Generation of a short pulse electron beam by using a photocathode RF gun and a picosecond pulse laser

Abstract

A bright femtosecond pulse X-ray source could provide new foundations of industrial technology and new tool in scientific investigation. Inverse Compton scattering between laser and electron beam is the most promise method for generation of such short X-ray pulses. For this purpose, production methods of ultrashort pulses for both laser and electron beam are needed. One candidate to-obtain the short electron pulses is a laser-driven photocathode RF gun because of its outstanding beam characteristics. A photocathode RF gun driven by a picosecond Nd:YAG laser has been manufactured It is composed mainly of 1.6-cell S-band RF cavity and pure copper photocathode, bearing a water cooling system which can keep the whole body at adequate temperature even in the high-duty operation up to 50Hz, using 3/spl mu/s RF pulses with peak power of 7MW. Electrons emitted from the surface of the photocathode are accelerated by the RF electric field. The final energy of the electron beam at the exit of the gun, is 4.5 MeV for the RF peak power of 7 MW. A solenoid magnet serves emittance compensation of the output electron beam. The laser system is a diode pumped solid state laser. The output pulses of the oscillator, Nd:YVO/sub 4/ laser, with the wavelength of 1064 nm are amplified by two stages of Nd:YAG amplifiers, and then converted to UV (266 nm) by two nonlinear-optical crystals. The oscillation frequency is stabilized by synchronization to external reference RF(119 MHz). The reference RF signal is generated from a highly precise RF generator in the timing synchronization of the RF gun control circuit. The characteristics of the laser pulse are given. An image relay optics, which is composed of pairs of prisms and a grating, is used to achieve light pulse irradiation with the wave plane parallel to the cathode surface under an oblique incidence angle.