Conveners
Fundamental Studies: Session 1
- Nathan Sitaraman (Cornell University)
Fundamental Studies: Session 2
- Michelle Kelley (Cornell)
Low BCS surface resistance and large superheating field make Nb3Sn a very attractive material for low-field SRF applications. At the same time, the performance of Nb3Sn at high RF fields can be limited by current-blocking grain boundaries, small lower critical magnetic field, poor thermal conductivity and high resistivity, which make Nb3Sn prone to premature penetration of vortices and...
Interest in Nb3Sn as a material for SRF cavities is driven by its potential to operate at higher temperatures with higher quality factors and accelerating fields. In practice, performance is limited by magnetic flux that is nucleated at defects and inhomogeneities on the scale of the superconducting coherence length. Because Nb3Sn has a small coherence length, it presents many fundamental...
We use Floquet theory to describe dynamics and losses of superconductors under extremely high fields and frequencies.Periodically driven superconductors at high fields provide an unexplored theoretical territory relevant in modern applications (lower cryogenic costs for particle accelerators), allowing for experimental validation using Superconducting Radio Frequency (SRF) cavities. We use the...
Point defects play a critical role in Nb$_3$Sn superconducting radio frequency (SRF) cavity physics. Using $\textit{ab initio}$ techniques, we can calculate key properties of defects including formation and interaction free energies, hopping barriers, and their effect on $T_c$. Here we will focus on the experimentally-relevant cases of antisite defects and oxygen and hydrogen interstitial...
We present the first comprehensive study of grain boundaries in Nb$_3$Sn from first principles. While most conventional superconductors, such as Nb, are not significantly impacted by the presence of grain boundaries, Nb$_3$Sn is much more sensitive to defects and disorder owing to its relatively short coherence length of ~3 nm. Indeed, experiments suggest a link between grain-boundary...
Incorporating nanoparticles into superconducting materials has been established as an efficient route to enhance their current-carrying capability. We explored vortex pinning by randomly distributed spherical nanoparticles using large-scale numerical simulations of time-dependent Ginzburg-Landau equations. First, we investigated a vortex lattice interacting with an isolated defect [1]. We...
Tunneling spectroscopy measurements were carried out at ANL and CEA on Nb3Sn/Nb samples made at Cornell and FNAL with différent growth conditions. We find a linear correlation between the average gap extracted from maps of the Density of states few hundreds microns of lateral size and the corresponding RF cavity tests made under the same conditions as the samples.
Superconducting Radio Frequency (SRF) cavities are being widely used in new generation particle accelerators, but their performance can be limited by surface defects which lead to cavity breakdown at high accelerating gradients. The microscopic origins of SRF cavity breakdown are still a matter of some debate. To study the electrodynamics of superconductors locally, a novel near-field magnetic...
Nb3Sn is currently the most promising material other than niobium for future superconducting radiofrequency (SRF) cavities. To achieve high accelerating gradient, the behavior of Nb3Sn thin films in an external magnetic field should be studied. The magnetic field at first flux penetration is one of the key physical parameters to characterize them. Therefore, it is important to have a simple,...
The field of first vortex penetration was measured on Nb$_3$Sn samples under DC and RF fields using the muon spin rotation technique and a quadrupole resonator. Those methods also enabled direct and indirect measurements of the London penetration depth from which the lower critical field and the superheating field are derived. The combined results confirm that Nb$_3$Sn cavities are indeed...
