skip to main content

DOE PAGESDOE PAGES

Title: Determination of bulk and surface superconducting properties of N2-doped cold worked, heat treated and electro-polished SRF grade niobium

In this study, nitrogen-doped cavities show significant performance improvement in the medium accelerating field regime due to a lowered RF surface resistivity. However, the mechanism of enhancement has not been clearly explained. Our experiments explore how N2-doping influences Nb bulk and surface superconducting properties, and compare the N2-doped properties with those obtained previously with conventionally treated samples. High purity Nb-rod was mechanically deformed and post treated based on a typical SRF cavity treatment recipe. The onset of flux penetration at Hc1, and the upper and the surface critical fields, Hc2 and Hc3, were characterized by magnetic hysteresis and AC susceptibility techniques. The surface depth profile responsible for superconductivity was examined by changing AC amplitude in AC susceptibility, and the microstructure was directly observed with EBSD-OIM. We are also investigating surface chemistry for detailed composition using XPS. We have found that N2-doping at 800 °C significantly reduces the Hc3/Hc2 ratio towards the ideal value of ~1.7, and conclude that AC susceptibility is capable of following changes to the surface properties induced by N2-doping.
Authors:
 [1] ;  [1] ;  [1] ;  [2] ;  [3]
  1. Florida State Univ., Tallahassee, FL (United States)
  2. Thomas Jefferson National Accelerator Facility (TJNAF), Newport News, VA (United States)
  3. United States Steel Research and Technology Center, Pittsburgh, PA (United States)
Publication Date:
OSTI Identifier:
1244545
Grant/Contract Number:
SC0009960
Type:
Accepted Manuscript
Journal Name:
Proc. of International Conference on RF Superconductivity
Additional Journal Information:
Conference: SRF15, Whistler, BC (Canada), 13-18 Sept 2015
Research Org:
Florida State Univ., Tallahassee, FL (United States)
Sponsoring Org:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; 43 PARTICLE ACCELERATORS SRF cavities; Nb, N-doping; superconductivity; AC susceptibility