Investigations of a steel reinforced NbTi superconducting flat cable for toroidal magnets

Studies of the mechanical and electrical properties of a steel reinforced NbTi superconducting flat cable (8 kA/8 T at 4.2 K) to be used in a toroidal magnet system (TESPE) are presented. Young´s moduli and tensile strength values of cable samples and single components were derived from stress-strain characteristics and compared with rule of mixtures calculations. Measurements of mechanical cyclic fatigue performed at room and liquid helium temperatures up to 10⁵cycles within the elastic strain range show different effects for NbTi/Cu single strands. Electrical measurements were performed in order to get information about changes in critical current and resistivity due to static and cyclic stress loading. For static strains less than 0.5%, no degradation in critical current was detected, but the residual resistivity ratio of the cable conductor was reduced by about 40 %. In addition, the training behavior was studied of prestrained and thermally treated samples.