The role of Coulomb fields in the formation of emittance in photoguns

A theoretical analysis is made of the formation of longitudinal and transverse emittance of beams of charged particles in photoguns under the influence of repulsive forces of Coulomb fields. In numerical calculations, the characteristics of bunches of charged particles with uniform and Gaussian charge density distributions are compared. The efficiency of the proposed numerical-analytical model is compared with calculations using the Astra program. The obtained numerical and analytical results can be useful in the design of photoinjectors to select the optimal parameters that determine the main characteristics of photoguns.