Characterization of scale-dependent roughness of niobium surfaces as a function of surface treatment processes

Conference · Fri Jun 01 04:00:00 EDT 2012

OSTI ID:1994843

Reece, Charles; Xu, Chen; Tian, Hui; Kelley, Michael

Micro-roughness is attributed to be a critical issue for realizing optimum performance of Superconducting Radio Frequency (SRF) cavities. Several surface processing methods such as chemical, mechanical and plasma, are used to obtain relatively smooth surfaces. Among those process methods, Buffered Chemical Polish (BCP) and Electro-Polishing (EP) are most commonly used in current niobium cavity production. The topography of such surfaces are can be very well characterized by Atomic Force Microscopy (AFM). The Power Spectral Density (PSD) of surface height data provides a more thorough description to the topography than a simple Rq (RMS) measurement and reveals useful information about the surface including fractal and superstructure contributions. It has been noticed that polishing conditions such as processing duration and temperature can have predictable effects on the evolution of fractal features and superstructures at different scale regions in PSD spectrum in this present study. In this work, 1 dimensional average PSD functions derived from morphologies of niobium surfaces treated by BCP and EP with different controlled starting conditions and durations have been fitted with a combination of fractal, K-correlation and shifted Gaussian models, to extract characteristic parameters of the precision surfaces at different spatial harmonic scales. Analyzing such local roughness parameters, plausible explanations on such processes are given in detail.

• Research Organization: Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Nuclear Physics (NP)
• DOE Contract Number: AC05-06OR23177
• OSTI ID: 1994843
• Report Number(s): JLAB-ACC-11-1531; DOE/OR/23177-6952
• Country of Publication: United States
• Language: English