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Matter with a high energy density (> [10.sup.5] joules per [cm.sup.3]) is prevalent throughout the Universe, being present in all types of stars (1) and towards the centre of the giant planets (2,3); it is also relevant for inertial confinement fusion (4). Its thermodynamic and transport properties are challenging to measure, requiring the creation of sufficiently long-lived samples at homogeneous temperatures and densities (5,6). With the advent of the Linac Coherent Light Source (LCLS) X-ray laser (7), high-intensity radiation (>[10.sup.17] watts per [cm.sup.2], previously the domain of optical lasers) can be produced at X-ray wavelengths. The interaction of single atoms with such intense X-rays has recently been investigated (8). An understanding of the contrasting case of intense X-ray interaction with dense systems is important from a fundamental viewpoint and for applications. Here we report the experimental creation of a solid-density plasma at temperatures in excess of [10.sup.6] kelvin on inertial-confinement time-scales using an X-ray free-electron laser. We discuss the pertinent physics of the intense X-ray-matter interactions, and illustrate the importance of electron-ion collisions. Detailed simulations of the interaction process conducted with a radiative-collisional code show good qualitative agreement with the experimental results. We obtain insights into the evolution of the charge state distribution of the system, the electron density and temperature, and the timescales of collisional processes. Our results should inform future high-intensity X-ray experiments involving dense samples, such as X-ray diffractive imaging of biological systems, material science investigations, and the study of matter in extreme conditions., The experiment was performed at the LCLS soft X-ray materials science instrument (SXR), where a 1.0-µm-thick aluminium (Al) foil was irradiated with 80-fs X-ray pulses at photon energies in the [...]

The standard model for the origin of galactic magnetic fields is through the amplification of seed fields via dynamo or turbulent processes to the level consistent with present observations (1-3). Although other mechanisms may also operate (4,5), currents from misaligned pressure and temperature gradients (the Biermann battery process) inevitably accompany the formation of galaxies in the absence of a primordial field. Driven by geometrical asymmetries in shocks (6) associated with the collapse of protogalactic structures, the Biermann battery is believed to generate tiny seed fields to a level of about [10.sup.-21] gauss (refs 7, 8). With the advent of high-power laser systems in the past two decades, a new area of research has opened in which, using simple scaling relations (9,10), astrophysical environments can effectively be reproduced in the laboratory (11,12). Here we report the results of an experiment that produced seed magnetic fields by the Biermann battery effect. We show that these results can be scaled to the intergalactic medium, where turbulence, acting on timescales of around 700 million years, can amplify the seed fields (13,14) sufficiently to affect galaxy evolution., We conducted these experiments at the Laboratoire pour l'Utilisation de Lasers Intenses (LULI 2000) laser facility. The intense laser was used to illuminate a small carbon rod inside a low-pressure [...]

