Charged particle beam targets

An apparatus comprising a charged particle beam source and a target for a charged particle beam, the target comprising a concave outer surface, the concave outer surface comprising at least a segment of a cylinder with a periodically structured surface, wherein a charged particle beam is directed in a direction parallel to a longitudinal axis of the cylinder, the charged particle beam is distanced from the periodically structured surface by less than or equal to twice a period of the periodically structured surface in a direction perpendicular to the charged particle beam, and the width of the charged particle beam in a direction that is perpendicular to the charged particle beam and that is parallel to the concave outer surface of the target is less than twice the period of the periodically structured surface in the direction perpendicular to the charged particle beam.

A method of allowing a charged particle beam to strike a target, the target comprising a concave outer surface, the concave outer surface comprising at least a segment of a cylinder with a periodically structured surface, the method comprising:

• generating the charged particle beam having a width, in a direction perpendicular to the charged particle beam and parallel to the concave outer surface of the target, less than twice a period of the periodically structured surface in a direction perpendicular to the charged particle beam;
• and
• directing the charged particle beam parallel to a longitudinal axis of the cylinder at a distance from the periodically structured surface that is less than or equal to twice the period of the periodically structured surface in the direction perpendicular to the charged particle beam.