Heat treatment issues for shrinkage alleviation of NbTi cable

Shrinkage of the NbTi conductor during coil curing has been observed to have a significant manufacturing impact. While controlled heat treating of superconductor cable prior to winding can dramatically improve the coil appearance and ease subsequent manufacturing operations, excessive heating can adversely affect conductor performance, e.g. critical current, interstrand resistance, residual resistance ratio and process sensitivity. Aluminum stabilized conductor, where aluminum is applied via conform cladding or co-extrusion, is also impacted by these concerns. Models of potential degradation mechanisms and the effect of heat treatment time and temperature on the superconductor properties are presented and compared to experiments. Within fairly wide limits, the considered parameters have low sensitivity to the heat treating conditions, so that process repeatability should be quite good. These results can be also be applied to stabilization of conductor with aluminum.<>