Global ETD Search

71	Underground measurements and simulations on the muon intensity and 12C-induced nuclear reactions at low energies Ludwig, Felix 04 January 2022 (has links) The reaction 12C(α,γ)16O is of paramount importance for the nucleosynthesis of heavier elements in stars. It takes place during helium burning and determines the abundance of 12C and 16O at the end of this burning stage and therefore influences subsequent nuclear reactions. Currently the cross section at astrophysically relevant energies is not known with satisfactory precision. Due to the low cross section of the reaction, low background, high beam intensities and target thicknesses are necessary for experiments. Therefore a new laboratory hosting a 5 MV ion accelerator, was built in the shallow-underground tunnels of Felsenkeller. The main background component in such laboratories was investigated with a muon telescope in this thesis. It was found, that the rock overburden of about 45 m vertical depth reduces the muons by a factor of about 40 compared to the surface. Furthermore the results of the measurements were compared to a simulation based on the geometry of the facility and showed good agreement. In the next step the accelerator was put into operation. Since the experiment on 12C(α,γ)16O will be done in inverse kinematics, an intense carbon beam is necessary to reach sufficient statistics. For this, the creation and extraction of carbon ions in an external ion source was improved. The external source now provides steady currents of 12C− of above 100 μA. In the following the transmission through the accelerator and the high-energy beamline was tested with a beam restricted in width. The pressure of the gas stripper in the centre of the accelerator and the parameters of different focusing elements after the accelerator were varied. It was found, that for a desired carbon beam energy of below 9 MeV, the 2+ charge state is suited best, where up to 35% of the inserted beam could be transmitted. To ease the planning of future experiments and aid the analysis of the data, the target chamber and two different kinds of cluster detectors were modelled in Geant4. The low-energy region was verified by comparing the simulations to measurements with radioactive calibration sources. Deviations for the detectors were below 10% without target chamber, and up to 30% for individual germanium crystals of the Cluster Detectors with the target chamber. A first test measurement was undertaken to investigate the capabilities of the new laboratory. Solid tantalum targets implanted with 4 He were prepared. An ERDA analysis of the used solid targets showed contaminations with carbon and oxygen. These led to beam-induced background in the region of interest during the irradiation. Then the targets were irradiated with a carbon beam at two different energies. While no clear signal of 12C(α,γ)16O could be observed, the beam could be steered on the target for the whole duration of the beam time spanning five days. Problems during this test, like low beam current, were identified. These could be partly remedied in the scope of this thesis. Suggestions for improvements for a second test run were developed as well. info:eu-repo/classification/ddc/530 ddc:530
72	A laser based straightness monitor for a prototype automated linear collider tunnel surveying system Moss, Gregory Richard January 2013 (has links) For precise measurement of new TeV-scale physics and precision studies of the Higgs Boson, a new lepton collider is required. To enable meaningful analysis, a centre of mass energy of 500GeV and luminosity of 10<sup>34</sup>cm<sup>-2</sup>s<sup>-1</sup> is needed. The planned 31km long International Linear Collider is capable of meeting these targets, requiring a final emittance of 10 micro-radians horizontally and 35nmrad vertically. To achieve these demanding emittance values, the accelerator components in the main linacs must be aligned against an accurately mapped network of reference markers along the entire tunnel. An automated system could map this tunnel network quickly, accurately, safely and repeatedly; the Linear Collider Alignment and Survey (LiCAS) Rapid Tunnel Reference Surveyor (RTRS) is a working prototype of such a system. The LiCAS RTRS is a train of measurement units that accurately locate regularly spaced retro-reflector markers using Frequency Scanning Interferometry (FSI). The unit locations with respect to each other are precisely reconstructed using a Laser Straightness Monitor (LSM) and tilt sensor system, along with a system of internal FSI lines. The design, commissioning, practical usage, calibration, and reconstruction performance of the LSM is addressed in this work. The commissioned RTRS is described and the properties of the LSM components are investigated in detail. A method of finding the position of laser beam spots on the LSM cameras is developed, along with a process of combining individual spot positions into a more robust measurement compatible with the data from other sub-systems. Laser beam propagation along the LSM is modelled and a robust method of reconstructing CCD beam spot position measurements into positions and orientations of the LSM units is described. A method of calibrating LSM units using an external witness system is presented, along with a way of using the overdetermined nature of the LSM to improve calibration constant errors by including data taken from unwitnessed runs. The reconstruction uncertainty, inclusive of both statistical and systematic effects, of the LSM system is found to be of 5.8 microns × 5.3 microns in lateral translations and 27.6 microradians × 34.1 microradians in rotations perpendicular to the beam, with an uncertainty of 51.1 microradians in rotations around the beam coming from a tilt-sensor arrangement. 539.7
