Design of a Compact, Multi‐Megawatt, Circular TE01 Mode Converter

Experience gained during the recent operation of high power 11.424 GHz rf sources for accelerators led to new, stricter requirements for system components. One of the basic components of such a system is a mode converter that transforms the rectangular waveguide mode into the TE01 circular waveguide mode. With such a converter, it is possible to minimize the use of WR90 rectangular waveguide which was shown to be a weak part of the previous system at power levels higher than 100 MW and pulse lengths on the order of a microsecond. We used several methods to design a compact mode converter with extremely low parasitic mode conversion. These methods employ HFSS and include multi‐parameter searches, concurrent optimization with a mode‐matching code CASCADE, cascading of resulting S‐matrices, and tolerance analyses. This paper describes the design methods and presents results.