STABILITY ANALYSIS OF RELATIVISTIC GYRO-TRAVELING WAVE DEVICES

The stability of parasitic modes in gyro-traveling wave tubes is studi ed, both with and without the operating mode present. Using a Hamilton ian formalism, linear equations are derived which describe the spatial evolution of parasitic modes in the absence of the operating mode. Co mplications such as a nonuniform waveguide and tapered magnetic field are taken into account. As an example, the linearized equations are ap plied to a 10 GHz, 430 kV, gyro-traveling wave tube to determine the s tart current in the absence of the operating mode. Included in the ana lysis is the effect of frequency-dependent reflection from the output window. A relatively low start current is found, well below the nomina l operating current of 240 A. Multi-mode equations are then derived wh ich can be used to analyze the suppression of parasitic modes by the o perating mode. An algorithm is developed that allows efficient computa tion of the nonlinear start current in this regime. The algorithm is a pplied to the 10 GHz, 430 kV device mentioned above, and a stable conf iguration is found. (C) 1995 American Institute of Physics.