Patent Number: 
Section: claims

1. A radiation source configured to produce extreme ultraviolet radiation, the radiation source comprising:a chamber in which, in use, a plasma is generated to provide the radiation;a heating system configured to maintain an evaporation surface at a temperature to evaporate a material formed as a by-product from the plasma and that is emitted to the evaporation surface; anda vessel having an inner wall and an outer wall, the inner wall comprising the evaporation surface, and the outer wall has a higher emissivity than the inner wall. 2. The radiation source according to claim 1, wherein inner wall comprises a polished metal material. 3. The radiation source according to claim 1, wherein the outer wall comprises a ceramic material. 4. The radiation source according to claim 1, wherein the inner wall is conically-shaped. 5. The radiation source according to claim 1, further comprising a cooler configured to cool the outer wall. 6. The radiation source according to claim 1, wherein the evaporation surface has a RMS roughness of between about 10 nm and about 1 mm, or is porous, or has a plurality of protrusions thereon or therein. 7. A radiation source configured to produce extreme ultraviolet radiation, the radiation source comprising:a chamber in which, in use, a plasma is generated to provide the radiation;a vessel structure within the chamber, the structure configured to receive the radiation in its interior;a gas injector arranged to inject a gas flow in the chamber at an edge of the structure; andan outlet to draw injected gas flow from the edge of the structure towards an interior of the structure. 8. The radiation source according to claim 7, further comprising a heating system configured to maintain an evaporation surface at a temperature to evaporate a material formed as a by-product from the plasma and that is emitted to the evaporation surface, the structure having the evaporation surface. 9. The radiation source according to claim 8, wherein the structure comprises an inner wall and an outer wall, the inner wall having the evaporation surface and the gas injector is configured to feed the gas between the inner and outer walls. 10. The radiation source according to claim 7, wherein a surface of the structure is at least partially conically-shaped. 11. The radiation source according to claim 7, wherein the injector is configured to feed gas along an outer surface of the structure towards and along the edge of the structure. 12. The radiation source according to claim 7, wherein the gas injector is configured to inject a ring-shaped gas curtain in the chamber. 13. The radiation source according to claim 7, wherein the vessel structure has an optical axis and the gas injector is configured to inject the gas flow in a direction substantially parallel to the optical axis. 14. The radiation source according to claim 7, wherein the vessel structure has a first opening to receive the radiation and a second different opening to discharge the received radiation, wherein the outlet is configured to draw injected gas through the first opening and toward second opening. 15. A radiation source configured to produce extreme ultraviolet radiation, the radiation source comprising:a chamber in which, in use, a plasma is generated to provide the radiation; andan outlet conduit to remove debris from the plasma, the outlet conduit having a cooling structure to condense the debris from a gas flow in the outlet conduit. 16. The radiation source according to claim 15, wherein the cooling structure comprises a cooling ring or spiral in a wall of the outlet conduit. 17. The radiation source according to claim 15, wherein an opening of the outlet conduit has a cone-shaped surface and the cooling structure is located at or in the cone-shaped surface. 18. The radiation source according to claim 15, wherein the cooling structure is further configured to capture the condensed debris and remove the condensed debris from the outlet conduit upstream of a pump for the outlet conduit. 19. The radiation source according to claim 15, wherein the cooling structure is further configured to prevent condensed debris from flowing out of the outlet conduit. 20. The radiation source according to claim 15, further comprising a heating system configured to maintain an evaporation surface at a temperature to evaporate the debris.