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The effectiveness of a dome-shaped wall covered by a thin gold foil (hollow wall) [M. Vandenboomgaerde et al., Phys. Plasmas 25, 012713 (2018)PHPAEN1070-664X10.1063/1.5008669] in holding back the high-Z plasma expansion in a gas-filled hohlraum is demonstrated for the first time in experiments reproducing the irradiation conditions of indirect drive at the ignition scale. The setup exploits a 1D geometry enabling record of the complete history of the gold expansion for 8 ns by imaging its emission in multiple x-ray energy ranges featuring either the absorption zones or the thermal emission regions. The measured expansion dynamics is well reproduced by numerical simulations. This novel wall design could now be tailored for the megajoule scale to enable the propagation of the inner beams up to the equator in low gas-filled hohlraum thus allowing the fine-tuning of the irradiation symmetry on the timescale required for ignition.

The advent of high-power lasers facilities such as the National Ignition Facility (NIF), and the Laser Megajoule (LMJ) in the near future, opens a new era in the field of High Energy Density Laboratory Astrophysics. These versatile laser facilities will provide unique platforms to study the rich physics of nonlinear and turbulent mixing flows. The extended laser pulse duration could be harnessed to accelerate targets over much larger distances and longer time periods than previously achieved. We report on the first results acquired on NIF with the ablative Rayleigh–Taylor Instability (RTI) platform. A 20-ns X-ray drive is tailored to accelerate planar modulated samples into the highly-nonlinear bubble merger regime. Based on the analogy between flames front and ablation front, highly nonlinear RTI measurements at ablation front can provide important insights into the initial deflagration stage of thermonuclear supernova of Type Ia. We also report on an innovative concept used to create even longer drive on multi-beam laser facilities. The multi-barrel hohlraum (Gattling Gun) approach consists, here, of three adjacent cavities, driven in succession in time. This novel concept has been validated on the Omega EP laser system. The three cavities were irradiated with three 6–10 ns pulse UV beams and a 30 ns, 90 eV X-ray radiation drive was measured with the time-resolved X-ray spectrometer μDMX. This concept is promising to investigate the pillar structures in the Eagle Nebula or for photoionization studies which require a steady light source of sufficient duration to recreate relevant physics.

The advent of high-power lasers facilities such as the National Ignition Facility (NIF), and Laser Megajoule (LMJ) in the near future opens a new era in the field of High Energy Density Laboratory Astrophysics. The LMJ, keystone of the French Simulation Program, is under construction at CEA/CESTA and will deliver 1.5 MJ with 176 beamlines. The first physics experiments on LMJ will be performed at the end of 2014 with 2 quadruplets (8 beams). The operational capabilities (number of beams and plasma diagnostics) will increase gradually during the following years. We describe the current status of the LMJ facility and the first set of diagnostics to be used during the commissioning phase and the first experiments. The PETAL project (PETawatt Aquitaine Laser), part of the CEA opening policy, consists in the addition of one short-pulse (500 fs to 10 ps) ultra-high-power, high-energy beam (a few kJ compressed energy) to the LMJ facility. PETAL is focalized into the LMJ target chamber and could be used alone or in combination with LMJ beams. In the later case, PETAL will offer a combination of a very high intensity multi-petawatt beam, synchronized with the nanosecond beams of the LMJ. PETAL, which is devoted to the academic research, will also extend the LMJ diagnostic capabilities. Specific diagnostics adapted to PETAL capacities are being fabricated in order to characterize particles and radiation yields that can be created by PETAL. A first set of diagnostics will measure the particles (protons/ions/electrons) spectrum (0.1–200 MeV range) and will also provide point projection proton-radiography capability. LMJ/PETAL, like previously the LIL laser [X. Julien et al., Proc. SPIE 7916 (2011) 791610], will be open to the academic community. Laboratory astrophysics experiments have already been performed on the LIL facility, as for example radiative shock experiments and planetary interiors equation of state measurements.

