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International audience; Generating thin and high density plasma slabs at a high repetition rate is a key issue for ultra-high intensity laser applications, such as plasma photonics, electron acceleration by few laser-cycle pulses, or collisionless shock acceleration of protons to high energies. In this paper, we present a scheme to generate such plasma slabs. It is based on the propagation and collision in a gas jet of two counter-propagating blast waves (BWs). Each BW is launched by a sudden and local heating induced by a nanosecond laser beam that propagates along the side of the jet. The resulting cylindrical BW expands perpendicular to the beam. The shock front, which is bent by the gas jet density gradient, pushes and compresses the plasma toward the jet center. By using two parallel ns laser beams, one on each side of the gas jet, this scheme enables us to tailor independently two opposite sides of the jet, while avoiding the damage risks associated with counterpropagating laser beams. A parametric study is performed using two and three dimensional hydrodynamic (single fluid), as well as kinetic (Fokker–Planck), simulations. This study shows that the BW bending combined with the collision in a stagnation regime increases the density by more than ten times and generates a very thin (down to few micrometers), near to over-critical plasma slab with a high density contrast (>100) and a lifetime of a few hundred picoseconds. Two dimensional particle-in-cell simulations are, then, used to study the influence of the plasma tailoring on proton acceleration by a high-intensity sub-picosecond laser pulse. It is shown that tailoring the plasma, not only at the entrance but also at the exit side of the picosecond-pulse, enhances the proton beam collimation and increases significantly the number of high energy protons, and their maximum energy.

We report experimental results on relativistic electron beam (REB) transport in a set of cold and shock-heated carbon samples using the high-intensity kilojoule-class OMEGA EP laser. The REB energy distribution and transport were diagnosed using an electron spectrometer and x-ray fluorescence measurements from a Cu tracer buried at the rear side of the samples. The measured rear REB density shows brighter and narrower signals when the targets were shock-heated. Hybrid PIC simulations using advanced resistivity models in the target warm-dense-matter (WDM) conditions confirm this observation. We show that the resistivity response of the media, which governs the self-generated resistive fields, is of paramount importance to understand and correctly predict the REB transport.

This work consists of the validation of a new Grid Based Boltzmann Solver (GBBS) conceived for the description of the transport and energy deposition by energetic particles for radiotherapy purposes. The entropic closure and a compact mathematical formulation allow our code (M1) to calculate the delivered dose with an accuracy comparable to the Monte-Carlo (MC) codes with a computational time that is reduced to the order of few minutes without any special processing power requirement. A validation protocol with heterogeneity inserts has been defined for different photon sources. The comparison with the MC calculated depth-dose curves and transverse profiles of the beam at different depths shows an excellent accuracy of the M1 model.

The direct and indirect drive schemes for Inertial Confinement Fusion (ICF) make use of a large number of laser beams arranged in a symmetric angular distribution. The preferential decay geometry of the three waves resonant couplings, mainly responsible for backscattered light in single beam experiments, may then be deeply modified in the region of crossing beams where collective laser plasma instabilities could develop. Such instabilities can occur for laser beams having a common symmetry axis along which they drive a common daughter wave. The collective coupling results in an increase of the growth gain with the increase of the number of interacting beams and produce energy losses in new backward directions. We have taken advantage of the multiple beams of the Omega laser facility and of its large battery of diagnostics to study the physics related to this multiple beams interaction in the regimes of high temperature plasmas relevant of the direct and indirect drive schemes to ICF. Experiments performed in a planar open geometry have evidenced the large amplification of stimulated Raman scattering (SRS) electromagnetic waves almost transverse to the density gradient as theoretically predicted 40 years ago. This was achieved in long scale-length high-temperature plasmas in which two beams couple to the same scattered electromagnetic wave further demonstrating this multiple-beams collective SRS interaction. The collective nature of the coupling and the amplification at large angles from the density gradient increase the global SRS losses and produce light scattered in novel directions out of the planes of incidence of the beams. Indirect drive experiments were performed in rugby ball shaped Hohlraum irradiated by 40 beams. Large instantaneous (peak reflectivity >30%) Brillouin sidescattering was evidenced to originate from the collective Brillouin amplification of a shared ion acoustic wave driven along the Hohlraum axis by a cone of 10 beams. In this paper, the scattering geometry is detailed for the two types of collective instabilities showing that they produce light scattered in novel very precise directions located far from the original aperture of the beams where the diagnostics are usually set-up. This scattered light could be measured on Omega thanks to the flexibility of the facility. Key features of the light scattered by collective instabilities are identified that would allow to recognize their signatures in more complex, less diagnosed experiments.

