Shcherbinin V. Cyclotron instabilities of the helical electron beams in a magnetized plasma-filled waveguide

The main goal of the thesis is to investigate theoretically the influence of background plasma filling in gyrotron cavity on the cavity electromagnetic properties, linear and nonlinear stage of high-frequency field excitation by helical electron beam. The special case of low-density plasma has been considered. Then the eigenmodes of plasma-filled cavity are quasi-TE modes. The plasma induced decrease of eigenfrequencies for quasi-TE modes has been discovered. The frequency downshift for different plasma densities has been calculated. The calculated frequency shift well agrees with experimental data. The dispersion equation for cyclotron resonance maser instability of electron beam in cylindrical plasma-filled waveguide in applied finite magnetic field has been obtained. Plasma influence on linear growth-rate, bandwidth and starting currents for quasi-TE modes has been determined. The nonlinear system of equation for stationary single-mode generation in plasma-filled gyrotron has been obtained. The analysis of efficiency modification due to plasma presence in the gyrotron cavity has been carried out.