The present paper contains a brief overview of the studies of mode and wave interaction in gyrodevices. The main part of it is devoted to the discussion of physical effects caused by mode interaction in the free-running and phase-locked gyrotron oscillators. Also, the problem of the stability of large-signal operation of gyro-forward-wave amplifiers with respect to excitation of parasitic backward waves is discussed.

Review of the theory of mode interaction in gyrodevices

The design of a 0.5 MW 140 GHz gyrotron with axial RF output operating in the TE/sub 10,4/ mode is presented. Experimental results and numerical simulations are compared. In particular the effects of RF reflections at the output window, velocity spread of the helical electron beam and startup of oscillations by simultaneous increase of pitch factor /spl alpha/ and relativistic factor /spl gamma/ are discussed. In short pulse operation (/spl les/5 ms) an output power of 690 kW has been obtained with an electronic efficiency of 31% and a mode purity of about 99%. The experiments have shown that it is possible to use for step frequency tuning the azimuthal neighbours of the TE/sub 10,4/ mode, TE/sub 9.4/ at 132.6 GHz (420 kW) and TE/sub 11,4/ at 147.3 GHz (300 kW) as working modes by decreasing and increasing the magnetic field, respectively. >

Experimental results and numerical simulations of a high power 140 GHz gyrotron

The dual frequency operation (DFO) of the coaxial gyrotron with two electron beams (CGTB) has been investigated in this part by means of both linear theory and computer simulation. In such an operation, the cavity is at degeneration and one beam works at the first harmonic while another at high harmonic. Making use of the coupled-mode theory, the dispersion equation considering the coupling of two beams and two modes has been obtained. The results of the numerical calculation and the particle in cell simulation show that CGTB with DFO can obtain high output power at two different frequencies simultaneously. In addition, the power of the high harmonic can be enhanced due to the nonlinear coupling between two beams, and some interesting and important phenomena of CGTB with DFO revealed in the paper are of significance in physics.

The coaxial gyrotron with two electron beams. II. Dual frequency operation

Fast design codes for the simulation of the particle-field interaction in the interior of gyrotron resonators are available. They procure their rapidity by making strong physical simplifications and approximations, which are not known to be valid for many variations of the geometry and the operating setup. For the first time, we apply a fully electromagnetic (EM) transient 3-D high-order discontinuous Galerkin particle-in-cell method solving the complete self-consistent nonlinear Vlasov-Maxwell equations to simulate a 30-GHz high-power millimeter-wave gyrotron resonator without physical reductions. This is a computational expensive endeavor, which requires today's high-performance computing capacity. However, this enables a detailed analysis of the EM field, the excited TE2,3 mode, the frequencies, and the azimuthal particle bunching in the beam. Therefrom, we present new insights into the complex particle-field interaction of the electron cyclotron maser instability transferring kinetic energy from the electron beam to the EM field.

Three-Dimensional Numerical Simulation of a 30-GHz Gyrotron Resonator With an Explicit High-Order Discontinuous-Galerkin-Based Parallel Particle-In-Cell Method

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Review of gyrotron theory

The equations for a fully self-consistent theory of mode competition in gyrotrons are derived and some possible methods of solution are discussed. The importance of including interaction in the resonator output taper is discussed in connection with the validity of linearizing the equations in the amplitude of the parasitic mode.

B. Jödicke

Papers

Self-consistent theory of mode competition for gyrotrons