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Title: Nanostructural features degrading the performance of superconducting radio frequency niobium cavities revealed by transmission electron microscopy and electron energy loss spectroscopy

Nanoscale defect structure within the magnetic penetration depth of ~100 nm is key to the performance limitations of niobium superconducting radio frequency cavities. Using a unique combination of advanced thermometry during cavity RF measurements, and TEM structural and compositional characterization of the samples extracted from cavity walls, we discover the existence of nanoscale hydrides in electropolished cavities limited by the high field Q slope, and show the decreased hydride formation in the electropolished cavity after 120°C baking. Furthermore, we demonstrate that adding 800°C hydrogen degassing followed by light buffered chemical polishing restores the hydride formation to the pre-120°C bake level. We also show absence of niobium oxides along the grain boundaries and the modifications of the surface oxide upon 120°C bake.
 [1] ;  [2] ;  [3] ;  [3] ;  [4]
  1. Illinois Institute of Technology, Chicago, IL (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  2. Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
  3. Univ. of Illinois, Urbana, IL (United States)
  4. Illinois Institute of Technology, Chicago, IL (United States)
Publication Date:
Grant/Contract Number:
AC02-07CH11359; AC02-98CH10886; FG02-01ER45923; AC0298CH10886; DEFG02-01ER45923
Published Article
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 117; Journal Issue: 15; Journal ID: ISSN 0021-8979
American Institute of Physics (AIP)
Research Org:
Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
43 PARTICLE ACCELERATORS; niobium; electron energy loss spectroscopy; grain boundaries; high resolution transmission electron microscopy; selected area electron diffraction
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1214094; OSTI ID: 1420709