The vacuum chamber in the interaction region of particle colliders: a historical study and developments implementations in the LHCb experiment at CERN

The history of particle colliders begins in the early 60's when an idea previously patented by R. Wideroe in 1953 is constructed. The design of the vacuum chamber in their experimental area became essential as it was the rst physical barrier that the particles to be detected needed to traverse. The interaction of the products of the collisions with the vacuum chamber structural materials, hindered the identification of the significative events. This Thesis analyses the historical evolution of the experimental vacuum chambers and summarizes the technical criteria that are to be fulfilled. The Large Hadron Collider (LHC) presently under construction at CERN is the last generation of particle colliders. Four big experiments will be in operation (ATLAS, CMS, ALICE and LHCb) in the LHC with diferent physics objectives. In particular, LHCb will be devoted to the study of CP violation and the design of its vacuum chamber is the scope of this Thesis. Physics simulations with an initial design consisting of a conical aluminium vacuum chamber with stainless steel flanges and bellows expansion joints, foresaw redundancies in the experiment detection channels that would make it inefficient. The reduction of the radiation background generated after the interactions of the products of the proton collisions with the vacuum chamber materials became essential. Berillium became the ideal candidate as structural material for the vacuum chamber due to its excellent mechanical properties and high transparency to radiation. Nonetheless, its toxicity, difficult machining and complicated weld hampers its use. TIG welding of beryllium to beryllium and to aluminium AA2219 was qualified for UHV applications as per ISO Norms applicable for aluminium welding. On the other hand, beryllium high price led to consider beryllium-aluminium composites for the fabrication of the LHCb vacuum chamber. The mechanical characterization of the berylliumaluminium HIP AlBeMet AM162 at the required bakeout temperatures of 200°C and 250°C was completed. In turn, the electron beam welding of beryllium-aluminium to beryllium-aluminium and to aluminium AA2219 was qualified for UHV applications following ISO Norms applicable for aluminium welding. Once characterized mechanically the materials and demonstrated the feasibility of the welding, nite element analysis were performed to design the vacuum chamber; as well as to design other special components integrated in it. The fabrication and thorough tests conducted with prototypes is described; in particular, an aluminium AA6061 OD860 mm window 2 mm thick that UHV seals one of the detectors, two bellows expansion joint aluminium fabricated in AA2219 and two optimized aluminium AA2219 UHV anges. The final design consisting of a TIG welded conical structure 12 m long fabricated in berillium with thickness ranging between 1 and 2.4 mm, implementing the validated aluminium window, optimized flanges and bellows expansion joints, will allow a factor 5 reduction of the radiation background generated by the initial vacuum chamber allowing the study of the physics that the LHCb experiment is designed for.