Broad-frequency range of a 250 GHz medium-power gyrotron traveling-wave amplifier with a distributed-loss structure

A gyrotron traveling-wave amplifier (gyro-TWA) with a distributed-loss structure can achieve high gain over a broad bandwidth. In this study, a low-voltage, low-current subterahertz gyro-TWA with medium power (∼10 W) over a broad-frequency range (∼10 GHz) is designed. The excessive length of the copper section in this gyro-TWA leads to reflective oscillations and absolute instabilities. Reflective oscillations can be suppressed for a gyro-TWA with a high lossy-section resistivity and a short copper section. Absolute instabilities, conversely, can be suppressed for a gyro-TWA with a long lossy section and high lossy-section resistivity. The proposed gyro-TWA has a high lossy-section resistivity, a long lossy section, and a short copper section, which not only avoids mode competition but also achieves the desired characteristics of a high gain and broad-frequency range. For a 12 kV, 0.3 A electron beam, the frequency range of the 250 GHz 10 W level gyro-TWA with a distributed-loss structure, is ∼10 GHz when the input power is between 1 and 10 mW.