Electron spectroscopy measurements with a shifted analyzing plane setting in the KATRIN main spectrometer

With the KATRIN (KArlsruhe TRItium Neutrino) experiment the endpoint region of the tritium beta decay will be measured to determine the electron-neutrino mass with a sensitivity of 200 meV/c² (90% C.L.). For the high precision which is needed to achieve the sub-eV range a MAC-E filter type spectrometer is used to analyze the electron energy. To understand the various background contributions inside the spectrometer vessel different electric and magnetic field settings were investigated during the last commissioning phase. This talk will focus on the so called shifted analyzing plane measurement in which the field settings were tuned in a way to provide non standard potential barriers within the spectrometer. The different settings allowed to perform a spectroscopic measurement, determining the energy spectrum of background electrons born within the spectrometer.