Speaker
Description
Superconducting cavities are used in particle accelerator machines to efficiently accelerate charged particles up to the desired energy. To characterize the resonator with respect to the interaction to moving particles the well-known concept of narrow-band impedances is used. A suitable method to determine the desired impedance is given by a proper eigenmode calculation of the given structure and a successive postprocessing of the available fields. While in the past the eigenmodes have been calculated for closed structures only, the consideration of coupling effects to the sources or to the dumps were completely neglected. In the last years sophisticated algorithms have been developed where the interaction of the resonator to the external devices can be incorporated into the system description. Analogous to frequency-domain solvers we apply the port boundary conditions straightaway into the original eigenvalue formulation without further postprocessing steps to enable the coupling. Unfortunately, this concept leads to large complex-valued systems with high numerical costs because a real-valued arithmetic is no longer useful. Since the port bondary conditions are frequency dependent, the underlying eigenvalue system is naturally nonlinear and proper eigenvalue solvers have to be applied. For large-scale applications, we implemented a complex-valued Jacobi-Davidson algorithm to extract one eigenvalue after the other starting from a given frequency target. In the presentation, the modeling of the open structures will be illustrated and real-life applications for TESLA-type resonators will be shown.
