Analysis of Thermal Grooving Effects on Vortex Penetration in Vapor-Diffused Nb3Sn

TL;DR

This study investigates how thermal grooving in vapor-diffused Nb3Sn coatings affects vortex penetration, revealing that increased coating duration deepens grooves and reduces the maximum achievable RF magnetic field in superconducting cavities.

Contribution

It provides a detailed analysis of how thermal grooving impacts vortex penetration and limits performance in Nb3Sn-coated RF cavities, highlighting the role of coating duration.

Findings

Thermal grooving increases with coating duration.

Grooves act as defects reducing the superheating field.

Longer coating times deepen thermal grooves.

Abstract

While Nb3Sn theoretically offers better superconducting RF cavity performance (Q0 and Eacc) to Nb at any given temperature, peak RF magnetic fields consistently fall short of the 400 mT prediction. The relatively rough topography of vapor-diffused Nb3Sn is widely conjectured to be one of the factors that limit the attainable performance of Nb3Sn-coated Nb cavities prepared via Sn vapor diffusion. Here we investigate the effect of coating duration on the topography of vapor-diffused Nb3Sn on Nb and calculate the associated magnetic field enhancement and superheating field suppression factors using atomic force microscopy topographies. It is shown that the thermally grooved grain boundaries are major defects which may contribute to a substantial decrease in the achievable accelerating field. The severity of these grooves increases with total coating duration due to the deepening of thermal grooves during the coating process.