Superconducting RF accelerating cavities are at the heart of modern accelerators. Today, there are two main technologies for their realisation: bulk Nb and thin SC film coated cavities. Bulk Nb is mainstream and several industries offer off the shelf systems, while the expertise on coated cavities is presently only available in large laboratories. In the past, it was possible to transfer successfully the series production of sputtered Nb on copper cavities for LEP2 to the European industry. Nb/Cu was employed in several accelerators, including the LHC. It is a particularly valid alternative to bulk Nb for low frequencies and 4.5 K operation, as opposed to superfluid helium cooling.
Coated cavities have a huge unexplored potential and are still a subject of R/D in several labs around the world. As RF currents only penetrate a thin layer of a few hundreds of nm, films offer the advantage of decoupling the functions of the superconducting surface to those of the substrate. The latter should have excellent heat transfer properties, while superconductors are inherently bad thermal conductors. High conductivity materials like copper are ideal substrates. There is a wide span of potential developments of cost effective solutions for the manufacturing of RF cavities in copper or other high thermal conductivity materials to serve as substrates for thin superconducting films. Surface finishing is another area of development. A third field are all the possible techniques to deposit high quality superconducting films on complex substrates.
The aim of this discussion is to identify existing industrial processes which could be relevant in the above areas, and the needed developments to adapt them to SRF applications for particle accelerators.