Trivalent Chrome Plating for ITER Strands

ITER conductors for Toroidal Field (TF) and Central Solenoid (CS) coils require many strands of and copper with a 1 to 2 micron thin coating of chromium. The purpose of the Cr is two-fold: to keep the strands from sintering during a prolonged high temperature reaction treatment and to offer inter-strand resistance. Up until recently Cr plating is applied using a hexavalent chrome (Cr-VI) electrolytic process. This process is highly toxic and requires expensive and strict environmental and safety controls. No reel-to-reel plating lines are available in the US suitable for plating wire since there has been no need for such plating of commercial wires. Therefore Summit Corp. of America and Luvata Waterbury, Inc. have developed an efficient and economical plating process based on environmentally friendly and less toxic trivalent chrome (Cr-III). We have studied adhesion of Cr to the base copper, its ductility, texture, thermal stability and residual resistivity ratio (RRR) of base copper following the high temperature heat treatment. After detailed evaluation and side-by-side comparison of Cr-III and Cr-VI plating we have successfully qualified the later for the ITER TF strands. The new process has coated over 15 tons of superconductor and Cu strand with stable and predictable performance. Process and performance details will be presented in this paper.