Suppression of Parasitic Modes in a Cylindrical Gyrotron Beam Tunnel by a Wall Corrugation With Schroeder Diffuser Structures

With the help of special edge structures, which correspond to the so-called Schroeder phase gratings, the electromagnetic field in a cylindrical waveguide can be perturbed in such a way that in large radial regions, an average electric field strength is reduced to a mean value for all eigenmodes existing in the frequency range of a cyclotron resonance. The perturbations break symmetry of the modes and suppress the magnitude of local maxima like in an anechoic room. The destruction of electromagnetic field distributions in a smooth-walled cylindrical waveguide due to the introduction of a Schroeder structure on a wall has been demonstrated with the help of computer simulations using the Ansys HFSS software. The proposed structure was compared with both smooth and symmetrically corrugated surfaces, which are applied in the beam tunnels of high-power gyrotrons. The application of the Schroeder structures in electron beam compression region of a gyrotron allows to increase the starting currents for parasitic before-cavity oscillations. Consequently, there is an attractive possibility to increase the operating beam current and enhance the output power of gyrotrons.