Design and High-Power Test of an Internal Coupler to HE11 Mode in Corrugated Waveguide for High-Power Gyrotrons

Gyrotrons produce power in high-order, transverse electric modes that are typically converted to a Gaussian beam inside the tube. In fusion plasma heating applications, the power is transmitted through a diamond window to an external mirror optical unit where it is coupled into an HE11 mode in corrugated waveguide. A new coupler is described that couples the cavity RF power directly into corrugated waveguide inside the gyrotron. A high-power gyrotron with the improved coupler was tested using 1-MW, 3-mu s pulses and demonstrated equivalent power and efficiency as a traditional coupler with HE11 mode output in corrugatedwaveguide. In addition, higher HE11 mode purity was achieved at the gyrotron output.