Measurements with the KATRIN pre-spectrometer

The objective of the KArlsruhe TRItium Neutrino experiment (KATRIN) is a direct measurement of the absolute mass of the electron (anti)neutrino by means of precise spectroscopy of the tritium ββ-spectrum near its endpoint.The pre-spectrometer is part of the KATRIN reference set-up where it will work as a pre-filter for low energy ββ-decay electrons that are inessential for the determination of the νν-mass. Since its delivery in autumn 2003 the pre-spectrometer has been the first major hardware component of KATRIN in operation at Forschungszentrum Karlsruhe (FZK). The vacuum measurements were successfully completed in early 2005. The main results are an outgassing rate for the stainless steel surface of the pre-spectrometer of 10−12 mbar l/s cm2 at room temperature and a final pressure below 10−11 mbar. This corresponds to the specification of the main spectrometer. The amount of Non-Evaporable-Getter (NEG) strips needed can be restricted to about 3000 m and the additional cooling of the main spectrometer is optional, if a combined pumping system of NEG and turbo-molecular pumps (TMPs) is installed, that will provide a sufficient pumping speed.The modification of the pre-spectrometer set-up for the electromagnetic measurements is nearly completed, and the measurements will start in spring 2006.