During its Run 2 (2015–2018), the Large Hadron Collider (LHC) operated at almost twice higher energy, and provided Pb-Pb collisions with an order of magnitude higher luminosity, than in the previous Run 1. In consequence, the power of the secondary beams emitted from the interaction points by the bound-free pair production (BFPP) process increased by a factor $\sim 20$, while the propensity of the bending magnets to quench increased with the higher magnetic field. This beam power is about 35 times greater than that contained in the luminosity debris from hadronic interactions and is focused on specific locations that fall naturally inside superconducting magnets. The risk of quenching these magnets has long been recognized as severe and there are operational limitations due to the dynamic heat load that must be evacuated by the cryogenic system. High-luminosity operation was nevertheless possible thanks to orbit bumps that were introduced in the dispersion suppressors around the ATLAS and CMS experiments to prevent quenches by displacing and spreading out these beam losses. Further, in 2015, the BFPP beams were manipulated to induce a controlled quench, thus providing the first direct measurement of the steady-state quench level of an LHC dipole magnet. The same experiment demonstrated the need for new collimators that are being installed around the ALICE experiment to intercept the secondary beams in the future. This paper discusses the experience with BFPP at luminosities very close to the future High Luminosity LHC (HL-LHC) target, gives results on the risk reduction by orbit bumps and presents a detailed analysis of the controlled quench experiment.

中文翻译：

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核碰撞和CERN大型强子对撞机主偶极子磁体的稳态失超极限产生无界对

在第2轮（2015-2018）的运行中，大型强子对撞机（LHC）的能量几乎是以前的第1轮的两倍，并为Pb-Pb碰撞提供了高出一个数量级的光度。无边对产生（BFPP）过程从相互作用点发出的次光束的数量增加了一个因子 $〜20$，而弯曲磁体的淬火倾向则随较高的磁场而增加。该束功率比强子相互作用产生的光度碎片中所包含的束功率大35倍，并且聚焦在自然落在超导磁体内部的特定位置上。长期以来，人们已经认识到淬火这些磁铁的风险非常严重，并且由于动态热负荷必须由低温系统排出，因此存在运行限制。尽管如此，由于在ATLAS和CMS实验周围的色散抑制器中引入了轨道凸点，从而可以通过移动和散布这些光束损失来防止失超，从而实现了高发光度操作。此外，在2015年，对BFPP梁进行了控制，以控制淬火，这样就可以直接测量LHC偶极磁体的稳态失超水平。相同的实验表明，将来需要在ALICE实验周围安装新的准直仪，以拦截次光束。本文讨论了在非常接近未来高光度LHC（HL-LHC）目标的光度下使用BFPP的经验，给出了通过轨道颠簸降低风险的结果，并对可控淬火实验进行了详细分析。