Efficiency Enhancement of a 1.5-MW, 110-GHz Gyrotron with a Single-Stage Depressed Collector

We report new experimental results from a 1.5-MW, 110-GHz gyrotron with a single-stage depressed collector. The gyrotron was operated in the TE_22,6 mode with 3-s pulse duration. An internal mode converter, which consists of a launcher and four mirrors, has been installed and tested. A highly Gaussian-like output beam was observed. A single-stage depressed collector has been operated for the study of efficiency enhancement using the same cavity V-2005 as was used in a previous experiment in the axial configuration, in which the output microwave beam propagated through a circular waveguide that also served as a collector. Output power of 1.5 MW, corresponding to 50% efficiency, was measured at 97 kV of beam voltage and 42 A of beam current at 25 kV of collector depression voltage. The results are compared between the axial configuration and the internal mode converter configuration.