Axial Compression Tests on ITER-TF Conductor Samples

As demonstrated in the -superconductor cable of the ITER TF Model Coil (TFMC) has an average longitudinal stiffness inside the stainless steel jacket of about 1/10 of that calculated supposing all components are fully bonded. This conductor was wound towards the inner circumference of the grooves of a stainless steel mould and heat treated in it showed an elongation of 0.048% after cooling to ambient temperature . This can only partially be due to the lower expansion coefficient of than the other constituents. The stiffness of three conductors (copper dummy, non-reacted and reacted TFMC) was nearly the same and independent of the constituents. It is expected that by reducing the void fraction the stiffness would increase, having the limit at zero void fraction equal to the average of the fully bonded constituents involved. We investigated pieces from the TFMC conductors (34% void) and 2 different ITER TF Coil conductors with 29.7% and 28.3% void fraction and different twist pitches. Heat treatments on short samples were performed and the change of length of the cable and the jacket were investigated. Compression tests just on the cables inside the jacket were performed. From these tests the stiffness of the ITER TF Coil conductor samples were found to remain in the same level. Nevertheless, the samples with lower twist pitches show higher yield strength in axial compression. Acoustic emission records on reacted samples containing showed that cracks occur already at small compression levels which the cable sees inside the jacket during cool down from reaction to room and helium temperature.