UBC Theses and Dissertations
Unidentified falling objects in the Large Hadron Collider : formation, charging mechanisms and dynamics of dust particulates in a high energy proton accelerator Belanger, Philippe
Micrometer-sized dust particulates present in the LHC beam pipe are known to be causing a large number of sporadic beam loss events all around the LHC, some of which are large enough to provoke protection dumps or induce magnet quenches. These so-called Unidentified Falling Objects (UFOs) remain one of the important unknowns related to LHC operation after several years of high intensity beam operation in the LHC. In this thesis, the current understanding of the UFO problem is reviewed. The dynamics of charged dust particulates interacting with the LHC proton beam is discussed based on observations, theoretical predictions and numerical simulations. Using a reviewed version of the UFO model, it is found that the time profile of proton losses from half of the observed events present a time asymmetry which can't be explained with the current understanding of UFO dynamics. Furthermore, loss profiles recorded over more than 4 years of LHC operation are analyzed. It is shown that UFOs must carry an initial negative charge to explain the length of proton losses observed experimentally. Theoretical considerations, originally developed for dust-in-plasma, are introduced to support this claim. Plausible release mechanisms of UFOs in the LHC are also discussed, and the energy required for dust particulates to leave the walls of the beam chamber is presented. Finally, the theoretical possibility of having negatively charged dust particulates orbiting the proton beam of the LHC is discussed. It is found that stable orbits exist, but that only unstable orbits could result in important proton losses.
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