摘要:
高温下等离子体的状态方程及其热力学性质在天体物理、可控核聚变以及武器设计与破坏效应等领域有着广泛应用.本文主要回顾了高温等离子体在不同状态区域的状态方程的理论模型和处理方法.对于理想等离子体,离子之间的相互作用可以忽略,其状态方程较简单,已趋于完善.在超高温下,原子完全电离,离子和电子都可以采用理想气体状态方程描述;当温度不太高时,离子部分电离,可以采用Saha方程及其修正模型描述;原子在高度压缩状态下,其状态方程可以采用Thomas-Fermi模型及其改进模型得到.对于非理想等离子体,离子之间存在强耦合,还没有单一的理论模型能够在任意密度和温度范围内对离子之间的相互作用进行统一描述.量子分子动力学方法原则上可以在较大温度密度范围内给出可靠结果,但由于计算量太大以及高温下的计算存在收敛问题,也较难应用到温度较高的稠密等离子体区域.半经验的经典分子动力学方法虽然简单、计算量小,但只能在一定的区域范围内给出较精确的状态方程结果.在不同温度密度区域内采用不同的计算模型,再在空白区域进行插值从而得到全局状态方程在目前不失为一种简单有效的方法.
Abstract:
The equations of state (EOS) and the thermodynamics properties of plasma under high temperature are widely applied to the fields of astrophysics, controllable fusion, weapon design and damage. In this paper we mainly review the theoretical model and computing method of the EOS of hot plasma on different density scales and temperature scales. For an ideal plasma, the interaction between ions can be ignored, the EOS is simple and the theories turn matured. Under the condition of extremely high temperature, ions are ionized completely and the EOSs of ions and electrons can be approximated by the EOS of ideal gas. When the temperature is not very high and ions are just partly ionized, the EOS can be obtained by Saha model or its modified model. When atoms are strongly compressed, the EOS can be calculated by Thomas-Fermi model or its modified model. For the non-ideal plasma, there is a strong coupling between ions. No unified theoretical model can completely describe the interaction between ions at arbitrary density and arbitrary temperature. In principle, the quantum molecular dynamics (QMD) can accurately describe the EOS of plasma in large density range and large temperature range. However, due to the enormous computation and the difficulty in converging, it is difficult to apply QMD to the plasma under high temperature. With simple computing method and small computation, classical molecular dynamics using semi-empirical potential can calculate the EOS accurately at high temperature. However, it will produce great error at lower temperature. It is a simple and effective way to obtain a global EOS by using different theoretical models in different density range and different temperature range and by interpolating in the vacant density range and vacant temperature range.