A new type of cathode-ray tube with a crossed-field gun

This paper introduces a new type of cathode-ray tube with a novel electron gun which produces an electron beam in a region where a nonuniform magnetic field and an electric field cross perpendicularly. The tube has the following features: 1. Increase in the beam current density makes possible a reduction in the accelerating voltage to 6 to 8 kV (that is, 20 to 30% lower than that of ordinary cathode-ray tubes) while maintaining the same screen brightness. 2. By using a directly heated cathode only 0.7 to 1.0 sec is necessary for warm-up, and only about 0.4 watt of heater power is required. 3. By an ion-trap effect, the fluorescent screen is protected from damage caused by negative ion bombardment. Accordingly, the thickness of the metal back layer can be reduced greatly to the limiting value required for good reflectivity. Furthermore, a long life can be expected because of a reduced probability of bombardment of the cathode with positive ions. 4. Cutoff voltage is --20 to -30 volts or about 1/3 to 1/2 that of ordinary tubes. The paper includes an analysis of electron motion in crossed fields with a nonuniform magnetic field. The equilibrium condition required to produce the electron beam in such crossed fields can be derived in terms of the magnetic field distribution function. The paper also shows practical configuration of electrodes and magnet and current characteristics of the gun.