Radiative Processes in Hot High-Density Plasmas

在惯性约束聚变实现的高密度热等离子体中，辐射过程对能量输运有重要贡献。在这些高密度等离子体中，这些过程的横截面可能受到带电粒子之间相关性的影响。我们研究了在激光聚变等离子体中占主导地位的自由-自由（韧致）跃迁和自由束缚跃迁。在某些情况下，自由-自由跃迁概率会因离子相关而显著降低，这取决于电子简并度、离子偶联强度和频率。对于离子混合物，这种还原可以用一种离子的结果用简单的标度来表示。对于自由束缚跃迁，周围离子的电场波动增加了离子是否相关的概率，而离子之间的相关性降低了离子是否相关的概率。因此，当离子相关性较弱或较强时，截面增大或减小。电子-离子相关的作用可以看作是筛选离子电荷的作用。当筛选用线性响应描述时，对离子电位的直接影响和削弱离子相关性的间接影响几乎相互抵消。当离子电荷较大且筛分非线性时，前者占优势，截面减小。自由-自由和自由结合过程的统一处理以及对自由结合过程的筛选作用有待于未来的研究。

In hot high-density plasmas realized in the inertial confinement fusion, radiative processes make important contributions to the energy transport. In these high-density plasmas, the cross sections of such processes may be affected by correlations between charged particles. We have investigated the free-free (bremsstrahlung) and teh free-bound transitions which are dominant in laser fusion plasmas.1. The free-free transition probability is signigicantly reduced by the ion correlation in some cases, depending on the degree of electronic degeneracy, the strength of ionic coupling, and the frequency. For ionic mixtures, this reduction can be expressed by the result for ions of one species by a simple scaling.2. For the free-bound transition, fluctuating electric fields of surrounding ions increase the probability whether ions are correlated or not, while correlations between ions decrease it. The coross section is thus enhanced or reduced when ion correlation is weak or strong.3. The effect of electron-ion correlation can be regarded as that of screening of ionic charges. When the screening is described by the linear response, the direct effect on ionic potentials and the indirect effect to weaken ion correlations almost cancel with each other. When the ionic charge is large and the screening is nonlinear, the former prevails and the cross section is reduced.4. Unified treatment of the free-free and free-bound processes as well as the screening effect on the free-bound process is left for future studies.