RF losses in selective laser melted GRCop-84 copper waveguide for an additively manufactured lower hybrid current drive launcher

Abstract

Abstract Recent advances in selective laser melting (SLM) 3D printing technology allow additive manufacture of lower hybrid current drive (LHCD) RF launchers from a new material, Glenn Research Copper 84 (GRCop-84), a Cr2Nb (8 at.% Cr, 4 at.% Nb) precipitation hardened alloy, in configurations unachievable with conventional machining. Rough surfaces in additively manufactured components are a limiting factor that increases RF losses. Surface roughness was found to be the dominant loss mechanism in SLM printed waveguide components. Wet blasting removes adhered powder grains from SLM printed GRCop-84 while vibratory mass finishing smooth’s and flattens waveguide surfaces. Mechanical polishing produced surfaces with low RF loss, however a further mass finishing step is recommended for the interiors of waveguides where polishing is not possible. Power loss in the upcoming LHCD launcher system for DIII-D is used to predict driven current in the plasma.