Operation of a Four Cavity, Frequency-Doubling Gyroklystron

Summary form only given. The University of Maryland Gyroklystron Program has as a goal the production of 80 MW of peak power at 17 GHz, using a 500 W, 500 A electron beam. Frequency-doubling gyroklystron circuits that had 3-4 cavities and that were driven by a 150 kW, X-band have to date only produced maximum powers of about 27 MW. The root cause of this inability to achieve the designed operating parameters has been non-uniform emission from the temperature-limited magnetron injection gun (MIG). The azimuthal current density varies by more than plusmn50% due in large part to a 60degC temperature variation on the emitter surface. A new MIG with superior azimuthal current uniformity has been constructed by Calabazas Creek Research, Inc. and has been installed in the UM test bed. In this paper we describe the design and hot test results for a four-cavity coaxial circuit being driven by this new MIG. The input cavity operates at 8.568 GHz in the TE₀₁₁ mode while the remaining cavities operate at twice the drive frequency in the TE₀₂₁ mode. The tube is predicted to have an efficiency of 34% for an average perpendicular-to-parallel velocity ratio of 1.4. The large signal gain is about 46 dB at the desired operating point. Tube cold-test results, as well as the hot test characterization of tube dependence on voltage, current, velocity ratio, and magnetic field, will be given. Tube stability and output mode purity will also be assessed