-
磁准直是塑造天体外流形貌的重要机制, 它的有效性已经在激光等离子体实验中被无量纲验证. 本文在现有磁准直射流研究框架的基础上, 综合实验与模拟, 通过改变激光等离子体烧蚀靶材引入不同冷却和耗散强度, 以观察这些非理想效应对准直流形态的影响. 使用低原子序数靶时, 烧蚀外流和外加强磁场的相互作用满足理想磁流体条件, 外流形成了抗磁空腔和沿磁场延展的射流; 而采用高原子序数靶时, 准直结构被磁扩散破坏, 强烈的冷却使得外流停滞, 形成与靶面分离的弱准直磁化密度团. 无量纲分析表明, 磁扩散对实验室等离子体准直形态的破坏, 有可能推广解释原恒星射流在大尺度上的消散; 而强耗散等离子体展现的弱准直腔与密度堆积, 有可能用来类比行星状星云中的弱极化椭球形腔体, 以及腔体头部的发光团簇. 本文通过考察实验室磁化等离子体演化, 支持了非理想效应能够塑造天体外流的理论猜想, 对研究非相对论性天体外流形态的形成机制具有重要参考意义.Central outflow’s collimation by magnetic field is an important theoretical mechanism for explaining the astrophysical objects’ morphology formation, and its credibility has been tested in many laser plasma experiments in a dimensionless manner. This article introduces integrated simulation and experiment work based on the present laboratory magnetically collimated jet framework, to explore how non-ideal terms’ strength including radiative cooling and magnetic diffusion from different targets can affect the outflow shape. The interaction between outflow from a target with low atomic number and external field satisfies the ideal magneto-hydrodynamic conditions, and the outflow shape results in diamagnetic cavity and jet; on the other hand, a heavy element target brings strong magnetic diffusion that destroys the collimation structure, together with the stagnation of outflow introduced by radiative cooling, and outflow shape results in weakly collimated hemisphere near the target and a detached magnetized density clump. The detailed dimensionless analysis shows that the large-scale dissipation of jets in young stellar objects can possibly be an analog of the laboratory jet’s magnetic diffusion breakup, also similar structures like the loosely collimated lobes and bright ansaes in planetary nebula can be observed in highly diffusive laboratory outflows. This article shows for the first time that a series of non-relativistic astronomical outflows’ dynamic behaviors can be explained by the non-ideal magneto-hydrodynamic evolution of laboratory plasmas.








下载: