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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.
Authors:
 [1] ;  [2] ;  [3] ; ;  [4] ;  [1]
  1. Physics Department, Illinois Institute of Technology, Chicago, Illinois 60616 (United States)
  2. (United States)
  3. Fermi National Accelerator Laboratory, Batavia, Illinois 60510 (United States)
  4. Materials Science and Engineering Department, University of Illinois, Urbana, Illinois 61801 (United States)
Publication Date:
OSTI Identifier:
22402881
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 15; Other Information: (c) 2015 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 77 NANOSCIENCE AND NANOTECHNOLOGY; CHEMICAL POLISHING; DEGASSING; ELECTRONS; ENERGY-LOSS SPECTROSCOPY; GRAIN BOUNDARIES; HYDRIDES; HYDROGEN; MODIFICATIONS; NANOSTRUCTURES; NIOBIUM; NIOBIUM OXIDES; PENETRATION DEPTH; PERFORMANCE; RADIOWAVE RADIATION; SURFACES; TRANSMISSION ELECTRON MICROSCOPY; VISIBLE RADIATION