激光烧蚀固体碳氢材料的离子组分分离研究

Separation of ion component from solid hydrocarbon materials by laser ablation

本文从双离子组分等离子体的Landau-Fokker-Planck方程出发,通过Chapman-Enskog方法约化得到离子输运方程,求得双离子组分等离子体的离子输运系数,给出了计及离子扩散的完备离子流体方程;再结合一维辐射流体力学程序Multi-1D模拟得到的烧蚀层的宏观状态,研究了激光烧蚀固体碳氢材料时的组分分离现象.计算结果显示,离子组分分离对等离子体流体演化的影响小,基本可以忽略;但对于敏感依赖于离子组分的其他物理过程,如汤姆孙散射,离子组分分离的影响显著,这意味着研究激光等离子体相互作用时,离子组分分离必须予以考虑.

Plasma usually consists of multiple ion component.Ion-component separation occurs in various conditions,and profoundly affects the plasma dynamic evolution.In this work,ion-component separation in two-ion-component plasma is investigated in the hydrodynamic condition.Starting from the Landau-Fokker-Planck equations of two-ion-component plasma,the ion transport equations are reduced through the Chapman-Enskog approach.The transport equations are then transformed into a set of linear algebraic equations and solved by expanding the perturbed ion distribution functions into the series of Sonine polynomials.The diffusive ion mass flows with inclusion of baro-diffusion,thermo-diffusion and electro-diffusion are thus obtained.With these efforts,the complete ion fluid equations are presented,which can be used to describe the processes of ion-component separation.We evaluate ion-component separation in the case of a solid CH plate target ablated with a laser pulse,by solving the ion diffusion equation with the hydro states output from the one-dimensional radiative hydro code Multi-1D.The simulation results show that ion-component separation mainly occurs around ablation front and under-dense region,and that the effect of ion-species separation on plasma hydrodynamic evolution is minor and can be neglected.For those physical processes sensitive to ion concentration such as Thomson scattering,however,the effect of ion-component separation is significant,which means that ion-component separation should be included in the study of laser plasma interaction.