  In particle accelerators, pumping holes in a vacuum chamber can be a source
of unwanted broadband coupling impedance, leading to beam instabilities.
Analytical methods have been previously developed to estimate the impedance of
holes in circular-like chambers e.g. the beamscreen of the Large Hadron
Collider (LHC). More sophisticated chamber designs like that of the High Energy
LHC (HE-LHC) and the Future Circular Collider (FCC-hh) call for a different way
to calculate the impedance. We propose using decomposition of the wakefield
into synchronous traveling waves and employing a numerical solver to find the
impedance of each wave. This method is compared to the direct time domain
wakefield calculation method and its greater sensitivity to small impedances is
shown.
