The Straw Tube Detector is the outermost detector of the FINUDA spectrometer studying hypernuclear physics at DAFNE, the Frascati Phi-factory.
Performance requirements on the outermost tracker are a space resolution better than 100um in the r-phi plane and 500um in the z-coordinate for pions of typically 270 MeV/c momentum, low mass and modular construction to cover a large (16 m^2) cylindrical surface. The chosen solution is an array of 2424 aluminized mylar straw tubes arranged in three (one axial and two approximately +-13^o) superlayers, each superlayer with two sub-layers of staggered straws. The inner radius is 110 cm with a full length of about 255 cm for axial superlayers. The basic array element is a 0.03 mm-thick mylar straw, with a 15mm inner diameter, for a total of 404*6=2424 straws.