This research disclosure relates to a sealing arrangement for use in a radiation source. The radiation source may be part of a lithographic system. The lithographic system also includes a lithographic apparatus. The lithographic apparatus may be. for example, an extreme ultraviolet (EUV) lithographic apparatus. Figure 1 schematically shows an exemplary radiation source. The radiation source comprises a droplet generator that is arranged to produce a stream of fuel droplets along a fuel droplet trajectory and a laser arranged to produce a laser beam that intersects this trajectory. Typically, tin is used as a fuel. The droplet generator may comprise a nozzle for directing the fuel droplets along the fuel droplet trajectory. The laser beam is incident on the fuel droplets and at least partially converts the droplets into a plasma at a plasma region. The plasma subsequently emits EUV radiation. The radiation source also comprises a collector mirror, which is arranged to collect the EUV radiation. The collector mirror may locus the EUV radiation at an intermediate locus, which may be proximate an exit aperture in an enclosure (not shown) of the radiation source. The collector mirror may comprise a central aperture through which the laser beam propagates towards the fuel droplets. This type of radiation source is known as a laser-produced plasma (LPP) source.
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