Investigation laser-produced chlorine plasmas for x-ray scattering experiments

For future investigations of strongly coupled plasmas with electron temperature above the Fermi temperature, Ne near solid density and the electron-electron coupling paramter Γee > 1, there is a need for new diagnostics. This matter has such a low temperature, that emission spectroscopy is not possible and probing with visible or UV-light is also impossible as it cannot penetrate the plasma due to the corresponding low critical electron density. One possibility to elude this problem is spectrally resolved x-ray scattering, which can be realized by the kilojoule PHELIX-laser as the driver for the x-ray source. Spectrally resolved x-ray scattering potentially provides both electron density and temperature from the red-shifted line-wings of the scattered radiation [1]. For these purposes it is important to know the underlying satellite structure in this wings. A future probing beam could be the Heα-resonance line of chlorine with a wavelength of λ = 0.4444 nm. A high-reflectivity Bragg-crystal spectrometer is needed to resolve this scattered radition. Here highly oriented pyrolytic graphite (HOPG, 2d = 6.708 Å) [2] seems to be a good candidate. Due to its rockingcurve the spectral resolution of the crystal is about 500. Unfortunately one cannot resolve the dielectronic structure that is underlying the probing Heα-transition radiation. To investigate the influence of these satellites on the spectrum of the source and to calibrate this spectrometer we used a focusing spectrometer with spatial resolution (FSSR) [3] with a spherically bent mica crystal (2d = 19.915 Å, R = 150 mm, λ/∆λ up to 10000) in a FSSR-1D scheme. The x-rays were recorded with Kodak DEF-5 films. With this set-up one can get the characteristics of the source with high spectral resolution and determine experimentally the blended transitions of the HOPG-spectrum. We used the chlorine Heα-line to calibrate a newly developed flat HOPG-spectrometer with the FSSR. The radiation was produced by illuminating massive PVC targets with the NHELIX laser beam (Nd:YAG, energy up to 140 J in 14 ns). The spectrometers were placed at a distance of 22.7 cm (FSSR) and 13.6 cm (HOPG) on opposite sides of the target at an angle of ≈ 10◦ according to the surface.