11 research outputs found
New Issues on Stimulated Brillouin Scattering in a Laser-Produced Plasma
Good agreement between Stimulated Brillouin Scattering (SBS) measurements and the convective theory of SBS in randomly distributed speckles has been achieved thanks to recent progress in both the experimental and the theoretical parts. Modification of SBS in presence of a secondary interaction beam demonstrates the sensitivity of SBS to initial ion density fluctuations in the plasma
New regime of Thomson scattering : Probing dense plasmas with X-ray lasers
In this paper we demonstrate through calculations and theoretical analysis the first application of a x-ray laser for probing hot, high-density plasmas ([MATH]) using a Ni-like transient collisional excitation x-ray laser as a probe. Theoretical predictions are used to diagnose the electron temperature in short pulse (500 fs) laser produced plasmas. The threshold power of the x-ray probe is estimated by comparing theoretical scattering levels with plasma thermal emission. The necessary spectral resolution of the instrument sufficient for resolving electron temperature is given
Laser-plasma interactions in high-energy density plasmas
Laser-plasma interactions (LPI) have been studied experimentally in
high-temperature, high-energy density plasmas. The studies have been
performed using the Omega laser at the Laboratory for Laser
Energetics (LLE), Rochester, NY. Up to 10 TW of power was incident
upon reduced-scale hohlraums, distributed in three laser beam cones.
The hot hohlraums fill quickly with plasma. Late in the laser pulse,
most of the laser energy is deposited at the laser entrance hole,
where most of the LPI takes place. Due to the high electron
temperature, the stimulated Raman scattering (SRS) spectrum extends
well beyond /2, due to the Bohm-Gross shift. This
high-temperature, high-energy density regime provides a unique
opportunity to study LPI beyond inertial confinement fusion (ICF)
conditions
Plasma-based studies with intense X-ray and particle beam sources
The construction of short pulse (<200 fs) tunable X-ray laser sources based on the X-ray free electron laser (XFEL) concept will be a watershed for plasma-based and warm dense matter research. These new fourth generation light sources will have extremely high fields and short wavelengths (andSIM;0.1 nm) with peak spectral brightnesses 10(10) greater than third generation sources. Further, the high intensity upgrade of the GSI accelerator facilities will lead to specific energy depositions up to 200 kJ/g and temperatures between 1 and 10 eV at almost solid-state densities, enabling interesting experiments in the regime of nonideal plasmas, such as the evolution of intense ion beams in the interior of a Jovian planet. Below we discuss several applications: the creation of warm dense matter (WDM) research, probing of near solid density plasmas, and laser-plasma spectroscopy of ions in plasmas. The study of dense plasmas has been severely hampered by the fact that laser-based methods have been unavailable and these new fourth generation sources will remove these restrictions
Finite temperature dense matter studies on next-generation light sources
The construction of short-pulse tunable soft x-ray free electron laser sources based on the self-amplified spontaneous emission process will provide a major advance in capability for dense plasma-related and warm dense matter (WDM) research. The sources will provide 1013 photons in a 200-fs duration pulse that is tunable from approximately 6 to 100 nm. Here we discuss only two of the many applications made possible for WDM that has been severely hampered by the fact that laser-based methods have been unavailable because visible light will not propagate at electron densities of ne ≥ 1022cm-3. The next-generation light sources will remove these restrictions. © 2003 Optical Society of America
First cladistic analysis of the trilobite family Olenidae from the Furongian and Ordovician
The Olenidae stands out for its abundance and biostratigraphical importance, especially in the Lower Palaeozoic rocks of northwestern Argentina. Their phylogenetic relationships have been traditionally determined stratigraphically and by direct morphological comparison. This study reports the first formal phylogenetic analysis of olenids. Eighty-six characters (24 quantitative and 62 qualitative) were coded for 65 taxa (58 olenids). Quantitative characters were treated both as discrete and as continuous variables. To explore the best way of character coding for this group, continuous characters were coded as: median, log-median, normalized and rescaled. Maximum parsimony and implied weighting were used as optimality criteria. A phylogenetic hypothesis more consistent with traditional taxonomy was reconstructed with both quantitative and qualitative partitions. All the trees obtained with quantitative characters coded as continuous and rescaled are better resolved, and those topologies were more similar among them. This treatment also reflects more effectively the behaviour of the original variables. Olenidae is not a monophyletic clade: Andrarina costata and Aphelaspis australis are included within the ingroup, as sister clade of Olenus gibbosus. Also, the results suggest that members of the Hypermecaspidinae constitute a new family within the Order Olenida. The traditional taxonomic scheme at subfamily level is partially supported. Triarthrinae and ‘pelturinds’ are recovered as monophyletic clades, but Oleninae is polyphyletic. This study proves, through a formal cladistic analysis, that characters disregarded by traditional taxonomy can be uncovered. Finally, this is the first step towards achieving a classification of the Olenidae taking into account the evolutionary process involved in its diversification history.Fil: Monti, Daniela Soledad. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; ArgentinaFil: Confalonieri, Viviana Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentin
Laser coupling to reduced-scale targets at NIF Early Light
Deposition of maximum laser energy into a small, high-Z enclosure in a short laser pulse creates a hot environment. Such targets
were recently included in an experimental campaign using the first four of
the 192 beams of the National Ignition Facility [J. A. Paisner, E. M.
Campbell, and W. J. Hogan, Fusion Technology 26, 755 (1994)], under
construction at the University of California Lawrence Livermore National
Laboratory. These targets demonstrate good laser coupling, reaching a
radiation temperature of 340 eV. In addition, the Raman backscatter spectrum
contains features consistent with Brillouin backscatter of Raman forward
scatter [A. B. Langdon and D. E. Hinkel, Physical Review Letters 89, 015003 (2002)]. Also,
NIF Early Light diagnostics indicate that 20% of the direct backscatter
from these reduced-scale targets is in the polarization orthogonal to that
of the incident light
X-ray flux and X-ray burnthrough experiments on reduced-scale targets at the NIF and OMEGA lasers
An experimental campaign to maximize radiation drive in small-scale
hohlraums has been carried out at the National Ignition Facility
(NIF) at the Lawerence Livermore National Laboratory (Livermore, CA,
USA) and at the OMEGA laser at the Laboratory for Laser Energetics
(Rochester, NY, USA). The small-scale hohlraums, laser energy, laser
pulse, and diagnostics were similar at both facilities but the
geometries were very different. The NIF experiments used on-axis
laser beams whereas the OMEGA experiments used 19 beams in three
beam cones. In the cases when the lasers coupled well and produced
similar radiation drive, images of x-ray burnthrough and laser
deposition indicate the pattern of plasma filling is very different