Status of the KATRIN experiment with special emphasis on source-related issues

Abstract: The Karlsruhe Tritium Neutrino experiment KATRIN will allow a model independent measurement of the neutrino mass scale with an expected sensitivity of 0.2 eV/c^{2} (90% C.L.) and so will help to clarify the role of neutrinos in the early universe is the direct measurement of the mass of the electron anti-neutrino. KATRIN investigates spectroscopically the electron spectrum from tritium beta- decay close to the kinematic endpoint of 18.6 keV with a high resolution electro-static filter of unprecedented energy resolution of 0.93 eV. KATRIN will be built at the Tritium Laboratory Karlsruhe on site of the KIT Campus North. For such a precise mass-determination a key parameter is the stability of the source in terms of beta-activity und isotopic purity. For that purpose KATRIN uses a strong windowless gaseous tritium source of almost pure molecular tritium (95%) with a throughput of 40 g tritium per day stabilized on 0.1% level. The decay electrons are guided adiabatically from the source to the spectrometer by means of superconducting magnets while at the same time the tritium flow rate to the spectrometers has to be reduced by a factor > 1E14. To reach the sensitivity KATRIN is aiming for, an high energy resolution as well as high statistics and low background are needed. A tandem spectrometer system is used for energy analysis. The transport section consists of a differential pumping system (DPS2-F) and a cryogenic pumping section (CPS). In the DPS2-F the tritium flow will be reduced by differential pumping while in the CPS tritium will be adsorbed on a pre-condensed argon layer prepared inside KATRIN's beamtube. To assure the required stability of the source on 0.1% level a stabilized tritium injection in the source is required. This is done by closed tritium loops. The purity and composition of the injected gas will be monitored by Laser Raman spectroscopy.