Validation of frequency extraction calculations from time-domain simulations of accelerator cavities

The frequency extraction algorithm (Werner and Cary 2008 J. Comp. Phys. 227 5200) that enables a simple finite-difference time-domain algorithm to be transformed into an efficient eigenmode solver is applied to a realistic accelerator cavity modeled with embedded boundaries. Previously, the frequency extraction method was shown to be capable of distinguishing M degenerate modes by running M different simulations and to permit mode extraction with minimal post-processing effort that requires solving only a small eigenvalue problem. Realistic calculations for an accelerator cavity are presented in this paper to validate the method for realistic modeling scenarios and to illustrate the complexities of the computational validation process. The approach is able to extract frequencies that differ by corrected experimentally measured frequencies by about 1 part in 10⁴, which is accounted for (in largest part) by machining errors. The extraction of frequencies and modes from accelerator cavities provides engineers and physicists with an understanding of potential cavity performance as it depends on the shape without incurring manufacture and measurement costs.