Mechanical Performance of Superconducting Cables Subject to Cyclic Stresses

Mechanical properties of internally-cooled cabled superconductor (ICCS) under cyclic loading were investigated. Conductor strand motion due to the inherent lack of internal strand support in an ICCS, coupled with the strain sensitivity of NbsSn, could lead to premature failure of the Nb₃Sn superconductor. A two-step approach was used to study this phenomenon.First, two small test coils were non-inductively wound with 27-strand NbTi ICCS of 64% and 32% void fractions respectively. The coils were subjected to cyclic Lorentz forces and monitored for strand motion using a voltage transient/acoustic emission technique. Motion- induced voltage transients were observed in the 64% test coil and no voltage transients were observed in the 32% test coil.The second step involved subjecting test coils wound with 58% and 36% void fraction 27-strand Nb₃Sn ICCS to cyclic Lorentz forces. After 100 cycles, the 58% test coil showed a 24% degradation in critical current with no further degradation; the 36% test coil showed no degradation after 750 cycles of testing.