Protons and heavy-ion beams at unprecedented energies are brought into collisions in the CERN Large Hadron Collider (LHC) for high-energy experiments. The LHC multistage collimation system is designed to provide protection against regular and abnormal losses in order to reduce the risk of quenches of the superconducting magnets as well as keeping background in the experiments under control. Compared to protons, beam collimation in the heavy-ion runs is more challenging despite the lower stored beam energies, because the efficiency of cleaning with heavy ions has been observed to be 2 orders of magnitude worse. This is due to the differences in the interaction mechanisms between the beams and the collimators. Ion beams experience fragmentation and electromagnetic dissociation at the collimators that result in a substantial flux of off-rigidity particles that escape the collimation system. These out-scattered nuclei might be lost around the ring, eventually imposing a limit on the maximum achievable stored beam energy. The more stringent limit comes from potential quenches of superconducting magnets. Accurate simulation tools are crucial in order to understand and control these losses. A new simulation framework has been developed for heavy-ion collimation based on the coupling of the SixTrack tracking code, which has been extended to track arbitrary heavy-ion species, and the fluka Monte Carlo code that models the electromagnetic and nuclear interactions of the heavy ions with the nuclei of the collimator material. In this paper, the functionality of the new simulation tool is described. Furthermore, SixTrack-fluka coupling simulations are presented and compared with measurements done with ${{}^{208}\mathrm{Pb}}^{82+}$ ions in the LHC. The agreement between simulations and measurements is discussed and the results are used to understand and optimize losses. The simulation tool is also applied to predict the performance of the collimation system for the high-luminosity LHC. Based on the simulation results and the experience gained in past heavy-ion runs, some conclusions are presented.

中文翻译：

---

CERN大型强子对撞机对重离子晕轮准直的模拟：具有测量和清洁性能评估的基准

在CERN大型强子对撞机（LHC）中，质子和重离子束以前所未有的能量发生碰撞，以进行高能实验。LHC多级准直系统旨在提供针对常规和异常损失的保护，以降低超导磁体淬火的风险，并使实验的背景得到控制。与质子相比，尽管存储的束能量较低，但重离子运行中的束准直更具挑战性，因为已观察到重离子清洁的效率差了2个数量级。这是由于光束和准直仪之间的相互作用机制不同。离子束在准直仪上会发生碎裂和电磁离解，从而导致大量的非刚性粒子流逸出准直系统。这些散布的原子核可能会在环周围丢失，从而最终限制了可达到的最大存储束能量。更为严格的限制来自超导磁体的潜在失超。准确的仿真工具对于理解和控制这些损失至关重要。已经开发了一个新的模拟框架，用于重离子准直。准确的仿真工具对于理解和控制这些损失至关重要。已经开发了一个新的模拟框架，用于重离子准直。准确的仿真工具对于理解和控制这些损失至关重要。已经开发了一个新的模拟框架，用于重离子准直。SixTrack跟踪代码（已扩展为跟踪任意重离子物种）和fluka Monte Carlo代码，该模型模拟了重离子与准直仪材料核之间的电磁相互作用和核相互作用。在本文中，描述了新仿真工具的功能。此外，还介绍了SixTrack - fluka耦合仿真并将其与使用${{}^{208}\mathrm{铅含量}}^{82+}$大型强子对撞机中的离子 讨论了仿真与测量之间的一致性，并将结果用于了解和优化损耗。该仿真工具还用于预测高亮度LHC准直系统的性能。基于仿真结果和过去重离子运行的经验，提出了一些结论。