Numerical Calculation of Eigenmodes in PETRA 7-cell Cavity under precise Consideration of Coupler Structures

The PETRA accelerator [1], which served originally as a pre-accelerator for the large HERA facility, is nowadays the world’s best storage-ring-based X-ray radiation source. It provides the scientists experimental opportunities with X-rays radiation. The PETRA accelerator is based on a 7cell normal conducting copper cavity operating at 500 MHz and delivers a particle beam with energy up to 6 GeV. To enable proper beam dynamics simulations, it is important to determine the eigenmodes in the accelerating cavities with high precision. In the real installation, the input coupler is required to transfer the energy from the sources to the particle beam. For this reason, a complex-valued eigenmode solver can be applied to properly calculate the eigenmodes. At the Computational Electromagnetics Laboratory (TEMF) a robust parallel eigenmode solver based on complex-valued finite element analysis is available. In this paper, the realvalued and complex-valued eigenmode solver have been applied to the PETRA 7-cell cavity to determine the resonance frequency, the quality factor and the corresponding field distribution of eigenmodes.