Energy Recovery LINACs -- an Overview

The seminar on energy recovery linacs (ERLs) is giving an overview of the field: How does an ERL work? What have been important milestones in ERL history? What are the reasons to use an ERL instead of a conventional accelerator? As examples of the landscape of machines, ranging from ancient ERLs up to future projects, this chapter will give results of the runs from CBETA (USA) and S-DALINAC (Germany). The two facilities bERLin-Pro/SEALab (Germany) and MESA (Germany) will belong to the next ERLs to be in operation and will be introduced briefly. The way to future ERLs will also be addressed.