Beam bender

A beam bender, comprising:

• an inner electrode having an inner curved surface;
• and
• an outer electrode having an outer curved surface,
• wherein different electrical potentials are applied to each of the inner electrode and the outer electrode to generate an electric field which bends an electron ray that passes between the inner curved surface and the outer curved surface,
• a curvature of the inner curved surface and a curvature of the outer curved surface are set to be fixed, and a center of curvature of the inner curved surface and a center of curvature of the outer curved surface are set to match each other in a first cross section along a direction of travel of the electron ray that passes between the inner curved surface and the outer curved surface,
• the curvature of the inner curved surface and the curvature of the outer curved surface are set to be fixed, and the center of curvature of the inner curved surface and the center of curvature of the outer curved surface are set to match each other in a second cross section perpendicular to the direction of travel of the electron ray,
• a radius of the curvature of the inner curved surface in the second cross section is set to be larger than a radius of the curvature of the inner curved surface in the first cross section, and
• a radius of the curvature of the outer curved surface in the second cross section is set to be larger than a radius of the curvature of the outer curved surface in the first cross section.