73	Designing radiation protection for a linear accelerator : using Monte carlo-simulations / Framtagning av förslag på förstärkt strålskydd för en linjäraccelerator : med hjälp av Monte Carlo-simuleringar Lindahl, Jonatan January 2019 (has links) The department of Radiation Sciences at Umeå University has obtained an old linear accelerator, intended for educational purposes. The goal of this thesis was to find proper reinforced radiation protection in an intended bunker (a room with thick concrete walls), to ensure that the radiation outside the bunker falls within acceptable levels. The main method was with the use of Monte Carlo-simulations. To properly simulate the accelerator, knowledge of the energy distribution of emitted radiation was needed. For this, a novel method for spectra determination, using several depth dose measurements including off-axis, was developed. A method that shows promising results in finding the spectra when measurements outside the primary beam are included. The found energy spectrum was then used to simulate the accelerator in the intended bunker. The resulting dose distribution was visualized together with 3D CAD-images of the bunker, to easily see in which locations outside the bunker where the dose was high. An important finding was that some changes are required to ensure that the public does not receive too high doses of radiation on a public outdoor-area that is located above the bunker. Otherwise, the accelerator is only allowed to be run 1.8 hours per year. A workaround to this problem could be to just plant a thorn bush, covering the dangerous area of radius 3m. After such a measure has been taken, which is assumed in the following results, the focus moves to the radiation that leaks into the accelerator’s intended control room, which is located right outside the bunker’s entrance door. The results show that the accelerator is only allowed to be run for a maximum of 6.1 or 3.3 hours per year (depending on the placement of the accelerator in the room), without a specific extra reinforced radiation protection consisting mainly of lead bricks. With the specific extra protection added, the accelerator is allowed to be run 44 or 54 hours per year instead, showing a distinct improvement. However, the dose rate to the control room was still quite high, 13.7 μGy/h or 11.2 μGy/h, compared to the average dose received by someone living in Sweden, which is 0.27 μGy/h. Therefore, further measures are recommended. This is however a worst case scenario, since the leakage spectrum from the accelerator itself was simulated as having the same energy spectrum as the primarybeam at 0.1 % of the intensity, which is the maximum leakage dose according to the specifications for the accelerator. This is probably an overestimation of the intensity. Also, the energy spectra of the leakage is probably of lower energy than the primary beam in at least some directions. Implementing more knowledge of the leak spectra in future work, should therefore result in more allowed run hours for the accelerator. linac linear accelerator accelerator mega voltage photons spectra determination high energy photons Monte carlo simulations radiation transport dose radiation radiation protection Accelerator Physics and Instrumentation Acceleratorfysik och instrumentering Atom and Molecular Physics and Optics Atom- och molekylfysik och optik Other Medical Engineering Annan medicinteknik
74	Corrections of high-order nonlinearities in the LHC and High-Luminosity LHC beam optics Dilly, Joschua 01 March 2024 (has links) Der Einfluss von Nichtlinearitäten höherer Ordnung der Magnetfelder auf die Leistung des Large Hadron Collider (LHC) und dessen geplante High-Luminosity-Aufrüstung, dem HL-LHC, wurde umfangreich untersucht. Insbesondere hat sich gezeigt, dass das Vorhandensein solcher Fehler in den Insertion Regions (IR) erhebliche Auswirkungen hat, bedingt durch hohe Beta-Funktionen und Feed-Down auf niedrigere Ordnungen aufgrund der Kreuzungsschemata. Augenmerk dieser Arbeit ist auf die Erforschung diverser Methoden zur effektiven Behandlung dieser Nichtlinearitäten höherer Ordnung gerichtet, mit dem Ziel, sie zu identifizieren und korrigieren, um die Strahloptik zu optimieren und die Maschinenleistung zu verbessern. Simulationsstudien werden eingesetzt, in denen mit verschiedenen Fehlerquellen