Lithographic projection apparatus equipped with extreme ultraviolet window serving simultaneously as vacuum window

1. Field of the Invention A lithographic projection apparatus has a discharge plasma radiation source that is contained in a vacuum chamber. The radiation source is to generate a beam of EUV radiation. A chamber wall of the vacuum chamber incorporates a channel structure comprising adjacent narrow channels separated by walls that are substantially parallel to a propagation direction of the radiation generated so as to pass the radiation from the vacuum chamber through the structure to another subsequent vacuum chamber. In the subsequent vacuum chamber, a much higher vacuum level (lower pressure) can be maintained than is present in the vacuum chamber of the radiation source.