Collisional Particle In Cell Modelling Of The Propagation Of Fast Electrons In Solid Density Plasma

Abstract

This thesis looks at the effects that electron-ion Coulomb collisions have on fast electron transport in solid density plasma. The study of the fast electrons generated in ultra-high intensity laser-plasma interactions is important due to their envisioned use in the fast ignition approach to inertial confinement fusion. Collisions have been added to the particle-in-cell (PIC) code EPOCH in order to study the propagation of fast electron beams in various solid density targets. By using a collisional PIC model several of the assumptions used in previous studies are not required. The code solves the full Maxwell equations (including the displacement current), does not require assumptions of Ohm’s law and of Spitzer resistivity and does not require the background distributions to be Maxwellian. The thesis begins with summaries of the background theory and of the previous work performed in this area. The PIC method is then discussed and the way in which collisions were added to EPOCH is outlined. The results from several collisional PIC simulations with different target Z values are then discussed and com- pared to both collisionless PIC simulation results and hybrid simulation results. The effects of collisions have then been examined by looking into numerous aspects of the simulations that have been performed. Firstly, the generation of fields within the plasma and the subsequent filamentation of the fast electron beam are examined. The effects that the collisions have on the electron distributions within the plasma are then investigated with particular attention given to the divergence of the fast electrons, the energy and momentum distributions of the electrons and the background temperatures within the plasma. Finally, the results of the simulations are used to assess the accuracy of the Spitzer resistivity approximation that is used in hybrid codes.