Technical challenges of neutrino factories

Using muons as a source of neutrinos can be traced back to 25 years ago but it is with the recent studies on muon colliders that this idea came back to the front of the stage. The threshold of interest for neutrino oscillation experiments is attained with about 1020 muons per year stored in the decay ring where the neutrinos created in the muon decay are emitted towards the detector. For ultimate CP violation experiments, at least 1021 muons per year have to be stored. A neutrino factory is a major investment and has to be built with ultimate performances in mind even if they cannot be achieved at the begining. The various stages of pion production by powerful proton beams, collection of secondary particles, fast acceleration and storage of muons are reviewed.