Innovative PVD technologies for depositing superconducting Nb films into TESLA-type 9-cell RF cavities for particle accelerators – Giorgio Keppel PhD Thesis

Author: Giorgio Keppel; Type of thesis: PhD Thesis
Abstract: Superconducting radiofrequency resonators have become standard components inside particle accelerators. This paper proposes the research and development of copper cavities internally coated with a niobium thin film, as an alternative to the niobium bulk cavities. This R&D work is part of the ISIDE experiment, of the National Institute of Nuclear Physics, and has been carried out at the Legnaro laboratories. Specifically, at the Material Science and Technologies for Nuclear Physics Service of INFN, it has been built a new system for coating, via magnetron sputtering, a thin film of superconducting niobium inside the TESLA-type 9-cell copper resonators. The work was divided into two main areas. A first phase consisted on the design of a sputtering configuration for coating superconductive cavities based on the construction of a vacuum system using a 3D CAD software and FEM simulations in order to verify the final structure of the vacuum system. Parallel to this a phase for the construction of the induction heating apparatus was followed. Afterward, the assembly of the vacuum system was performed, with connected vacuum tests, and followed by the commissioning of the induction and pumping systems. A second phase, however, focused on the study of coating configurations, particularly on the benefits and/or problems that each configuration can lead. This study ended with the design of four different coating configurations; which will be short-tested in order to check the most suitable for coating the 9-cell copper cavity with good uniformity and excellent superconducting properties. The most promising configuration is definitely the last taken into account, which involves the use of the inductor to heat the cavity during the process and the use of an innovative cylindrical magnetron with a rotating magnet pack inside that confine the plasma on the target surface. The target consists on a Niobium tube, and the study of the magnetic configuration and at the same time rotation of magnet pack permit to have a constant deposition rate along the whole cavity (high cathode erosion rate in the cavity cell regions and low cathode erosion rate along cavity cut-off). Even if the work is still evolving and the deposition tests are just starting, what as been performed is definitely innovative and original; up to now, in literature, there are no reports of coating performed by coupling the induction heating with the magnetron sputtering. The development of a plant that allows coupling these two technologies is the main aim of this work.