Beam-beam Effects of 'Gear-changing' in Ring-Ring Colliders

TL;DR

This paper investigates the beam dynamics challenges caused by 'gear-changing' schemes in ring-ring colliders, where changing bunch structures to scan energy introduces complex beam-beam effects and stability issues.

Contribution

It provides an analysis of the beam-beam effects and stability problems associated with 'gear-changing' schemes in colliders, a topic not extensively studied before.

Findings

Identification of beam-beam interaction issues during 'gear-changing'

Analysis of stability constraints for bunch structure changes

Discussion of potential mitigation strategies

Abstract

In ring-ring colliders, the collision frequency determines the bunch structures, e.g. the time between the bunches in both rings should be identical. Because of relatively low relativistic speed of the hadron beam in sub-TeV hadron-hadron- and electron-ions-colliders, scanning the hadron beam's energy would require either a change in the circumference of one of the rings, or a switching of the bunch (harmonic) number in a ring. The later would cause so-called 'gear-changing', i.e. the change of the colliding bunches turn by turn. In this article, we study the difficulties in beam dynamics in this 'gear-changing' scheme.