A review of the US joining technologies for plasma facing components in the ITER fusion reactor

This paper is an overview of joining technologies developed for the fabrication of duplex armor/heat sink structures for use as actively cooled plasma facing components (PFCs). Tore Supra has been facing the challenge of implementing such technology with carbon armor brazed to copper alloy heat sinks for several years. Also, extensive preparations were made for the deployment of actively cooled limiters with beryllium armor joined to copper alloy heat sinks in the Joint European Torus (JET). With the development of plasma facing components for the International Thermonuclear Experimental Reactor (ITER), there has been a trend toward fabrication of more sophisticated structures to deal with the challenges of relatively long component lifetimes under high thermal loads. This paper summarizes earlier work on Tore Supra and JET as well as current efforts in the US in developing adequate joining technologies for ITER plasma facing components. For ITER, many unique and innovative joining techniques are being considered in the quest to join two candidate armor materials (beryllium and tungsten) to a copper base alloy heat sink (CuNiBe, DS copper, or CuCrZr). These techniques include brazing and diffusion bonding, incorporating compliant layers, diffusion barrier coatings and diffusion enhancing coatings at the bond interfaces. At this writing, two beryllium-copper divertor mock-ups have survived 1000 thermal cycles at 10 MW/m² without damage during testing at the electron beam test system (EBTS) facility at Sandia National Laboratories in New Mexico. A plasma-sprayed (Be on Cu) ITER first wall mock-up has survived 3000 cycles at 1 MW/m² without damage