Abstract: A radio-frequency (RF) cavity apparatus for accelerating charged particles includes first and second cavity arms. The first and second cavity arms have respective first and second axes of rotational symmetry and each cavity arm includes at least one cell. The first and second cavity arms are connected by a resonance coupler. The cell(s) of the first cavity arm have an axial dimensional parameter that is equal to a corresponding axial dimensional parameter of the cell(s) of the second cavity arm, and the cell(s) of the first cavity arm have at least one non-axial dimensional parameter that differs from corresponding non-axial dimensional parameter(s) of the cell(s) of the second cavity arm.

Abstract: A radio-frequency (RF) cavity apparatus for accelerating charged particles includes first and second cavity arms. The first and second cavity arms have respective first and second axes of rotational symmetry and each cavity arm includes at least one cell. The first and second cavity arms are connected by a resonance coupler. The cell(s) of the first cavity aim have an axial dimensional parameter that is equal to a corresponding axial dimensional parameter of the cell(s) of the second cavity arm, and the cell(s) of the first cavity arm have at least one non-axial dimensional parameter that differs from corresponding non-axial dimensional parameter(s) of the cell(s) of the second cavity arm.

Abstract: An apparatus comprises a charged particle beam source and a target (1) for a charged particle beam. The target comprises a concave outer surface which is at least a segment of a cylinder (2) having a periodically structured surface (4). The charged particle beam is directed parallel to the axis of the cylinder (2), with the distance of the charged particle beam from the surface being less than or equal to twice the period of the periodically structured surface (4) in a direction perpendicular to the charged particle beam. The width of the charged particle beam in a direction perpendicular to the charged particle beam and parallel to the outer surface of the target is less than twice the period of the periodically structured surface (4) in a direction perpendicular to the charged particle beam.