AVS 53rd International Symposium
    Applied Surface Science Thursday Sessions
       Session AS-ThA

Paper AS-ThA5
Multi-Technique Characterization of Niobium Surfaces for Superconducting Radio Frequency (SRF) Accelerators

Thursday, November 16, 2006, 3:20 pm, Room 2005

Session: Combined Methods or Multiple Methods
Presenter: H. Tian, College of William & Mary
Authors: H. Tian, College of William & Mary
C.E. Reece, Thomas Jefferson National Accelerator Facility
M.J. Kelley, College of William & Mary
S. Wang, Boston University
L. Plucinski, Boston University
K.E. Smith, Boston University
M.M. Nowell, Edax Tsl
Correspondent: Click to Email
The accelerator structure for the proposed International Linear Collider (ILC) comprises more than 20,000 Nb cavities operating at 2 K, and having a total internal surface area in excess of 16,000 m2. Upgrade of Jefferson Lab's CEBAF accelerator from 6 GeV to 12 GeV is about to begin. It will require 80 new cavities and will be preceded by refurbishment of about 40 of the original 338. Other applications of RF superconductivity to particle accelerators are being actively explored. The shallow microwave penetration (with local electric fields exceeding 55 MV/m) causes superconducting RF accelerator performance to be strongly influenced by the chemistry, topography and structure of the top several nanometers of the internal surface.@footnote 1@ These are substantially determined by post-fabrication etching and conditioning. We examined single and polycrystal Nb material , etched by chemical polishing and electropolishing and post-treated by extended low-temperature baking at ultra high vacuum condition which are commonly used for cavity production. The combined use of XPS, synchrotron-based (variable photon energy) photoemission, atomic force microscopy (AFM), stylus profilometry and electron backscatter diffraction (EBSD) provides key insights into the effect of post-fabrication treatments on the Nb surface. The improved knowledge of materials aspects of RF superconductivity provides a stronger foundation for future major accelerator projects. @FootnoteText@ @footnote 1@ H. Padamsee, J. Knobloch, T. Hays; RF Superconductivity for Accelerators, Wiley, New York, (1998).