​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).

ERLs are likely to be applied in the next generation of accelerators for high energy physics, nuclear physics, and free-electron lasers with myriad applications in industry and wider society. This is because they 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 occurs when the same beam passes the linac multiple times. The more times this happens the greener the machine is, but the BBU limit is approached rapidly.

This paper shows that for such a machine one is able to make a judicious choice of the order in which the bunches pass the linac with respect to each other. Solving this combinatorial problem both analytically and numerically, the work shows 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.

The paper can be read here.