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.
