SRF2011 - List of Authors (Xu, C.)

Paper	Title	Page
THPO046	Characterization of Scale-Dependent Roughness of Niobium Surfaces as a Function of Surface Treatment Processes	832
	C. Xu, M.J. Kelley The College of William and Mary, Williamsburg, USA C.E. Reece, H. Tian JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. 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 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 including fractal and superstructure contributions. Polishing duration and temperature can have predictable effects on the evolution of such features at different scale regions in PSD spectrum. 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 at different spatial harmonic scales.

THPO073	Laser Melt Smoothing of Niobium Superconducting Radio-Frequency Cavity Surfaces	917
	S. Singaravelu, M.J. Kelley, J.M. Klopf, G.A. Krafft JLAB, Newport News, Virginia, USA C. Xu The College of William and Mary, Williamsburg, USA
	Superconducting Radio Frequency (SRF) niobium cavities are at the heart of an increasing number of particle accelerators. Their performance is dominated by a several nm thick layer at the interior surface. Maximizing the smoothness of this surface is critical and aggressive chemical treatments are now employed to this end. We describe laser-induced surface melting as an alternative “greener” approach. Modeling predicts the surface temperature as a function of per-pulse energy density. Guided selection of laser parameters achieves melting that reduces the surface roughness and may also mitigate surface damage from the fabrication process. The resulting topography was examined by SEM, and AFM. PSD spectra computed from AFM data were used for studying the topography of the treated niobium.

Paper

Title

Page

Characterization of Scale-Dependent Roughness of Niobium Surfaces as a Function of Surface Treatment Processes

832

C. Xu, M.J. Kelley
The College of William and Mary, Williamsburg, USA
C.E. Reece, H. Tian
JLAB, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
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 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 including fractal and superstructure contributions. Polishing duration and temperature can have predictable effects on the evolution of such features at different scale regions in PSD spectrum. 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 at different spatial harmonic scales.

THPO073

Laser Melt Smoothing of Niobium Superconducting Radio-Frequency Cavity Surfaces

917

S. Singaravelu, M.J. Kelley, J.M. Klopf, G.A. Krafft
JLAB, Newport News, Virginia, USA
C. Xu
The College of William and Mary, Williamsburg, USA

Superconducting Radio Frequency (SRF) niobium cavities are at the heart of an increasing number of particle accelerators. Their performance is dominated by a several nm thick layer at the interior surface. Maximizing the smoothness of this surface is critical and aggressive chemical treatments are now employed to this end. We describe laser-induced surface melting as an alternative “greener” approach. Modeling predicts the surface temperature as a function of per-pulse energy density. Guided selection of laser parameters achieves melting that reduces the surface roughness and may also mitigate surface damage from the fabrication process. The resulting topography was examined by SEM, and AFM. PSD spectra computed from AFM data were used for studying the topography of the treated niobium.