Niobium near-surface composition during nitrogen infusion relevant for superconducting radio-frequency cavities
G. D. L. Semione, A. Dangwal Pandey, S. Tober, J. Pfrommer, A. Poulain, J. Drnec, G. Schütz, T. F. Keller, H. Noei, V. Vonk, B. Foster, A. Stierle
DOI 10.1103/PhysRevAccelBeams.22.103102 · Physical Review Accelerators and Beams
Active bibliographic source — not scientific approval
Bibliographic access preserves source history; it does not approve extracted materials or validate reported claims. Review warnings on each occurrence separately.
Abstract
A detailed study of the near-surface structure and composition of Nb, the material of choice for superconducting radio-frequency accelerator (SRF) cavities, is of great importance in order to understand the effects of different treatments applied during cavity production. By means of surface-sensitive techniques such as grazing incidence diffuse x-ray scattering, x-ray reflectivity, and x-ray photoelectron spectroscopy, single-crystalline Nb(100) samples were investigated in and ex situ during annealing in an ultrahigh vacuum as well as in nitrogen atmospheres with temperatures and pressures similar to the ones employed in real Nb cavity treatments. Annealing of Nb specimens up to 800 °C in a vacuum promotes a partial reduction of the natural surface oxides (Nb2O5, NbO2, and NbO) into NbO. Upon cooling to 120°C, no evidence of nitrogen-rich layers was detected after nitrogen exposure times of up to 48 h. An oxygen enrichment below the Nb-oxide interface and posterior diffusion of oxygen species towards the Nb matrix, along with a partial reduction of the natural surface oxides, was observed upon a stepwise annealing up to 250 °C. Nitrogen introduction to the system at 250 °C promotes neither N diffusion into the Nb matrix nor the formation of new surface layers. Upon further heating to 500 °C in a nitrogen atmosphere, the growth of a new subsurface NbxNy layer was detected. These results shed light on the composition of the near-surface region of Nb after low-temperature nitrogen treatments, which are reported to lead to a performance enhancement of SRF cavities.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| Nb Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 9.25 | Pressure unresolved | unknown |
Similar papers
Universal behavior of the intermediate mixed state domain formation in superconducting niobium
similarity 0.95A. Backs et al.
Source status unknown — claims are unverified
Thermal feedback in coaxial superconducting radio frequency cavities
similarity 0.95Mattias McMullin et al.
Source status unknown — claims are unverified
Laser polishing of niobium for superconducting radio-frequency accelerator applications
similarity 0.95Liang Zhao et al.
Source status unknown — claims are unverified
Equilibrium properties of superconducting niobium at high magnetic fields: A possible existence of a filamentary state in type-II superconductors
similarity 0.94V. Kozhevnikov et al.
Source status unknown — claims are unverified
First experience with He conditioning of a superconducting rf photoinjector
similarity 0.94I. Petrushina et al.
Source status unknown — claims are unverified
Niobium's intrinsic coherence length and penetration depth revisited using low-energy muon spin spectroscopy and secondary-ion mass spectrometry
similarity 0.93Ryan M. L. McFadden et al.
Source status unknown — claims are unverified