Self-absorption of heliumlike satellite lines in high-density fusion plasmas

The high densities obtained in recent laser fusion experiments have created a need for additional plasma density diagnostics. The ratio of two heliumlike satellite lines, the $1s2p{}_{}{}^3{}_{}{}^{}P\to 2p^2{}_{}{}^3{}_{}{}^{}P$ and $1s2s{}_{}{}^3{}_{}{}^{}S\to 2s2p{}_{}{}^3{}_{}{}^{}P$ transitions, has shown promise as a spectral diagnostic when laser-imploded microballoons are seeded with medium-atomic-weight gases. In this study results are presented from a collisional-radiative ionization-dynamics model with photoexcitation processes included that indicate that the emission from these satellite lines is strongly affected by opacity in density and temperature regimes common to plasmas to which this diagnostic could be applied effectively. The radiation emission attenuated by photon reabsorption is presented for neon, aluminum, and argon plasmas and compared with results predicted when the calculation is undertaken in an optically-thin-plasma approximation. The opacity effects are seen to cause multivaluedness in the line ratio at several temperatures, and an overall loss of sensitivity of the ratio with density is predicted.