Designing and simulating COLTRIMS spectrometer

ABSTRACTDESIGNING AND SIMULATING COLTRIMS SPECTROMETERAfyon Kocatepe UniversityGraduate School of Natural and Applied SciencesCOLTRIMS (Cold Target Recoil Ion Momentum Spectroscopy), is a technique forinvestigating the dynamics of ionizing ion, electron or photon impact reactions with atomsor molecules. The goal of COLTRIMS is to provide a tool for kinematically completestudies of three - and more - particle collisions. It allows the high-resolution measurementof the previously undetectable small three-dimensional momentum vector of the recoilingtarget ion created in these collisions. Accurately identifying the momentum vector of theparticles creates the basis for determining the reaction?s multiplicity due to ion chargestates. Using the momentum vectors one can determine the dynamical mechanism of thereaction with the help of other charged particle collisions taking place in the reaction.Combined with novel 4π electron momentum analyzers, COLTRIMS is a momentummicroscope for kinematically complete scattering experiments.The COLTRIMS system consists of an internally and geometrically cold gas target,produced in vacuum with a supersonic expansion, and a part which resolves ion-electronmomentum. Ions and electrons are produced by ionizing radiation of any kind of gas target.All charged fragments from an atomic or molecular reaction are projected by a combinationof electric and magnetic fields onto position-sensitive detectors. From the measured time-of-flight of the particles and their position of impact on the detector, one can obtain theirthree-dimensional momentum vector. Cooling of the target atoms before the fragmentationby super sonic expansion allows a momentum resolution for the ion momenta of a fewatomic units.In this work, we studied the COLTRIMS technique and the setup of the COLTRIMSapparatus. In this framework, we worked on the technical description of the setup: vacuumchambers, detectors, spectra of positions, timing on the detectors and designing thespectrometer.Parallel to the technical description of the COLTRIMS setup it has been made somesimulations of the spectrometer using SIMION 7. The spectrometer is one of the mostimportant components of the experimental setup. Its purpose is to guide ions and electronsonto position sensitive detectors. It typically consists of two regions: the extraction regionwhere a homogeneous electric field is generated to extract the charged particles from theinteraction zone and a field-free drift region. Both are separated by meshes of variabletransmission. Using SIMION one can calculate the spread of transverse momentadepending on extraction field and initial kinetic energy of the target. This spread can laterbe used in the data analysis to reconstruct the ion momenta.2007, 159 PagesKeywords: COLTRIMS, TOF spectrometer, simulation, dedector, vacuum, jet, atomiccollisions.