Klimo Ondrej, Tikhonchuk V T, Debayle A
Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University in Prague, Brehova 7, 115 19 Praha 1, Czech Republic.
Phys Rev E Stat Nonlin Soft Matter Phys. 2007 Jan;75(1 Pt 2):016403. doi: 10.1103/PhysRevE.75.016403. Epub 2007 Jan 17.
Recent experiments demonstrate an efficient transformation of high intensity laser pulse into a relativistic electron beam with a very high current density exceeding 10(12) A cm(-2). The propagation of such a beam inside the target is possible if its current is neutralized. This phenomenon is not well understood, especially in dielectric targets. In this paper, we study the propagation of high current density electron beam in a plastic target using a particle-in-cell simulation code. The code includes both ionization of the plastic and collisions of newborn electrons. The numerical results are compared with a relatively simple analytical model and a reasonable agreement is found. The temporal evolution of the beam velocity distribution, the spatial density profile, and the propagation velocity of the ionization front are analyzed and their dependencies on the beam density and energy are discussed. The beam energy losses are mainly due to the target ionization induced by the self-generated electric field and the return current. For the highest beam density, a two-stream instability is observed to develop in the plasma behind the ionization front and it contributes to the beam energy losses.
最近的实验表明，高强度激光脉冲能够有效地转化为相对论电子束，其电流密度非常高，超过10¹² A cm⁻²。如果这种束流的电流被中和，那么它在靶内的传播是可能的。这种现象尚未得到很好的理解，尤其是在介电靶中。在本文中，我们使用粒子模拟代码研究了高电流密度电子束在塑料靶中的传播。该代码既包括塑料的电离，也包括新生电子的碰撞。将数值结果与一个相对简单的解析模型进行了比较，发现两者吻合较好。分析了束流速度分布的时间演化、空间密度分布以及电离前沿的传播速度，并讨论了它们对束流密度和能量的依赖性。束流能量损失主要是由于自生电场和回流电流引起的靶电离。对于最高的束流密度，在电离前沿后面的等离子体中观察到双流不稳定性的发展，它导致了束流能量损失。
