Inhalt

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  Introduction
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   A brief historical outline of neutrino physics
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   Neutrinos as a probe of physics beyond the Standard Model
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   The role of neutrinos in astrophysics and cosmology
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  Methods to determine the absolute neutrino mass scale
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   Cosmological bounds on neutrino mass
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   Direct kinematic methods
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   Neutrinoless double beta decay
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  The KATRIN experiment
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   Tritium beta-decay
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  The MAC-E filter technique
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   General working principle
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   Energy resolution and transmission function
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  Overview of the components of the KATRIN setup
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   Basic parameters of the KATRIN experiment
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   Tritium source and pumping sections
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   Spectrometer section
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   Electron detector system
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   Systematic and statistical uncertainties
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   Sources of background in the KATRIN experiment
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  Background suppression in MAC-E filters by electrostatic screening
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   Concept of background reduction by a screening wire electrode
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   Development of the concept and tests at the Mainz MAC-E filter
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   Implementation of the concept at the KATRIN pre-spectrometer
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   Transfer of the concept to the KATRIN main spectrometer
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   Parameters of a double-layer wire electrode system
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  Design studies for the wire electrode of the KATRIN main spectrometer
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   Technical requirements
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  Design criteria
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   Homogeneity of electric retardation potential and magnetic field in the analyzing plane
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   Transmission properties
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   Adiabaticity
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   Avoidance of traps for charged particles
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  Simulation tools
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   Calculation of magnetic fields
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   Calculation of electric fields
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   Trajectory calculation for charged particles in electromagnetic fields
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   Auxiliary programs
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  Implementation of the wire electrode design as a computer model
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   General layout of the wire electrode system
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   Modification of relevant parameters
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   Estimation of tolerances for fabrication and mounting of the electrode system
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   Tolerance estimates regarding the bending of wires
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   Tolerance estimates for the radial displacement of modules
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   Tolerance estimates for the shape of the spectrometer vessel
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   Technical implications of the tolerance simulations
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   Measures to improve the homogeneity of the electric field
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   Simple model using full rotational symmetry
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   Enhanced model using discrete rotational symmetry
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   Further design details obtained with a model using discrete rotational symmetry
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   Overview of final parameters of the wire electrode system for the KATRIN main spectrometer
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   Assembly of the modules and quality assurance procedures
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   Summary and status
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   Penning traps in the KATRIN setup as a potential background source
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  Discharge mechanisms
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   Townsend discharge
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   Vacuum breakdown
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   Penning trap and Penning discharge
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   Methods to counteract discharge problems due to particle traps
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   The Penning trap inside the pre-spectrometer
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   Location of the Penning trap
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   Modification of the electrode system to remove the Penning trap in the cone region
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   Operational modes of the KATRIN pre-spectrometer
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   Proposal for an additional pair of electrodes
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   Electric field strength: original versus modified setup
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   Behavior of the system after installation of the new electrodes
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   The Penning trap inside the main spectrometer
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  The Penning trap between pre- and main spectrometer
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   Trapping mechanisms and relevance for background concerns
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   Validity of the simulation results in view of the new KATRIN reference design
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   Countermeasures
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   Effects of Penning discharges in other experiments
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  Experimental tests of a method to empty the Penning trap between pre- and main spectrometer
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   Aim and requirements of the experimental test
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  Setup and field configurations at the Mainz MAC-E filter
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   Pre-spectrometer mockup: vacuum chamber and ``backplate''
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   Mechanical device to sweep a wire through the beam line: the ``wire scanner''
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   Configuration of electric and magnetic fields
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   Methods of filling the trap
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   Electron detection, data acquisition, and high-voltage system
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  First measurement phase: proof of principle
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   Increased background rate caused by backplate on high voltage
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   Characteristics of the Penning effect without extra filling of the trap
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   Characteristics of the Penning effect with injection of photoelectrons
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  Second and third measurement phases: ignition and specific quenching of Penning discharges
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   Observations from the second measurement phase
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   Results of the third measurement phase
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   Discussion of results and application to KATRIN
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  Tests of a UV LED-based photoelectron source
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   Motivation
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   Time-of-flight simulations for the KATRIN main spectrometer
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   Details of the transmission function and proposal of an enhanced time-of-flight mode
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   Suitable light sources for fast-pulsed photoelectron production
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  Pulsed photoelectron production from a stainless steel cathode
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   Timing properties, photoelectron yield and photoelectron multiplicities
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   Energy scan of photoelectrons at 18 keV
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   Time-of-flight spectrum of photoelectrons at 18 keV
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   Prototype studies of a pulsed photoelectron source with angular selectivity
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   Mechanical construction of the fiber-coupled photoelectron gun
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   Measurement of integrated energy spectra: comparison between outer and inner fiber
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  Evaluation of results and outlook
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   Summary of simulation studies for time-of-flight measurements at the KATRIN main spectrometer and experimental tests at the Mainz spectrometer
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   Upgraded design of an angular-selective photoelectron gun
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   Conclusions and outlook
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   Electric screening factor of a single-layer cylindrical wire electrode
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  Technical drawings
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   Pre-spectrometer shielding electrode
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   Disc-shaped high voltage electrode for Penning trap experiments at Mainz
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   Scanning wire device to disturb the trapping conditions of charged particles
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   Prototype of a fiber-coupled photoelectron source
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  Technical data of the electron detector and the UV LEDs
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   Silicion PIN diode Hamamatsu S3590-06
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   UV LED 265 nm and 255 nm
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   Run descriptions (phase II of wire scanner measurements)
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  Operation and control of UV LEDs
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   First measurement phase (2007)
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   Second and third measurement phases (2008)
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  Photoelectron current and quantum efficiency
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   Measurement of the current of photoelectrons
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   Determination of the quantum efficiency
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   List of figures
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   List of tables
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   References