International audience; Ion stopping experiments in plasma for beam energies of few hundred keV per nucleon are of great interest to benchmark the stopping-power models in the context of inertial confinement fusion and high-energy-density physics research. For this purpose, a specific ion detector on chemical-vapor-deposition diamond basis has been developed for precise time-of-flight measurements of the ion energy loss. The electrode structure is interdigitated for maximizing its sensitivity to low-energy ions, and it has a finger width of 100 μm and a spacing of 500 μm. A short single α-particle response is obtained, with signals as narrow as 700 ps at full width at half maximum. The detector has been tested with α-particle bunches at a 500 keV per nucleon energy, showing an excellent time-of-flight resolution down to 20 ps. In this way, beam energy resolutions from 0.4 keV to a few keV have been obtained in an experimental configuration using a 100 μg/cm2 thick carbon foil as an energy-loss target and a 2 m time-of-flight distance. This allows a highly precise beam energy measurement of δE/E ≈ 0.04%–0.2% and a resolution on the energy loss of 0.6%–2.5% for a fine testing of stopping-power models.

A novel concept for using hybrid targets to create multi-keV X-ray sources was tested on the GEKKO XII facility of the OSAKA University and on the OMEGA facility of the University of Rochester. The sources were made via laser irradiation of a titanium foil placed at the end of a plastic cylinder, filled with a very low-density (2 and 5 mg/cm3) silicon-dioxide aerogel that was designed to control the longitudinal expansion of the titanium plasma. Preliminary calculations were used to determine optimal conditions for the aerogel density, cylinder diameter and length that maximize multi-keV X-ray emission. The X-ray emission power was measured on OMEGA using absolutely calibrated broad-band, diode-based CEA diagnostics, in addition to high resolution crystal spectrometers. On GEKKO XII, the heat wave propagation velocity in the aerogel was also measured with an X-ray framing camera. The advantage of using the thermal wave generated in the aerogel to heat a solid material to increase the conversion efficiency has not been fully demonstrated in these experiments. However, it was shown that a 5 mg/cm3 aerogel placed in front of a titanium foil can improve the x-ray conversion efficiency with respect to the case of 2 mg/cm3 for some target diameter and length.

The time resolved crystal x-ray spectrometers called SXDHR-lt of the Ligne d’Integration laser is presented. It is necessary to calibrate all x-ray sensitive elements of diagnostics before using them in laser matter interaction experiments. In particular, crystals need to be calibrated. Measurements of the integrated coefficient of reflection of a beryl cylindrical crystal used in this spectrometer were performed with synchrotron radiation and with an x-ray tube and are presented. A test of the homogeneity of the reflection of the crystal was also performed. Aging or accidental pollution of x-ray diagnostics installed around target chambers is always possible. This happened to the DMX broadband spectrometer installed on the OMEGA Laser Facility at the University of Rochester (Laboratory for Laser Energetics) and this changed the spectral sensitivity of its channels. The evolution over time of the x-ray sensitivity needs to be critically assessed and if necessary x-ray sensitive elements will need to be recalibrated.

This work describes measurements of laser propagation through very low-density aerogels and subsequent multi-keV photon production from titanium foils. For efficient foil heating, SiO 2 aerogel with densities of 2 and 5 mg/cm 3 have been cast into a plastic cylinder, which are then mounted to Ti foils that are 3–20 μm thick. Experiments have been performed on the GEKKO-XII laser facility to characterize laser propagation through the aerogel and X-ray production from the Ti foil. Multi-keV emission is diagnosed with a full set of diagnostics giving laser-to-X-ray conversion efficiencies, time-dependent X-ray power and two-dimensional X-ray imaging.

In high flux (1013–15 W/cm2) laser-plasma interaction, a large part of the incoming laser energy is radiated into soft x-rays. To determine both the shape of this spectrum and the conversion efficiency, we have designed and tested an absolutely calibrated broadband soft x-ray spectrometer with a high temporal resolution (100 ps). The detector in this spectrometer is a new coaxial x-ray diode coupled with a fast single shot oscilloscope (French IN7100 with 7 GHz frequency response cutoff). Both absolute calibrations (x-ray response of diodes) and relative calibrations (filters and mirrors) have used the French synchrotron beam lines at Laboratoire pour l’utilisation du Rayonnement Electromagnetique (LURE) in Orsay. The initial version of this instrument was first successfully implemented on laser plasmas experiments at the Phebus facility in France and an improved version is now operating at the Omega laser facility in Rochester, New York. The emitted x-ray spectrum is absolutely measured in 18 broad bands...

