Patent Number: 
Section: abstract

Apparatus and methods are disclosed for producing a flux of X-rays, from a plasma, wherein the flux remains rotationally symmetrical about a propagation axis over a period of use, even if the plasma produce flying debris. The plasma can be generated by a laser-plasma source or a discharge-plasma source, for example. The X-rays produced by the plasma are directed by an optical element to a downstream location. To such end, the optical element is located where it is subject to deposition and accumulation of flying debris from the plasma. The optical element has an axis of rotational symmetry. A rotational actuator is situated relative to the optical element and is configured to rotate the optical element about the axis of rotational symmetry during use. Hence, if deposits of flying debris form on the optical element, the deposits will be rotationally symmetrical and thus have an identical affect on the X-ray flux at any angle about the axis of rotational symmetry.