STABILITY ANALYSIS OF RELATIVISTIC GYRO-TRAVELING WAVE DEVICES

The stability of parasitic modes in gyro-traveling wave tubes is studied, both with and without the operating mode present. Using a Hamiltonian formalism, linear equations are derived which describe the spatial evolution of parasitic modes in the absence of the operating mode. Complications such as a nonuniform waveguide and tapered magnetic field are taken into account. As an example, the linearized equations are applied to a 10 GHz, 430 kV, gyro-traveling wave tube to determine the start current in the absence of the operating mode. Included in the analysis is the effect of frequency-dependent reflection from the output window. A relatively low start current is found, well below the nominal operating current of 240 A. Multi-mode equations are then derived which can be used to analyze the suppression of parasitic modes by the operating mode. An algorithm is developed that allows efficient computation of the nonlinear start current in this regime. The algorithm is applied to the 10 GHz, 430 kV device mentioned above, and a stable configuration is found. (C) 1995 American Institute of Physics.