The feasibility of efficient X-ray sources for radiography on the LMJ (Laser MegaJoule) in the multi-kJ/ns range was demonstrated on the OMEGA laser facility (Univ. Rochester) from 2002 to 2004 [1,2]. We significantly enhanced the conversion efficiency of titanium (4–6 keV), copper (8–10 keV) and germanium (9–13 keV) foils by using an optimized pre-pulse/pulse combination. Since higher X-ray energy and therefore electronic temperature need hydroconfinement, plastic cylindrical hohlraums internally coated with titanium, copper and germanium with various OMEGA beam configurations were successfully tested from 2005 to 2009 [3–5]. In addition, many shots with metal-doped aerogel (Ti, Fe, Ge) were tested on OMEGA [6].Recently we tested a new concept of “HYBRID sources” based on the combination of a thin titanium foil at the exit hole of a plastic cylinder filled with very low density SiO 2 aerogel (2 and 5 mg/cc). The benefit of the underdense medium is, first, to transport the laser energy to the titanium foil after its conversion into a supersonic ionization front and, second, to prevent foil expansion and excessive kinetic energy losses by longitudinal hydroconfinement.

In 2009 a series of metal-lined hohlraums were tested on the Omega laser facility. The main aims of the campaign were to improve our understanding of the multi-keV energy production and our capability to numerically reproduce the measured conversion efficiencies (CE's). Two studies have been primarily planned: the effect of the metallic plasma mean ionization states and that of hydrodynamics. Six targets were experimented for which the metallic materials (titanium, copper, germanium), the cavity diameter, and the irradiation energy were varied. Here we compare experimental and calculated results. The numerical simulations are performed with the 2D hydro-radiative code FCI2. For all the cavities, the measured multi-keV x-ray powers versus time are qualitatively well reproduced by the simulations, indicating that hohlraum hydrodynamics seems to be well calculated. But we have an underestimation by a factor of ∼2 for the calculated CEs versus experimental values for titanium and copper hohlraums. By contrast there is a good agreement between measurements and calculations for the germanium hohlraum. To explain these results, we have calculated off-line integrated emissivities for couples of (ρ, Te) values contributing to the multi-keV production with several non-local-thermal-equilibrium (NLTE) atomic physics models.

We use the LIL (Ligne d'Integration Laser ) facility to study the coalescence of two planar shocks in an indirectly-driven planar sample of polystyrene. This experiment represents the preliminary stage of the future shock-timing campaign for the Laser Megajoule (LMJ). The main objectives are to validate the experimental concept and to test the numerical simulations. We used a gold spherical hohlraum to convert into X-ray the 351 nm wavelength laser pulse and to initiate the two shocks in the sample. To access time resolved shock velocities and temperature, we used two rear-side diagnostics: a VISAR (Velocity Interferometer System for Any Reflection) working at two different wavelengths and a streaked optical self-emission diagnostic. We observed the coalesced shock, in good agreement with the numerical simulations. We also observed a loss of signal during the first nanoseconds probably due to sample heating from the hohlraum X-ray flux.

International audience; A new channel of an X-ray broadband spectrometer has been developed for the 2 – 4 keV spectral range. It uses a spectral filtering by using a non-periodic multilayer mirror. This channel is composed by a filter, an aperiodic multilayer mirror and a detector. The design and realization of the optical coating mirror has been defined such as the reflectivity is above 8% in almost the entire bandwidth range 2 – 4 keV and lower than 2% outside. The mirror is optimized for working at 1.9° grazing incidence. The mirror is coated with a stack of 115 chromium / scandium (Cr / Sc) non-periodic layers, between 0.6 nm and 7.3 nm and a 3 nm thick top SiO2 layer to protect the stack from oxidization. To control thin thicknesses, we produced specific multilayer mirrors which consist on a superposition of two periodic Cr / Sc multilayers with the layer to calibrate in between. The mirror and subnanometric layers characterizations were made at the “Laboratoire Charles Fabry” (LCF) with a grazing incidence reflectometer working at 8.048 keV (Cu Kα radiation) and at the synchrotron radiation facility SOLEIL on the hard X-ray branch of the “Metrology” beamline. The reflectivity of the mirrors as a function of the photon energy was obtained in the Physikalisch Technische Bundesanstalt (PTB) laboratory at the synchrotron radiation facility Bessy II.

