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.