Radiative Processes in Hot High-Density Plasmas

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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.