Multiphysics Design of a High Power CW Mode Converter at 3.7 GHz for Tokamak Applications

Mode converters are often used to change the input dominant mode to some other desired mode. One such application of the mode converter is in the Passive Active Multijunction (PAM) antenna which is often used in the Lower Hybrid Current Drive (LIICD) systems of tokamaks. This paper describes the design and simulation results of such a mode converter. As the mode converter would handle large Continuous Wave (CW) power, multiphysics analysis to determine its thermal behaviour is carried out. The evaluated return loss of the mode converter was 35 dB with an insertion loss of 0.01 dB. An efficient water cooling scheme was designed to restrict the maximum temperature rise to about 7 degrees C and to ensure that the eventual stress generated was within the acceptable limits.