2018 - Modeling of Ultrafast High-Current Electron Beam Transport in Air

The overall goal of this project was to understand the physics of the generation and propagation of ultrashort electron beams in atmosphere using advanced simulation tools relevant to experiments on the PHEENIX laser at AFRL Kirtland. Propagation of electron beams in air has been of interest to the Department of Defense for decades. The use of electron beams to disrupt shielded electronic components at a distance is a possible application, but a large body of prior research shows that beams are susceptible to instabilities that prevent it being deployed effectively. However, the ultrashort duration of beams generated by plasma wakefield accelerators means that the bunch duration is much shorter than the Langmuir period in atmospheric density plasma, which means that some instabilities may be mitigated for beam propagation because they are mediated at the plasma frequency. The ability to easily generate beams in excess of 1 GeV may enable penetration of radiation hardened targets. With a highly compact set-up and pencil beam potentially completely directional over all angles, LWFA allows more flexibility compared with a conventional accelerator. However, in additional to addressing technical challenges associated with the source, such as the repetition rate, there is limited experimental data on the propagation of such femtosecond duration beams in plasma or air. In work proposed here, we worked in collaboration with the AFRL group on computational model development, physics and simulation of the beam propagation. As outcomes from the project, we have implemented a new algorithm for simulating collisional ionization within a particle-in-cell framework. Our method treats and calculates ionization events deterministically as each particle's contribution to the ionization rate is calculated explicitly and deposited onto a grid.