I. N. Ellis, D. J. Strozzi, W. B. Mori, F. Li, F. R. Graziani

Three-dimensional (3D) simulations of electron beams propagating in high-energy-density plasmas using the quasistatic Particle-in-Cell (PIC) code QuickPIC demonstrate a significant increase in stopping power when beam electrons mutually interact via their wakes. Each beam electron excites a plasma wave wake of wavelength $\sim 2\pi c/{\omega}_{pe}$, where $c$ is the speed of light and ${\omega}_{pe}$ is the background plasma frequency. We show that a discrete collection of electrons undergoes a beam-plasma-like instability caused by mutual particle-wake interactions that causes electrons to bunch in the beam, even for beam densities ${n}_{b}$ for which fluid theory breaks down. This bunching enhances the beam's stopping power, which we call “correlated stopping,” and the effect increases with the “correlation number” ${N}_{b}\equiv {n}_{b}{(c/{\omega}_{pe})}^{3}$. For example, a beam of monoenergetic 9.7 MeV electrons with ${N}_{b}=1/8$, in a cold background plasma with ${n}_{e}={10}^{26}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{-3}$ (450 g ${\mathrm{cm}}^{-3}$ DT), has a stopping power of $2.28\pm 0.04$ times the single-electron value, which increases to $1220\pm 5$ for ${N}_{b}=64$. The beam also experiences transverse filamentation, which eventually limits the stopping enhancement.