Monte Carlo simulation of gas flow through the KATRIN DPS2-F differential pumping system

The Karlsruhe Tritium Neutrino experiment (KATRIN) is a large vacuum system and aims to measure the electron neutrino mass from the β decay of tritium with unprecedented sensitivity. To achieve this purpose, the tritium gas flow has to be significantly reduced along the beamline by means of a modular differential pumping system. This paper studies systematically the vacuum performance of one of the differential pumping systems (known as DPS2-F) based on turbomolecular pumps. The flow reduction rates in the complete system are described by a matrix equation as a function of the capture factor of the turbomolecular pumps employed. The results show that a total reduction factor greater than 10⁵ can be attained, which is one of the prerequisites to achieve XHV conditions in the spectrometers used in the downstream end of the experiment.