A novel laser driven RF structure for the generation of bright electron beams

Abstract

Most X-UV FEL schemes proposed so far need intense and bright electron beams as those typically delivered by laser driven RF injectors. It is well known that the lower the radiation wavelength the tighter are the beam requirements in terms of peak current, emittance and energy spread. In this paper we present a novel RF gun structure suitably designed for the exploitation of the disk bunch technique which is foreseen to neutralize the beam quality deterioration induced by space charge forces. The new RF gun is based on a Wide Plane Wave Transformer (WPWT) structure, that is essentially a modified Plane Wave Transformer operating on a TEM-TM 010π mode. The iris aperture is so enlarged to be comparable to the RF wavelength: this allows one to minimize the beam quality deterioration induced by non-linear transverse RF components. A principal design of a full scale injector, based on a array of WPWT accelerating sections, is presented.