A radiation source, e.g. for EUV for use in a lithographic apparatus, generates radiation by illuminating droplets of fuel with first radiation to form a plasma and collects second radiation omitted by the plasma using a collector (CO). The collector has an aperture and the fuel passes along a vertical trajectory through that aperture before being irradiated by the first radiation. In an embodiment the first radiation is directed along a beam, the final part of which is coincident with the final part of the trajectory of the fuel droplets. In an embodiment a gas flow is arranged coincident with the fuel trajectory and/or the beam of first radiation.