Asymmetric emittance beam generation using round beam RF guns and nonlinear optics

Future generation electron-positron linear colliders need asymmetric flat beams in order to properly control the beam-beam interaction at the final focus. Room temperature collider designs ask for normalized rms transverse emittances which look not attainable by RF photo-injectors, whilst the requirements of the TESLA superconducting collider (ε_nx=20 mm mrad, ε_ny=1 mm mrad) are at the edge of the present RF gun status of the art, except for the asymmetric emittance requirements. In this paper we explore the efficiency of conventional round-beam RF guns in conjunction with non-linear optical devices, namely sextupole triplets, as converters of round beams into flat beams, in order to match the TESLA specifications. Basically the beam emittance, at the exit of the gun, must be dominated by non-linear effects (spherical aberrations). A quadrupole doublet and a sextupole triplet, placed downstream the beam transport line, provide respectively a geometric astigmatism and an asymmetric emittance correction in the vertical and in the horizontal phase-spaces. The possibilities to produce asymmetric beams using this technique are presented