Suppression of the Parasitic Oscillations in an X-Band Relativistic Coaxial Gyrotron Driven by an Intense Beam Current

In 100-MW level relativistic gyrotrons driven by explosive emission cathodes (EECs), significant parasitic oscillations are caused by the high beam current and the large beam velocity spread. In this study, the parasitic oscillations in an X-band coaxial relativistic intense current gyrotron were explored. The oscillations were suppressed in particle-in-cell (PIC) simulations through modifications of design. Lossy ceramics were inserted to suppress the parasitic modes in the beam tunnel. The beam collector was optimized to keep the electron beam from the cyclotron resonance region of the parasitic modes. In the 3-D PIC simulation of the whole tube, the output power of 35 MW and efficiency of 20.6% were achieved under the voltage of 300 kV, the beam current of 567 A, the pitch factor of 1.24, and the velocity spread of 25.6%. A single TE
₀₁
mode operation was achieved in this relativistic coaxial gyrotron.