Assembly and method for reducing foil wrinkles

A method for reducing wrinkles in an exit window foil of an electron beam device, which wrinkles may arise due to surplus foil arising in the assembly process, said exit window foil being bonded to a support plate along a closed bonding line bounding an area in which the support plate is provided with apertures and foil support portions and in which area the exit window foil serves as a portion of a wall of a vacuum tight housing of the electron beam device,

• the method comprising:
• providing, within said area, a pattern of apertures and foil support portions alternately in the support plate, which pattern, when vacuum is created in the housing, forms a topographical profile of the exit window foil absorbing any surplus foil,
• the exit window foil and support plate area, within the closed bonding line, being defined by a cylindrical coordinate system having an axial axis, a radial axis and an angular axis, said axial axis being aligned with an axial centre axis of the support plate, and said radial axis being aligned with a radius of the support plate within the closed bonding line,
• the absorbing of the surplus foil occurring by a dominant bending of the exit window foil in the apertures created around either the radial axis or the angular axis,
• the foil support portions of the support plate, within said area, being comprised of concentric rings connected to each other by radially directed spokes, the radially directed spokes each having an arc-shaped concave upper surface facing the foil.

An electron beam generating device comprising:

• a vacuum chamber configured to be connected to a vacuum source to create a vacuum in the vacuum chamber;
• a filament positioned in the vacuum chamber and configured to emit electrons;
• a control grid positioned in the vacuum chamber;
• an electron exit window through which, electrons emitted by the filament, pass;
• the electron exit window comprising an exit window foil and a support plate serving as a support for the exit window foil, the exit window foil being bonded to the support plate along a closed bonding line bounding an area, the support plate including apertures and foil support portions that alternate with one another and form, when the vacuum is created in the vacuum chamber, a topographical profile of the exit window foil absorbing any surplus foil;
• and
• the foil support portions comprising concentric rings connected to each other by radially directed spokes, the radially directed spokes each having an arc-shaped concave surface extending between radially adjacent concentric rings and facing the foil.