Transverse Impedance of a Smooth Flat Taper

Stupakov has used a perturbation method to estimate the transverse impedance at zero frequency of a rectangular collimator having characteristic taper length (ell), half-width w, and average vertical half-aperture b0, under the condition b0 << w << (ell). We use the boundary perturbation method to approximate the transverse impedance of a flat, slowly tapered chamber in the complementary limit, w = ∞