For the second time in a month, experts from the Cockcroft Institute have had a paper selected as an “Editor’s Suggestion” in Physical Review – Accelerators and Beams. Drs Rob Apsimon and Sadiq Setiniyaz of Lancaster University Engineering Department, together with Peter Williams of the ASTeC Accelerator Physics Group have authored a ground-breaking paper that describes a method to lift a limitation on the beam current one can support in an Energy Recovery Linac (ERL).
In the 2020 European Strategy for Particle Physics, superconducting energy recovery linacs were identified as a key accelerator technology requiring priority research and development to underpin the future anticipated needs of the community. Applications in particle physics cover both ERL-based colliders and beam coolers for hadron colliders. ERLs are also seen as a very promising option, in both academic and industrial contexts, for future free electron lasers. They help improve performance whilst cutting energy usage – a true green technology.
Traditionally a major limitation on their application has been the so-called “beam breakup” instability (BBU). This effect occurs when the same beam passes the linear accelerator multiple times. The more times this happens, the “greener” the machine is, but at the same time the BBU limit is approached rapidly.
The authors studied different filling patterns as indicated in the above figure. They showed how these affect the beam breakup instability and how this effect can be minimised through design optimisation. They demonstrate that for such a machine one is able to make a judicious choice of the order in which the bunches pass the linear accelerator with respect to each other. Solving this combinatorial problem both analytically and numerically, they find that the current limit can be raised by at least a factor of 5. This has the exciting consequence that multipass ERLs can perform much better than previously thought. This knowledge and a new ERL tracking code which was developed as part of the study to numerically scan for the best filling pattern to maximise the threshold current will be of great use in the design of future energy recovery linacs.
Dr Apsimon said: “We are delighted that our work was recognised as an “editor’s suggestion” by this important journal. It highlights the quality of the work and the excellent prospects our study offers for the optimisation of future cutting edge research facilities.”
More information can be found at:
S. Setiniyaz, R. Apsimon, and P. H. Williams, “Filling pattern dependence of regenerative beam breakup instability in energy recovery linacs“, Phys. Rev. Accel. Beams 24, 061003 – Published 23 June 2021
https://journals.aps.org/prab/abstract/10.1103/PhysRevAccelBeams.24.061003