Patent Number: 
Section: claims

1. An assembly comprising:a detector comprising at least one wire configured to be positioned in a beam of radiation so that electrons are ejected from the at least one wire when the at least one wire is exposed to the beam of radiation, the detector being configured to generate a detector signal correlated to the electrons being ejected from the at least one wire;a meter configured to measure the detector signal;a memory coupled to the meter; anda processing device coupled to the meter and the memory, wherein the processing device is programmed to store the detector signal in the memory as a function of time and as an indication of contamination. 2. An assembly according to claim 1, wherein the detector signal is related to a current in the at least one wire and the meter comprises a current meter. 3. An assembly according to claim 1, wherein the assembly is located in a vicinity of an optical component. 4. An assembly according to claim 1, wherein the at least one wire is negatively biased. 5. An assembly according to claim 1, wherein the at least one wire comprises at least one dielectric material and a portion of a closed loop connected to a voltage source. 6. An assembly according to claim 5, wherein the voltage source is configured to supply a voltage in synchronism with the radiation flux. 7. An assembly according to claim 1, wherein the at least one wire comprises an electrically conducting material and a portion of a closed loop connected to a voltage source. 8. An assembly according to claim 7, wherein the voltage source is configured to supply a voltage in synchronism with the radiation flux. 9. An assembly according to claim 5, wherein the at least one wire is at least partly covered with a conducting layer. 10. An assembly according to claim 5, wherein the at least one dielectric material comprises Al2O3 and/or Si02. 11. An assembly according to claim 9, wherein the conducting layer comprises Si. 12. An assembly according to claim 1, wherein the at least one wire is placed in the vicinity of a radiation source in order to measure an amount of debris ejected by the radiation source and the at least one wire is connected to a voltage source. 13. An assembly according to claim 1, wherein the at least one wire is located on an optical component. 14. An assembly according to claim 13, wherein the optical component comprises a multilayer minor. 15. An assembly according to claim 1, wherein the at least one wire comprises at least one fluorescent portion. 16. An assembly according to claim 1, wherein the detector comprises a plurality of wires electrically isolated with respect to each other and form a mesh, and wherein the assembly further comprises a plurality of meters configured to measure individual detector signals generated by each of the plurality of wires. 17. An assembly according to claim 12, wherein the voltage source is configured to supply a voltage in synchronism with the radiation flux. 18. An assembly according to claim 1, wherein the at least one wire is at least partly enclosed by a shielding device. 19. An assembly according to claim 18, wherein the shielding device is configured to shield the at least one wire from an electrical field and/or a magnetic field. 20. A lithographic apparatus, comprising:an illumination system configured to provide a beam of radiation;a support configured to support a patterning structure, the patterning structure configured to impart the beam of radiation with a pattern in its cross-section;a substrate table configured to hold a substrate;a projection system configured to project the patterned beam onto a target portion of the substrate; andan assembly for determining a radiation flux, the assembly comprising:a detector comprising at least one wire configured to be positioned in the beam of radiation so that electrons are ejected from the at least one wire when the at least one wire is exposed to the beam of radiation, the detector being configured to generate a detector signal correlated to the electrons being ejected from the at least one wire;a meter configured to measure the detector signal;a memory coupled to the meter; anda processing device coupled to the meter and the memory, wherein the processing device is programmed to store the detector signal in the memory as a function of time and as an indication of contamination. 21. A device manufacturing method, comprising:positioning at least one wire in a beam of radiation so that electrons are ejected from the at least one wire when the at least one wire is exposed to the beam of radiation;patterning the beam of radiation;projecting the patterned beam of radiation onto a target portion of a substrate;generating a signal correlated to the electrons being ejected from the at least one wire;measuring the signal with a meter; andstoring, using a programmed processing device, in a memory the measured signal as a function of time, wherein the stored measured signal is an indication of contamination. 22. An assembly according to claim 1, wherein the beam of radiation comprises EUV radiation. 23. A lithographic apparatus according to claim 20, wherein the beam of radiation comprises EUV radiation. 24. A device manufacturing method according to claim 21, wherein the beam of radiation comprises EUV radiation. 25. A method, comprising:positioning at least one wire in a beam of radiation so that electrons are ejected from the at least one wire when the at least one wire is exposed to the beam of radiation;generating a signal correlated to the electrons being ejected from the at least one wire;measuring the signal with a meter; andstoring, using a programmed processing device, in a memory the measured signal as a function of time, wherein the stored measured signal is an indication of contamination.