Speaker
Description
We report calculations of a dc superheating field $H_s$ in superconductors with nanostructured surfaces. Numerical simulations of the Ginzburg-Landau (GL) equations were performed for a superconductor with an inhomogeneous impurity concentration, a thin superconducting layer on top of another superconductor, and superconductor-insulator-superconductor (S-I-S) multilayers. The superheating field was calculated taking into account the instability of the Meissner state with a nonzero wavelength along the surface, which is essential for realistic values of the GL parameter $\kappa$, particularly $\kappa\simeq 1$ for Nb. Simulations were done for the materials parameters of Nb and Nb$_3$Sn at different values of $\kappa$ and the mean free paths. We show that the impurity concentration profile at the surface and thicknesses of S-I-S multilayers can be optimized to enhance $H_s$ above the bulk superheating fields of both Nb and Nb$_3$Sn. For example, a S-I-S structure with 90 nm thick Nb$_3$Sn layer deposited on Nb can boost the superheating field up to $\approx$ 500 mT, while protecting the SRF cavity from dendritic thermomagnetic avalanches caused by local penetration of vortices.
