Investigation of material migration and characterization of the film layer on the surfaces of HPM generator structures

During high-power microwave (HPM) generation experiments, oscillator components frequently exhibit complex surface discoloration and pronounced breakdown marks induced by strong electric fields. This study focuses on the anode head of a relativistic backward wave oscillator (RBWO), specifically examining the localized discoloration observed on its surface after HPM generation experiments. A comprehensive analysis of the surface composition and precise measurement of film thickness are conducted to determine the material characteristics and elucidate the underlying coloration mechanism. The results indicate that the thin films present in the discolored micro-regions primarily consist of diamond-like carbon (DLC). The film thickness ranges from 183 nm to 460 nm, with these variations accounting for the distinct coloration via thin-film interference theory. Furthermore, the material migration and the non-uniform distribution of film thickness across the anode head surface are attributed to the expansion and subsequent deposition of carbon plasma, which is generated during explosive electron emissions from the cathode under intense electric fields.