Study on High Power Circular Waveguide TE0n-TE11 Mode Conversion

Gyrotrons are sources of high-power millimeter waves. Current interest in gyrotrons is mainly because they can act as a source of microwave power for electron-cyclotron-resonance heating (ECRH) for fusion experiments. However, the field pattern of these gyrotron modes is unsuitable for long path waveguide transmission or plasma heating. Here, it is desired to have a linearly polarized wave requiring the use of a mode conversion system which consists of many nonuniform waveguide components. Based on the theory of mode coupling, this paper discusses the circular waveguide mode conversion with waveguide axis curved and radius tapered in detail. It also carries out the optimized analysis about the geometry structure of TE_0n-TE₁₁ mode converter. Adopting different phase rematch techniques, the optimal geometry parameter can be obtained. The mode converter designed in this way owns high conversion efficiency exceeding 98%.