Study of axial modes in the gyrotron backward-wave oscillator

Formation of different orders of axial modes in the gyrotron backward-wave oscillator are shown to be governed by the optimum conditions for the beam-wave interaction. Distinctive linear properties of oscillating modes in the nonresonant structure are revealed and interpreted physically in such a perspective. Implications of these properties to the nonlinear behavior are examined with time-dependent simulations. Self-modulation, rather than axial modes competition, is found to be the cause of nonstationary behavior and regimes of stable frequency tuning are identified as a remedy.