II.5 — Superconducting RF cavities

The application of superconducting materials in RF cavities has gained a huge interest in the particle accelerator field over the last five decades. In particular, the accelerating gradients have been increased considerably due to progress in the understanding of the limiting factors at the beginning. Such limiting factors were in particular multipacting and issues in surface preparation and related technology. Also, advances in material technology play a very important role. Today superconducting RF cavities are indispensable elements for many particle accelerators. A number of examples are presented and also measurement techniques for the characterisation of important RF properties.