Development of high strength electrical connections using copper electrodeposition

The poloidal field coils on the Alcator C-Mod Tokamak are manufactured from C107 or C110 half hard copper strip. A copper C10100 flag is joined to the ends of the coil turns in order to transfer the current from the coaxial leads. The coil design requires that any joint made between the flag and the coil turn be as strong, statically and in fatigue, as the coil strip. Standard methods such as welding, brazing and hard soldering would reduce the tensile strength by annealing the copper in the area of the joint. A soft solder connection with a full lap joint was not considered due to a premature failure in an initial test. In investigating alternative joining methods, tests were performed on samples of electrodeposited copper provided by the A.J. Tuck Co., of Brookfield, Connecticut. The tests showed that the joint met C-Mod structural specifications at 77K. Encouraged by these results, M.I.T., embarked on a testing program involving electroformed butt joints. Through an extensive engineering-program, reliable electroformed joints were obtained in production. The production engineering involved the construction of a special facility to control the process parameters. Details are presented here for duplicating this facility.