TESLA FEL PHOTO-INJECTOR SIMULATIONS GIVING HIGH-QUALITY BEAMS

To obtain a high-brightness beam for the TESLA FEL project, operating in the VUV region, a photo-injector providing a high-quality beam is n eeded, i.e., the rms radial and longitudinal emittances must be, respe ctively, of the order of 1 mm mrad and 20 mm KeV [1]. With these drast ic conditions, we cannot use an analytical model with some approximati ons or scale laws, a refined study of the beam dynamics with a numeric al code is necessary. The quality optimization is all the more difficu lt since many parameters play a role in the beam dynamics. The beam dy namics is simulated by the numerical code ATRAP (Acceleration and TRAn sport of Particles) [2-5], using the Lienard-Wiechert's equations to d escribe the self-electromagnetic held. To reduce the total time of thi s optimization, we have chosen the RF peak field on the cathode, betwe en 40 and 60 MV/m, high enough to decrease the space charge effect and not too high to avoid the defocusing effect of the RF field. In this paper, we show the influence of the different parameters on the beam q uality.