Chemical and Chemical-Mechanical Polishing of Surface Roughness on PBF-LB/GRCop-42 Cu-Cr-Nb Additive Manufactured 10 GHz RF Structures

Powder Bed Fusion-Laser based (PBF-LB) allows Additive Manufacture (AM) of lower hybrid current drive (LHCD) RF launchers from Glenn Research Copper, a Cr2Nb precipitation hardened alloy (GRCop-42) in configurations unachievable with conventional machining. Rough surfaces in AM components increase RF losses and lead to arcing in high-power vacuum RF applications. Chemical polishing, chemical-mechanical polishing, or a combination of both were utilized to planarize the internal surfaces of RF structures, resulting in surface roughness as low as Ra = 0.2 µm. Refinement in polishing techniques now enables GRCop-42 alloys (4 at. % Cr, 2 at. % Nb) to achieve similar surface roughness to GRCop-84 (8 at. % Cr, 4 at. % Nb) and equivalent cavity losses to extruded oxygen-free copper waveguides at 10 GHz.