[Back]

A. Moros, M. Ortino, S. Löffler, M. Alekseev, A. Tsapleva, P. Lukyanov, I. Abdyukhanov, V. Pantsyrny, S. Hopkins, M. Eisterer, M. Stöger-Pollach, J. Bernardi:
"Nb3Sn Wires for the Future Circular Collider at CERN: Microstructural Investigation of Different Wire Layouts";
IEEE Transactions on Applied Superconductivity, 31 (2021), 5; 1 - 5.

In the challenging project concerning the realization
of theCERNFutureCircularCollider (FCC),Nb3Sn represents the
best candidate material for the construction of high-field superconducting
dipole magnets, since it is able to satisfy the requirements
of Jc (non-Cu) = 1.5 kA/mm2 at 16 T and 4.2 K. In that context,
a cluster layout of prototype internal tin Nb3Sn wires, developed
by TVEL and the Bochvar Institute (Russia), was analyzed and
compared to a standard layout produced by the same manufacturer.
The main reason for dividing the sub-element into clusters is
reducing the effective sub-element size (deff). The microstructural
characterization of such a wire layout can provide fundamental
contributions to steer the manufacturing processes towards higher
performing wires. In particular, since the homogeneity in Sn concentration
influences the superconducting properties, the effect
of cluster and standard layouts on the Sn concentration gradient
over the wire cross-section was evaluated. For this purpose,
energy dispersive X-ray (EDX) spectroscopy was employed with
both scanning electron microscopy (SEM) and transmission electron
microscopy (TEM). Finally, scanning Hall probe microscopy
(SHPM) measurements were performed to understand how these
cluster wire sub-elements, with their specific geometry, influence
the local currents flowing through the wire cross-section on a microscopic
scale. The comprehension of the correlation between the
microstructural characteristics and superconducting performance
is crucial for obtaining wires meeting the requirements of FCC
dipole magnets.

http://dx.doi.org/10.1109/TASC.2021.3066541