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

Derong Xu; J Scott Berg; Michael M Blaskiewicz; Yue Hao; Yun Luo; Christoph Montag; Sergei Nagaitsev; Boris Podobedov; Vadim Ptitsyn; Ferdinand Willeke; Binping Xiao

arXiv · 2506.21289

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

Derong Xu·J Scott Berg·Michael M Blaskiewicz·Yue Hao·Yun Luo·Christoph Montag·Sergei Nagaitsev·Boris Podobedov·Vadim Ptitsyn·Ferdinand Willeke·Binping Xiao

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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.

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Derong Xu, J Scott Berg, Michael M Blaskiewicz, Yue Hao, Yun Luo, Christoph Montag, Sergei Nagaitsev, Boris Podobedov, Vadim Ptitsyn, Ferdinand Willeke, Binping Xiao. 2025-06-26. Dynamic Focusing to Suppress Emittance Transfer in Crab-Crossing Flat Beam Collisions. https://arxiv.org/abs/2506.21289

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