Abstract
Niobium thin film coated copper superconducting radio frequency elliptical cavities have demonstrated for many years their strong potential as an alternative to bulk niobium cavities. The thin film lower performance at high rf field is often attributed to the defects observed in the elaborated Nb layer, sometimes originated from defects inherited from the substrate itself. The currently used methods of manufacturing the copper elliptical substrates include several steps of electron-beam welding in order to join the half cells and the cutoffs which can contribute to defects and porosities. Seamless methods are nowadays developed in order to avoid welding steps and to decrease the global manufacturing cost of the cavities. We propose in this study an innovative alternative route in which the cavity is formed by electrodeposition of copper on a sacrificial aluminum mandrel. The strength of the process relies on the total absence of welding joints. Two different electroforming techniques using either direct current or pulsed plating have been investigated. The electroformed copper exhibited similar mechanical robustness, cryogenic properties and purity as the oxygen-free copper. In addition, the fabrication process was validated on test mandrels which mimic the geometry of 1.3 GHz cavities.
Highlights
Radio frequency cavities are resonant devices used in particle accelerators to accelerate charged particle beams
At CERN, Nb coating on copper technology was developed and was successfully used for the production of cavities for the Large Electron Positron Collider (LEP) and was chosen again for the quarter wave resonators (QWR) fabrication of the HIE-ISOLDE beam facility [4]
The bottleneck of Nb thin films is the strong increase of surface resistance as a function of the rf field amplitude which makes the technology adapted only to low-accelerating gradient
Summary
Radio frequency cavities are resonant devices used in particle accelerators to accelerate charged particle beams. Very good performance is obtained from massive niobium cavities which have a very low surface resistance [1]. The high cost of niobium triggered the research of less expensive and more efficient cavity fabrication methods as, for example, through the use of thin films [2,3]. At CERN, Nb coating on copper technology was developed and was successfully used for the production of cavities for the Large Electron Positron Collider (LEP) and was chosen again for the quarter wave resonators (QWR) fabrication of the HIE-ISOLDE beam facility [4]. The bottleneck of Nb thin films is the strong increase of surface resistance as a function of the rf field amplitude which makes the technology adapted only to low-accelerating gradient
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