A radiation source includes a radiation emitter configured to emit radiation, a collector configured to collect the radiation, and a contamination trap configured to trap contamination emitted by the radiation source. The contamination trap includes a plurality of foils that extend substantially radially, a first magnet ring configured to lie outside of an outer conical trajectory of radiation that is collected by the collector, and a second magnet ring configured to lie within the trajectory of radiation that is collected by the collector. The magnet rings are configured to provide a magnetic field that includes a component that is parallel to the foils.