Development of a Multialkali Photocathode Dc Gun for a Smith-Purcell Terahertz Free-Electron Laser

We have developed a photocathode dc gun for a compact Smith-Purcell free-electron laser in the terahertz wavelength region. The gun system consists of an alkali antimonide photocathode preparation chamber, a dc gun with a 250 kV-50 mA Cockcroft-Walton high-voltage power supply, and a downstream beamline with a water-cooled beam dump to accommodate a beam power of 5 kW. We fabricated a Cs3Sb photocathode with quantum efficiency of 5.8% at a wavelength of 532 nm and generated a 150 keV beam with current of up to 4.3 mA with a 500 mW laser. A vacuum chamber for the Smith-Purcell free-electron laser has been installed in the downstream beamline. We describe the present status of our work.