2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/153320Electron bunches with charge densities $ρ$ of the order of $10^2$ to $10^3$ [nC/cm$^3$], energies between $20.$ and $100.$ [MeV], peak current $>100$ [A], bunch lengths between 0.3 and 1.8 [cm], and bunch charge of 2.0 to $20.$ [nC] are relevant to the design of Free Electron Lasers and future linear colliders. In this paper we present the results of numerical simulations performed with a particle in a cell (pic) code of an electron bunch in a drift tube. The electron bunch has cylindrical symmetry with the $z$-axis oriented in the direction of motion. The charge density distribution is constant in the radial and Gaussian in the longitudinal direction, respectively. The electron bunch experiences both a radial pinch in the middle of the pulse, corresponding to the peak electron density, and a significant growth of the correlated emittance. This behavior is explained, and an approximate scaling law is identified. Comparisons of the results from the pic and PARMELA codes are presented.Latex2e format; requires elsart and epsfig packages; 16 PS pages; 14 embedded figures from 16 EPS filesAccelerator PhysicsClassical PhysicsComputational PhysicsPlasma Physicstext