Modeling the coaxial double z-pinch for the Al x i - Mg i x laser at 228 Å

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Abstract
A magnetically embedded coaxial z‐pinch configuration is proposed for the resonantphotoexcitation laser at 228 Å in Mg ix pumped by the 48.338 Å line of Al xi. This laser configuration consists of an annular Al z‐pinch plasma imploded (final electron density of about 1020 cm−3) onto an inner, Mgplasma (final electron density of about 1018 cm−3) on the axis. The Mgplasma is confined and stabilized by an axial magnetic B z field, which is compressed to a final magnitude of about 130 T from an initially applied field of about 1 T by the Al implosion, thus serving to stabilize and physically separate the Al and Mgplasmas. Separate numerical simulations of the Al and Mgplasmas designed to guide exploratory experiments are reported. A 0D dynamic z‐pinch model captures the Al implosion, including trapped B z field and power losses due to line radiation. Initial conditions required to produce the intense Al xi pump line at 48.338 Å are derived assuming an 800 kA, 100 ns implosion current pulse. Assuming a pinch length of 2 cm, a pump power of 3.5 GW/eV is predicted for the 48.338 Å Al xi line. With the pump so defined, a separate, detailed atomic physics model is used to study the photoexcitation kinetics in the Mg ix lasant plasma. It is found that a gain of 1.0–1.5 cm−1 is obtainable on the 2s3d 1 D 2 ‐ 2s4f 1 F 3 transition at 228 Å in Mg ix.