Summary form only given. In high-power gyrotrons sweeping systems are used in order to distribute the energy of the spent beam in a larger area of the collector1. Currently, there are two common types of sweeping systems, the axial and transversal sweeping system2. In the first case, the sweeping coils surround the collector creating a harmonically varying magnetic field that is coaxial to the externally applied one. In the second one, the coils are distributed symmetrically around the collector creating a rotating magnetic field normal to the external one. In both cases the periodic variation of the magnetic field induces eddy currents in the conductive walls of the collector, which tend to cancel the magnetic field of the sweeping coils, reducing in this way the efficiency of the sweeping system.

Summary form only given. Coaxial gyrotrons offer the potential to generate microwave power in the multi-megawatt levels at frequencies well above 100 GHz1, since very high-order volume modes can be used. The presence of the coaxial insert reduces the voltage depression and eliminates the restrictions of mode selectivity, making it possible to maintain the cavity ohmic losses at a reasonable low level (<2kW/cm2) allowing the use of very high-order volume modes.

A transmission-line model is reformulated and combined with field theory to study the propagation characteristics in coaxial waveguides with wedge-shaped corrugations, either on the outer wall or the inner conductor. Numerical results show that this equivalent-circuit approach is in agreement with conventional full-wave methods presented in the literature. Additionally, this formulation overcomes numerical issues in the calculation of higher order Bessel functions, which usually conscript sophisticated expansion techniques.

Recent high-power gyrotrons, capable of producing radio-frequency power above 1 MW, often suffer from parasitic oscillations in the beam tunnel, despite the presence of dielectric loading materials intended to prevent the growth of such modes. Such oscillations affect the operation and the efficiency of these devices significantly. Lately, a variety of dielectric materials have been used, with limited success, in ring-loaded beam tunnels to suppress unwanted oscillations. In this paper, we perform an extended parametric study of the effects of beam-tunnel geometry and lossy material properties on the damping of such oscillations.