Tradeoff studies of a high-order-mode gyrotron traveling-wave amplifier

Performance of a fundamental cyclotron harmonic, TE₀₁-mode gyrotron traveling-wave amplifiers (gyro-TWTs) is studied theoretically under the marginal stability criterion. The interaction circuit is shown in Fig. 1. As is illustrated in Fig. 2 for the parameters in Table I, absolute instabilities on both lower and higher order modes and at the fundamental and second cyclotron harmonic frequency present severe constraints to the stable operating current. General methods for stabilizing these unwanted oscillations are outlined, on the basis of which the parametric dependence of gain, power, bandwidth and efficiency on the beam velocity ratio, circuit lengths, wall resistivity, and velocity spread is obtained under the marginal stability criterion. The results allow a tradeoff among gain, power, bandwidth, and efficiency to reach a desired design.