Cathode-ray tube

摘要

A cathode-ray tube having an electron gun to generate an electron beam and a focusing lens to focus the electron beam on a target. The anode of the electron gun forms part of the focusing lens and has a very small aperture to limit the electron beam. In order to prevent positive ions formed in the tube from poisoning the cathode the potential of the anode is at most 75 volts relative to the cathode potential and the distance from the center of the focusing lens to the aperture in the anode is at least equal to 1.5 times the largest dimension of the anode taken in a cross-section at right angles to the axis.