At CEA/Bruyeres-le-Châtel (Service CEM), there are facilities to calibrate X-ray detectors from 200 eV to 100 keV, with an accuracy of 4% at high energies ( E > 3 keV). The source is the direct radiation from the X-ray tubes [C Kα (277 eV) to Ti KαKβ (4.51/4.93 keV)] or fluorescence emission from secondary targets [Mg Kα (1.25 keV) to U Kα (98 keV)]. In addition, calibrations are carried out with the synchrotron radiation of the Super-ACO storage ring (LURE-Orsay), by selecting the monoenergetic beams with a double crystal monochromator which is tunable between 0.8 and 8 keV. The resolution is better than 1 eV. This last tool is very useful in the study of the absorption edges of the detector compounds (for example, Si K-edge and Ar K-edge). Some examples are presented of results obtained between 1 and 50 keV, with special reference to high flux detectors such as gold photocathodes and silicon avalanche photodiodes. Thick silicon photodiodes (for the high energy range) were also calibrated.

A novel surface diffractometer devoted to structural studies of surfaces and interfaces by X-ray scattering is described. It is composed of a very precise goniometer, onto which different UHV chambers can be rapidly aligned and interchanged without breaking the vacuum, thus allowing a more efficient use of the synchrotron X-ray beam. Two UHV chambers have been designed, one for horizontal sample surface, and one for vertical sample surface. The latter is equipped with all necessary tools to prepare the surface and perform molecular beam epitaxy at the same time as surface X-ray scattering. Both allow one to reach very large out-of-plane momentum transfer values with high accuracy.

An x-ray grating spectrometer was built in order to measure opacities in the 50 eV to 250 eV spectral range with an average spectral resolution ⟨E/δE⟩ ∼ 50. It has been used at the LULI-2000 laser facility at Ecole Polytechnique (France) to measure the Δn = 0, n = 3 transitions of several elements with neighboring atomic number: Cr, Fe, Ni, and Cu in the same experimental conditions. Hence a spectrometer with a wide spectral range is required. This spectrometer features one line of sight looking through a heated sample at backlighter emission. It is outfitted with one toroidal condensing mirror and several flat mirrors cutting off higher energy photons. The spectral dispersion is obtained with a flatfield grating. Detection consists of a streak camera sensitive to soft x-ray radiation. Some experimental results showing the performance of this spectrometer are presented.

International audience; We have developed non-periodic Cr/Sc multilayer mirrors specifically designed to reflect energy photons between 2 and 4 keV with a pre-defined reflectivity profile. Furthermore, these mirrors have to work as filters in the 1-2 keV and 4-12 keV energy bandpass with a reflectivity as low as possible in these bandwidths. The mirrors were designed and optimized with the help of a commercial calculation code. Numerous combinations of layers have been investigated with two or three different materials in the multilayer. The interfacial effect, leading to thickness modifications, has been investigated. Layer thicknesses were accurately controlled, taking into account compaction effect at interfaces. The best results lead to non-periodic mirrors dedicated to work at 1.5° grazing incidence with a reflectivity above 15% in almost the entire energy range 2-4 keV and lower than 1% outside, except in the total reflection zone. The final choice of material was made from the experimental knowledge of corresponding layer deposited behavior. The multilayers have been deposited by magnetron sputtering. Grazing-incidence X-ray reflectance at 8.05 keV (0.154 nm) and at the Physikalisch-Technische Bundesanstalt laboratory (PTB) at the synchrotron radiation facility BESSY II in Berlin for X-ray reflectance over the whole range were used both in order to characterize the multilayers (thicknesses, complex indices, and roughnesses). The final results show good agreement with the requested reflectivity profile.