A new deterministic method for calculating the dose distribution in the electron radiotherapy field is presented. The aim of this work was to validate our model by comparing it with the Monte Carlo simulation toolkit, GEANT4. A comparison of the longitudinal and transverse dose deposition profiles and electron distributions in homogeneous water phantoms showed a good accuracy of our model for electron transport, while reducing the calculation time by a factor of 50. Although the Bremsstrahlung effect is not yet implemented in our model, we propose here a method that solves the Boltzmann kinetic equation and provides a viable and efficient alternative to the expensive Monte Carlo modeling.

A new type of proton acceleration stemming from large-scale gradients, low-density targets, irradiated by an intense near-infrared laser is observed. The produced protons are characterized by high-energies (with a broad spectrum), are emitted in a very directional manner, and the process is associated to relaxed laser (no need for high-contrast) and target (no need for ultra-thin or expensive targets) constraints. As such, this process appears quite effective compared to the standard and commonly used Target Normal Sheath Acceleration technique (TNSA), or more exploratory mechanisms like Radiation Pressure Acceleration (RPA). The data are underpinned by 3D numerical simulations which suggest that in these conditions a Low Density Collisionless Shock Acceleration (LDCSA) mechanism is at play, which combines an initial Collisionless Shock Acceleration (CSA) to a boost procured by a TNSA-like sheath field in the downward density ramp of the target, leading to an overall broad spectrum. Experiments performed at a laser intensity of 1020 W/cm2 show that LDCSA can accelerate, from ~1% critical density, mm-scale targets, up to 5 × 109 protons/MeV/sr/J with energies up to 45(±5) MeV in a collimated (~6° half-angle) manner.

International audience; The goal of this paper is twofold: first, we demonstrate shock generation with ultra-short (24 fs) and low-energy (J) laser pulse, following the energy deposition in the target by fast electrons; second, we show that such shocks can be used to provide information on compressed matter. For a target with 50 mu m thickness we have clearly inferred the formation of a shock wave with pressure >= 100 Mbar. We have also measured the color temperature of the emitting target rear side at breakout time (T approximate to 0.6 eV), which is in good agreement with predictions from equation-of-state models (SESAME tables) and hydrodynamic simulations.

Recent progress in the generation in the laboratory of a strong ($g100$-T) magnetic field enables us to investigate experimentally unexplored magnetohydrodynamics phenomena of a high-energy-density plasma, which an external magnetic field of 200--300 T notably affects due to anisotropic thermal conduction, even when the magnetic field pressure is much lower than the plasma pressure. The external magnetic field reduces electron thermal conduction across the external magnetic field lines because the Larmor radius of the thermal electrons in the external magnetic field is much shorter than the mean free path of the thermal electrons. The velocity of a thin polystyrene foil driven by intense laser beams in the strong external magnetic field is faster than that in the absence of the external magnetic field. Growth of sinusoidal corrugation imposed initially on the laser-driven polystyrene surface is enhanced by the external magnetic field because the plasma pressure distribution becomes nonuniform due to the external magnetic-field structure modulated by the perturbed plasma flow ablated from the corrugated surface.

Fast-electron beam stopping mechanisms in media ranging from solid to warm dense matter have been investigated experimentally and numerically. Laser-driven fast electrons have been transported through solid Al targets and shock-compressed Al and plastic foam targets. Their propagation has been diagnosed via rear-side optical self-emission and Kα X-rays from tracer layers. Comparison between measurements and simulations shows that the transition from collision-dominated to resistive field-dominated energy loss occurs for a fast-electron current density ~5 × 1011 A cm−2. The respective increases in the stopping power with target density and resistivity have been detected in each regime. Self-guided propagation over 200μm has been observed in radially compressed targets due to ~1kT magnetic fields generated by resistivity gradients at the converging shock front.

Experiments have been performed evidencing significant stimulated Raman sidescattering (SRS) at large angles from the density gradient. This was achieved in long scale-length high-temperature plasmas in which two beams couple to the same scattered electromagnetic wave further demonstrating for the first time this multiple-beam collective SRS interaction. The collective nature of the coupling and the amplification at large angles from the density gradient increase the global SRS losses and produce light scattered in novel directions out of the planes of incidence of the beams. These findings obtained in plasmas conditions relevant of inertial confinement fusion experiments similarly apply to the more complex geometry of these experiments where anomalously large levels of SRS were measured.

