SRF2011 - List of Authors (Inman, M.E.)

Paper

Title

Page

Niobium Electropolishing in an Aqueous, Non-Viscous HF-Free Electrolyte: A New Polishing Mechanism

377

M.E. Inman, T.D. Hall, E.J. Taylor
Faraday Technology, Inc., Clayton, USA
C.E. Reece, O. Trofimova
JLAB, Newport News, Virginia, USA

Faraday is working with the Jefferson Lab to develop an improved process for electropolishing niobium RF superconducting cavities in an electrolyte free of hydrofluoric acid, to create microscopically clean and smooth niobium surfaces on the cavity interior. Conventional electropolishing of niobium cavities is based on a viscous electrolyte with an approximately 20 micron thick diffusion layer*, containing hydrofluoric acid as a depassivation agent. The FARADAYIC Electropolishing process combines pulse reverse electric fields and aqueous, low acid, non-viscous electrolytes to control current distribution and oxide film formation during metal removal. This eliminates the need for a depassivation agent, such as hydrofluoric acid. This program is aimed at understanding this new electropolishing mechanism, and optimizing it to achieve the desired oxide formation, reduced defect density and high performance. The feasibility of the process has been demonstrated using an aqueous sulfuric acid solution in conjunction with the FARADAYIC Process to electropolish niobium to surface finishes below 1 nm over a 2 x 2 micron area.
* Hui Tian and Charles E. Reece, Evaluation of the diffusion coefficient of fluorine during the electropolishing of niobium, Phys. Rev. ST Accel. Beams, 13, 083502 (2010)

Poster TUPO012 [1.932 MB]

TUPO017

Development and Scale-Up of an HF Free Electropolishing Process in Single-Cell Niobium SRF Cavities

397

M.E. Inman, H.M. Garich, S.T. Snyder, E.J. Taylor
Faraday Technology, Inc., Clayton, USA
L.D. Cooley, C.A. Cooper, A.M. Rowe
Fermilab, Batavia, USA

The performance of niobium SRF cavities is strongly dependent on a microscopically smooth and clean surface, achieved using buffered chemical polishing or electropolishing, which require a viscous electrolyte containing hydrofluoric acid to achieve niobium oxide breakdown and current distribution control. An ideal polishing process would include: electrolyte free of hydrofluoric acid; control of surface roughness to less than 0.1 micron; surface free from contamination; current distribution control enabling uniform polishing; removal of at least 100 microns. Faraday is working with Fermilab to develop and scale-up the FARADAYIC Electropolishing process to achieve these conditions. FARADAYIC Electropolishing combines pulse reverse electric fields and low viscosity aqueous electrolytes to control current distribution and oxide formation during metal removal. Recent results on coupon polishing will be presented including polishing rates up to 1 micron/min, control of electrolyte temperature to below 20 C, and surface finishes less than 0.2 microns over 4 mm length scales. Construction of a single-cell cavity electropolishing apparatus at Faraday are discussed.

Poster TUPO017 [1.931 MB]

Paper	Title	Page
TUPO012	Niobium Electropolishing in an Aqueous, Non-Viscous HF-Free Electrolyte: A New Polishing Mechanism	377
	M.E. Inman, T.D. Hall, E.J. Taylor Faraday Technology, Inc., Clayton, USA C.E. Reece, O. Trofimova JLAB, Newport News, Virginia, USA
	Faraday is working with the Jefferson Lab to develop an improved process for electropolishing niobium RF superconducting cavities in an electrolyte free of hydrofluoric acid, to create microscopically clean and smooth niobium surfaces on the cavity interior. Conventional electropolishing of niobium cavities is based on a viscous electrolyte with an approximately 20 micron thick diffusion layer, containing hydrofluoric acid as a depassivation agent. The FARADAYIC Electropolishing process combines pulse reverse electric fields and aqueous, low acid, non-viscous electrolytes to control current distribution and oxide film formation during metal removal. This eliminates the need for a depassivation agent, such as hydrofluoric acid. This program is aimed at understanding this new electropolishing mechanism, and optimizing it to achieve the desired oxide formation, reduced defect density and high performance. The feasibility of the process has been demonstrated using an aqueous sulfuric acid solution in conjunction with the FARADAYIC Process to electropolish niobium to surface finishes below 1 nm over a 2 x 2 micron area. Hui Tian and Charles E. Reece, Evaluation of the diffusion coefficient of fluorine during the electropolishing of niobium, Phys. Rev. ST Accel. Beams, 13, 083502 (2010)
	Poster TUPO012 [1.932 MB]

TUPO017	Development and Scale-Up of an HF Free Electropolishing Process in Single-Cell Niobium SRF Cavities	397
	M.E. Inman, H.M. Garich, S.T. Snyder, E.J. Taylor Faraday Technology, Inc., Clayton, USA L.D. Cooley, C.A. Cooper, A.M. Rowe Fermilab, Batavia, USA
	The performance of niobium SRF cavities is strongly dependent on a microscopically smooth and clean surface, achieved using buffered chemical polishing or electropolishing, which require a viscous electrolyte containing hydrofluoric acid to achieve niobium oxide breakdown and current distribution control. An ideal polishing process would include: electrolyte free of hydrofluoric acid; control of surface roughness to less than 0.1 micron; surface free from contamination; current distribution control enabling uniform polishing; removal of at least 100 microns. Faraday is working with Fermilab to develop and scale-up the FARADAYIC Electropolishing process to achieve these conditions. FARADAYIC Electropolishing combines pulse reverse electric fields and low viscosity aqueous electrolytes to control current distribution and oxide formation during metal removal. Recent results on coupon polishing will be presented including polishing rates up to 1 micron/min, control of electrolyte temperature to below 20 C, and surface finishes less than 0.2 microns over 4 mm length scales. Construction of a single-cell cavity electropolishing apparatus at Faraday are discussed.
	Poster TUPO017 [1.931 MB]