Effects of the Direct Space Charge on Transverse Coupled-Bunch Instabilities

Chao Li

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arXiv · 2609.03771

Effects of the Direct Space Charge on Transverse Coupled-Bunch Instabilities

Chao Li

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Abstract

The ultralow transverse emittance of diffraction-limited electron storage rings leads to high beam densities, making direct space-charge effects increasingly relevant despite their relativistic suppression at high energy. In this work, we investigate the impact of direct space charge on transverse coupled-bunch instabilities, using PETRA-IV as a representative example. A Vlasov solver, multi-bunch particle tracking, and analytical calculations in normalized phase space are combined to study the coupled-bunch mode spectrum, the nonlinear incoherent tune spread, and the associated Landau damping. Particle-tracking simulations show that the space-charge-induced tune spread can provide sufficient Landau damping to stabilize higher-order head-tail modes. Landau stability diagrams constructed from the analytical tune spread of a frozen bi-Gaussian beam predict the stabilization of these higher-order modes, in agreement with the tracking simulations. These results demonstrate the important role of direct space charge in transverse coupled-bunch dynamics. The analysis framework developed here can also be extended to collective-instability studies in both electron and hadron accelerators.

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Chao Li. 2026-09-03. Effects of the Direct Space Charge on Transverse Coupled-Bunch Instabilities. https://arxiv.org/abs/2609.03771

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