Dynamic Focusing to Suppress Emittance Transfer in Crab-Crossing Flat Beam Collisions

TL;DR

This paper investigates the limitations of flat hadron beam collisions due to emittance transfer caused by fluctuations and resonance effects, and proposes a dynamic focusing scheme combining sextupoles and crab cavities to mitigate these issues.

Contribution

It introduces a novel dynamic focusing method using sextupoles and crab cavities to suppress emittance transfer and enhance flat-beam collision stability.

Findings

Fluctuations can cause emittance transfer via synchro-betatron resonance.

The proposed scheme increases tolerance to fluctuations.

Simulation results show improved robustness of flat-beam collisions.

Abstract

Flat hadron beam collisions, though expected to enhance peak luminosity by about an order of magnitude, have not yet been demonstrated. Our study reveals a critical limitation: realistic fluctuations, when amplified by synchro-betatron resonance, lead to transverse emittance transfer in flat-beam collisions. Using beam-beam simulations based on Electron-Ion Collider design parameters, we show that this effect leads to vertical emittance growth, which can distort the flat-beam profile and degrade luminosity. We propose a dynamic focusing scheme that combines sextupoles with crab cavities to suppress the hourglass-induced resonance. This approach increases tolerance to fluctuations and improves the robustness of flat-beam collisions. This practical mitigation facilitates the adoption of flat-beam collisions in next-generation lepton-hadron colliders.