Evaluation of the effects of mechanical cycles on bonding of Al-superconducting cable in high-performance stabilized NbTi conductor

The compact muon solenoid (CMS) solenoid is presently the superconducting magnet with the highest stored energy (about 2.6 GJ) and one with the highest energy/mass ratio (11.3 kJ/kg). The latter is directly related with the mechanical deformation of the conductor under the action of the magnetic force, inducing a strain as high as 0.15%, close to the elastic limit of materials. In order to provide the hoop strength in CMS magnet, an innovative reinforced Al-stabilized conductor was involved in the design. After 10 years of successful operation and in view of further runs (20 years or more), it seems appropriate to evaluate the robustness of the conductor with respect to thermal disturbances of mechanical origin. In order to understand the effects of magnet cycles on the bonding between the Rutherford cable and the pure aluminum stabilizer, we perform an experimental study on short samples of the full conductor. After stressing the conductor with mechanical cycles, electrical measurements at T = 4.2 K in magnetic field up to 5 T allowed us to evaluate the current transfer length, the relevant figure of merit for the bonding quality.