The beam-ion interaction is one of the potential limitations of beam performance in ultralow-emittance electron light sources. Conventionally, the beam-ion instability is attributed to two effects: the ion-trapping effect and fast ion effect, which are usually studied individually emphasizing the beam performance in different timescales. However, in accelerators, the electron beam suffers from both effects, requiring a self-consistent treatment. In this study, we do not regularly distinguish the ion-trapping effect and the fast ion effect but treat the beam-ion interaction in a general sense. To clarify the beam-ion dynamics process and evaluate the beam characteristics, a numerical simulation code based on the “quasi-strong-strong” model has been developed, including modules for ionization, beam-ion interaction, synchrotron radiation damping, quantum excitation, bunch-by-bunch feedback, etc. The lattice of the High Energy Photon Source is used as an example to show the beam-ion instability and its mitigation. It is found that the beam-ion instability seriously occurs in a certain low beam current region. When the beam-ion instability is significantly driven and cannot be damped by the synchrotron radiation damping, a bunch-by-bunch feedback system based on a finite impulse response filter can be adopted to mitigate it effectively.

中文翻译：

---

束离子不稳定性及其通过反馈系统的缓解

束离子相互作用是超低发射电子光源中束性能的潜在限制之一。常规上，束离子的不稳定性归因于两个效应：离子捕获效应和快速离子效应，通常对它们进行单独研究，以强调不同时间范围内的束性能。但是，在加速器中，电子束会同时受到两种影响，因此需要进行自洽处理。在这项研究中，我们没有定期区分离子捕获效应和快速离子效应，而是从一般意义上对待离子束-离子相互作用。为了阐明离子束动力学过程并评估离子束特性，已经开发了基于“准强-强”模型的数值模拟代码，包括电离，离子束相互作用，同步加速器辐射阻尼，量子激发，逐束反馈等。以高能光子源的晶格为例，说明束离子的不稳定性及其缓解方法。发现在一定的低电子束电流区域中严重发生电子束离子不稳定性。当束流离子的不稳定性被极大地驱动并且不能被同步加速器辐射阻尼所抑制时，可以采用基于有限脉冲响应滤波器的逐束反馈系统来有效地减轻它。