SRF2021 - List of Authors (Ring, T.J.)

Paper	Title	Page
SUPCAV016	Studies on the Fundamental Mechanisms of Niobium Electropolishing	50
	E.A.S. Viklund, D.N. Seidman NU, Evanston, Illinois, USA L. Grassellino, S. Posen, T.J. Ring Fermilab, Batavia, Illinois, USA
	To improve the superconducting performance of niobium SRF cavities, electropolishing (EP) with a sulfuric and hydroflouric acid mixture is used. The chemistry of this reaction is complex due to the interactions between diffusion mechanisms, surface oxide structure, and multiple chemical species. Past studies on the EP process have produced a certain set of optimum parameters that have been used successfully for a long time. However, two recent developments have called the efficacy of the existing EP process into question. Since the introduction of nitrogen doping the surface quality of some cavities has been very poor. Also, EP performed at colder than standard temperatures leads to an increase in the cavity performance. To understand these questions, we perform a multivariate study on the EP process using niobium test samples electropolished at different temperatures and potentials. We find that electropolishing at lower potentials leads to rough surface features such as pitting and grain etching. Some of the surface features show similarities to features seen in niobium cavities. The effect of electropolishing temperature is not clear based on the results of this study.
	Poster SUPCAV016 [2.452 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2021-SUPCAV016
About •	Received ※ 22 June 2021 — Revised ※ 21 August 2021 — Accepted ※ 29 September 2021 — Issue date ※ 15 November 2021
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPTEV012	Extra-Cold EP Process at Fermilab	230
	F. Furuta, D.J. Bice, M. Martinello, T.J. Ring Fermilab, Batavia, Illinois, USA
	FNAL has established a cold Electro-Polishing (EP) method which maintains the outer surface temperature of cavity cell around 12~15°C during EP process. Cold EP has been applied on the various SRF cavities and contributed to achieve high RF performances with them. To investigate more feasibility and capability of EP at lower temperature, the FNAL EP temperature control tool was recently improved. Extra-cold EP process below 0°C at cavity cell region was successfully performed on 1.3 GHz 1-cell cavity. A compatible RF performance with cold EP method was also demonstrated during the cavity vertical testing. The details of extra-cold EP process and the cavity test results will be presented.
	Poster MOPTEV012 [2.038 MB]
DOI •	reference for this paper ※ doi:10.18429/JACoW-SRF2021-MOPTEV012
About •	Received ※ 21 June 2021 — Accepted ※ 14 December 2021 — Issue date ※ 16 May 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Studies on the Fundamental Mechanisms of Niobium Electropolishing

50

E.A.S. Viklund, D.N. Seidman
NU, Evanston, Illinois, USA
L. Grassellino, S. Posen, T.J. Ring
Fermilab, Batavia, Illinois, USA

To improve the superconducting performance of niobium SRF cavities, electropolishing (EP) with a sulfuric and hydroflouric acid mixture is used. The chemistry of this reaction is complex due to the interactions between diffusion mechanisms, surface oxide structure, and multiple chemical species. Past studies on the EP process have produced a certain set of optimum parameters that have been used successfully for a long time. However, two recent developments have called the efficacy of the existing EP process into question. Since the introduction of nitrogen doping the surface quality of some cavities has been very poor. Also, EP performed at colder than standard temperatures leads to an increase in the cavity performance. To understand these questions, we perform a multivariate study on the EP process using niobium test samples electropolished at different temperatures and potentials. We find that electropolishing at lower potentials leads to rough surface features such as pitting and grain etching. Some of the surface features show similarities to features seen in niobium cavities. The effect of electropolishing temperature is not clear based on the results of this study.

Poster SUPCAV016 [2.452 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2021-SUPCAV016

About •

Received ※ 22 June 2021 — Revised ※ 21 August 2021 — Accepted ※ 29 September 2021 — Issue date ※ 15 November 2021

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

MOPTEV012

Extra-Cold EP Process at Fermilab

230

F. Furuta, D.J. Bice, M. Martinello, T.J. Ring
Fermilab, Batavia, Illinois, USA

FNAL has established a cold Electro-Polishing (EP) method which maintains the outer surface temperature of cavity cell around 12~15°C during EP process. Cold EP has been applied on the various SRF cavities and contributed to achieve high RF performances with them. To investigate more feasibility and capability of EP at lower temperature, the FNAL EP temperature control tool was recently improved. Extra-cold EP process below 0°C at cavity cell region was successfully performed on 1.3 GHz 1-cell cavity. A compatible RF performance with cold EP method was also demonstrated during the cavity vertical testing. The details of extra-cold EP process and the cavity test results will be presented.

Poster MOPTEV012 [2.038 MB]

DOI •

reference for this paper ※ doi:10.18429/JACoW-SRF2021-MOPTEV012

About •

Received ※ 21 June 2021 — Accepted ※ 14 December 2021 — Issue date ※ 16 May 2022

Cite •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)