Tritium migration along the cryopumping section

Abstract

The transport section of the Karlsruhe Tritium Neutrino experiment (KATRIN) must provide the dramatic reduction of tritium flow and gas density from the end of a 10-m-long windowless gaseous tritium source throughout several stages of a differential pumping system. The final stage of this section, the cryogenic pumping section (CPS) based on pumping of tritium on argon frost at 4.5 K, should provide the flow ratio between inlet and outlet in the range of 107. Cryosorbed tritium may decay, emitting a few keV electrons. These electrons in their turn cause the electron-stimulated desorption of cryosorbed argon and tritium, which is redistributed along the CPS (migration process). This effect was modeled with the use of the method of angular coefficients. The main result is that the tritium migration process does not affect the CPS performance at KATRIN for a given inlet flow. Meanwhile, if the flow chosen is larger, the migration effect could be dominant.