This work was supported by Grant No. E1127 from Région Ile de France, the LABEX Plas@Par project, the Grant No. 11‐IDEX‐0004‐02 from Agence Nationale de la Recherche, and Grant No. 001528 from LaserLab-Europe. This work was also supported in part by Grant-in-Aid for Scietific Res (S) (Grant No. 15H05751) of the Japan Society for the Promotion of Science (JSPS). This work was also supported in part by the Ministry of Education and Science of the Russian Federation under Contract No. 14.Z50.31.0007. The ability to produce long-scale length (i.e. millimeter scale-length), homogeneous plasmas is of interest in studying a wide range of fundamental plasma processes. We present here a validated experimental platform to create and diagnose uniform plasmas with a density close or above the critical density. The target consists of a polyimide tube filled with an ultra low-density plastic foam where it was heated by x-rays, produced by a long pulse laser irradiating a copper foil placed at one end of the tube. The density and temperature of the ionized foam was retrieved by using x-ray radiography and proton radiography was used to verify the uniformity of the plasma. Plasma temperatures of 5-10 eV and densities around 1021 cm-3 are measured. This well-characterized platform of uniform density and temperature plasma is of interest for experiments using large-scale laser platforms conducting High Energy Density Physics investigations. Publisher PDF

Introduction The majority of patients affected by cancer are nowadays treated by radiotherapy, which consists in delivering a homogeneous dose with energetic particles. Magnetic Resonance Imaging (MRI)-guided radiotherapy shows precisely the tumor position in real time and allows to direct the photon beams to the tumor while sparing organs at risks. Our work consists in the validation of a new model developped to simulate the energy deposition of the particles used in radiotherapy (electrons, photons and protons) in the presence of strong magnetic field, within human tissues, and its adaptation to this new technology. Material and methods This model is based on a kinetic entropic closure of the linearized Boltzmann equation [1] , which describes the transport of energetic particles in the matter. This equation takes a lot of computation time to be solved due to the high number of variables. To simplify this, we replace fluences by angular moments, which allows getting rid of the angular variables and improve the calculation time. We obtain a set of angular moments equations, and we close this set using the Boltzmann’s principle of entropy maximization on the two first equations of the set. This model has an accuracy comparable to references Monte-Carlo (MC) codes [2] (Geant4, MCNPx, Penelope), and is less time-consuming than these ones. We added the Lorentz force into our code to study the influence of a magnetic field on the dose deposition, and compared it to the reference full MC code FLUKA. To further validate our model, we have carried out an experimental campaign in which we irradiated a composition of materials of different mass densities, with 6 and 18 MV photon beams of a Varian Clinac 21Ex accelerator, without and with the influence of a 0.87 T magnetic field of amplitude induced by a permanent magnet. Results We show a good agreement between our model and the FLUKA code ( Fig. 1 ). We highlight the effects that occur on the propagation of particles in the matter in presence of a magnetic field of a few Tesla. Indeed, it modifies the dose deposition by shifting the deposition of energy, leading to an increased diffusion depending on the orientation of the magnetic field. Moreover, it also leads to an increase or decrease of the dose deposited at the interfaces between materials depending on their difference between mass densities. The results of our experiments lead to the same conclusions. These effects have to be taken into account in order to prevent creation of hot spots or a spread of energy distribution in a human body, within computation times compatible with the clinical environment. Conclusion Our model is a good candidate for future Treatment Planning Systems since it allows a faster and efficient way to plan a viable treatment for a patient in presence of strong magnetic fields. A magnetic field modifies the profile of the dose deposition such as it has to be taken into account in calculations to prevent the dramatic changes which occur at interfaces between media of different density. This work takes place in the framework of POPRA (Programme Optique Physique et Radiotherapie en Aquitaine), which involves several laboratories around problematics on the topic of cancer treatment.

Introduction This work proposes a completely new Grid-Based Boltzmann Solver (GBBS) developed for the transport and energy deposition by energetic particles. Its entropic closure and mathematical formulation allow our entropic model to calculate the delivered dose with an accuracy comparable to Monte Carlo (MC) codes with a computational time that is reduced to the order of few seconds without any special processing power requirement. Methods In contrast to discrete ordinates angular discretization methods, such as Acuros®, our method is based on a reduced number of moment equations closed with Boltzmann’s H-theorem. Keeping a good accuracy of calculations, the algorithm can simulate different treatment techniques such as the external radiotherapy even in presence of magnetic field [1] , [2] (e.g., MRI-guided radiotherapy), brachytherapy or intra-operative radiation therapy. The first validation step consists in simulating dose distributions in complex numerical phantoms including a large number of heterogeneity shapes such as bone, lung and air. For both brachytherapy and external beam radiotherapy, simulations based on CT scan, using the real phase-space of the source, have been performed. The entropic model is validated by a direct comparison with the reference MC code PENELOPE. Results The code is capable of calculating 3D dose distributions with 1 mm3voxels without statistical uncertainties in few seconds instead of several minutes like PENELOPE. In brachytherapy applications the dose distributions significantly differ from those calculated with the TG-43 approximations, thanks to its capability to account for inhomogeneities and strong density gradients. Moreover, for both applications the code shows an excellent agreement with PENELOPE within the 1%/1 mm gamma-index criterion. Conclusions In the comparison with the MC results the excellent accuracy of the model is demonstrated. Thanks to its reduced computational time and its accuracy, this model is a promising candidate to become a real-time dose calculation algorithm.

