A thermionic-cathode RF gun for compact FEL use

Conventionally designed thermionic-cathode RF guns, such as the one used in the Stanford Far-Infrared Free-Electron Laser (FIRFEL) experiment, typically generate electron beams with large energy spreads. In order to use such a gun as the sole accelerator, most of the beam must be discarded to reduce the energy spread to acceptable levels. It is possible to design a thermionic-cathode RF gun, which produces an electron beam essentially monochromatic in energy. One- and three-dimensional simulations indicate that an electron beam can be produced with more than 90% of the beam current in a 1% energy spread, over a range of kinetic beam energies of 2–6 MeV. This may be accomplished while retaining reasonable beam emittances. Such a gun is ideal for use with a compact FEL, such as the FIRFEL experiment. Potential benefits include a larger operational wavelength range, higher power output, greater efficiency, and shorter beamlines.