Additively Manufactured High Power Microwave Anodes

Additively manufactured components were successfully fielded for the first time in a relativistic crossed-field device. Anode structures for a relativistic planar magnetron were 3-D printed from a photopolymer using a stereolithography printing process. One anode was electroplated with copper (RPM-12b), whereas the other was thermal sprayed with copper (RPM-12c). The coating thicknesses at the vane tips were approximately 0.18 and 0.23 mm, respectively. The performance and durability of these structures were evaluated in comparison with a solid aluminum anode (RPM-12a) fabricated via conventional machining. The experimental parameters were cathode voltages between -150 and -300 kV, voltage pulse lengths of 200 to 600 ns, axial magnetic fields of 0.13 to 0.31 T, peak anode currents from 1 to 7 kA, and a base operating pressure of 9 × 10
^-6
torr. The 3-D printed anodes demonstrated microwave performance comparable to the aluminum anode, generating microwave powers in excess of 150 MW, with an average instantaneous peak total efficiency of 27% ± 10%. After 100 shots on each structure, neither anode showed any signs of operationally induced damage. The anodes did, however, have a higher rate of postshot outgassing, emitting 32% and 23% more CO
₂
per shot, respectively.