Theory predicts that the presence of strong single-frequency electric fields results in appearance of satellite or dip structures in X-ray spectral lines emitted from hot dense plasmas. Emission from multicharged ions is measured to determine the effects of laser field. A ps-laser beam was split into two parts: the first created an expanding plasma, while the second, which was temporally synchronized, irradiated the plasma at a varying distances in a direction perpendicular to the target normal. The field introduced by the second beam perturbed the plasma environment in the vicinity of radiators. The spatially resolved X-ray spectra were recorded using the high-resolution toroidally bent crystal spectrometer combined with a CCD detector. Spectrally resolved features are observed in broadened Al Heβ line profiles that are consistent with predicted spectra. The predicted spectra are derived from a combination of hydrodynamic plasma modeling post-processed by theoretical models that include the effect of externally introduced laser fields. The possible mixing of higher-intensity fields is qualitatively explained by a combination of fluid and one-dimensional PIC simulations that indicate redistribution of the fields and density fluctuations due to a presence of parametric instabilities.

Results of both methods of gastric closure (omental and biodegradable patch) were similar suggesting that a biodegradable patch glued to the outside of the stomach may be a viable alternative for closure of perforations of the digestive tract., Background: The current treatment of perforated peptic ulcers is primary closure, supported by the application of an omental patch. It is difficult and time consuming to perform this procedure by laparoscopic surgery, largely because of the required suturing. It was our aim to develop and test a new method of closure for gastric perforation that is similar in efficacy and safety to a traditional repair. This technique could have utility in laparoscopic repair, as it does not require sutures or mobilization of the omentum. Method: The new method, called the “stamp” method consists of closure of the perforation by gluing a biodegradable patch made of lactide-glycolide-caprolacton (LGC, Polyganics, B.V. Groningen, The Netherlands) on the outside of the stomach. It was compared with the omental patch procedure. Perforations were made in the stomach of 20 rats and closed by either method (10 rats in each group). The rats were followed for 10 weeks. Results: No complications were seen in any of the rats. In both groups, histological degradation of the patch by giant cells started at week 2. No signs of inflammation existed in either group. Signs of closure of the mucosa were seen after 2 weeks, and the muscular layer started to regenerate after 8 weeks in both groups. Conclusion: Results of both methods were similar, which means that treatment of a gastric perforation through the application of a biodegradable patch to the outside of the stomach is a feasible option and might even be an interesting technique for closure of other perforations in the digestive tract.

The interaction of supersonic plasma jets with dense gases and plasmas has been studied experimentally and theoretically. Collimated plasma jets were generated from the laser pulse interaction with solid targets. The jet propagates with the velocity exceeding 400 km/s and transports the energy of a few kJ/cm2. The interaction of such a jet with an Ar and He gases at various pressures has been studied by using optical and X-ray diagnostics. Qualitative estimates and numerical simulations with a radiative hydrodynamic code explain a sequence of physical processes during the interaction. Experimental and numerical results show that, by changing ambient material, the working surface structure changes from an adiabatic outflow to a radiative cooling jet. The applications of this phenomenon to astrophysical conditions and the inertial confinement fusion are discussed.

Formation of three-dimensional (3D) patterns of 0.2–0.5 μm diameter voids inside a transparent solid has been demonstrated. The nano-voids could be created with a spacing ∼2 μm thus suggesting the possibility of permanent 3D optical memory with density ∼100 Gbit/cm3. Extremely high pressures of ∼10 TPa and temperatures up to 105 K can be produced by a single sub-picosecond laser pulse tightly focused inside transparent dielectrics. Analysis of the size of the void and the shock affected zone as a function of the deposited energy shows that the experimental results can be explicitly understood on the basis of conservation laws and be modeled by plasma hydrodynamics. Therefore, the size of the void can be controlled and predicted by proper focusing conditions and laser parameters.

International audience; The knowledge of the absolute energy distributions of the particles emitted from a clinical accelerator is important for the evaluation of Monte Carlo simulations developed for treatment planning. In this paper, an original approach is presented which allows to measure the absolute energy distribution of the electron beam delivered by a Varian 21Ex medical accelerator. The electron beam was characterized at the isocenter with calibrated image plates covering the exit window of a magnetic spectrometer. The characteristics of the electron beam emitted from an effective source have been inferred from the measurements using the Geant4 Monte Carlo code. The contribution of direct electrons to the absolute depth-dose curve in a water phantom is estimated.

