Jincheng Xiao | Searcharxiv

arXiv2026

A Realistic Proportional-Integral RF Feedback Model for Longitudinal Beam Dynamics Simulation

Modern fourth-generation storage ring light sources predominantly utilize digital I/Q-based proportional-integral (PI) feedback for their radio-frequency (RF) systems. This paper introduces a dedicated PI feedback model implemented in the STABLE tracking code to enable accurate and fast longitudinal beam dynamics simulations. The model's key innovation lies in its treatment of the continuous generator current, which is discretized into electron-bunch-like charge pulses, while the cavity voltage is refreshed on an RF-cycle basis. This methodology offers a more physically accurate model of the beam-cavity-feedback coupling, providing a versatile tool for precise longitudinal beam dynamics studies in single- and multi-rf configurations.

physics.acc-ph↗

arXiv2025

Impact of short-range wakefields from radio-frequency cavity resonant modes on bunch lengthening

The high-performance operation of fourth-generation synchrotron light sources critically depends on harmonic cavities (HCs) to alleviate statistical collective effects through bunch lengthening. Active HCs are preferred over passive ones for achieving theoretically optimum bunch lengthening in Timing-mode operation, which is characterized by low average current and high bunch charge. This advantage stems from their ability to control cavity voltages via generator current. However, this study reveals a previously overlooked limitation: the detrimental impact of short-range wakefields from RF cavity resonant modes on bunch lengthening at high bunch charge. Using Hefei Advanced Light Facility parameters, we demonstrate that these wakefields can significantly degrade bunch lengthening. Further analysis with PETRA-IV parameters reveals that fine-tuning the HC voltage can optimize bunch lengthening. Notably, under specific HC settings, there exists two equilibrium bunch distributions. Our findings highlight the critical influence of RF cavity short-range wakefields on beam dynamics at high bunch charge, emphasizing their essential inclusion in the evaluation and optimization of HC performance for new-generation synchrotron light sources.

physics.acc-ph↗