Radiation source

A radiation source includes a chamber, a supply constructed and arranged to supply a substance to the chamber at a location that allows the substance to pass through an interaction point within the chamber, a laser constructed and arranged to provide a laser beam to the interaction point so that a radiation emitting plasma is produced when the laser beam interacts with the substance at the interaction point, and a conduit constructed and arranged to deliver unheated buffer gas into the chamber at a location adjacent to the interaction point at a rate that removes heated buffer gas from a region around the interaction point before a subsequent interaction between the laser beam and the substance at the interaction point.