EMITTANCE MEASUREMENT ON THE CEB6 ELECTRON GUN FOR THE SPRING-8 COMPACT SASE SOURCE

A 500 kV pulsed electron gun has been developed for the injector system of the X-ray FEL project at SPring-8. A single-crystal CeB6 cathode is chosen as a thermionic emitter, because of its excellent emission properties, i.e., high resistance against contamination, uniform emission density, and smooth surface. A gun voltage of -500 kV was chosen as a compromise between the need for suppressing emittance growth and reducing the risks of high voltage arcing. We have succeeded in producing a 500 keV beam with 1 A peak current and 3 µsec width. A normalized rms emittance of 1.1π mm.mrad has been measured by means of double-slit method. In this paper, we report on the result of the emittance measurement and discuss improvements for X-ray FEL.