A radiation system for providing a projection beam of radiation in a lithographic apparatus is disclosed. The radiation system includes an EUV source for providing EUV radiation, and a contamination barrier that includes a plurality of foil plates for trapping contaminant material coming from the EUV source. The foil plates are arranged in an optically closed arrangement so that at least one of the foil plates reflects EUV radiation passing the contamination barrier at least one time.