Research and Development of the Positron Damping Rings for the Proposed International Linear Collider and at CERN in Geneva, Switzerland for the Large Hadron Collider ATLAS Experiment\u27s Integrated Simulation Framwork

The topic of part I of my capstone is electron clouds, studied in the Cornell synchrotron accelerator. Electron clouds are an important phenomenon to study in circular particle accelerators such as the Large Hadron Collider (LHC), the Cornell synchrotron, and the damping ring for the proposed International Linear Collider (ILC). Low energy background electrons are normally present in high energy accelerators and are often not detrimental to beam performance, but certain operation conditions cause them to interact strongly with the beam, as was first observed in the 1980s in positron storage rings. The generation and amplification of the electron cloud is caused by ionization of residual gas in the vacuum chamber and irradiation of the chamber wall by synchrotron radiation. The Cornell CesrTA group researches the mitigation of the electron cloud in the Cornell synchrotron beam pipe by taking measurements of the cloud density and cloud effects on the beam. Various simulation programs are then used to try to study the physics behind cloud formation and beam quality at different cloud densities. The results presented here are from the ECLOUD program and concentrate on matching data from witness bunch scans that studied the relative cloud density at different bunch spacings to measure cloud decay over time. After many simulations runs, parameters were found for both 2.1 and 5.3 GeV of beam energy at 5 mA per bunch that successfully caused agreement between simulation and data. The values for these parameters will be given in the report. Upper and lower bounds were also found for the SEMAX parameter in the secondary energy distribution, and the secondary energy distribution was optimized to cause better agreement between peak shapes in the simulation and data. For part II, I will discuss particle simulation studies for the LHC ATLAS detector at CERN, in Geneva, Switzerland. By 2015, the ATLAS experiment will have surpassed the limits of the amount of data it can handle in a reasonable amount of time. Using Monte Carlo simulations to model particle interactions inside the detector is an increasingly complex and computationally intense task, but is vital for data analysis. This is in large part because the very small cross-sections for new physics signatures with respect to background processes need a large quantity of events for the simulation. The greatest portion of computing time is spent on the active and passive interactions with the detector material. Since ATLAS is the biggest particle detector in volume ever created and is packed with tiny complex circuits, doing this modeling in the very detailed full simulation Geant4 is not always feasible. Fatras, a fast track simulation engine of the ATLAS inner detector and muon system, is a way around this by parametrizing the calorimeter response. So far, Fatras’ agreement with Geant4 has been extremely promising and reduces the computing time by two orders of magnitude. In the report, hadronic interactions were studied in the inner detector for both Geant4 and Fatras using a Geant4 hadronic interaction processor. The number of child particles coming out of simulated particle decays and their particle types were looked at for each simulator, and first attempts at parametrizing the hadronic interactions inside the inner pixel layers and SCT for the ATLAS detector were made