Wakefield effects on the beam accelerated in a photo injector: perturbation due to the exit aperture

The influence of the photoinjector exit aperture on the wakefield generated by the strongly accelerated electron beam, has been theoretically studied in a companion paper. In this communication we study the effects of such a wakefield on the beam, in that propagation stage where the beam approaches the hole and enters it, i.e. the propagation stage where the influence of the photoinjector exit hole must be taken into account. First, the perturbated wakefield map (E , B)(x, t) is shown for various instants, and for photoinjector and beam parameters corresponding to typical values on ELSA, the CEA-Bruyeres-le Chatel high-current, high-brilliance electron beam facility. Then, the effects on the beam quality are studied in terms of emittances, when the beam approaches the hole. These effects are compared to the corresponding ones, previously obtained for a wakefield map where the exit hole perturbation had been neglected