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

Abstract

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.

Analysis methods for the first KATRIN neutrino-mass measurement

“…An angular-selective source of monoenergetic photoelectrons (electron gun) (36) is used to measure the gas density in the tritium source down to sub-percent precision. The co-circulation of 83m Kr with tritium and other carrier gases (37,38) allows us to determine the electron starting potential within the source and the electromagnetic fields in the spectrometer.…”

“…The variations of the source potential are measured with 83m Kr conversion electrons, using the new operation mode of the tritium loops, which allows co-circulation of krypton and tritium in the same conditions as in the β-spectrum scanning mode (38). The rear-wall bias voltage was chosen to provide the best radial homogeneity of the source potential, measured with the position of L 3 -32 line.…”