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We present the features of the three-dimensional (3D) radiative transfer code IRIS, which synthesizes spectra emitted from hydrodynamics structures. We discuss our first application of IRIS to the analysis of a laboratory radiative shock. We demonstrate, with the help of the radiation hydrodynamics (RHD) code HERACLES, the existence of a radiative precursor. We validate the gray approximated model M1 used by HERACLES. We show a couple of synthesized X-UV spectra of such a shock. We finally open up our discussion to the future possibilities of spectroscopic diagnostics of accreting streams onto the surface of Classical T Tauri stars (CTTSs).

We present new experiments to study the formation of radiative shocks and the interaction between two counter-propagating radiative shocks. The experiments were performed at the Orion laser facility which was used to drive shocks in xenon inside large aspect ratio gas-cells. The collision between the two shocks and their respective radiative precursors, combined with the formation of inherently 3-dimensional shocks, provides a novel platform particularly suited for benchmarking of numerical codes. The dynamics of the shocks before and after the collision were investigated using point-projection X-ray backlighting while, simultaneously, the electron density in the radiative precursor was measured via optical laser interferometry. Modelling of the experiments using the 2-D radiation hydrodynamic codes NYM/PETRA show a very good agreement with the experimental results., Comment: 6 pages, 4 figures, accepted for publication in Physical Review Letters on 14/06/2017

International audience; The formation of radiative shocks, shocks in which the structure of density and temperature is affected by radiation from the shock-heated matter, is ubiquitous in many astrophysical scenarios. Experiments were performed at the Orion laser using a new target configuration that allows studying the formation of single and counter-streaming radiative shocks in gas-filled targets (Ne, Ar, Kr, Xe), with initial pressures ~0.1-1 bar and a driver intensity of ~6x10**14 W/cm2. The shocks propagate at velocities ~60 km/s and were diagnosed with optical interferometry (streaked and time-resolved) and point-projection X-ray backlighting allowing to probe simultaneously the pre-shock radiative precursor and the shock front itself. Besides varying the extent of the radiative precursor the results show that different gases seem to have an effect on the shock front as evidenced by a number of spatial features. The results are compared with radiative hydrodynamics simulations in 1-D (HELIOS) and 2-D (NYM/PETRA). http://absimage.aps.org/image/DPP16/MWS_DPP16-2016-000529.pdf

International audience; S 04 Atelier général PNPS Radiative shocks are present at different stages of stellar evolution, for instance in the stellar infancy when matter is accreted from the stellar disk to the photosphere of the young star and is also ejected in the form of stellar jets, up to the final stages as supernovae and the interaction of their remnants with the interstellar medium. Such shocks are strongly influenced by the radiation through its coupling with hydrodynamics. Thus their topology and dynamics are quite complex. Generating such hypersonic shocks in the laboratory, with controlled conditions, is thus an adequate tool to study the influence of radiation and to compare them with numerical simulations. So far, such laboratory astrophysics studies are performed on large-scale laser facilities, addressing hydrodynamic radiative shocks, in Xenon with very high velocity (50 - 150 km/s) and moderate pressure (0.1 - 1 bar). These experiments advance the understanding of the effect of radiation on the different shock components (radiative precursors, shock collapse, walls heating etc.). In continuation of these laboratory experiments, we recently performed experiments at PALS laser facility to study a fairly new topic focusing on the interaction of two counter propagating shocks. The objective is to understand the influence of one radiative precursor onto another, to achieve higher temperature in the compressed medium. In the astrophysical context, aforementioned studies are relevant for instance, collision of supernovae remnants and more indirectly the interaction of supernovae remnants with dense molecular clouds and the impact of accretion flows on a stellar atmosphere. The experiments have been able to launch shocks with different shock speeds (~30-55 km/s and 10-25 km/s), in varying gases (Ar, Xe) and pressures (~0.1-0.3 bar). Optical interferometry allowed us to estimate several physical parameters such as shock speed and electron density in the precursor, XUV spectroscopy allowed to give information about the shock temperature. We will present some preliminary results together with numerical simulations.

