Electron Bunch Space Charge Influence upon Its Energy Spread and Sizes under the Motion in Free Space

The influence of Coulomb repulsion in electron bunch upon its energy spread and sizes under the motion in free space after leaving the linac is considered. Space charge field calculations based upon the model of charged ellipsoid, were carried out in the range of electron energies from 1.0 to 10.0 MeV and beam pulse currents from 0.2 to 10 mA. The bunch travelling path being 2.5 m longitudinal Coulomb repulsion results in relative energy spread of a bunch from 10-4 to 2.10-2. The effect examined should be taken into account when electron linac with high energy resolution is designed.