Landau cavities in third generation synchrotron light sources

The new 3^rd generation synchrotron light sources coming up are designed for a small transverse emittance. But the small beam size gives a low Touschek lifetime and calls for good beam stability. In some storage rings higher harmonic cavities are installed for bunch lengthening to overcome the lifetime limitations. The higher harmonic cavities also induce Landau damping that improves the beam stability; they are therefor often called Landau cavities. A brief introduction to Landau cavities is given. Then the commissioning and use of these cavities at ALS, Bessy, MAX-lab and Super-ACO is described