Ellis I N, Strozzi D J, Mori W B, Li F, Graziani F R
Lawrence Livermore National Laboratory, Livermore, California 94550, USA.
Department of Physics and Astronomy, University of California, Los Angeles, California 90095, USA.
Phys Rev E. 2021 Sep;104(3-2):035203. doi: 10.1103/PhysRevE.104.035203.
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 ∼2πc/ω_{pe}, where c is the speed of light and ω_{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}≡n_{b}(c/ω_{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}cm^{-3} (450 g cm^{-3} DT), has a stopping power of 2.28±0.04 times the single-electron value, which increases to 1220±5 for N_{b}=64. The beam also experiences transverse filamentation, which eventually limits the stopping enhancement.
使用准静态粒子模拟细胞（PIC）代码QuickPIC对在高能量密度等离子体中传播的电子束进行的三维（3D）模拟表明，当束电子通过其尾波相互作用时，阻止本领会显著增加。每个束电子激发一个波长约为2πc/ωpe的等离子体波尾波，其中c是光速，ωpe是背景等离子体频率。我们表明，即使对于流体理论失效的束密度nb，由相互的粒子-尾波相互作用引起的离散电子集合也会经历类似束-等离子体的不稳定性，这种相互作用会导致电子在束中聚束。这种聚束增强了束的阻止本领，我们称之为“相关阻止”，并且这种效应随着“相关数”Nb≡nb(c/ωpe)³的增加而增大。例如，在ne = 10²⁶cm⁻³（450 g cm⁻³ DT）的冷背景等离子体中，一束单能9.7 MeV电子，当Nb = 1/8时，其阻止本领是单电子值的2.28±0.04倍，当Nb = 64时，该值增加到1220±5。该束还会经历横向丝化，这最终会限制阻止增强。
