短脉冲强激光驱动磁重联过程的靶后电势分布特征

Potential distribution behind target in intense and short pulsed laser-driven magnetic reconnection

超短超强激光因其极端的物理参数范围以及可用于研究相对论等离子体等特征,成为当前激光驱动磁重联物理的研究热点.通常采用两路激光与平面靶相互作用实现激光驱动磁重联,然而在实验诊断中,由于激光等离子体自身的复杂性导致很难辨别磁重联的物理特征.本文对两路短脉冲激光驱动平面靶磁重联进行了数值模拟,重点分析了靶后电势分布特征和磁重联之间的关系.模拟结果显示,靶后电势分布可以直接影响被加速离子在探测面上的空间分布,因此可用来直接诊断短脉冲激光驱动磁重联实验.

Recently,the short-pulse intense laser has become a common tool for studying the relativistic plasma with tremendous physical parameters.And the laser-driven magnetic reconnection is one of the hot topics and has received much attention.The laser-driven magnetic reconnection experiments are usually conducted by closely focusing two laser beams on a planar coil target.However,it is always hard to distinguish the physical property of magnetic reconnection from the complex background of laser-produced plasma.In this paper,we present the particle-in-cell simulation results of magnetic reconnection driven by two short-pulse lasers as well as a single laser pulse irradiating the solid planar target,and discuss the correlation between the potential distribution behind the target and the magnetic reconnection.When a single laser is used,the potential behind the target shows a double-peak distribution,which is in agreement with recent experimental results.When two lasers irradiate the target,the potential behind the target shows a three-peak distribution.The accumulated spatial distribution of plasma ions with fixed energy(4.5 and 6 MeV)at 3μm behind the target shows several peaks,which is in agreement with the potential distribution when either a single laser or two lasers are used.In addition,after the laser pulse terminates,in the two-laser case there is extremely strong effect on the topological structure of the electric field compared with in the singlelaser case.When the magnetic reconnection happens(which can be identified through the reconnection electric field and the electron energy spectrum),the amplitude of the x component of the electric field has different evolution characteristics from the single laser case.The line outs of the y component of the electric field in two cases also have completely different shapes.In summary,the simulation results reveal that the potential distribution behind the target can directly affect the spatial distribution of the accelerated ions.This could be possibly used to identify the short pulse laser-driven magnetic reconnection in experiment.