October 1, 2025Open Access

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

ASAndrew SeltzmanFusion (United States)SWS.J. WukitchFusion (United States)

Key Points

Polishing techniques reduced surface roughness to Ra = 0.2 µm, improving RF efficiency.
Chemical-mechanical polishing achieves comparable low surface roughness to GRCop-84 alloys.
Additive manufacture of RF structures enhances design capabilities beyond conventional methods.
Refined polishing techniques enable reduced cavity losses similar to oxygen-free copper waveguides.

Abstract

Laser-based powder bed fusion (L-PBF) allows additive manufacture (AM) of lower hybrid current drive (LHCD) radio-frequency (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.

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