Operation of a large-orbit high-harmonic gyro-traveling-wave tube amplifier

The high-harmonics gyro-traveling-wave tube (gyro-TWT) is a high-power (⩾1-kW) millimeter wave amplifier based on the synchronous interaction of a beam of large-orbit axis-encircling electrons with a high-order cylindrical waveguide mode. Since the interaction occurs at a high harmonic of the cyclotron frequency, the intense magnetic fields required for the conventional fundamental-mode gyro-TWT are not required. A proof-of-principle experiment designed to demonstrate the interaction of a 150-mA, 350-keV electron beam with the TE₈₁ mode of a cylindrical waveguide is described. Principal results include a small signal gain of 10 dB, an interaction bandwidth of 4.3%, and a saturated power transfer from electron beam to wave of 0.5 kW. Additional measurements include the dependence of gain on electron beam current and the measurement of the beam´s γ, β ₄F, β_||, and Δβ_||. Sufficient agreement between the experimental results, the simulation codes, and an analytic description of the interaction is demonstrated to permit the design of high-performance millimeter wave amplifiers