Field-emission cathodes for television displays: Electron optics

Field-emission cathodes are a potential alternative to thermionic cathodes in electron tubes. The constraints placed on the use of field-emission cathodes in modulated electron-beam display tubes by the electron optics of the focusing lenses are established in this work. These constraints, which include a sensitivity to spherical aberrations in the electron lenses, a large cathode magnification, and the necessity of modulating the electron beam, require the use of an array of field-emitters. They also require that an electron lens must be associated with each field-emitter of the array, i.e., the cathode must be an emitter-lens array. The cathode magnification of this emitter-lens array is evaluated and compared to the cathode magnification of a field-emission cathode with a single lens and that of a thermionic cathode. The definition of these constraints narrows the selection of field emission cathodes for potential use in electron tubes.