This paper will present a novel genetic-algorithm-based code~GASPED!, developed for the analysis of fine features e.g., satellite structure and line shifts! in X-ray spectra emitted by hot dense plasmas. The problem dependent modification of standard genetic-algorithm concepts allows efficient decomposition of spectra in concrete physical terms, such as resonance and intercombination lines, dielectronic satellites, or prospective nuclear transitions. Two examples of the code application demonstrate the proposed approach. High resolution K-shell spectra emitted from Heand Li-like Al ions immersed in dense, constrained-flow plasma are decomposed into individual pseudo-Voigt components, by using anticipatory theoretical knowledge of the satellite structure simulated by the multilevel collisionalradiative code~MARIA!. Line shifts of the He-like resonance and intercombination line are deduced assuming the aggregate plasma-induced shifts of the parent lines and their satellites. The trend in the frequency shifts observed as a function of the variable plasma parameters qualitatively follows the theoretical predictions. The found variations of the exchange energy between the singlet and triplet levels provide a new impact for the line shift theories. The second example concerns the search for low-lying nuclear transitions in hot dense laser-produced plasmas. The spectra of highly ionized Ta are decomposed by combining the GASPED code with results of ab initio atomic data calculations performed by the RELAC code. Upper limits for observation of the controversial radiative decay of Ta nuclei at 6.238 eV are estimated.

One-dimensional particle-in-cell and Monte-Carlo (FLUKA) simulation methods were used together, in order to investigate the production of positrons in lead targets, illuminated by a short-pulse high-intensity laser. The study is focused on lead targets of 1 mm thickness and more and pulses of intensity in the range 1019–1022 W/cm2. The calculations provided an estimate of an absolute number of positrons and the ratio of electrons and positrons emerging from the target. The thickness of the target is scaled in order to find an optimal thickness that could provide a neutral electron-positron beam.

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The interaction of ultrashort laser pulses with a fully ionized plasma is investigated in the plane geometry by means of numerical simulation. The impact of the space oscillations in the amplitude of the laser electric field on the shape of the electron distribution function, on laser beam absorption, and on electron heat transport is demonstrated. Oscillations in the absorption rate of laser radiation with the minima coincident to the maxima of the laser electric field lead to a further decrease in the absorption of laser radiation. Heat flux in the direction of increasing temperature in the underdense region is caused by the modification of the electron distribution function and by the density gradient. A limitation of heat flux to the overdense plasma is observed with the flux limiter in range 0.03-0.08, growing moderately with the intensity 10 14 -10 16 W/cm 2 of the incident 1.2-ps laser pulse.