Plasma Effect on the Fast- and Mixed-Wave Modes of Gyrotron Devices

The linear theory of a plasma-loaded gyrotron amplifier is studied in the fast- and mixed-wave modes. The dispersion relation is derived using the Vlasov-Maxwell equations. The effects of beam location, plasma column radius, electron beam parameters, and azimuthal harmonic number on the growth rate for the fast- and mixed-wave modes are investigated. In addition, the radial behavior of the electric field is studied. The results show that the growth rate and bandwidth of the mixed-wave mode are larger than those of the fast-wave mode. It is shown that the bandwidth of this structure is largest for a small value of the axial momentum spread. Moreover, it is indicated that for a lower harmonic number, the axial electric field has its maximum value at the center of the plasma.