Construction of Self-Consistent Longitudinal Matches in Multi-Pass Energy Recovery Linacs

TL;DR

This paper introduces a semi-analytic method for designing self-consistent longitudinal phase space matches in multipass Energy Recovery Linacs, crucial for collider and FEL applications, highlighting the impact of recirculation transport choices.

Contribution

The paper presents a novel semi-analytic approach to determine self-consistent longitudinal matches in multipass ERLs, analyzing effects of recirculation transport types on feasibility and performance.

Findings

Common recirculation transport complicates longitudinal matching in high-energy ERLs.

Separate transport simplifies achieving self-consistent matches and reduces RF beam load.

The method applies to collider and FEL scenarios, guiding design choices.

Abstract

Any proposal for an accelerator facility based upon a multipass Energy Recovery Linac (ERL) must possess a self-consistent match in longitudinal phase space, not just transverse phase space. We therefore present a semi-analytic method to determine self-consistent longitudinal matches in any multipass ERL. We apply this method in collider scenarios (embodying an energy spread minimising match) and FEL scenarios (embodying a compressive match), and discuss the consequences of each. As an example of the utility of the method, we prove that the choice of common or separate recirculation transport determines the feasibility of longitudinal matches in cases where disruption, such as synchrotron radiation loss, exists. We show that any high energy multipass ERL collider based upon common recirculation transport will require special care to produce a self-consistent longitudinal match, but that one based upon separate transport is readily available. Furthermore we show that any high energy multipass ERL FEL driver based upon common recirculation transport requires a larger resultant rf beam load than the one based on separate transport, favouring the separate transport designs.