SRF2017 - List of Authors (Ferreira, L.M.A.)

Paper	Title	Page
TUPB078	SUBU Characterisation: Bath Fluid Dynamics vs Etching Rate	575
	A. Perez Rodriguez, L.M.A. Ferreira, A. Sublet CERN, Geneva, Switzerland
	The chemical polishing bath SUBU is widely used at CERN to prepare copper RF cavities surfaces before niobium thin film coating; examples are HIE-ISOLDE, LHC and future FCC accelerating cavities. The performance of the polishing process is affected by bath temperature and fluid dynamics. As part of on-going activities to characterise SUBU, the actual study was done to identify a correlation between the etching rate and physical parameters linked to the bath fluid dynamics. A first approach was made using experimental data from a simplified model setup, transposing them via numerical simulation to a real cavity geometry and verifying the agreement with an experiment in a real size (HIE-ISOLDE) mock-up. In a second approach to improve the accuracy of the calculation, the relation of the measured local etching rates, extracted from the mock-up, to flow dynamics quantities extracted from simulation was investigated. As a result, a correlation between the local etching rate and the turbulence kinetic energy was obtained. This correlation can be exploited to improve the polishing tools and so optimise the current process, as well as to predict the etching rate in other cavity geometries.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB078
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TUPB100	Determining BCP Etch Rate and Uniformity in High Luminosity LHC Crab Cavities	635
	T.J. Jones STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom G. Burt Cockcroft Institute, Lancaster University, Lancaster, United Kingdom R. Calaga, O. Capatina, L.M.A. Ferreira, R. Leuxe CERN, Geneva, Switzerland T.J. Jones, J.A. Mitchell Lancaster University, Lancaster, United Kingdom S.M. Pattalwar STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Verdú-Andrés, B. P. Xiao BNL, Upton, Long Island, New York, USA
	The compact SRF Crab Cavities required for HL-LHC have complex geometries making prediction of average and local BCP etch rates a difficult task. This paper describes a series of experiments and simulations used to determine the etch uniformity and rate within these structures. An initial experiment was conducted to determine the correlation between etch rate and flow rate in a Nb tube. These results were then incorporated into Computational Fluid Dynamics simulations of acid flow in the Double Quarter Wave (DQW) cavity to predict etch rates across the surface and allow optimisation of the BCP setup. There were several important findings from the work; one of which is that the flow rate in the relatively large body of the cavity is predominantly driven by natural convection due to the exothermic reaction. During BCP processing of the DQW cavity a significant difference in etching was observed between upper and lower horizontal surfaces which was mitigated by etching in several orientations. Two DQW cavities manufactured by CERN have received a heavy BCP of 200μm followed by 2 light BCPs of 30μm each with subsequent vertical cold tests showing performance exceeding specification.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB100
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

SUBU Characterisation: Bath Fluid Dynamics vs Etching Rate

575

A. Perez Rodriguez, L.M.A. Ferreira, A. Sublet
CERN, Geneva, Switzerland

The chemical polishing bath SUBU is widely used at CERN to prepare copper RF cavities surfaces before niobium thin film coating; examples are HIE-ISOLDE, LHC and future FCC accelerating cavities. The performance of the polishing process is affected by bath temperature and fluid dynamics. As part of on-going activities to characterise SUBU, the actual study was done to identify a correlation between the etching rate and physical parameters linked to the bath fluid dynamics. A first approach was made using experimental data from a simplified model setup, transposing them via numerical simulation to a real cavity geometry and verifying the agreement with an experiment in a real size (HIE-ISOLDE) mock-up. In a second approach to improve the accuracy of the calculation, the relation of the measured local etching rates, extracted from the mock-up, to flow dynamics quantities extracted from simulation was investigated. As a result, a correlation between the local etching rate and the turbulence kinetic energy was obtained. This correlation can be exploited to improve the polishing tools and so optimise the current process, as well as to predict the etching rate in other cavity geometries.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB078

Export •

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

TUPB100

Determining BCP Etch Rate and Uniformity in High Luminosity LHC Crab Cavities

635

T.J. Jones
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
G. Burt
Cockcroft Institute, Lancaster University, Lancaster, United Kingdom
R. Calaga, O. Capatina, L.M.A. Ferreira, R. Leuxe
CERN, Geneva, Switzerland
T.J. Jones, J.A. Mitchell
Lancaster University, Lancaster, United Kingdom
S.M. Pattalwar
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
S. Verdú-Andrés, B. P. Xiao
BNL, Upton, Long Island, New York, USA

The compact SRF Crab Cavities required for HL-LHC have complex geometries making prediction of average and local BCP etch rates a difficult task. This paper describes a series of experiments and simulations used to determine the etch uniformity and rate within these structures. An initial experiment was conducted to determine the correlation between etch rate and flow rate in a Nb tube. These results were then incorporated into Computational Fluid Dynamics simulations of acid flow in the Double Quarter Wave (DQW) cavity to predict etch rates across the surface and allow optimisation of the BCP setup. There were several important findings from the work; one of which is that the flow rate in the relatively large body of the cavity is predominantly driven by natural convection due to the exothermic reaction. During BCP processing of the DQW cavity a significant difference in etching was observed between upper and lower horizontal surfaces which was mitigated by etching in several orientations. Two DQW cavities manufactured by CERN have received a heavy BCP of 200μm followed by 2 light BCPs of 30μm each with subsequent vertical cold tests showing performance exceeding specification.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2017-TUPB100

Export •

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