Disclosed are methods and apparatus for generating an illumination beam. In one embodiment, the apparatus includes a vacuum chamber configured to hold a target material, an optical element positioned within the vacuum chamber or within a wall of such vacuum chamber, and an illumination source system for generating at least one excitation source that is focused on the target in the vacuum chamber for generating a plasma in the vacuum chamber so as to produce illumination radiation. The apparatus further includes a debris protection system for flowing gas out of a plurality of nozzles and away from the optical element at a velocity towards the plasma so as to prevent debris from reaching such optical element.