Analysis of LHC Beam Gas Ionization monitor data and simulation of the Electron transport in the detector

Since July 2012 I had an honor to work in the European Organization for Nuclear Researc\n(CERN) as a member of the Technical Student Programme. This thesis presents the research concerning the electron transport in the Beam Gas Ionization (BGI) monitor in order to study the effects of the electrons interaction with a high energy particle beam.\nIn the first chapter the Beam Gas Ionization monitor is described together with its operating \nprinciple to give an overview of the analyzed detector. Chapter 2 contains the introduction to the \ntransverse beam dynamics in the particle accelerator which is the theoretical background for the \nemittance measurements. The analyzed BGI data are presented in chapter 3. As the research was based on the computer simulations, its description together with the results are given in the chapter 4. \nFinally the chapter 5 contains the investigation of the magnetic field threshold in the BGI \nelectron dynamics. In very short words the Beam Gas Ionization monitors installed in the CERN LHC make use of the ionization of a small volume of the injected neon gas by the circulating beam. The electrons produced are guided towards the readout system using a combination of electric and magnetic fields. In the presence of the beam field their tracks are modified and the resulting profile is distorted. The Geant4 particle simulation package is used to simulate the ionization process, while the CERN developed PyECLOUD code is used for tracking of the resulting ionized particles.\nIt turned out that the space charge effects of the beam strongly affect the electron distribution \nof the liberated electrons. The profile broadening and distortion therefore occur which causes the \nwrong indications of the BGI monitors. Those effects strongly depend on the beam density which is defined by the bunch intensity and the beam size. It is important to mention that those phenomena occur only for proton beam which is more intense than the ion beam.\nBy running the simulations it was found that the stronger magnetic field dumps the space charge \neffects. The simulations have shown that a magnetic field of 1 T is enough to reproduce the beam \nprofile correctly and obtain right value of the beam emittance. The further investiga- tion of this \nissue resulted in obtaining the empirical formula for magnetic field threshold needed to keep the \nspace charge effects at the expected level.\nThe performed research is a justification for possible BGI magnet exchange in order to\nensure the correct operation also for a proton beam.