The 13 C(α,n)16 O reaction is the prevalent neutron source for the main s-process. The direct measurement of this reaction at stellar temperature (kT =8 keV) has so far not been possible due to the very low cross section at the corresponding energy. The extrapolation of the astrophysical S -factor of this reaction into the Gamow window (Eα,c.m. =140-230 keV) is complicated by the large uncertainties of the low-energy experimental data and the existence of a state of 17 O near the α-threshold that can have a large effect on low energy cross section. The aim of this paper is to introduce the new LUNA experimental setup, dedicated to the investigation of 13 C(α,n)16 O reaction below Eα,lab =400 keV.