First Results of Corrugated Circular Waveguide Fabrication by Copper Cold Spray

Corrugated circular waveguides are essential radio-frequency (RF) components in electron cyclotron heating systems for magnetic confinement fusion devices such as tokamaks and stellarators. These waveguides enable low loss transmission of millimeter wave power over long distances (>10 m) between RF sources and in-vessel launching structures. Cold spray (CS) manufacturing, in which metallic microparticles are accelerated by a gas jet and impact a substrate to form a coating with high density and low oxidation, offers a novel fabrication pathway for these components. The method proposed in this paper deposits copper onto an externally corrugated cylindrical substrate followed by chemical removal of the substrate to produce an internally corrugated structure. As a first step to enabling fabrication by this method, spray experiments were conducted on flat corrugated substrates using a VRC Gen III high-pressure CS system controlled by a Fanuc M-710iC 6-axis robotic arm. Copper depositions onto these substrates, representative of ~100- to 200-GHz waveguides, are presented. Cross-sectional micrographs, material porosity, and surface roughness are reported for various spray parameters, postdeposition treatments, substrate materials, and corrugation aspect ratios and sizes.