The CERN Large Hadron Collider (LHC) is the world’s largest and most powerful accelerator. Highly energized particles are accelerated to 9.9999991% the speed of light following a pencil lead thin path around a 27km tunnel. This $4.75B investment is protected by a complex system that must detect and react to a dangerous beam loss in a matter of milliseconds.

Between 2009 and 2010, CSL performed a series of technical reviews focused on the CERN LCH Machine Protection System (MPS) focusing on different parts of this complex system-of-systems including the Beam Loss Monitoring System (BLMS) and the Beam Interlock System (BIS). In 2022, CSL led a research collaboration involving researchers at the University of Toronto, McMaster University and CERN experts to develop an assurance argument for this system.

Numerous publications by CERN experts and other open source documentation provide intricate technical details about almost every aspect of the design of the MPS. Our objective in developing an assurance case argument for the MPS was to capture the overarching reason why CERN experts have trusted the MPS to protect the CERN LHC during its operation since “first beam” in September 2008.

We used Eliminative Argumentation to capture some of the “what if …?” reasoning used by CERN experts during the design of the MPS. Unsurprisingly, this “retrospective argument” did not reveal any significant concerns about the reliability of MPS. However, this effort produced a structured top-down view of the critical thinking used by CERN experts responsible for the design of this system. CSL’s web-based assurance case tool, Socrates, was used to support the collaborative efforts of researchers and experts in the development of this assurance case argument.

A PDF report available on the CERN website provides the entire assurance case argument for the CERN LHC MPS. You can learn more about this argument and our experience in its development in a paper, “Assurance Case Arguments in the Large: the CERN LHC Machine Protection System”, presented at the 2023 SafeComp conference.