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Jets of laser-generated plasma represent a flexible and well-defined model environment for investigation of plasma interactions with solid surfaces (walls). The pilot experiments carried out on the iodine laser system (5-200 J, 0.44 μm, 0.25-0.3 ns, <1 x 1016 W/cm²) at the PALS Research Centre in Prague are reported. Modification of macroscopic characteristics of the Al plasma jets produced at laser-irradiated double-foil Al/Mg targets is studied by high-resolution, high-dispersion X-ray spectroscopy. The spatially variable, complex satellite structure observed in emission spectra of the Al Lya group proves a formation of rather cold dense plasma at the laser-exploded Al foil, an occurrence of the hot plasma between both foils and subsequent thermalization, deceleration and trapping of Al ions in the colliding plasma close to the Mg foil surface. The spectra interpretation based on the collisional-radiative code is complemented by 1D and 2D hydrodynamic modeling of the plasma expansion and interaction of counter-propagating Al/Mg plasmas. The obtained results demonstrate a potential of high resolution X-ray diagnostics in investigation of the laser-produced plasma-wall interactions. [ABSTRACT FROM AUTHOR]

Abstract: Precise X-ray spectroscopic investigation of the colliding plasmas produced at single-side laser-irradiated double-foil Al/Mg targets is reported. The spatially resolved, time-integrated line spectra of the Al Lyα group were measured using a high-dispersion vertical-geometry Johann spectrometer. The X-ray spectra were evaluated with the multilevel collisional-radiative code MARIA. The complex satellite-rich structure observed in the Al Lyα emission indicates a presence of relatively cold dense plasma close to the Al foil surface, hot plasma between both foils, and Al ion trapping close to the Mg foil. An unusual formation of the Al spectra at the Mg foil surface is discussed in terms of interaction of counter-propagating plasmas, in particular trapping, deceleration and thermalization of the Al ions in the colliding plasmas. The qualitative analysis of the observed spectral emission is supported by 2D hydrodynamic modeling and by time-resolved imaging of the expanding plasma. Prospective use of the J-satellite line shifts in diagnosis of colliding laser-produced plasmas is discussed. [Copyright &y& Elsevier]

Abstract: Precise spectroscopic observations of K-shell emission from highly stripped Al ions immersed in dense, constrained-flow laser-produced plasma is reported. By using a vertical dispersion Johann spectrometer, the time-integrated spectra of the Al Heα group were measured with a high spectral and spatial resolution. The complex spectral profiles modified by the satellite formation, line broadening and frequency shifts were decomposed into individual pseudo-Voigt components by using a code GASPED based on a problem-dependent genetic algorithm. The method uses eight operators tailored to the problem of spectral decomposition and variable-size genomes to fit the data with a varying number of spectral lines. The spectra fitting was based on anticipatory theoretical knowledge of the satellite structure simulated by the multilevel collisional-radiative code MARIA and on an assumption of the aggregate plasma-induced shift of the parent lines and their satellites. The analysis of the spectral profiles revealed systematic red shifts of the resonance and the intercombination lines. Their magnitude is commensurate with predictions of the atomic data and spectral line shape codes combined with the 1D hydrodynamic modeling of the plasma conditions and independent electron density measurements. The results obtained corroborate the feasibility of an accurate decomposition of the spectral profiles encompassing optically thick and thin lines overlapped by a strong satellite emission. [Copyright &y& Elsevier]

An astrophysically relevant experiment is compared to the output of a multidimensional radiation transfer code in which populations and radiation are self-consistently treated. Experimental Al Ly α spectra obtained with a very high-resolution spectrometer are presented as quantitative evidence of dot plasma non-planar expansion. Analysis of these spectra using the code is performed, in particular examining the effects of velocity gradients in directions other than that of the primary expansion. These calculations are found to be in good agreement with the experimental results. Usage of the Ly α doublet as a planarity diagnostic is discussed. [ABSTRACT FROM AUTHOR]

Theoretical design of a new type of the bent crystal spectrometer based on a combination of the vertical dispersion principle with diffraction of x rays from the asymmetrically cut crystal is reported. The novel instrument produces simultaneously two sets of mirror-symmetric spectra, and provides large dispersion, high spectral and 1D spatial resolution with a variable magnification. The analytic formulas describing the function of the spectrometer are complemented by its detailed quantitative analysis based on the ray tracing procedure. The method for reconstruction of the recorded spectra is described, the parameters influencing the precision of the wavelength determination are discussed. The comparison of the main predicted and experimentally observed characteristics verifies the developed theory and demonstrates the spectrometer performance. The novel instrument is particularly suitable for precise measurements of profiles and positions of the narrow-band spectral features observed in the emission of laser-generated plasmas. [ABSTRACT FROM AUTHOR]

Detailed spectroscopic analysis of K-shell emission simultaneously observed at the irradiated and unirradiated surface of laser-exploded foils is reported. The space-dependent spectral line widths and relative shifts in the positions of the Al Lyman transition are interpreted in terms of the plasma density variations; the trend in the shifts data supports the idea of a density-dependent line shift. The significant features of the spectra emitted from the densest part of the plasma are compared with predictions from standard diagnostics modeling based on codes MEDUSA and FLY, and with the results of 2D ATLANT hydrodynamic simulations post-processed with a novel suite of atomic physics codes XEPAP. The results obtained corroborate the feasibility of the plasma density diagnostics based on line shifts in the intermediately coupled plasmas. [Copyright &y& Elsevier]

Spatially resolved x-ray spectra of the Al Lyman α group emitted from the surface of the laser- irradiated targets display plasma regions where the resonance line is suppressed and the dielectronic satellites dominate. Calculations based on multilevel collisional-radiative code and two-dimensional hydrodynamic simulations relate this spectral distribution to a presence of the cold overcritical density plasma inside the crater at the target surface. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: Strong oscillating electric fields modify the emission spectra of ions and can result in the appearance of additional field-induced satellites, field ionisation, and alter spectral line shapes. In addition, these high fields may alter the atomic kinetics. Experiments observing these strong oscillating electric fields in highly ionised systems are limited. Here we describe experiments using a combination of long and short pulse lasers to look for field-induced satellites, and spectral line shape modification in uniform well-characterised plasmas. A hydrogen-like and helium-like aluminium plasma was preformed using a long-duration (∼1ns), moderate intensity (∼1014 W/cm2) laser pulse. A second short-duration (10ps), high-intensity (∼5×1016 W/cm) laser pulse was propagated transversally through this plasma to locally modify the oscillating electric field. The X-ray spectra were recorded using high-dispersion, high-luminosity spectrometers providing spatial resolution. Current analysis indicates that the predicted strong field effects have not been identified. [Copyright &y& Elsevier]