SRF2011 - List of Authors (Trofimova, O.)

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]

THPO071

Detailed Surface Analysis of Incremental Centrifugal Barrel Polishing (CBP) of Single-Crystal Niobium Samples

908

A.D. Palczewski, C.E. Reece, H. Tian, O. Trofimova
JLAB, Newport News, Virginia, USA

Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
We performed Centrifugal Barrel Polishing (CBP) on single crystal niobium samples housed in a stainless steel sample holder following a polishing recipe recently developed at FNAL [*]. We were able to obtain a mirror-like finish after the final stage of tumbling, although some defects and imbedded particles remain. Our presentation will discuss the initial results from the coupon study, including qualitative and quantitative analysis of the surface characteristics from each step in the CBP process, followed by HPR and well controlled incremental EP. These will include surface roughness, size and character of contaminants, surface crystal structure, and overall finish. We will discuss how the surface characteristics should guide the SRF community in exploiting or adapting the Fermi recipe; including why minimal subsequent EP is needed, and possible places for modification of the recipe to reduce polishing time.
* CA Cooper, LD Cooley , “Mirror Smooth Superconducting RF Cavities by MechanicalPolishing with Minimal Acid Use,” http://lss.fnal.gov/archive/2011/pub/fermilab-pub-11-032-td.pdf, (May 31, 2011)

THPO079

Surface Preparation of Metallic Substrates for Quality SRF Thin Films

936

J.K. Spradlin, O. Trofimova, A-M. Valente-Feliciano
JLAB, Newport News, Virginia, USA

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.
Surface preparation is an essential prerequisite for thin film depositions. Rough or chemically impure surfaces adversely affect the nature of the thin film. Understanding the properties of the substrate and how they influence the quality of the thin film is necessary to transfer thin film deposition technologies to SRF cavity applications. A substrate that is flat, has sufficient grain size, and is chemically pure is the ideal starting point for thin film depositions. A method for copper substrate preparation is reviewed for niobium thin film deposition that provides epitaxy on large and fine grain copper as well as single crystal copper. Preliminary data on niobium and aluminum substrate preparation will also be included.

Poster THPO079 [0.637 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]

THPO071	Detailed Surface Analysis of Incremental Centrifugal Barrel Polishing (CBP) of Single-Crystal Niobium Samples	908
	A.D. Palczewski, C.E. Reece, H. Tian, O. Trofimova JLAB, Newport News, Virginia, USA
	Funding: This work is authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. We performed Centrifugal Barrel Polishing (CBP) on single crystal niobium samples housed in a stainless steel sample holder following a polishing recipe recently developed at FNAL []. We were able to obtain a mirror-like finish after the final stage of tumbling, although some defects and imbedded particles remain. Our presentation will discuss the initial results from the coupon study, including qualitative and quantitative analysis of the surface characteristics from each step in the CBP process, followed by HPR and well controlled incremental EP. These will include surface roughness, size and character of contaminants, surface crystal structure, and overall finish. We will discuss how the surface characteristics should guide the SRF community in exploiting or adapting the Fermi recipe; including why minimal subsequent EP is needed, and possible places for modification of the recipe to reduce polishing time. CA Cooper, LD Cooley , “Mirror Smooth Superconducting RF Cavities by MechanicalPolishing with Minimal Acid Use,” http://lss.fnal.gov/archive/2011/pub/fermilab-pub-11-032-td.pdf, (May 31, 2011)

THPO079	Surface Preparation of Metallic Substrates for Quality SRF Thin Films	936
	J.K. Spradlin, O. Trofimova, A-M. Valente-Feliciano JLAB, Newport News, Virginia, USA
	Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Surface preparation is an essential prerequisite for thin film depositions. Rough or chemically impure surfaces adversely affect the nature of the thin film. Understanding the properties of the substrate and how they influence the quality of the thin film is necessary to transfer thin film deposition technologies to SRF cavity applications. A substrate that is flat, has sufficient grain size, and is chemically pure is the ideal starting point for thin film depositions. A method for copper substrate preparation is reviewed for niobium thin film deposition that provides epitaxy on large and fine grain copper as well as single crystal copper. Preliminary data on niobium and aluminum substrate preparation will also be included.
	Poster THPO079 [0.637 MB]