Review of the development of RF cavities for high currents

To fulfill the need for ever higher luminosities, the magnitude of the beam currents continues to increase. This is true for the electron-positron rings, the hadron colliders, and the synchrotron light sources. These high currents bring a set of new and difficult challenges. Both normal conducting and superconducting cavity structures will be considered. While these two alternatives have significant differences, the challenges addressed are rather similar.