Numerische Simulation der Gyrotron- Wechselwirkung in koaxialen Resonatoren

Gyromonotrons, or briefly gyrotrons, are at the moment the most powerful millimeter wave oscillators. However, an absolute limit of the output power of conventional hollow waveguide gyrotrons of for example 1 2 MW CW at 140 GHz is given by walllosses, voltage depression and mode competition. The present work describes the complete interaction theory of coaxial gyrotron cavities, including corrugations on the outer cavity wall and on the rod, which are used to suppress possible competing modes, as well as misalignment of the rod. Computer codes for fast simulations of the interaction are described. These interaction calculations make use of several approximations for speed up. Investigations of the behavior of coaxial cavities with longitudinal corrugations lead to design criteria that enable output powers two to four times higher than with hollow waveguide cavities. In the last chapter the cavity design for the 1.5 MW / 140 GHz experiment at the Forschungszentrum Karlsruhe (FZK) is discussed, and a comparison to experimental results is presented. The achieved experimental values of nearly 1.2 MW with an efficiency of 27 % represent an important step towards the realization of plasma heating with millimeter waves. This is the first experiment at 140 GHz where more than 1 MW of rf-power is reached with cw-relevant parameters for the electron gun and the cavity.