The x-ray broadband spectrometer, DMX, is among the first plasma diagnostics to be deployed on Laser Megajoule (LMJ). The emitted x-ray spectrum from laser-produced plasmas is measured in 20 channels from 50 eV up to 20 keV. Each band combines mirrors and filters which realize x-ray band-pass filter and a coaxial diode coupled by a coaxial cable with a fast digitizer that realize the acquisition. The measurement accuracy depends on the equipment performance and the spectrum to acquire. In this context, Commissariat a l'Energie Atomique (CEA) is developing a numerical method called Acquisition Channel Simulator (ACS) whose purpose is to define and optimize all electrical acquisition channels of such diagnostics. The ACS goals are to define numerical model for each element the electrical channel and optimize it. This paper introduces the work led by CEA regarding the development of the ACS method particularly for the equipment model and the first results for the DMX diagnostic.

Experimental investigation of stimulated Raman (SRS) and Brillouin (SBS) scattering have been obtained at the Ligne-d'Integration-Laser facility (LIL, CEA-Cesta, France). The parametric instabilities (LPI) are driven by firing four laser beamlets (one quad) into millimeter size, gas-filled hohlraum targets. A quad delivers energy on target of 15 kJ at 3ω in a 6-ns shaped laser pulse. The quad is focused by means of 3ω gratings and is optically smoothed with a kinoform phase plate and with smoothing by spectral dispersion-like 2 GHz and/or 14 GHz laser bandwidth. Open- and closed-geometry hohlraums have been used, all being filled with 1-atm, neo-pentane (C5H12) gas. For SRS and SBS studies, the light backscattered into the focusing optics is analyzed with spectral and time resolutions. Near-backscattered light at 3ω and transmitted light at 3ω are also monitored in the open geometry case. Depending on the target geometry (plasma length and hydrodynamic evolution of the plasma), it is shown that, at maximu...

A direct experimental comparison of rugby-shaped and cylindrical shaped gas-filled hohlraums on the Omega laser facility demonstrates that higher coupling and minimal backscatter can be achieved in the rugby geometry, leading to significantly enhanced implosion performance. A nearly 50% increase of x-ray drive is associated with earlier bangtime and increase of neutron production. The observed drive enhancement from rugby geometry in this study is almost twice stronger than in previously published results.

With the advent of new x-ray sources, the detection of radiation with picosecond temporal resolution becomes increasingly important. We used the time structure of the radiation at the European Synchrotron Radiation Facility (ESRF) to characterize fast detectors developed for x-ray diagnostics. The detectors tested were neutron pre-irradiated Gallium Arsenide (GaAs) detectors and chemical-vapor-deposited (CVD) diamond detectors. The experiments were performed on beamline BM5, both in single-bunch and multi-bunch mode. The response of the detectors to the hard x-ray pulses was recorded using a single shot 7 Ghz oscilloscope or using a digital oscilloscope in sampling mode. For a current of the electrons in the storage ring of typically 10 - 15 mA in monomode-bunch, the pulse length was between 100 ps and 150 ps (FWHM). In multi-bunch mode, the X-ray pulse length was independent of the current and shorter. We measured FWHM pulse duration values down to 50 ps. Comparison with data obtained with a streak camera showed that the time resolution of our detectors was at best 25 ps.

In an earlier paper the emission of synchrotron radiation was studied theoretically for the current induced by a single electron interacting with a bending magnet showing that a chirp of the hard x-ray could be expected that could be used for a compression of x-ray bunches using dispersive optics. In this paper we will present results of an experimental study that was conducted on a bending magnet beamline (BM5) at the ESRF to learn if such a chirp exists for an electron bunch as a function of the x-ray energy and of the emission angle below and above the electron orbit plane. Our results for the pulse shape show that such a chirp could not be clearly detected at a level of several tens of picoseconds FWHM. This means that the phase relationships of all the electrons producing the x- ray bunch are averaged out leading to the absence of a net chirp. However, a fast Fourier transform of the observed signal showed that there was a phase lag. This will be described in a companion paper. Here, the details of the experimentally observed time structure will be given.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

should be replaced by Table I andFigure 1 below.Modified sentences are the followings. Conversion effi-ciencies (CEs) obtained from titanium L-type hohlraum are3.6% and more than 7% for the S-type hohlraum with thesquared laser pulse shape. The Ti-halfraum gives a CE of6.7%, very comparable to the S-type hohlraum ones. HEN-WAY spectrometer gives higher values than DMX, and as aconsequence, the argument of LEH apparent size is not validanymore. For titanium, conversion efficiencies are up to!7% into 4p integrating between 4.6 and 6.5 keV, when alarge-inner-diameter hohlraum is used with a squared laserpulse shape. As titanium emitters at 4.7 keV, lined hohl-raums are less efficient than gas targets, which are consid-ered as an upper limit for x-ray yields since their low densityallows good laser absorption and small kinetic losses. Tita-nium-hohlraum CEs are comparable than those fromexploded foils.