We present experimental results at intensities relevant to Shock Ignition obtained at the sub-ns Prague Asterix Laser System in 2012. We studied shock waves produced by laser-matter interaction in presence of a pre-plasma. We used a first beam at 1ω (1315 nm) at 7 x 1013 W/cm2 to create a pre-plasma on the front side of the target and a second at 3ω (438 nm) at ∼ 1016 W/cm2 to create the shock wave. Multilayer targets composed of 25 (or 40 m) of plastic (doped with Cl), 5 m of Cu (for K diagnostics) and 20 m of Al for shock measurement were used. We used X-ray spectroscopy of Cl to evaluate the plasma temperature, K imaging and spectroscopy to evaluate spatial and spectral properties of the fast electrons and a streak camera for shock breakout measurements. Parametric instabilities (Stimulated Raman Scattering, Stimulated Brillouin Scattering and Two Plasmon Decay) were studied by collecting the back scattered light and analysing its spectrum. Back scattered energy was measured with calorimeters. To evaluate the maximum pressure reached in our experiment we performed hydro simulations with CHIC and DUED codes. The maximum shock pressure generated in our experiment at the front side of the target during laser-interaction is 90 Mbar. The conversion efficiency into hot electrons was estimated to be of the order of ∼ 0.1% and their mean energy in the order ∼50 keV. © Published under licence by IOP Publishing Ltd.

We present here the experimental and theoretical studies of drastic transformations induced by a single powerful femtosecond laser pulse tightly focused inside a transparent dielectric, that lead to void formation in the bulk. We show that the laser pulse energy absorbed within a volume of less than 1μm3 creates the conditions with pressure and temperature range comparable to that formed by an exploding nuclear bomb. At the laser intensity above 6 × 1012 W/cm2 the material within this volume is rapidly atomized, ionized, and converted into a tiny super-hot cloud of expanding plasma. The expanding plasma generates strong shock and rarefaction waves which result in the formation of a void. Our modelling indicates that unique states of matter can be created using a standard table-top laser in well-controlled laboratory conditions. This state of matter has temperatures ≈105 K, heating rate up to the 1018 K/s, and pressure more than 100 times the strength of any solid. The laser-affected sites in the bulk were detected ("read") by generation of white continuum using probe femtosecond pulses at much lower laser intensity of 1010 W/cm2 − 1011 W/cm2. Post-examination of voids with an electron microscope revealed a typical size of the void ranges from 200 to 500 nm. These studies will find application for the design of 3D optical memory devices and for formation of photonic band-gap crystals.

It is demonstrated that the processes leading to nano-void formation under single-pulse tight focusing in dielectrics are described by the same laws used to describe macroscopic explosions but with energies 10 21 times lower and space and time scales reduced by 10 7 .

A high order practical scheme for a model of nonlocal transport is here proposed to be used in multidimensional radiation hydrodynamic codes. The various investigations on electron heat transport in the Inertial Confinement Fusion (ICF) context, have shown the limits of the classical local SpitzerHarm heat flow model [1]. Monodimensionnal accurate models lying on convolution formulations have been proposed by Luciani and Mora [2] and improved by many other authors [3]. Schurtz, Nicolai and Busquet [4] purposed a practical multidimensional extension of the original convolution formula. The numerical implementation of non local models can be usually very delicate since an implicit resolution is considered. It is of use to force a diffusive formulation by introducing an ill-posed artificial nonlocal conductivity [3]. This choice can lead to mathematical and physical prejudicial anomalies (negative conductivity). An stability analysis leads us to consider an alternative for the implicit discretization of the non local operator. These remarks then led us to naturally set up a high order scheme [5] to solve the nonlocal problems on strongly deformed meshes. The use of such scheme is indeed essential to give a good description of the ablation front and of the hot spot induced by the implosion of the target during a nuclear fusion experience.

This paper deals with the computation of laser beam intensity in large-scale radiative hydrocodes applied to the modeling of nonlinear laser-plasma interactions (LPIs) in inertial confinement fusion (ICF). The paraxial complex geometrical optics (PCGO) is adapted for light waves in an inhomogeneous medium and modified to include the inverse bremsstrahlung absorption and the ponderomotive force. This thick-ray model is compared to the standard ray-tracing (RT) approach, both in the chic code. The PCGO model leads to different power deposition patterns and better diffraction modeling compared to standard RT codes. The intensity-reconstruction technique used in RT codes to model nonlinear LPI leads to artificial filamentation and fails to reproduce realistic ponderomotive self-focusing distances, intensity amplifications, and density channel depletions, whereas PCGO succeeds. Bundles of Gaussian thick rays can be used to model realistic non-Gaussian ICF beams. The PCGO approach is expected to improve the accuracy of ICF simulations and serve as a basis to implement diverse LPI effects in large-scale hydrocodes.

