Thermal degradation study of the NEA-GaAs surface at high temperature

We report that a thermal property of GaAs photocathode activated the surface to negative electron affinity (NEA) at various temperatures. An electron source with the NEA-GaAs photocathode is an important device for high-average-current electron accelerators, such as a next-generation light source based on an energy recovery linac, in which a high power laser is illuminated to the photocathode for generation of the electron beam of 100 mA. Consequently the high power laser causes to rise the GaAs temperature. The achievable temperature estimated by numerical calculations is 72℃ for the laser power of 7.5 W. We have measured the cathode lifetime at various temperatures to evaluate the thermal property of the NEA surface. The degradation of photo emission from the cathode is enhanced by a thermal desorption of Cs/O adlayer due to the temperature rise, even if the beam is not extracted. (author)