Photocathode dc electron gun for next-generation light-sources

Nagai, Ryoji; Hajima, Ryoichi; Nishimori, Nobuyuki

An energy-recovery linac (ERL) is a new class of electron accelerator to generate a small-emittance and high average current electron beam at high-repetition rate. Now, ERL is considered as a promising device for next-generation light sources which have ultra-short pulse and high-coherency. An electron gun to produce a small-emittance electron beam with high-average current is the most important component for an ERL to exploit its full potential because the emittance and current of the ERL beam are determined by performance of its electron gun. A dc electron gun is able to generate a high-current electron beam of ultrasmall initial emittance, when it is equipped with a semiconductor photocathode having a negative electron affinity (NEA) surface. To suppress emittance growth by space charge effect, the gun voltage must be 500 kV or higher. In this paper, we present details of the electron gun design and results of a high-voltage testing.