A novel approach to characterizing the surface topography of niobium superconducting radio frequency (SRF) accelerator cavities

Journal Article · Tue Mar 01 04:00:00 EST 2011 · Applied Surface Science

DOI:https://doi.org/10.1016/j.apsusc.2010.11.159· OSTI ID:1028732

As superconducting niobium radio-frequency (SRF) cavities approach fundamental material limits, there is increased interest in understanding the details of topographical influences on realized performance limitations. Micro- and nano-roughness are implicated in both direct geometrical field enhancements as well as complications of the composition of the 50 nm surface layer in which the super-currents typically flow. Interior surface chemical treatments such as buffered chemical polishing (BCP) and electropolishing (EP) used to remove mechanical damage leave surface topography, including pits and protrusions of varying sharpness. These may promote RF magnetic field entry, locally quenching superconductivity, so as to degrade cavity performance. A more incisive analysis of surface topography than the widely used average roughness is needed. In this study, a power spectral density (PSD) approach based on Fourier analysis of surface topography data acquired by both stylus profilometry and atomic force microscopy (AFM) is introduced to distinguish the scale-dependent smoothing effects, resulting in a novel qualitative and quantitative description of Nb surface topography. The topographical evolution of the Nb surface as a function of different steps of well-controlled EP is discussed. This study will greatly help to identify optimum EP parameter sets for controlled and reproducible surface levelling of Nb for cavity production.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1028732
• Report Number(s): JLAB-FEL-11-1412; DOE/OR/23177-1876
• Journal Information: Applied Surface Science, Journal Name: Applied Surface Science Journal Issue: 11 Vol. 257; ISSN ASUSEE; ISSN 0169-4332
• Country of Publication: United States
• Language: English

Related Subjects

43 PARTICLE ACCELERATORS
ACCELERATORS
ATOMIC FORCE MICROSCOPY
CHEMICAL POLISHING
DAMAGE
ELECTROPOLISHING
FOURIER ANALYSIS
FUNCTIONS
LAYERS
MAGNETIC FIELDS
NIOBIUM
PERFORMANCE
QUENCHING
RF SYSTEMS
ROUGHNESS
SPECTRAL DENSITY
SPECTROSCOPY
SUPERCONDUCTING CAVITY RESONATORS
SUPERCONDUCTIVITY
SURFACE TREATMENTS
SURFACES
TOPOGRAPHY