Abstract: An electron beam window structure for broad area electron beam generators wherein a stream of electrons generated in an evacuated enclosure and extending over a broad area are passed through a thin window to a region of high pressure outside the enclosure. The structure is positioned between the metal window and the electron emission means of the electron beam generator and comprises a generally flat metal plate of high thermal conductance having closely spaced parallel slots extending over and covering the intended area of the electron beam. The bottom of each slot is disposed adjacent one surface of the plate and over its length and is provided with a row of closely spaced holes of the same diameter as the bottom width of the slot. The holes go through the remaining material leaving a small web between adjacent holes. The metal window is mounted on the slotted side of the plate while the side of the plate with the holes faces the emission means disposed in the evacuated enclosure.