International audience; It was recently shown that a promising way to accelerate protons in the forward direction to high energies is to use under-dense or near-critical density targets instead of solids. Simulations have revealed that the acceleration process depends on the density gradients of the plasma target. Indeed, under certain conditions, the most energetic protons are predicted to be accelerated by a collisionless shock mechanism that significantly increases their energy. We report here the results of a recent experiment dedicated to the study of longitudinal ion acceleration in partially exploded foils using a high intensity (similar to 5 x 10(18) W/cm(2)) picosecond laser pulse. We show that protons accelerated using targets having moderate front and rear plasma gradients (up to similar to 8 mu m gradient length) exhibit similar maximum proton energy and number compared to proton beams that are produced, in similar laser conditions, from solid targets, in the well-known target normal sheath acceleration regime. Particle-In-Cell simulations, performed in the same conditions as the experiment and consistent with the measurements, allow laying a path for further improvement of this acceleration scheme. (C) 2014 AIP Publishing LLC.

In the shock ignition scheme, the ICF target is first compressed with a long (nanosecond) pulse before creating a convergent shock with a short (∼100 ps) pulse to ignite thermonuclear reactions. This short pulse is typically (∼2.1015–1016 W/cm2) above LPI (Laser Plasma Instabilities) thresholds. The plasma is in a regime where the electron temperature is expected to be very high (2–4 keV) and the laser coupling to the plasma is not well understood. Emulating LPI in the corona requires large and hot plasmas produced by high-energy lasers. We conducted experiments on the LIL (Ligne d'Integration Laser, 10 kJ at 3ω) and the LULI2000 (0.4 kJ at 2ω) facilities, to approach these conditions and study absorption and LPI produced by a high intensity beam in preformed plasmas. After introducing the main risks associated with the short pulse propagation, we present the latest experiment we conducted on LPI in relevant conditions for shock ignition.

We present an overview of the interpretation of laser plasma interaction (LPI) experiments carried out on the LIL facility. These multikilojoule experiments have been done using underdense foam targets at 0.351 μm laser light leading to high temperature and large plasmas. We discuss the interpretation using our different numerical tools: hydrodynamics simulations carried out with the code FCI2 to characterize the plasma, linear gain estimates with the postprocessor Piranah and paraxial simulations with the code HERA.

Under imperfect competition, the effect of a cap-and-trade system on indus- try profits depends on the type of abatement technology that is used by firms: industries that use process-integrated technologies are more affected than those using end-of-pipe abatement technologies. The interaction between environmental policy and the evolution of the market structure is then studied. In particular, a reserve of pollution permits for new entrants is justified when the industry uses a process-integrated abatement technology, while a system with a preemption right may be justified in the case of end-of-pipe abatement technology.

Shock ignition (SI) is an appealing approach in the inertial confinement scenario for the ignition and burn of a pre-compressed fusion pellet. In this scheme, a strong converging shock is launched by laser irradiation at an intensity Iλ2 > 1015 W cm-2 μm2 at the end of the compression phase. In this intensity regime, laser-plasma interactions are characterized by the onset of a variety of instabilities, including stimulated Raman scattering, Brillouin scattering and the two plasmon decay, accompanied by the generation of a population of fast electrons. The effect of the fast electrons on the efficiency of the shock wave production is investigated in a series of dedicated experiments at the Prague Asterix Laser Facility (PALS). We study the laser-plasma coupling in a SI relevant regime in a planar geometry by creating an extended preformed plasma with a laser beam at ∼7 × 1013 W cm-2 (250 ps, 1315 nm). A strong shock is launched by irradiation with a second laser beam at intensities in the range 1015-1016 W cm-2 (250 ps, 438 nm) at various delays with respect to the first beam. The pre-plasma is characterized using x-ray spectroscopy, ion diagnostics and interferometry. Spectroscopy and calorimetry of the backscattered radiation is performed in the spectral range 250-850 nm, including (3/2)ω, ω and ω/2 emission. The fast electron production is characterized through spectroscopy and imaging of the Kα emission. Information on the shock pressure is obtained using shock breakout chronometry and measurements of the craters produced by the shock in a massive target. Preliminary results show that the backscattered energy is in the range 3-15%, mainly due to backscattered light at the laser wavelength (438 nm), which increases with increasing the delay between the two laser beams. The values of the peak shock pressures inferred from the shock breakout times are lower than expected from 2D numerical simulations. The same simulations reveal that the 2D effects play a major role in these experiments, with the laser spot size comparable with the distance between critical and ablation layers. © 2013 IOP Publishing Ltd.

The paper describes the preparation of the short-pulse high-energy laser PETAL that will be coupled to the French megajoule laser (LMJ) of CEA. The LMJ/PETAL facility will be opened to academic access for the international research community. In parallel diagnostics are being developed within the PETAL project and many physical problems are being addressed ranging from the study of the problems of radiation generation and activation issues to the problem of generation of large amplitude electromagnetic pulses.

