Numerical solution of fields in lossy structures using MAGY

Lossy structures are used in vacuum electronic devices to control and suppress modes. Numerical simulation of the effect of these lossy structures is critical to the design and optimization of devices. The gyrotron simulation code MAGY makes use of the generalized telegraphist´s equations in which the transverse structure of fields is represented as a sum of local modes of a metallic waveguide. If the wall is not a perfect conductor then sum over modes is not uniformly convergent. We have developed an algorithm to deal with this problem and allow for the simulation of structure with highly lossy walls. The theory and implementation of this algorithm are presented