KATRIN design report 2004

After the KATRIN Letter of Intent in 2001 and the Addendum to the LoI in 2002, this Design Report 2004 gives a detailed overview of the KATRIN experiment in its phase of building and testing of the first components. We critically assess the actual status in neutrino physics with respect to direct and indirect searches on the neutrino mass in particle physics and cosmology and the impact by KATRIN. The physical parameters as well as the schemes for the technical realization of the central experimental components and their status are reported. Having optimized the experimental configuration compared to the LoI, we anticipate a KATRIN sensitivity on the neutrino mass of m(ν e ) = 0.2 eV (90% C.L.) corresponding to a 5 σ discovery potential for m(ν e ) = 0.35eV, based on a detailed assessment of systematic and statistical uncertainties.