A quasi-optical mode converter has been designed for a 140 GHz gyrotron operating in the TE28,8 mode. This development is crucial for the efficient operation of gyrotrons, high-power microwave devices that are fundamental in various fields, including nuclear fusion research and industrial applications. The design aims to optimize the conversion of the microwave mode generated by the gyrotron into a Gaussian beam, which is more suitable for transmission and coupling to external systems.

The main challenge in designing these converters lies in the complexity of the high-order microwave modes generated by high-power gyrotrons. The TE28,8 mode, in particular, presents an intricate electromagnetic field structure that requires precise manipulation to achieve efficient conversion. The approach taken in this work focuses on optimizing the reflective surfaces of the converter to minimize losses and maximize the purity of the resulting Gaussian beam.

The significance of this advancement lies in its contribution to improving the efficiency and reliability of microwave heating systems in fusion reactors like ITER, where gyrotrons are essential for heating plasma to fusion temperatures. An efficient mode converter ensures that most of the energy generated by the gyrotron is transferred to the plasma, reducing energy waste and operational costs. This design lays the groundwork for future developments in high-frequency, high-power gyrotron technology.