Experimental validation of fringing field effects for the multipactor phenomenon

The multipactor effect is a constraining phenomenon in the design of RF components. Due to an increasing number of channels and power levels for multicarrier signals, specific requirements of design must be taken into account in order to prevent the multipactor effect. The current methods of analysis are based on the Hatch and Williams diagrams, which provide the multipaction threshold voltage for a parallel plate geometry as a function of the frequency gap product. However, whereas experimental results have shown good correlation with the theoretical charts for the parallel plate geometry, discrepancies have been found for complex geometries such as irises. In the present work a detailed analysis has been made of multipactor breakdown in the iris geometry. The first step of the analysis has resulted in a deeper physical understanding of the phenomenon and accurate numerical prediction tools have been developed to determine the multipactor breakdown in irises. In addition, new charts applicable for the iris configuration have been carried out. One important physical aspect in the iris case is that three new mechanisms of electron losses have to be taken into account: the random walk in the (finite) iris width direction; the Miller force pushing electrons out of the region with strong electric field; the centrifugal force perpendicular to the curved electric field lines In order to increase margins for flight models components, the objective of the second step of the analysis has been to determine the evolution of the multipactor threshold versus the ratio of the height of the iris and the length along the propagation axis. Specific samples have been designed and manufactured in C band in order to have reachable threshold values for the tests. The performed measurements have demonstrated different behavior compared to the parallel plate case.