Friction Stir Welding for a Nuclear Fusion Reactor

During a recent upgrade to the U.S. Department of Energy’s Princeton Plasma Physics Laboratory operates an experimental nuclear fusion reactor known as the National Spherical Torus Experiment (NSTX) a new center stack design was selected that required an innovative joining method to fabricate the bundled copper extrusions found in the center stack. Each of the 20-ft long copper extrusions used in the center stack was made from a quarter hard copper alloy (CDA10700) joined to lead extensions made from a high-strength copper alloy (CDA 18150). A team consisting of PPPL, Major Tool, and EWI selected Friction Stir Welding (FSW) to join these two materials together as its solid-state nature would provide a higher joint efficiency while minimizing distortion and preserving properties of the heat treatable lead extension flag.