NUMERICAL SIMULATIONS OF SPACE CHARGE COMPENSATION EFFECTS IN ION BEAMS

Two axisymmetric, transverse models of space-charge compensation are proposed in order to compute the selfconsistent potential of a proton beam and of the plasma generated by the beam when it evolves in a residual gas and ionises its molecules. The first model consists in a stationary hydrodynamic description. The limitation of this model is shown in an experimental case where electrons are not thermalized. A kinetic model which computes the build up of space-charge compensation towards a stationary state is presented. Its numerical resolution is based on an explicit PIC method. Tests of this model on the same experimental case are shown and compared to measurements.