Novel Coating Materials for RF Windows

The multipactor effect is a major challenge that is encountered in a number of areas involving high-power radio frequency or microwave systems. Particle accelerator systems associated with high energy physics research are limited by radio frequency window breakdown largely due to multipaction. The multipactor effect is highly dependent on the secondary electron coefficient of the window, which is highly surface sensitive. In this effort, recent developments in coating technologies are leveraged to integrate coating materials with extremely low secondary electron emission rates, allowing systems to perform at higher power with increased dependability. The Phase I research focused on two areas. First, exploring challenges associated with integration of the coating material with suitable radio frequency window bulk ceramics (e.g., Al2O3), and second, demonstrating that the coating material does in fact suppress secondary electron yield even at nanoscale thicknesses. For the former, coating recipes were developed during the Phase I that will be of value during follow-on efforts. For the latter, the Phase I successfully demonstrated an extreme degree of secondary electron yield suppression after application of nanometer-scale coatings. The goals of the planned Phase II are to make direct measurements comparing the coating performance against competing options, such as Titanium Nitride (TiN), to produce a prototype coated window and to test the prototype window at high power. A significant portion of global research in physics is based on data produced at the few major particle accelerator laboratories located around the world. These key facilities would see major benefits in terms of producing higher accelerator energies, decreasing the number of klystrons required for energy input, or reducing bottom line project costs, each of which results in the availability of more and better data for analysis by the many interested research institutions. Beyond that, the particle accelerator industry includes a wide range of medical, research, and security applications that would benefit from improved window performance and reliability.