Most feasibility studies for modern accelerator concepts, including superconducting multicell RF-cavity-resonators in circular accelerators, depend on computing a large number of eigenmode frequencies and field patterns to obtain typical figures of merit. This task includes computational intensive numerical studies. To obtain the full eigenfrequency spectra most of these studies are performed in 3D, require a great amount of computation resources and thus are limited to a few hundred or

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... eigenmodes. To overcome this issue, some codes make use of the axisymmetric geometry of most of the RF-cavity-resonator structures and solve the problem in 2D. Solving in 2D however reduces the eigenmode spectra to eigenmodes with no azimuthal dependencies (so called monopole-modes). Due to the lack of freely available and easy to use 2.5D eigenmode solvers which are able to solve for the full 3D field in a reduced 2.5 dimensional problem, we developed yet another cavity solver (Yacs), a simple FEM based solver capable of solving for the full 3D eigenmodes of axisymmetric problems while only requiring a fraction of the computation resources required by most modern 3D codes.