High-brightness electron injectors: a review

The approaches now being explored for attaining intense, bright electron beams are described. The methods for producing bright electron beams include photocathode-based short-pulse injectors; DC electrostatic accelerator sources; long-pulse beams, which are then compressed in time using subharmonic bunching; combining first and third harmonics in an accelerator to attain the equivalent of high-gradient DC fields; and LaB/sub 6/ RF guns. For several of the approaches, the temporal length of the electron pulse is decreased after acceleration to relativistic energies by impressing an energy spread on the electron bunch and using a nonisochronous beam-transport system to increase the peak current.<>