III.6 — Beam coupling impedance measurements with beam and on a bench

The beam coupling impedance is one of the key quantities describing the interaction between a particle beam travelling in a particle accelerator and its surroundings. Under specific circumstances, the impedance can lead to severe beam instabilities which limit the overall performance of a running accelerator or pose challenges for the achievement of a project.In this contribution, we present the main techniques in use to characterize the impedance either with beam-based procedures, or with RF measurements on a test bench. The former is usually performed on running machines for which limitations are found or need to be assessed, the latter is typically performed before/after equipment installation and for validation purposes.We will also introduce some of the measurement techniques used to characterize the electromagnetic properties of materials. This is relevant, for example, for the correct material modelling in simulations, or to validate a fabrication process.