Spatial periodic and homogeneous transverse stress loading on ITER TF Nb3Sn bronze and internal tin strand

TL;DR

This study investigates how spatial periodic and homogeneous transverse stress affect the critical current of Nb3Sn strands used in ITER, providing insights for stable magnet operation.

Contribution

It compares the effects of spatially periodic versus homogeneous stress on Nb3Sn strands, using a new setup for uniform load application.

Findings

Homogeneous stress influences critical current differently than periodic stress.

Experimental data at 4.2 K and 12 T field show stress-dependent variations.

Results inform design considerations for ITER superconducting cables.

Abstract

The transport properties of the superconducting Nb3Sn layers in the strands strongly depend on the strain state. Knowledge of the influence of axial strain, periodic bending and contact stress on the critical current (Ic) of the used Nb3Sn strands is inevitable to gain sufficient confidence in an economic design and stable operation of ITER CICCs. In the past years we have measured the Ic and n-value of various ITER Nb3Sn strands with different layout in the TARSIS facility, when subjected to spatial periodic contact stress at a temperature of 4.2 K and in a magnet field of 12 T. Recently we have made the setup suitable for application of homogeneous load along the length of the wire (125 mm) in order to evaluate possible differences related to spatial stress and possible current distribution. We present an overview of the results obtained so far on an ITER TF bronze and internal tin strand.