Two-dimensional radiation hydrodynamic simulations of high-speed head-on collisions between high-density plasma jets

Abstract

Collisions of plasma jets are common hydrodynamic phenomena in astrophysical and laser-plasma interaction processes. Deriving scaling relationships between colliding plasmas and initial conditions of plasma jets is of great significance for the optimization design and data analysis of the relevant experiments. Double-Cone Ignition (DCI) scheme is an excellent platform for the study of plasma jets collision, since the collision of high-speed, high-density plasma jets can be easily generated and characterized in both simulations and experiments.<br>In this paper, we employ the upgraded two-dimensional arbitrary Eulerian-Lagrange (ALE) program MULTI-2D to simulate collision process of plasma jets with high speed (≥ 100 km/s) and high density (≥ 10 g/cc). Using the database obtained from the simulations, hydrodynamic scaling laws that describing the collision process of plasma jets are derived with the Bayesian inference method in machine learning. The Bayesian inference method not only has the parameter estimation function of traditional least square method, but also has other potential advantages such as giving the probability distribution of estimated parameters. Numerical results show that the collision of plasma jets with open boundaries is easy to form an isochoric plasma distribution with high-density. Increasing the initial density and velocity of the plasma jets is helpful to enhance the density and temperature of the colliding plasmas. Increasing the initial temperature of plasma jets is beneficial to achieve colliding plasmas with a higher temperature, while leading to a decreased plasma density and pressure after collision. When the initial density, temperature and velocity of the plasma jets are set to be 15 g/cc, 30 eV and 300 km/s, respectively, the colliding plasma density can reach more than 300 g/cc. This is very favorable for the following fast electron heating process in the double-cone ignition (DCI) scheme.<br>The issue about quantum degeneracy after collision is discussed in this work. Under the typical initial conditions of plasma jets in DCI scheme (100km/s ≤<i>V</i><sub>0</sub>≤500km/s, 10eV ≤<i>T</i><sub>0</sub>≤ 100eV, 10g/cc ≤<i>ρ</i><sub>0</sub>≤ 50g/cc, both quantum degenerate plasma and classical non-degenerate plasma can be obtained with the temperature between 0.3<i>T</i><sub><i>F</i></sub> (Fermi temperature) and 3<i>T</i><sub><i>F</i></sub>. By comparing the plasma temperature and Fermi temperature of the collision, the criterion for achieving quantum degenerate plasma or non-degenerate plasma under given initial conditions is obtained with the help of the derived hydrodynamic scaling laws. The criterion shows that higher initial velocity, higher temperature and lower density of plasma jets are required if we want to obtain non-degenerate plasma after collision.

Formation of fast-ignition hotspots and propagartion of burning waves in pre-compressed isochoric plasmas

“…定义为热斑 [7] , 近年来随着实验的发展, 逐渐改用 聚变反应率 [8] (聚变反应率大于峰值反应率10%的 区域)和中子产额 [9] (中子产额占总产额98%的球 形区域)等方式定义热斑. 但是, 对等容构型预压 缩等离子体中的热斑点火的研究尚不充分, 如何定 义等容构型等离子体中的热斑也尚未明确.…”