We present an overview of recent experiments fielded on the LIL facility. A key issue for mega-joule class laser facilities is shrapnel fragment generation. A specific collector was therefore developed to capture debris in aerogel and dedicated shots were done to quantitatively evaluate target fragmentation phenomena. The LIL panel of transmitted and backscattered light diagnostics is well suited for laser-plasma interaction (LPI) experiments. This include gas-filled hohlraum configurations relevant to Indirect Drive ignition targets in order to test the specific LMJ longitudinal SSD technique, as well as LPI experiments with foam targets for laser beam smoothing in underdense plasma in the context of Direct Drive. After Visar commissioning a campaign was dedicated to boron Equation of State (EOS).

As multi-keV x-ray radiators, hohlraums and halfraums with inner walls coated with metallic materials (called liner) have been tested for the first time with laser as the energy drive. For titanium, conversion efficiencies (CEs) are up to ∼14% for emission into 4π, integrating between 4.6 and 6.5 keV when a large diameter hohlraum is used. Germanium CE is ∼0.8% into 4π between 9 and 13 keV. The highest CEs have been obtained with a 1 ns squared pulse and phase plates giving laser absorption near 99%. These high CEs are due to long-lasting, good plasma conditions for multi-keV x-ray production maintained by plasma confinement inside the plastic cylinder and plasma collision leading to a burst of x rays at a time that depends on target size. As photon emitters at 4.7 keV, titanium-lined hohlraums are the most efficient solid targets and data are close to CEs for gas targets, which are considered as the upper limit for x-ray yields since their low density allows good laser absorption and low kinetics losses....

The Ligne d'Integration Laser (LIL) facility has been designed as a prototype for the Laser MegaJoule (LMJ) which is a cornerstone of the French 'Simulation Program'. This laser has been intensively used to test and improve the LMJ components. In addition, a large panel of plasma diagnostics has been installed and is currently used to perform laser–plasma experiments. After a brief discussion about the LIL design, we present the last results in various plasma physics domains.

The diagnostic designs for the Laser Megajoule (LMJ) will require components to operate in environments far more severe than those encountered in present facilities. This harsh environment will be induced by fluxes of neutrons, gamma rays, energetic ions, electromagnetic radiations, and, in some cases, debris and shrapnel, at levels several orders of magnitude higher than those experienced today on existing facilities. The lessons learned about the vulnerabilities of present diagnostic parts fielded mainly on OMEGA for many years, have been very useful guide for the design of future LMJ diagnostics. The present and future LMJ diagnostic designs including this vulnerability approach and their main mitigation techniques will be presented together with the main characteristics of the LMJ facility that provide for diagnostic protection.

A set of materials—titanium, copper, and germanium—has been experimented with at the OMEGA laser facility [Boehly, Opt. Commun. 133, 495 (1997)] by irradiating thin foils with a prepulse prior to a main pulse with variable delay, in order to design efficient x-ray laser-sources for backlighting, material testing, and code validation. This concept led to increasing factors from 2 to 4 comparing to cases without prepulse, in the experimental conditions. As a result, high multi-keV x-ray conversion rates have been obtained: 9% for titanium around 4keV, 1% for copper around 8keV, and 2.5 to 3% for germanium around 10keV, which places these pre-exploded metallic targets close to the gas with respect to their performance, with wider energy range. A good agreement with hydroradiative code FCI2 [Schurtz, Phys. Plasmas 7, 4238 (2000)] calculations is found for titanium and copper on all diagnostics, with nonlocal-thermal-equilibrium atomic physics and, either nonlocal thermal conduction taking self-generated B-fields into account, or limited thermal conduction with intensity-dependent factor f. The results for germanium indicate that dielectronic processes could play a more significant role when higher irradiation intensity on higher Z material.

