CNES — Chalmers — IAP — Onera activities in the domain of high rf power breakdown phenomena

Multipactor breakdown is an important potential failure mechanism in many different microwave devices working under close to vacuum conditions. Applications range from space borne rf equipment to high-power microwave generators. The basic physics involved in the multipactor phenomenon is well known for the case of two infinite parallel plates. However, most realistic rf device geometries involve inhomogeneous rf electric fields and curved field lines. In such situations, breakdown threshold extrapolations based on the parallel plate results tend to be overly pessimistic and lead to non-optimized designs. Iris geometry is quite commonly used in microwave components. In this case, the spread in emission angles leads to a random walk of the corresponding electron trajectories that ultimately carries them out of the finite iris region and thus constitutes a loss mechanism that tends to increase the multipactor breakdown threshold. The importance of this diffusion out of the iris is determined by the ratio of the width, a, and height, h, of the iris and it was shown in [1] (assuming that the electric field was homogeneous inside the iris). A more rigorous and detailed analysis of the iris problem was made in [2] where the geometry of the iris was transformed into the classical two infinite parallel plate geometry using conformal mapping assuming that the electric field in the iris was approximately quasi-static. Cross-validations were performed between the conformal mapping software using ONERA measured SEY data and Multipactor measurements. A septum polarizer is a RF component used mainly inside antenna sub-system in spacecraft payloads. A software [3] was developed to simulate the multipactor avalanche inside a separate section of rectangular septum polarizer. It contains the electromagnetic field solver and the Multipactor simulator based on the Monte-Carlo algorithm. Numerical results in such complex devices will be described. Perspectives will also be drawn in terms of needs in the domain of the prediction of the Multipactor phenomenon inside space RF components.