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KATRIN
Abstract:
The KArlshrue TRItium Neutrino (KATRIN) experiment is probing the absolute mass scale of neutrinos using precise measurement of electron energy close to the end-point of tritium beta decay. The final sensitivity goal of KATRIN on the effective mass of electron anti-neutrino is 0.2 eV at 90 % C.L. Achieving this goal requires high statistics and unprecedented understanding of systematic effects. An important contribution to the systematic uncertainty comes from the instabilities of the energy scale of KATRIN. The work in this thesis focuses on two important aspects of this energy scale, namely the main spectrometer high voltage and the source potential in the Windowless Gaseous Tritium Source (WGTS) of KATRIN. The main spectrometer high voltage is set to 18.6 kV in the b scans and must be measure with precision of 3 ppm or better over one measurement campaign. The stability of this voltage is independently assessed by electrically coupling the monitor Spectrometer to the high voltage and measuring the K-32 line of 83mKr at monitor spectrometer in parallel to b scans at the main spectrometer. The measurements in the second and fourth neutrino mass measurement campaign are analyzed to provide an upper limit on the main spectrometer high voltage fluctuations. Further, different systematic effects at the monitor spectrometer setup are studied using the K-32 and the L3 lines of 83mKr and the analysis of these measurement provides additional knowledge on the energy scale of the monitor spectrometer. The second component that determines the energy of b-electrons is the source potential experienced in the WGTS. The source potential is modified by the existence of plasma in the WGTS during b scans. The characterization of the plasma potential is achieved by introducing gaseous 83mKr in the WGTS and measuring the L3-32 and N2,3-32 lines. The L3-32 measurements from the third neutrino mass measurement campaign are analyzed in this thesis with focus on the systematic effect of background slope on the line width. The results of this analysis provide insight into the plasma potential fluctuations and its evolution with various experimental parameters, an invaluable input for the future of KATRIN.
