The Enhancement of the Magnetization of Twisted Superconducting Strands due to the Distortion of the Filament Shape

Magnetization measurement is one of acceptance criteria for strands in the LHC (Large Hadron Collider) cable production. In a magnetic field, the superconducting filaments become magnetized due to the persistent currents and generate field errors in magnets. Over 3500 strands measured, we have observed an enhancement of magnetization for strands with filaments strongly deformed. Generally the strands are designed to have filaments with a circular cross-section, however these filaments can be deformed during the fabrication process. This paper presents detailed magnetization measurements on samples with increasing filament deformation and develops a simple theory, which enables to calculate the increase of the magnetization of independent twisted filaments as function of the roundness of the filaments and compare it with measurements. However we show that interfilament coupling is important and increases with filament deformation.