The production of X-rays from electron transitions into K-shell vacancies ([K.sub.α,β]) emission) is a well-known process in atomic physics and has been extensively studied as a plasma diagnostic in low- and mid-Z materials. However, X-ray spectra from near neutral high-Z ions are very complex, and their interpretation requires the use of state-of-the-art atomic calculations. In this experiment, the Titan laser system at Lawrence Livermore National Laboratory was used to deliver an approximately 350 J laser pulse, with a 10 ps duration and a wavelength of 1054 nm, to a gold (Au) target. A transparent bent quartz crystal spectrometer with a hard X-ray energy window, ranging from 17 to 102 keV, was used to measure the emission spectrum. [K.sub.α1,α2] and [K.sub.β1,γ1] transitions were observed over a range of target sizes. Additionally, a series of shots were conducted with a pre-ionizing long pulse (3 ns, 1-10 J, 527 nm) on the backside of the target. FLYCHK, an atomic non-LTE code, designed to provide ionization and population distributions, was used to model the experiment. [K.sub.α] / [K.sub.β] ratios were found to be in good agreement with the predicted value for room temperature Au targets. PACS No: 52.38.Ph La production de rayons-X provenant de transitions electroniques dans les lacunes de la couche K (emission [K.sub.α,β]) est un mecanisme bien connu en physique atomique qui a ete tres etudie comme diagnostique de plasma dans les materiaux de Z bas et intermediate. Cependant, les spectres X d'ions de Z eleve presque neutres sont tres complexes et leur interpretation exige l'utilisation de calculs atomiques de pointe. Dans cette experience, nous utilisons le systeme laser Titan du Lawrence Livermore National Laboratory qui envoie environ 350 J par impulsion d'une duree de 10 ps et une longueur d'onde de 1054 nm sur une cible d'or (Au). Nous avons utilise un spectrometre a cristal de quartz courbe avec une fenetre d'entree de rayons-X allant de 17 a 102 keV, afin de mesurer le spectre d'emission. Nous avons observe les transitions [K.sub.α1,α2] et [K.sub.β1,γ1] sur un domaine de grandeur de cible. De plus, une serie d'impulsion pre-ionisante (3 ns, 1-20 J, 527 nm) a ete tiree sur la partie arriere de la cible. Nous avons utilise le code atomique sans equilibre thermodynamique local FLYCHK pour obtenir les distributions d' ionisation et de population, afin de modeliser les resultats experimentaux. Les rapports [K.sub.α] / [K.sub.β] obtenus sont en bon accord avec les valeurs predites pour des cibles d'Au a la temperature de la piece. [Traduit par la Redaction], 1. Introduction The absorption of laser energy during high-intensity shortpulse laser-plasma interactions results in the production of a large current of hot electrons, which can subsequently generate energetic protons, ions, [...]

The use of targets with surface structures for laser-driven particle acceleration has potential to significantly boost the particle and radiation energies because of enhanced laser absorption. We investigate, via experiment and particle-in-cell simulations, the impact of micron-scale surface-structured targets on the spectrum of electrons and protons accelerated by a picosecond laser pulse at relativistic intensity. Our results show that, compared with flat-surfaced targets, structures on this scale give rise to a significant enhancement in particle and radiation emission over a wide range of laser–target interaction parameters. This is due to the longer plasma scale length when using micro-structures on the target front surface. We do not observe an increase in the proton cutoff energy with our microstructured targets, and this is due to the large volume of the relief. [ABSTRACT FROM AUTHOR]

The energy spectra of protons generated by ultra-intense (1020 W cm−2) laser interactions with a preformed plasma of scale length measured by shadowgraphy are presented. The effects of the preformed plasma on the proton beam temperature and the number of protons are evaluated. Two-dimensional EPOCH particle-in-cell code simulations of the proton spectra are found to be in agreement with measurements over a range of experimental parameters. [ABSTRACT FROM PUBLISHER]

Abstract: We combine experiments and theoretical models to characterize warm dense deuterium. A shockwave was driven in a planar target by the OMEGA laser without a standard pusher making the analysis independent of a quartz or aluminium pressure standard. The conditions of the shocked material were diagnosed with VISAR and optical pyrometry which yields the shock velocity (16.9 ± 0.9 km/s) and the temperature (0.57 ± 0.05 eV). We find a self-consistent description of the data when using ab initio simulations (DFT-MD), but not for other equation of state (EOS) models tested. [Copyright &y& Elsevier]

High-power lasers that fit into a university-scale laboratory can now reach focused intensities of more than 1019?W?cm-2 at high repetition rates. Such lasers are capable of producing beams of energetic electrons, protons and?-rays. Relativistic electrons are generated through the breaking of large-amplitude relativistic plasma waves created in the wake of the laser pulse as it propagates through a plasma, or through a direct interaction between the laser field and the electrons in the plasma. However, the electron beams produced from previous laser-plasma experiments have a large energy spread, limiting their use for potential applications. Here we report high-resolution energy measurements of the electron beams produced from intense laser-plasma interactions, showing that-under particular plasma conditions-it is possible to generate beams of relativistic electrons with low divergence and a small energy spread (less than three per cent). The monoenergetic features were observed in the electron energy spectrum for plasma densities just above a threshold required for breaking of the plasma wave. These features were observed consistently in the electron spectrum, although the energy of the beam was observed to vary from shot to shot. If the issue of energy reproducibility can be addressed, it should be possible to generate ultrashort monoenergetic electron bunches of tunable energy, holding great promise for the future development of‘table-top’particle accelerators. [ABSTRACT FROM AUTHOR]

