High-current density, high-brightness electron beams from large-area lanthanum hexaboride cathodes

Large (∼5 cm) diameter lanthanum hexaboride (LaB6) cathodes operated at 10 kV have produced 1–5-μs electron pulses with current density between 10 and 20 A/cm2. Normalized beam brightness, Bn =I/(πβγε)2, approximately 3×105 A/cm2 rad2 has been consistently measured. To obtain this high-current density, the LaB6 cathodes have been heated to temperatures between ∼1600 and 1800 °C. Very uniform temperature profiles are obtained by applying a carefully tailored electron bombardment heating power distribution. These measurements have been made between pressure 10−6–10−5 Torr, i.e., under much less demanding vacuum conditions than that required by conventional dispenser-type cathodes.