Many experiments, based on the road map of the European High Power laser Energy Research facility project, were performed to study fast electron transport in compressed matter in the context of fast ignition approach to inertial confinement fusion. The generation of high intensity beams from laser-matter interaction extends the possibility to use protons as a diagnostic to image imploding targets in these experiments. The analysis of experimentally obtained proton images requires a careful analysis and accurate numerical simulations using both hydrodynamic and Monte Carlo (MC) codes. An experiment has been performed in 2008 at Rutherford Appleton Laboratory to study fast electron propagation in cylindrical imploding targets illuminated by four laser pulses. In this paper, we present new simulation results in 3-D geometry. Three-dimensional density map is generated by running the 3-D version of the MULTI code. Proton radiography images are then simulated using the MC code MCNPX. © 2011 IEEE.

This paper presents the goals and some of the results of experiments conducted within the Working Package 10 (Fusion Experimental Programme) of the HiPER Project. These experiments concern the study of the physics connected to "Advanced Ignition Schemes", i.e. the Fast Ignition and the Shock Ignition Approaches to Inertial Fusion. Such schemes are aimed at achieving a higher gain, as compared to the classical approach which is used in NIF, as required for future reactors, and making fusion possible with smaller facilities. In particular, a series of experiments related to Fast Ignition were performed at the RAL (UK) and LULI (France) Laboratories and were addressed to study the propagation of fast electrons (created by a short-pulse ultra-high-intensity beam) in compressed matter, created either by cylindrical implosions or by compression of planar targets by (planar) laser-driven shock waves. A more recent experiment was performed at PALS and investigated the laser-plasma coupling in the 1016 W/cm2 intensity regime of interest for Shock Ignition. © 2011 SPIE.

This paper presents the goals and some of the results of experiments conducted within the Working Package 10 (Fusion Experimental Programme) of the HiPER Project. These experiments concern the study of the physics connected to 'advanced ignition schemes', i.e. the fast ignition and the shock ignition approaches to inertial fusion. Such schemes are aimed at achieving a higher gain, as compared with the classical approach which is used in NIF, as required for future reactors, and make fusion possible with smaller facilities. In particular, a series of experiments related to fast ignition were performed at the RAL (UK) and LULI (France) Laboratories and studied the propagation of fast electrons (created by a short-pulse ultra-high-intensity beam) in compressed matter, created either by cylindrical implosions or by compression of planar targets by (planar) laser-driven shock waves. A more recent experiment was performed at PALS and investigated the laser-plasma coupling in the 10 16 W cm -2 intensity regime of interest for shock ignition. © 2011 IOP Publishing Ltd.

We present results from an experimental characterization of fast electron transport in high density plasmas created by 1D shock wave compression. The Kα fluorescence from a Cu layer embedded in Al or CH foil targets is measured. We use long laser pulses (LP) with 180 J, 1.5 ns, 0.53μm to compress the foils by shock wave propagation to 2-3 times their solid density and heat them to ~ 4eV (close to the Fermi temperature). A counter-propagating high-intensity short laser pulse (SP), with 40 J, 1 ps, 57×1019 Wcm−2, generates intense currents of fast electrons which propagate through the deep regions of the target just before shock breakthrough. The results are compared to the uncompressed, solid density case (without the LP beam). The complete set of measurements is compared to numerical results, including a 2D hydrodynamic description of the compression and pre-pulse effects, 2D PIC simulations of the SP beam interaction and both hybrid and PIC simulations of the electron transport in the target depth and sheaths. In the case of the non-compressed targets we need to take fast electron refluxing into account to reproduce the experimental results. By exploring the domain of warm temperatures, we identify a regime for the incident fast electron current density, 1010 < jh < 1012 Acm−2, for which the collective mechanisms of electron transport differs appreciably between solid density and compressed matter.

The paper describes the key points contained in the short term HiPER (High Power laser Energy Research) experimental road map, as well as the results of two phases of the experiment performed in "HiPER dedicated time slots. Experimental and theoretical results of relativistic electron transport in cylindrically compressed matter are presented. This experiment was achieved at the VULCAN laser facility (UK) by using four long pulse beams (similar to 4 x 50 J, 1 us, at 0.53 mu m) to compress a hollow plastic cylinder filled with plastic foam of three different densities (0.1, 0.3, and 1 g cm(-3)). In the first phase of the experiment, protons accelerated by a picosecond laser pulse were used to radiograph a cylinder filled with 0.1 g/cc foam. Point projection proton backlighting was used to measure the degree of compression as well as the stagnation time. Results were compared to those from hard X-ray radiography. Finally, Monte Carlo simulations of proton propagation in cold and compressed targets allowed a detailed, comparison with 2D numerical hydro simulations. 2D simulations predict a density of 2-5 g cm(-3) and a plasma temperature up to 100 eV at maximum compression. In the second phase of the experiment, a short pulse (10 ps, 160 J) beam generated fast electrons that propagated through the compressed matter by irradiating a nickel foil at an intensity of 5 x 10(18) Wcm(-2). X-ray spectrometer and imagers were implemented in order to estimate the compressed plasma conditions and to infer the hot electron characteristics. Results are discussed and compared with simulations.

