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Energy-recovery linacs for energy-efficient particle acceleration

Nature Reviews Physics volume 5, pages 708–716 (2023)Cite this article

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Abstract

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.

Key points

  • Energy-recovery linacs (ERLs) have already demonstrated impressive efficiency in routine operation.

  • If ERLs are to move into the mainstream of high-energy colliders, these advantages need to be enhanced with targeted R&D and be demonstrated at higher energies in a multiturn configuration.

  • The cryogenic plant is the largest contributor to the electrical efficiency of an ERL facility.

  • The most effective way to reduce the energy required by the cryoplant is to reduce the cryogenic load of the superconducting RF cavities, either by decreasing the surface resistivity of the cavity material or by operating at a higher temperature of 4 K.

  • Operation at 4 K is expected to have the biggest impact on energy efficiency, and this will also benefit smaller ERLs for universities and smaller research institutes, ushering in a new era of energy-efficient electron accelerators.

  • Other R&D is directed at energy savings from the RF power.

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Fig. 1: The principle of energy-recovery linacs.
Fig. 2: The landscape of past, present and proposed energy-recovery linacs.
Fig. 3: Qualitative Sankey Diagram for an energy-recovery linac.
Fig. 4: Comparison of the best niobium cavity results at 2 K with the best Nb3Sn-coated cavity results at 2 K and 4.4 K.
Fig. 5: Calculated reduction in electrical power for the PERLE RF cavities using FE-FRTs to minimize reflected power.

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Acknowledgements

This work was supported by the U.S. Department of Energy, Office of Science, Office of Nuclear Physics under Contract No. DE-AC05-06OR23177. In developing this Review, the author has received an enormous amount of help from friends and co-workers around the world, unfortunately too many to enumerate without forgetting someone. The author thanks them all and note that any errors in the text are his alone.

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  1. Jefferson Lab, Newport News, VA, USA

    Andrew Hutton

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Hutton, A. Energy-recovery linacs for energy-efficient particle acceleration. Nat Rev Phys 5, 708–716 (2023). https://doi.org/10.1038/s42254-023-00644-6

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