Numerical analysis of radiation dynamics in a combined hohlraum in the X-ray opacity experiments on the "Iskra-5" laser facility

We report the results of numerical analysis of radiation dynamics (laser absorption and X-ray generation) by using SNDLIRA code in a combined box used in the X-ray opacity measurements on the "Iskra-5" facility (laser radiation wavelength, λ = 0.66 μm; laser pulse duration, τ_0.5 ≈ 0.6 ns; and energy, 900 J). Combined boxes used in these experiments comprised three sections: two illuminators delivering laser radiation and a central diagnostic section with a test sample. We have proposed a scheme for step-by-step calculation of the heating dynamics of the sample under study in a three-section hohlraum. Two designs of a combined box, which differ in the ways the laser radiation is injected, are discussed. It is shown that the axial injection of the beams results in intense secondary laser irradiation of the illuminator edge which leads to its partial disruption and penetration of laser radiation into the central diagnostic section. In this case the sample under study is exposed to additional uncontrolled action of scattered laser radiation. Such an undesirable action may be avoided by using the lateral injection of the beams through four holes on the lateral side of the illuminators. For the latter case we have calculated the heating dynamics for the sample and found an optimal time delay for an X-ray probe pulse.