We report on X-ray diagnostics results from an experiment on fast electrons propagation in cylindrically compressed targets. It was performed on the VULCAN TAW laser facility at RAL (UK) using four long pulses (1ns, 70 J each at 2ω) to compress a cylindrical polyimide target filled with CH foam at 3 different initial densities. The cylindrical geometry allows us to reach temperatures and densities higher than those obtained in planar geometry compression. 2D hydrodynamic simulations predicted a core density range from 4 to 8 g/cm3 and a core temperature from 30 eV up to 175 eV at maximum compression. An additional short laser pulse (10 ps, 160 J at ω) was focused on a Ni foil at one of the cylinder edges in order to generate a fast electrons current propagating along the compressed target. A X-ray radiography diagnostic was implemented in order to estimate the core plasma conditions of the compressed cylinder. Moreover two Bragg X-ray spectrometers collected the Kα fluorescence from the target so as to determine the variations of fast electrons population during the compression.

Dans un contexte avec commerce bilatéral entre deux zones géographiques et pollution globale, nous étudions l'impact de la mise en œuvre unilatérale d'une taxation des émissions dans une des zones. Pour compenser une perte de compétitivité de son industrie, le gouvernement de cette zone peut vouloir mettre en œuvre des ajustements aux frontières sous la forme de subventions aux exportations ou de taxes sur les importations. Nous étudions l'interaction entre les instruments de la politique environnementale et les ajustements aux frontières en mettant en lumière le rôle des structures de marché et de la concurrence imparfaite.

In the last few years, intense research has been conducted on laser-accelerated ion sources and their applications. Recently, experiments have shown that a gaseous target can produce proton beams with characteristics comparable to those obtained with solid targets. In underdense laser proton acceleration, volume effects dominate the acceleration, while in target normal sheath acceleration, the electric field value is directly related to the electron surface density. Using Particle-In-Cell simulations, we have studied in detail the effect of an underdense density gradient on proton acceleration with high intensity lasers. Underdense laser ion acceleration strongly depends on the length, the shape and the amplitude of the density gradient and on the laser pulse shape. The accelerated proton beam characteristics in the shock-like regime are very promising.

A recent experiment was performed at the Rutherford Appleton Laboratory (UK) to study fast electron propagation in cylindrically compressed targets, a subject of interest for fast ignition. In this experiment, protons accelerated by a picosecond laser pulse have been used to radiograph a 220 µm diameter cylinder (10 µm wall filled with 0.1 g/cc foam), imploded with _ 200 J of green laser light in 4 symmetrically incident beams of wavelength and pulse length 1 ns. Point projection proton backlighting was used to measure the compression degree as well as the stagnation time. Results were also compared to those from a hard X-ray radiography diagnostics. Finally, Monte Carlo simulations of proton propagation in the cold and in the compressed targets allowed a detailed comparison with 2D numerical hydro simulations.

International audience; Smoothing of laser beam non-uniformities using gas jets has been studied. The experiment has been performed with the PALS laser working at 0.44 ?m with an intensity of about 1015 W/cm2. The laser beam has been split in two by a prism thus creating an artificial large-scale non-uniformity (?90 ?m). We recorded time resolved and static images of laser-gas jet interaction with and without an Al target. Multi 1D and 2D simulations show that such interaction acts redistributing the over-intensities over larger surface. This effect has to be attributed to ionization processes with consequent laser beam refraction. Results show that Argon gas jet produces a strong refraction of the laser beam thus strongly reducing the initial two spots separation. © EDP Sciences and Springer 2009.

High‐resolution x‐ray spectroscopy is capable of providing complex information on environmental conditions in hot dense plasmas. Benefiting from application of modern spectroscopic methods, we report experiments aiming at identification of different phenomena occurring in laser‐produced plasma. Fine features observed in broadened profiles of the emitted x‐ray lines and their satellites are interpreted using theoretical models predicting spectra modification under diverse experimental situations.

International audience; Beams of fast electrons have been generated from the ultra-intense laser interaction with Aluminium foil targets. The dynamics of the fast electrons propagation and the level of induced in-depth heating have been investigated using the optical emission from the foils rear side. Important yields of thermal emission, consequence of high target temperatures, were detected for targets thinner than 50 μm. We precisely characterized the targets in-depth temperature profile in order to reproduce the emission yields. At shallow depth, we show the important heating (estimated to > 100 eV till 15 μm depth) has a resistive origin upon the neutralizing return current. For deeper regions, because of the bulk component divergence, the fast electron energy losses and induced heating are due to collisions. Coupling the model to the experimental measurements, we were able to quantify the bulk of the fast electron population, corresponding to 35% of the laser energy and a 500 keV temperature.