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Frequency-Replaceable Ferroelectric Cathode Gyrotron for the Entire Ka-Band Using Replaceable Resonator

A modular, mid-power, Ka-band frequency (27-40 GHz) gyrotron is reported. The gyrotron is known as a dominant tube for millimeter waves, but once fabricated its frequency changing is limited. In this paper, a gyrotron with a replaceable resonator was designed and built. By a rather simple action of resonator replacement, the operating frequency of the gyrotron can be replaced. The use of a ferroelectric cathode supports a quick opening and closing of the tube for the resonator replacement in less than half an hour. With the view of covering a wide range of frequencies, a wide range magnetic field pulsed copper solenoid was designed, supporting the gyrotron operation on either the fundamental or the second harmonic of the electron-cyclotron frequency. The gyrotron design is based on a ferroelectric electron gun designed and built to provide the appropriate electron beam to a wide variety of resonators, operating at the fundamental or at the second harmonic. The gyrotron with two differently designed resonators has been constructed and tested in the TE01, TE21, and TE11 modes at 39, 31, and 27 GHz, respectively. With an accelerating beam voltage of ~35 kV and a beam current of ~1-1.7 A, an output power of ~1-6 kW was obtained at single pulse and at ~200-ns micropulse in ~6-μs macropulse with ~25% duty cycle. In addition, the system was operated with 5-s repetition rate for half an hour, and a high stability was measured for all the mentioned frequencies.