Manufacturing Process Development for Joining GRCop-84 and -42 Alloys for DIII-D LHCD

GRCop-84 and GRCop-42 precipitation hardened copper alloys have high tensile strength while maintaining high electrical and thermal conductivity and can be additively manufactured (AM) by a selective laser melting (SLM) process. Because of these favorable material properties and the design freedom afforded by additive manufacturing, these materials show promise for use in tokamak radio frequency (RF) systems, such as lower hybrid current drive (LHCD). The implementation of these alloys requires the development of scalable and repeatable joining processes that overcome the unique challenges posed by the chemistry of these alloys, their post AM properties, and unique geometries relevant to these RF systems. While work has been done to qualify many of the joining methods described here on the small scale, the implementation of these methods at system-relevant scales has yet to be shown. Presented are the detailed descriptions of medium-scale production processes for the joining of RF components developed to support the high field side (HFS) LHCD system at DIII-D. Fixture design, surface and weld preparation, assembly, and power and temperature profiles are presented for the following joining processes: electron beam welding (EBW) of GRCop-84 and GRCop-42 waveguides (WGs), vacuum brazing of AL995 alumina vacuum windows into GRCop-42/C101 bimetallic WGs, diffusion bonding of GRCop-84 to C101, vacuum brazing of GRCop-84 and GRCop-42 to C101, vacuum brazing of 304L stainless steel vacuum flanges to GRCop84 wavegudies, and laser welding of GRCop-84 and GRCop-42 WGs.