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 HE11mode in corrugated waveguide. Anew coupler is described that couples the cavity RF power directly into corrugated waveguide inside the gyrotron. A highpower gyrotron with the improved coupler was tested using 1-MW, 3-μs pulses and demonstrated equivalent power and efficiency as a traditional coupler with HE11mode output in corrugated waveguide. In addition, higher HE11mode purity was achieved at the gyrotron output.