Reliability of nm-Scale Dielectric Coatings for Multipactor Suppression in Resonant Cavities

Thin polymer coatings are employed in vacuum electron devices to reduce secondary electron emission and mitigate multipactor susceptibility. However, the introduction of dielectrics introduces the risk of electrical breakdown in high-energy systems. This paper presents an analysis of the electrical breakdown conditions for sub-micron thickness PTFE coatings used for multipactor suppression. The cavity under consideration operates with a peak electric field intensity of 10MV/m, with an 11.2nm PTFE coating. The breakdown thresholds are calculated using the breakdown power law across a range of PTFE thicknesses and temperatures. Using standard PTFE parameters, it is determined that the coating has a breakdown threshold of 19.8MV/m. The Weibull statistical method shows 50% probability of breakdown at 50MV/m, at a temperature of 200°C. From these results, it is determined that a nm-thickness coating serves to viably suppress multipactor without risk of electrical breakdown.