Design of a W-band TE01 mode gyrotron traveling-wave amplifier with high power and broad-band capabilities

A high-power gyrotron traveling-wave amplifier operating in the low-loss TE₀₁ mode has been constructed at the University of California, Davis that will be driven by a 100-kV, 5-A electron beam with a pitch angle (υ_⊥/υ_z) of unity and velocity spread of 5%. The amplifier is predicted by large-signal simulations to generate 140 kW at 92 GHz with 28% efficiency, 50-dB saturated gain and 5% bandwidth. The stability of the amplifier from oscillation has been investigated with linear codes. The threshold current for the absolute instability of the TE₀₁ operating mode for the chosen operating parameters is predicted to be 10 A. To suppress the potential gyro-backward-wave oscillator interactions, the interaction circuit with a cutoff frequency of 91 GHz has been loaded with distributed loss so that the single-pass attenuation is 90 dB at 93 GHz. The coaxial input coupler has a predicted and measured coupling of 1 and 2 dB, respectively.