Thermionic sources for high-brightness electron beams

The capabilities and limitations of modern thermionic electron sources for producing high-emission-density (>10 A/cm/sup 2/) high-brightness beams are surveyed. The emphasis is on dispenser cathodes. The fabrication techniques and operating mechanisms that determine the operating limitations of existing commercial cathodes are discussed. In addition, cathode improvements that have been demonstrated in various prototype structures are described. >