Operation modes of the KATRIN experiment Tritium Loop System using ^83mKr

The KArlsruhe TRItium Neutrino (KATRIN) experiment aims to search for the effective electron antineutrino mass with a sensitivity of 0.2 eV (90 % C.L.). In order to achieve this goal, KATRIN measurement phases focusing on the neutrino mass search are alternated with phases of investigations of systematic effects. During these phases, metastable ^83mKr is used as a calibration source. The monoenergetic conversion electrons emitted accompanying the decay of ^83mKr allow a direct access to the starting conditions of β-electrons produced inside the windowless gaseous tritium source (WGTS) of KATRIN. To make use of ^83mKr in the WGTS, the Tritium Loop System, which provides a stable flow of tritium to the WGTS, needs to be operated in special modes. This paper focuses on the technical implementation of these modes and their performance with regard to the achievable ^83mKr-rates, gas densities, and gas compositions inside the WGTS.