Penetration of a plasma by a beam in multipulse radiography

Summary form only given. In multipulse radiography, electron beam pulses will encounter a background plasma consisting of low atomic weight elements such as water vapor and hydrocarbons, and also vaporized target material, generated by previous pulses. This is important because subsequent pulses penetrating the plasma plumes may suffer spot size increase and misalignment with the radiographic axis if the beam propagation is unstable. The region of this material that is farthest from the target will have a low density and will be collisionless. The beam will collisionlessly penetrate this intervening plasma, rather than pushing a hole through it as would happen in the high density fluid regime. The particle in cell code MERLIN is used to simulate this interaction.