mainly determined through axial strain experiments on the wires and tapes [49][50][51][52][53][54][55][56][57][58], and through transverse pressure experiments on Rutherford cables [33,[59][60][61][62][63][64][65]. In the sections below we review the main results obtained to date.…”

“…Such large loads are not problematic in Nb-Ti Rutherford cables, due to the limited sensitivity to strain in combination with the ductility of the alloy. However, for Nb 3 Sn, with its brittleness and large sensitivity to strain, [59][60][61][62], and by Lawrence Berkeley National Laboratory, Berkeley, CA, USA (LBNL), at the National High Magnetic Field Laboratory in Tallahassee, FL, USA in an 11 T split pair magnet [63,65]. These measurements were performed to establish the acceptable load limits for the first Nb 3 Sn dipole magnets poised to surpass the 10.5 T magnetic field record of dipoles made using Nb-Ti technology [44,69], namely Twente's 11 T MSUT magnet [70] and LBNL's 13.5 T D20 [71].…”

Brittle superconducting magnets: an equivilent strain model

“…Transport properties measurements in [1][2][3][4][5][6][7][8] were based on the principle of applying transverse pressure on a sample and then measuring its critical current I c . We can think of at least two different boundary conditions for the cable, which may produce different current density performances: plane stress with free sides, and plane stress with constrained sides (Fig.…”

“…ORK in literature on the sensitivity of Nb 3 Sn cables to strain has been conducted in a number of stress states, including uniaxial [1][2][3][4][5] and multi-axial [6][7][8] stress states, using some very different experimental setups. In order to determine a model that assigns to each tensor a scalar representation, we need data exploring all the dimensions of the tensor by means of an experiment that provides consistent and controlled conditions.…”