Classical axial VIRCATORS have low power conversion efficiency, typically less than 1% depending on the different designs proposed in the literature. The goal of this webinar is to propose new VIRCATOR structures with reflectors embedded in the output circular waveguide in order to increase the output power. For instance, to design such structures for up to 2 reflectors, the dispersion diagram is plotted and analyzed to predict the potential operating modes. In order to predict a robust design for an experimental setup, the environment influence, such as the vacuum quality is discussed in terms of losses which can affect the operating frequencies and thus the output power. First steps for an optimized virtual prototype will be proposed in this context.