Investigations of 7Li(p,n)7Be reactions using Cu and CH primary and LiF secondary targets were performed using the VULCAN laser [C.N. Danson et al., J. Mod. Opt. 45, 1653 (1997)] with intensities up to 3×1019 W cm-2. The neutron yield was measured using CR-39 plastic track detector and the yield was up to 3×108 sr-1 for CH primary targets and up to 2×108 sr-1 for Cu primary targets. The angular distribution of neutrons was measured at various angles and revealed a relatively anisotropic neutron distribution over 180° that was greater than the error of measurement. It may be possible to exploit such reactions on high repetition, table-top lasers for neutron radiography. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The synthesis of halogenated compounds in biological systems is well established, yet the mechanisms by which these compounds are formed are poorly understood. Many commercially important compounds, such as pharmaceuticals and agrochemicals, contain halogens; indeed some halogenated natural products, such as the antibiotic vancomycin, are themselves valuable. Furthermore, several environmentally significant organohalogens can be formed naturally, for example it is likely that a significant proportion of the atmospheric bromomethane is produced by higher plants (Gan et al. 1998). While chemical synthesis of organohalogens can be difficult, the biological production of these compounds occurs under relatively mild conditions and often with a greater degree of specificity. Therefore an understanding of the biosynthesis of halometabolites, and in particular, the enzymology of carbon-halogen bond formation, may provide convenient biotechnological methods for the halogenation of organic compounds. For over 30 years haloperoxidases were the only halogenating enzymes that had been identified and it was largely accepted that these enzymes were responsible for almost all biological halogenation reactions. However, in recent years evidence has accumulated pointing to the existence of other halogenases and now the nature of these enzymes is being revealed. This review concentrates on the occurrence, mechanism and biocatalytic potential of the halogenating enzymes that are currently known. [ABSTRACT FROM AUTHOR]

Dense ceramic tubes of the multi phase mixed ionic/electronic conductor SrFeCo0.5Oy (SFC2) have been .synthesized by solid-state reaction. Stability of the component phases of SFC2 was studied by insitu neutron diffraction in the temperature range of 900–1200 °C in air and Ar environments. In air between 900 and 1050 °C, the material is stable, with Sr2(Fe,Co)3Oy (236) being the major phase. Above 1050 °C, 236 undergoes decomposition into perovskite and rocksalt phases, and at 1200 °C, only a small fraction of the 236 phase is stable. In Ar, the 236 phase is completely stable at 900 °C but is completely decomposed by 1100 °C, whereupon only the perovskite and rocksalt phases remain. Rietveld analysis indicates that the 236 and perovskite phases become more Fe-rich as decomposition occurs, while the perovskite phase lattice parameter and oxygen content vary readily as temperature and gas environment are changed. [ABSTRACT FROM AUTHOR]

Abstract: The underlying physics triggering core collapse supernovae is not fully understood but observations of material ejected during such events helps to solve this puzzle. In particular, several satellite based γ-ray observations of the isotope 44Ti have been reported recently. Conveniently, the amount of this isotope in stellar ejecta is thought to depend critically on the explosion mechanism. The most influential reaction to the amount of 44Ti in supernovae is . Here we report on a direct study of this reaction conducted at the REX-ISOLDE facility, CERN. The experiment was performed with a 44Ti beam at , corresponding to an energy distribution, for reacting α-particles, centred on with a 1σ width of 0.23 MeV. This is, for the first time, well within the Gamow window for core collapse supernovae. The material from which the 44Ti beam was extracted originates from highly irradiated components of the SINQ spallation neutron source of the Paul Scherrer Institute. No yield above background was observed, enabling an upper limit for the rate of this reaction to be determined. This result is below expectation, suggesting that the reaction proceeds more slowly than previously thought. Implications for astrophysical events, and remnant age, are discussed. [Copyright &y& Elsevier]