Dafne Lifetime Optimization with Compensating Wires and Octupoles

TL;DR

This paper discusses the mitigation of long-range beam-beam interactions in the DAFNE collider using compensating wires and octupoles, improving beam lifetime and luminosity through combined theoretical and experimental methods.

Contribution

It introduces a combined approach of wire and octupole compensation to mitigate parasitic crossings, supported by theoretical analysis and experimental validation.

Findings

Improved beam lifetime with wire compensation during KLOE operation.

Less evident benefits observed during FINUDA run.

Theoretical analysis of nonlinearities and experimental measurements are consistent.

Abstract

Long-range beam-beam interactions (parasitic crossings) were one of the main luminosity performance limitations for the lepton F-factory DAFNE in its original configuration. In particular, the parasitic crossings led to a substantial lifetime reduction of both beams in collision. This puts a limit on the maximum storable current and, as a consequence, on the achievable peak and integrated luminosity. In order to mitigate the problem, numerical and experimental studies of the parasitic crossings compensation by current-carrying wires have been done. During the operation for the KLOE experiment two such wires have been installed at both ends of the interaction region. They produced a relevant improvement in the lifetime of the weak beam (positrons) at the maximum current of the strong one (electrons) without luminosity loss, in agreement with the numerical predictions. The same compensating mechanism has been adopted during the run for the FINUDA experiment as well, with less evident benefits than in the previous case. The interplay between nonlinearities originating from the beam-beam interaction and the ring lattice has been studied by theoretical simulation and experimental measurements. Compensation procedures have been set up relying on the electromagnetic octupoles installed on both rings and used in addition to wire compensation. In this paper the parasitic crossings effects in the DAFNE interaction regions and their compensation by wires and octupoles are described. A detailed theoretical analysis of the interplay about different non-linearities is presented; eventually experimental measurements and observations are discussed.