Innovative Computational Strategies for Minimizing Plasma Formation, and Reducing Outgassing in High-Power Microwave (HPM) Devices

This research aims to enhance the operational efficiency of High-Power Microwave (HPM) devices by minimizing undesirable plasma formation during operation. Plasma formation occurs primarily due to the emission of gases dissolved in the anode host and the desorption of surface contaminants, followed by the ionization of such species. The presence of plasma in HPM systems can lead to pulse shortening and reductions in repetition rate. These issues need to be overcome through the development of various outgassing reduction techniques and the design of advanced anodes with minimal outgassing properties. Firstly, the present study investigates thermally driven desorption of surface impurities using coupled Monte Carlo-heat flow-Molecular Dynamics simulations. The research seeks to determine the temperature thresholds required to desorb different surface contaminants such as C2, O2, CO, and CO2. The findings indicate that carbon-based adsorbates on copper, chosen as an example anode material, can be removed at a relatively low surface temperature of 650K. In contrast, reactive species like oxygen remain highly stable due to their large cohesive energies. Additionally, Molecular Dynamics (MD) simulations are conducted to highlight the advantages of using a platinum coating layer due to its significant resistance to oxidation. Next, the study explores a potential solution for reducing outgassing from a material's bulk through quasi-isentropic compression (QIC), supported by quantitative predictions from MD simulations. For QIC analyses, copper is again chosen as a sample anode but with hydrogen gaseous impurities embedded in the host. The findings suggest that applying a strong, short pressure ramp to one surface can lead to the accumulation of hydrogen atoms on the opposite face. This gathering of gaseous impurities could facilitate efficient surface treatment and cleaning. Moreover, it is demonstrated that upon compression, the surface becomes denser and more resistant to the subsequent diffusive uptake of hydrogen atoms from the environment, thereby creating a surface seal. Expanding on previous Quasi-Isentropic Compression (QIC) studies, molecular dynamics simulations-based laser-induced surface densification of copper anodes has been studied. The findings demonstrate that exposing the copper anode surface to a high-energy laser beam leading rapid temperature surge followed by rapid cooling alters the material's microstructure, leading to the formation and solidification of a dense surface layer. The computational model indicated a significant densification effect, with the material's density increasing by approximately 8.16% through this process. The densification would contribute to reductions in outgassing.