CERN Accelerating science

Published Articles
Title	Determining BCP Etch Rate and Uniformity in High Luminosity LHC Crab Cavities
Author(s)	Jones, Thomas (Daresbury ; Lancaster U. (main)) ; Burt, Graeme (Lancaster U. (main)) ; Calaga, Rama (CERN) ; Capatina, Ofelia (CERN) ; Ferreira, Leonel (CERN) ; Leuxe, Raphael (CERN) ; Mitchell, James (Lancaster U. (main)) ; Pattalwar, Shrikant (Daresbury) ; Verdú-Andrés, Silvia (Brookhaven Natl. Lab.) ; Xiao, Binping (Brookhaven Natl. Lab.)
Publication	2018
Number of pages	5
In:	18th International Conference on RF Superconductivity, Lanzhou, China, 17 - 21 Jul 2017, pp.TUPB100
DOI	10.18429/JACoW-SRF2017-TUPB100
Subject category	Accelerators and Storage Rings
Abstract	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 simple 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 200 µm followed by 2 light BCPs of 20 µm each. Subsequent testing has shown performance exceeding required accelerating gradient and Q factor.
Copyright/License	CC-BY-3.0

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