Rapid electrographic and electrophotographic processes. Lenard window for electrostatic printing tubes

Lenard-windows consisting of plastic, metal, mica, or alumina foils for use on printing tubes, were investigated. For better mechanical stability metallic grids were used, in some cases bound to the foil. The transmission of the windows is about 50 % for 20 keV electrons. The transmitted current is amplified about 20 times by ionization in the air gap between window and paper (0.2 to 0.3 mm), reaching 50 microamps. The current is sustained by a voltage of 300 to 500 volts, causing no avalanche multiplication. Thus, a resolution of 10 1 p/mm is possible at a writing velocity of 500 m/s with an optical density smaller than 1.4 on the dielectric paper.