The Large Hadron Collider (LHC) at in Geneva, Switzerland is the largest particle accelerator in the world, having a nominal beam energy of 7 TeV. Following an end-of-year stop, before particle collisions can again take place in its four major experiments, the LHC is being re-commissioned to ensure that beam operation and physics data-taking can take place safely. This year, beams were first injected on 28 March 2023. The LHC is equipped with a beam cleaning system, comprising over 50 movable collimators per counter-rotating beam, each with four degrees of freedom, which remove the highly-energetic proton or heavy ion particles forming the beam halo before they end up in the superconducting magnets, potentially quenching them.
The collimators need to be precisely aligned with respect to the beam, forming a multi-stage hierarchy. Errors of even a few tens of micrometres can impact its performance. Once the operational settings are determined through a beam-based alignment process, which needs to be done at multiple stages of the LHC machine cycle, the settings are validated by intentionally causing beam losses, which are then observed in beam loss monitors. Other commissioning activities where collimators are involved include beam threading and aperture measurements.
For the past 13 years, through collaborations between UM and CERN, several research activities have been conducted with regards to the LHC collimation system. In particular, one such activity involves the automatic beam-based alignment of the LHC collimators, made possible in part through the use of machine learning techniques. Dr Ing. Gianluca Valentino, a Senior Lecturer with the Department of Communications and Computer Engineering, initially developed the automatic alignment of the collimators for his PhD thesis, which was then further optimised by Dr Gabriella Azzopardi. Presently, Mr Andrea Vella, a UM M.Phil. / Ph.D. student based at CERN is continuing the research in this area, developing anomaly detection and virtual diagnostics methods for LHC operation to detect issues with the collimation hierarchy over months of operation, while also taking responsibility for the collimation control software and testing an angular collimator alignment technique to allow for a tighter collimation hierarchy. This is necessary to correct tilts in the collimator jaws of the order of a 100 microradians, as the LHC moves towards the upgrade for the High Luminosity LHC (HL-LHC), which is scheduled to commence in 2029.
