Simulation of background by Rydberg states in the KATRIN mainspectrometer

The KArlsruhe TRItium Neutrino (KATRIN) experiment is a large-scale experiment for the model independent determination of the mass of electron anti-neutrinos with a sensitivity of 200 meV/c². It investigates the kinematics of electrons from tritium β-decay close to the endpoint of the energy spectrum with a highresolution electrostatic spectrometer (ΔE=0.93 at 18.6 keV). Due to the low signal rate near the endpoint a low background level is of very high importance. Rydberg atoms excited and desorbed from the spectrometer surface can penetrate in the sensitive flux tube uninfluenced by fields and be ionised by thermal radiation. The talk presents detailed simulation and analysis of this particular background process.