Energy-recovery linacs for energy-efficient particle acceleration

Energy-recovery linacs are inherently energy-efficient because the RF power needed for acceleration is recovered during deceleration. Energy recovery enables extremely high-power beams that are not economically or ecologically possible using a simple linac. The fundamental technology is not new, but has taken on an increased importance in recent years. In this Review, I describe the positive aspects of the technology, the areas that are under active study to improve the overall efficiency and areas that need further R&D. The need for validation of the entire system is explained and the active proposals described.