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Interaction Point Backgrounds from the CLIC Post Collision Line
[Thesis]. Manchester, UK: The University of Manchester; 2012.
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The proposed CLIC accelerator is designed to collide electrons and positrons ata centre of mass energy of 3 TeV, and a luminosity of 5.9 x 10^(34) cm^(−2) s^(−1) at the interactionpoint (IP). Being a single-pass machine, luminosity must be maximised byminimising the beam spot size to the order of a few nanometres. The effects of the finalfocussing and the intense beam-beam effects lead to a high production cross sectionof beamstrahlung photons, and highly divergent outgoing beams, both spatially and inenergy. Pair-production of the beamstrahlung photons leads to coherent pairs.The proposed CLIC post-collision line must transport electrons, positrons and photonsfrom the IP to their respective dumps with minimal losses and background contribution.It is favourable to separate the particle species for diagnostic purposes, andthus the proposed post-collision line contains vertically bending magnets to separatebased on charge. This process introduces dispersion to the energetically divergentbeam, requiring the vertical apertures of the accelerator components to increase withdistance from the IP. Particles in the low energy extreme of the beam cannot realisticallypass through the components, which must therefore be protected by carbon-basedabsorbers. Losses in these absorbers and in the various dumps of the accelerator leadto electromagnetic showering within the material, some of which may be directed ontothe IP. Optimisation of the apertures and positions of these components is presented asoriginal research in this thesis.It is the purpose of this thesis to study the CLIC post-collision line, beam transportand the production and effects of secondary particles at the IP. Primarily, the backscatteredphotons are evaluated, with an introduction to the effect of neutrons. Photonsincident on silicon detectors have the potential to produce false hits, and neutrons todegrade the detectors. The effect of losses on the accelerator components is studiedand the survivability of these components discussed.