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We report on experiments aimed at the generation and characterization of solid density plasmas at the free-electron laser FLASH in Hamburg. Aluminum samples were irradiated with XUV pulses at 13.5 nm wavelength (92 eV photon energy). The pulses with duration of a few tens of femtoseconds and pulse energy up to 100 µJ are focused to intensities ranging between 1013 and 1017 W/cm2. We investigate the absorption and temporal evolution of the sample under irradiation by use of XUV and optical spectroscopy. We discuss the origin of saturable absorption, radiative decay, bremsstrahlung and atomic and ionic line emission. Our experimental results are in good agreement with simulations.
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, <1×1016 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 Lyα 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.
The chlorine Heα radiation of polyvinyl chloride (PVC)
was investigated with respect to X-ray scattering experiments on dense
plasmas. The X-ray source was a laser-produced plasma that was observed
with a highly reflective highly oriented pyrolytic graphite (HOPG) crystal
spectrometer as it is used in current x-ray scattering experiments on
dense plasmas. The underlying dielectronic satellites of
Heα cannot be resolved, therefore the plasma was observed
at the same time with a focusing spectrometer with spatial resolution. To
reconstruct the spectrum a simple model to calculate the spectral line
emission based on dielectronic recombination and inner shell excitation of
helium- and lithium-like ions was used. The analysis shows that chlorine
dielectronic satellite emission is intense compared to Heα
in laser-produced chlorine plasmas with a temperature of 300 eV in this
wavelength range of Δλ = 0.07 Å (ΔE = 43 eV).
The method proposed in this paper allows deducing experimentally the role
of the underlying dielectronic satellites in the scatter spectrum measured
with a HOPG crystal spectrometer. It is shown that the dielectronic
satellites can be neglected when the scattering is measured with low
spectral resolution in the non-collective regime. They are of major
importance in the collective scatter regime where a high spectral
resolution is necessary.
High energy heavy ions were generated in laser produced plasma at
moderate laser energy, with a large focal spot size of 0.5 mm diameter.
The laser beam was provided by the 10 GW GSI-NHELIX laser systems, and the
ions were observed spectroscopically in status nascendi with high spatial
and spectral resolution. Due to the focal geometry, plasma jet was formed,
containing high energy heavy ions. The velocity distribution was measured
via an observation of Doppler shifted characteristic transition lines. The
observed energy of up to 3 MeV of F-ions deviates by an order of magnitude
from the well-known Gitomer (Gitomer et al.,
1986) scaling, and agrees with the higher energies of relativistic
The final beam transport in the reactor chamber for heavy ion
fusion in preformed plasma channels offers many attractive
advantages compared to other transport modes. In the past few
years, experiments at the Gesellschaft für
Schwerionenforschung (GSI) accelerator facility have addressed
the creation and investigation of discharge plasmas, designed
for the transport of intense ion beams. Stable, self-standing
channels of 50 cm length with currents up to 55 kA were initiated
in low-pressure ammonia gas by a CO2-laser pulse
along the channel axis before the discharge is triggered. The
channels were characterized by several plasma diagnostics including
interferometry and spectroscopy. We also present first experiments
on laser-guided intersecting discharges.
Correlations of Doppler shifted line shapes with time-of-flight
spectra of fast ions has been established for nanosecond-laser
pulses. Fast ion energies of different velocity groups have
been established in the large interval of Iλ2
= 4 × 1012–5 × 1016
W/cm2 μm2. The obtained scaling
relations differ markedly from those reported by Gitomer
et al. (1996).
The X-ray spectral distribution of swift heavy Ti and Ni ions
(11 MeV/u) observed inside aerogels (ρ = 0.1
g/cm3) and dense solids (quartz, ρ = 2.23
g/cm3) indicates a strong presence of simultaneous
3–5 charge states with one K-hole. We show that the
theoretical analysis can be split into two tasks: first, the
treatment of complex autoionizing states together with the
originating spectral distribution, and, second, a charge-state
distribution model. Involving the generalized line profile function
theory, we discuss attempts to couple charge-state distributions.
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