Accelerator Seminar - Akira Miyazaki: SRF R&D and projects in Europe -- cavities from bulk niobium to thin film

SRF R&D and projects in Europe - Cavities from bulk niobium to thin film

The Superconducting RadioFrequency (SRF) is a choice of technology in modern accelerators in energy and luminosity frontiers, as well as long-pulsed or CW linacs for fixed target experiments. A unique feature of this research field is a balance between fundamental researches and serious projects for a user facility. The current de facto standard is bulk niobium cavities in most of the SRF projects in the world. In this seminar, we start with the on-going bulk niobium project in Europe, European Spallation Source, to see practical aspects of the huge international project. We focus on the first deployment of double spoke cavities in the low-b section in ESS and then a double-quarter wave resonator, fabricated by Niowave and originally tested by JLab, for HL-LHC at CERN. Here, we address the influence of trapped magnetic flux in complicated shape cavities made of bulk niobium. The trapped magnetic flux also plays an essential role in the thin film cavities, promising alternatives toward beyond the state-of-the-art of SRF technology. By controlling the trapped flux, the long-lasting Q-slope problem was solved in quarter-wave resonators for HIE-ISOLDE at CERN. This led to the best peak RF magnetic fields in niobium film cavities ever made in the world. We have a close look at the issue of thermoelectric currents in the context of Q-slope problem in layered cavities.