SRF Theory Developments from the Center for Bright Beams

TL;DR

This paper presents theoretical and computational studies on superconducting radio frequency (SRF) materials, focusing on disorder effects, vortex nucleation, and material growth processes, aiming to improve SRF cavity performance.

Contribution

It integrates multiple theoretical approaches to understand SRF material limitations and proposes strategies for enhancing cavity quality through material processing insights.

Findings

Disorder affects maximum surface field in SRF cavities.

Inhomogeneities influence vortex nucleation and residual resistance.

DFT reveals mechanisms of tin-depleted region formation in Nb$_3$Sn.

Abstract

We present theoretical studies of SRF materials from the Center for Bright Beams. First, we discuss the effects of disorder, inhomogeneities, and materials anisotropy on the maximum parallel surface field that a superconductor can sustain in an SRF cavity, using linear stability in conjunction with Ginzburg-Landau and Eilenberger theory. We connect our disorder mediated vortex nucleation model to current experimental developments of Nb$_3$Sn and other cavity materials. Second, we use time-dependent Ginzburg-Landau simulations to explore the role of inhomogeneities in nucleating vortices, and discuss the effects of trapped magnetic flux on the residual resistance of weakly- pinned Nb$_3$Sn cavities. Third, we present first-principles density-functional theory (DFT) calculations to uncover and characterize the key fundamental materials processes underlying the growth of Nb$_3$Sn. Our calculations give us key information about how, where, and when the observed tin-depletedregions form. Based on this we plan to develop new coating protocols to mitigate the formation of tin depleted regions.