Speaker
Description
We extend the model of Kubo et al. [1] in two ways: first, by generalizing it to a arbitrary sequences of planar layers of arbitrary type, e.g. superconducting (S), normal conducting and insulating (I); and second,
by accounting for all contributions, including Ohmic losses and dielectric effects. We examine the maximum applicable field for (SI)$^n$S structures and find that the optimum configuration corresponds to $n=1$. However, allowing for $n>1$, the thickness of the superconducting coatings can be chosen such that they are below the penetration depth with minor performance penalty. We further discuss the ability to model transitions in SS bilayers by introducing a set of virtual layers that represent the transition region through interpolated parameters. We find a degradation of the maximum applicable field and a larger effective penetration depth of the electromagnetic fields with thicker transition layers. Finally, we determine the surface impedance of such multilayer structures in a formulation suitable for integration into numerical electromagnetic field solvers, which we applied in a recent work [2] currently under the peer-review process at Physical Review: Accelerator and Beams. The discussed work is currently available on arXiv [3].
[1] T. Kubo, Multilayer coating for higher accelerating fields in superconducting-radio-frequency cavities: a review of theoretical aspects, Supercond. Sci. Technol. 30(2), 023001 (2016).
[2] A. Gobeyn, W. Ackermann, H. De Gersem, Numerical quality factor statistics for SRF cavities with spatially inhomogeneous multilayer coatings modeled by Gaussian random fields, arXiv:2605.05505, (2026).
[3] A. Gobeyn, W. Ackermann, H. De Gersem, Multilayer model for coatings with arbitrary layers for superconducting radio-frequency applications, arXiv:2605.07958 (2026).