assoziierte Resonanzantreibende Terme (RDTs) gezielt angegangen werden. Besondere Aufmerksamkeit gilt Dekapol- und Dodekapolfehlern, die in früheren Messungen im LHC schädliche Auswirkungen durch Feed-Down auf Amplituden-Detuning gezeigt haben. Die erwartete Erhöhung der Sensitivität der Optik gegenüber Fehlern in den IRs des HL-LHC unterstreicht weiter die Bedeutung der Behandlung dieser Fehler. Des Weitern werden Korrekturoptionen mit Hilfe der nichtlinearen Korrektorpaketen entwickelt. Experimentelle Studien werden durchgeführt, um die Ergebnisse zu validieren. Erhebliche Anstrengungen wurden unternommen, um die Feed-Down Effekte von Dekapol- und Dodekapol-Feldfehlern zu mindern. Um diese Herausforderung anzugehen, wurden neuartige Korrekturalgorithmen eingeführt, die erstmals die Dodekapol-Korrektoren in den IRs im operationellen Betrieb ansteuern. Die Ergebnisse dieser Experimente liefern wertvolle Erkenntnisse zur Minderung von Fehlern höherer Ordnung und tragen zum besseren Verständnis der Strahldynamik in modernen und zukünftigen Teilchenbeschleunigern bei. / The impact of high-order nonlinear magnetic field errors on the performance of the Large Hadron Collider (LHC) and its planned High-Luminosity upgrade, the HL-LHC, has been extensively studied. Particularly, the presence of such errors in the Insertion Regions (IR) has shown significant repercussions due to the high beta-functions and feed-down to lower orders caused by crossing schemes. This thesis aims to explore different methods for effectively addressing these high-order errors, with the ultimate goal of identifying and correcting them to optimize beam optics and enhance machine performance. Simulation studies are employed, using a novel and flexible correction algorithm developed during the course of this PhD research. Various strategies are investigated to improve corrections by targeting Resonance Driving Terms (RDTs) associated with diverse error sources. Special attention is devoted to decapole and dodecapole errors, which have demonstrated detrimental effects on amplitude detuning due to feed-down based on previous measurements in the LHC. The anticipated increase in optics sensitivity to errors in the IRs of the HL-LHC further underscores the importance of addressing these errors. Correction options are evaluated, focusing on the utilization of the nonlinear corrector packages to address errors in the new separation and recombination dipoles in the HL-LHC, where increased decapole errors had been expected. Experimental studies are conducted to validate the findings. Significant efforts are dedicated to mitigating the feed-down effects arising from decapole and dodecapole field errors. To address this challenge, novel corrections involving the operational implementation of dodecapole correctors in the IRs have been introduced for the first time. The results of these experiments provide valuable insights into the mitigation of high-order errors and contribute to the overall understanding of beam dynamics in advanced particle accelerators. Teilchenbeschleuniger Beschleunigerphysik Hohe Ordnung Dekapol Dodekapol Nichtlinear Korrekturen LHC HL-LHC Strahlenoptik Magnete Magnetische Felder Collider Accelerator Physics High Order Decapole Dodecapole Nonlinear Corrections LHC HL-LHC Beam Optics Magnets Magnetic Fields 530 Physik ddc:530
75	Exotic Decays of a Vector-liketop Partner at the LHC Skwarcan-Bidakowski, Alexander January 2019 (has links) An evaluation of how sensitive some ATLAS searches for new physics are to a new beyond standard model (BSM) vector-like quark (VLQ) and a pseudo Nambu-Goldstone boson (pNGB) scalar. This was done by simulating a signal containing these new particles and making a recast of it onto existing verified ATLAS searches for new physics at center-of-mass (CM) energy of 13 TeV (Run 2) at the Large Hadron Collider (LHC). Signals for recasting were tailored such that their final states would be appropriate in relation to each respective ATLAS search in order to use the same selection criteria as applied in the existing searches. The results are summarized in the form of significances (Z) for each masspoint of the new top-partner and S particle. Significances did not show any expectiation of excluding any masspoint in the examined mass range for the recasts at 95% CL. This suggests that a dedicated search for these particles in the considered masspoints would be required. Particle physics Vector-like quarks VLQ Composite Higgs model CHM Top-partner pseudo Nambu-Goldstone boson pNGB NGB ATLAS LHC CMS Significance Recast CheckMate CM MadGraph Pythia Delphes Detector Analysis Hierarchy Problem Exotic Decay QFT Quantum Field Theory fermions bosons Jets photons leptons 13 TeV Missing Transverse Energy momentum hypothetical selection criteria Standard model Signal background event Higgs Mechanism Simulation Confidence limit Other Physics Topics Annan fysik Accelerator Physics and Instrumentation Acceleratorfysik och instrumentering Subatomic Physics Subatomär fysik

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