Resistive Filamentation and Collimation of Relativistic Electron Beams in Collisional PIC

Experiments on OMEGA EP using one beam in high-intensity mode (eA/m_ec > 1, duration ~ 10ps) to accelerate electrons, and optionally a second (earlier) beam with nanosecond duration to create a plasma transport layer, find significantly different electron transport through CH plasma as compared to cold CH foam. We use the particle-in-cell code OSIRIS, together with a Monte Carlo Coulomb collision calculation, to model the experiment in 2D. We find the transport is greatly affected by the self-generated magnetic field, in particular the field whose growth is governed by the collisional resistivity of the return current; transport of the field with the material current of the return flow is also a significant effect. We find the cause of the differing evolution of the field is the different density in the plasma and foam case, which affects the heat capacity. In the simulations, we find the collimation to be sensitive to the target size, with reduced-scale targets showing more divergent beams.