A Device for Characterizing the Circumferential Strain Dependence of the Critical Current in React and Wind Superconductors

CEA/Saclay has launched an R&D program that aims at developing design tools and technologies for conduction-cooled MgB
₂
magnets. Considering that the superconducting properties of MgB
₂
are very sensitive to strains that develop in magnets during the winding process or as a result of thermal contraction and Lorentz forces, the electromechanical characterization of MgB
₂
wires is clearly paramount for magnet design calculations. For this purpose, a device for investigating the degradation of the critical current density in R&W superconductors as a function of circumferential strain has been designed. The spring geometry has been conceived for testing long length samples (>1 m) in a magnet-like configuration, where a uniformly distributed circumferential strain ([0-1]%) is applied to the superconductor through a ring-shaped spring. The paper reports on the conceptual design, analytic calculations, and numerical simulations of the spring geometry. Moreover, the working principle is validated by experimental tests on a mock-up model.