CERN Accelerating science

Published Articles
Report number	CERN-ACC-2015-228
Title	Characterization of Nb Coating in HIE-ISOLDE QWR Superconducting Accelerating Cavities by means of SEM-FIB and TEM
Author(s)	Bártová, Barbora (CERN) ; Aebersold, Arthur (Ecole Polytechnique, Lausanne) ; Alexander, Duncan (Ecole Polytechnique, Lausanne) ; Calatroni, Sergio (CERN) ; Cantoni, Marco (Ecole Polytechnique, Lausanne) ; Sublet, Alban (CERN) ; Taborelli, Mauro (CERN)
Publication	2015
Number of pages	4
In:	6th International Particle Accelerator Conference, Richmond, VA, USA, 3 - 8 May 2015, pp.WEPHA022
Subject category	Accelerators and Storage Rings
Accelerator/Facility, Experiment	CERN ISOLDE
Abstract	The Quarter Wave Resonators (QWR) high-β cavities (0.3m diameter and 0.9m height) are made from OFE 3D-forged copper and are coated by DC-bias diode sputtering with a thin superconducting layer of niobium. The Nb film thickness, morphology, purity and quality are critical parameters for RF performances of the cavity. They have been investigated in a detailed material study. The coating structure at different positions along a test cavity was observed by cross-section imaging using SEM-FIB instrument. The samples from the top of the cavity showed presence of unexpected porosities, whose volume was investigated using FIB tomography. TEM lamella was prepared for two samples (top part and inner conductor of the cavity) to study in detail the grain orientation in the coating, its chemical composition and structure. The 14-layer structure in thick coating was indeed evidenced by the TEM analysis. Chemical mapping revealed the presence of a few nm in size copper precipitates close to the Nb/Cu interface and a passivating oxide layer of 10 nm thickness on top of the coating and around porosities. However no impurities or interface layer along the coating profile were present.
Copyright/License	publication: © 2015-2025 The Author(s) (License: CC-BY-3.0)

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