电磁不稳定性和自生磁场饱和机制的数值模拟研究

Numerical simulation of electromagnetic instability and saturation mechanism of self-generated magnetic field

为深入理解超强脉冲激光与等离子体相互作用所产生的电磁不稳定性和自生磁场饱和机制,选用等离子体薄靶,用数值粒子模拟法对超强脉冲激光与等离子体薄靶相互作用中形成的电磁不稳定性和自生磁场饱和机制进行了数值模拟,分析了电磁不稳定性及其激发的自生磁场随时间演化情况,估算了自生磁场在不同时间段的变化关系与各向异性参数之间的关系。数值模拟结果表明,等离子体薄靶与超强脉冲激光相互作用时,很强的准静态自生磁场会出现在等离子体薄靶表面附近,且将会抑制电子在纵向的扩散,而这有利于电子或质子定向传播。

In order to understand the saturation mechanism of self-generated magnetic field and electromagnetic instability in the process of interaction between ultra-intense laser and plasma,this paper used theoretical analysis and numeral simulation to investigate the saturation mechanism of self-generated magnetic field and electromagnetic instability. Analyzed time evolution relation of spatial distribution of electromagnetic instability and self-generated magnetic fields. Meanwhile,the relationship between the variation of the self-generated magnetic field in different time periods and the anisotropic parameters were estimated. The simulation results indicate that after the ultra-intense laser interacts with plasma target,electrons are accelerated to relativistic speed,cross the target and exist at the rear surface of the target. Most electrons are bound to the surface of the slab by the electrostatic field and expand along it. Their current is closed by a return current in the target and this current configuration generates strong surface magnetic fields. The exists of self-generated magnetic field would be restrain longitudinal dispersion of electrons,thermal flux propagating to the internal plasma which is helpful to develop electron or proton directional propagation.