Conceptual design of a quasi-optical transition from rectangular oversized waveguide to corrugated waveguide

At the current stage of design of the ICRH antenna for ITER by the CYCLE Consortium [1], a reflectometer is used for edge plasma density measurements [2]. The transmission line inside the Port Plug (PP) is WR28 rectangular waveguide, used for the 50-150GHz band. Transition to a larger waveguide outside the PP is mandatory for the long transmission line to the instruments, because of losses. Corrugated circular waveguide, as used in JET [3], would be very convenient for the task. This report provides a conceptual study for assessing the expected performance of a quasioptical transition based on the same concept as JET's Quasi Optical Boxes (QOB) [4]. First-order calculations are made using the first Gaussian beam TEM00, and Physical Optics simulations with GRASPTM[5] are used to validate results and compute the coupling between the ports of the device. This study is provided as a voluntary contribution outside the Third Party Agreement [6] between CEA and IFP for electromagnetic design of a reflectometer window.