Issue 76

Beam Dynamics Newsletter

5.5 Numerical simulation of electromagnetic fields in complex multi-cavity superconducting radio frequency resonators

CANDIDATE: Johann Heller, Rostock University, Germany
SUPERVISOR: Prof. Dr. Ursula van Rienen
GRADUATION: December 2018



This thesis deals with the computation of electromagnetic fields in complex, superconducting resonators. For the operation and design of such resonators, an efficient and accurate computation of these fields is necessary, which is hardly possible on conventional hardware in many cases. Due to this limitation, there are generally two different approaches in practice: on the one hand, the parallelization of the problem on costly hardware with high power consumption and, on the other hand, the simplification of the structure. In this thesis a method is investigated and automated to close this gap, which can solve the considered problems without extensively simplifying the structure on workstation computers. The used method, State-Space Concatenation (SSC) employs a combination of model order reduction and domain decomposition to significantly reduce the computational effort needed. For an efficient use of SSC, in this thesis an automation, ready to handle almost arbitrary high-frequency resonators is implemented and tested. Another problem is the efficient calculation of the losses of such resonances by the couplers and beampipes. Hence, this work is using a perturbation approach based on SSC. The resulting nonlinear eigenvalue problem is solved by using the Newton method, which allows for the comparatively fast computation of such losses. The exploited method is tested for physical consistency and partly compared to measurement results. In summary, all the methods discussed and implemented in this work are tested for three state of the art problems from accelerator physics. In the process current research questions for the Third Harmonic Module of the FLASH accelerator, the bERLinPro linear accelerator (linac) and the BESSYVSR cavity-design will be answered.