Implosion of inertial confinement fusion (ICF) capsule is very sensitive to the growth of sphericity perturbations. The control of the feeding of such perturbations and their transport ('feedthrough') through the ablator is a key point to reach ignition. Since 2002 [1, 2], experiments have been designed and performed on the Omega laser facility in order to study these phenomena in planar geometry. A new 'rugby shaped' hohlraum was used [3, 4]. We present experimental results and comparisons with numerical simulations.

This paper presents experimental results obtained at LULI 2000 and LIL about (i) the compared laser plasma coupling at 526 (2ω) and 351 nm (3ω) and (ii) the early laser imprint suppression using foam targets as plasma smoother of the laser beam. Both experiments are described, part of the experimental results are presented and discussed.

Feasability of efficient X-ray sources for LMJ (LaserMegaJoule) targets radiography in the multi-keV/ns regime was demonstrated on OMEGA laser facility (University of Rochester) from 2002 to 2004 [1][2][3]. We significantly enhanced the conversion efficiency of titanium, copper and germanium foils using an optimized prepulse/pulse combination [4]. Since higher X-ray energy and therefore high electronic temperature require more confinement, we built and successfully tested in 2005, plastic cylindrical hohlraums internally coated with titanium in various OMEGA beam configurations, pulse types (with and without prepulse) and target designs. The conversion efficiency (CE), depends on hohlraum length and diameter and the highest CE was measured above 17%, which is better than any other x-ray sources in this photon energy range (i.e. 4.7 keV). The best experimental setup was a 2-cone irradiation scheme without prepulse i.e. the simplest and the most economic configuration in view of radiographic purposes. These studies were carried on in february 2007 with Ge-lined hohlraums and Ti-lined halfraums. We describe and show comparisons between experimental results (time integrated and resolved x-ray imaging, pinholes and x-ray diode) with 2D hydrorad simulations.

The Laser Integration Line (LIL) is part of the Laser Megajoule (LMJ) project. The LMJ installation, which is of the National Ignition Facility (NIF) class, will deliver 1.8MJ at 0.35μm wavelength on target with 60 quadruplets of elementary beams. The energy on target of LIL is 30kJ corresponding to one quadruplet, it is housed in a separate building and has its own experimental setup. Target diagnostics have been progressively installed in the LIL target area. Energy and imaging diagnostics as well as the broadband and high resolution spectrometers have been fabricated in the frame of a unique industrial contract. Optical pointers are used to align the diagnostics to the target. The supervisory system controlling the diagnostics configuration and data acquisition is now able to manage cooperative and Commissariat a l’ Energie Atomique (CEA) shots. The calibration data base is accessible from the processing network and will very soon include the characterization of all the streaked, gated, and charge coup...

In the context of target design for multi-keV x-ray laser-produced experiments, the concept of exploding metallic thin foils by two laser pulses delayed in time has been tested at the OMEGA laser facility [J. M. Soures, R. L. McCrory, C. P. Verdon et al., Phys. Plasma 3, 2108 (1996)]. The first laser pulse creates an underdense plasma (ne∕nc≈0.2), and the second laser pulse heats the plasma plume which produces strong line emission from the titanium K shell (Heα at 4.7 keV and Hα at 4.9 keV). Six OMEGA beams (500-ps duration) for the prepulse and nine beams (1-ns duration) for the heating pulse irradiate one side of the foil. Different experimental conditions have been investigated in order to optimize the conversion efficiency enhancement on titanium foils. The influences of the foil thicknesses (5 and 6 μm), the delays (3, 4, and 5 ns) between the laser pulses, and the laser intensities (1.3 and 2.2×1015Wcm−2) have been tested. The absolute output power was measured by a set of filtered x-ray diodes, gi...

We present here a study of the influence of the reconstruction induced by hydrogen on the photoelectron diffraction pattern of W(110). The experiments have been performed on a clean and hydrogen covered W(110) surface. The comparison of the resulting azimuthal pattern with theoretical calculations performed within a single scattering plane wave theory, allows us to conclude that this surface is unreconstructed when clean, and rigidly displaced along the 〈 1 10〉 direction in presence of hydrogen.