K-shell spectroscopy of an independently diagnosed uniaxially expanding laser-produced aluminum plasma

Abstract

We present detailed spectroscopic analysis of the primary K-shell emission lines from a uniaxially expanding laser-produced hydrogenic and heliumlike aluminum plasma. The spectroscopic measurements are found to be consistent with time-dependent hydrodynamic properties of the plasma, measured using Thomson scattering and shadowgraphy. The K-shell population kinetics code FLY with the measured hydrodynamic parameters is used to generate spectra that are compared to the experimental spectra. Excellent agreement is found between the measured and calculated spectra for a variety of experimental target widths employed to produce plasmas with different optical depths. The peak emission from the hydrogenic Lyman series is determined to be from a temporal and spatial region where the hydrodynamic parameters are essentially constant. This allows a single steady-state solution of FLY to be used to deduce the electron temperature and density, from the measured line ratios and linewidths, for comparison with the Thomson and shadowgraphy data. These measurements are found to agree well with time-dependent calculations, and provide further validation for the FLY calculations of the ionization and excitation balance for a K-shell aluminum plasma. We also discuss the possible application of this data as a benchmark for hydrodynamic simulations and ionization/excitation balance calculations.

Laboratory measurements of geometrical effects in the x-ray emission of optically thick lines for ICF diagnostics

“…Given that the above effect depends on the mean chord (which can be obtained by means of the Dirac-Fuchs theorem 41,42 ) and LOS lengths, this effect is what we call geometric anisotropy, and has been previously used to characterize the geometry of astrophysical bodies 40,43 . It has also been observed in HED experiments 44 , and further experiments to explore it have been proposed 40 . In the experiments described here the optically thick line, for which we seek to observe these opacity effects, is the resonance (w) line of the He-α complex of V, and the optically thin line to which we reference its intensity is the associated intercombination (y) line.…”

Spectroscopic characterisation of the effects of plasma geometry on the angular distribution of X-Ray emission in HED plasmas

“…in HED experiments [77]. In the past few years, a series of additional experiments to study this effect have been proposed, such as using an Argon gas bag [75] or confining the plasma geometry by burying the targets in aerogel foam [75,78].…”

“…The absolute spectral flux obtained from the cylindrical simulations used in this thesis was benchmarked against the results in Chambers et al [77]. In their work, Chambers and coauthors studied the time-integrated K-shell emission of laser-generated aluminium plasmas.…”

“…Their results for the electron temperature and density are shown in The synthetic spectra obtained for each timestep were then integrated and convolved with a Gaussian curve with a FWHM of 20 m A to account for the instrumental resolution in the experiment (as described in [77]). The raw result was also shifted 19 m A to greater wavelengths to reproduce the experimental line positions, and a constant background of 1.07 × 10 14 Photons cm −2 sr −1 m A −1 was added.…”

Spectroscopic characterization of plasma densities of laser-irradiated Al foils

“…The spectroscopic measurements of the plasma density are typically based on absolute continuum or line intensities, relative line intensities or spectral line widths and proÿles. Most of these techniques require some knowledge of plasma temperature, which must be provided either by independent measurements, e.g., by Langmuir probe or Thomson scattering diagnostics, or by spectroscopic methods [2].…”