International audience; The Orion high-power laser facility at AWE Aldermaston, UK, was used to produce hyper-sonic (M>>1) radiative shocks in a variety of noble gases. These experiments aimed to study the radiative precursor, a heat and ionization wave preceding the shock front and, for the first time, the dynamics of colliding, counter propagating radiative shocks. Laser ablation of a piston, at intensities of ~6x1014 W/cm2, drove counterpropagating shocks, with velocities between 60 km/s and 120 km/s, into a gas cell, filled to pressures between 0.1 bar and 1.0 bar. Targets were 4mm long octagonal gas cells, produced by SciTech Precision, with a diameter of 8mm to remove the effect of wall shocks. X-ray backlighting and optical self-emission streak Imaging were used to image the shock front and collision dynamics. Multi-frame and streaked interferometry were used to image the radiative precursor and determine its electron density. These experiments compared the shock and collision dynamics in different gases (e.g. Ne, Ar, Kr, Xe), maintaining a constant mass density in order to keep the hydrodynamics in the shock consistent while varying the strength of the radiative precursor losses. In some cases the shocks exhibited features suggesting the formation of hydrodynamic or radiative instabilities. The experimental data is in good agreement with 2-D numerical radiative-hydrodynamic simulations and provides a new benchmark for codes to be tested against. Project supported by Orion’s Academic Access Programme (through AWE and CLF), and in part by the Royal Society, and by EPSRC through a DTA Scholarship and by Labex PLAS@PAR (ANR-11-IDEX-0004-02). The authors would like to acknowledge the help and support from the staff at AWE Aldermaston.

International audience; Radiative shocks are present in various astrophysical contexts and can be proxy of fundamental accretion processes, for instance X-ray signatures from accretion shocks can be related to the rate of mass accretion onto forming stars. Thus the study of hypersonic shocks (Mach number >> 1) in the laboratory Under controlled conditions is of primary interest in order to study the influence of radiation, and to compare with numerical simulations. In the past decade, several experiments on radiative shocks have been performed on various large-scale laser facilities, demonstrating the formation of shocks in Xenon with velocities ~50 - 150 km/s in background gas pressures ~0.1 - 1 bar (Bouquet et al. 2004, Gonzalez et. al. 2006, Reighard et. al. 2007, Stehlé et al. 2010, Doss et al. 2011, Drake et al. 2011, Dizière et al. 2012, Stehlé et al. 2012, Chaulagain et al. 2015). Many advances have been achieved in understanding the effect of radiation on the different shock components (radiative precursor, shock collapse, wall heating etc.), however, these studies were focused solely on the case of a single radiative shock. We have recently conducted experiments at the PALS laser facility, looking at the collision between two counter streaming radiative shocks. Besides providing a new experimental platform, these experiments aimed at studying how one radiative precursor is influenced by the presence of another. The experiments launched shocks with different shock speeds (~30-55 km/s and 10-25 km/s), at a range of different pressures (~0.1-0.3 bar), and with different gases (Ar, Xe). Optical interferometry allowed us to estimate several physical parameters such as shock speed and electron density in the precursor, whereas the use of time and spatially resolved optical spectroscopy led to a number of spectral signatures. We will present preliminary results together with numerical simulations.

International audience; The Orion high-power laser facility, at AWE Aldermaston UK, was used to produce hyper-sonic radiative shocks, travelling at ~60km/s, in noble gases, between 0.1 and 1.0 bar. These experiments aimed to study the radiative precursor, a heat and ionization wave preceding the shock front, and dynamics of colliding radiative shocks. X-ray backlighting and optical self-emission streak imaging were used to study the shock front and collision dynamics, while multi-frame and streaked interferometry were used to simultaneously study the radiative precursor. These experiments compared the shock and collision dynamics in different gases (e.g. Ne, Ar, Kr, Xe), while maintaining a constant mass density, to vary the strength of the radiative precursor. Some shocks exhibited features suggesting the formation of hydrodynamic or radiative instabilities. The experimental data is in good agreement with 2-D rad-hydro simulations and provides a new benchmark for codes to be tested against. http://absimage.aps.org/image/DPP16/MWS_DPP16-2016-000820.pdf

International audience; Counter-propagating are created and studied on Orion laser facility.

International audience; affiche P71 atelier 12 PNPS The interstellar medium (ISM) is a wide object of research, especially for the phenomena leading to the building up of protostellar objects, like mass accretion or outflows and jets. Accretion shocks are of particular interest as their radiative signature can be related to the rate of mass accretion onto the forming star. In recent years, laboratory plasma experiments have been developed to study radiative shocks relevant to astrophysics. These scaled models of accretion shocks have been successfully generated on high power lasers by launching a fast moving piston in a stationary gaseous medium. Complementary to experiments on lasers, pulsed power generators are also able to create astrophysically relevant shocks. On these facilities, high-intensity currents can produce magnetic fields of several Tesla which act as a piston, accelerating an annular plasma sheath and driving a strong shock in a tenuous gas. The results presented will describe the pulsed power setup and a lumped-parameter model, linking the transient discharge dynamics and quantities like mass and speed of the plasma sheath. The results of this 0-D model will be compared to 3-D MHD simulations performed with the code GORGON. This work has lead to an optimization process of the setup. The diagnostics which are currently implemented will be presented to illustrate the model as well as experimental records of the plasma speed. Work supported by DIM ACAV – Île-de-France region, Labex PLAS@PAR (ANR-11-IDEX-0004-02), Observatoire de Paris-Meudon and UPMC university.

International audience; affiche P53 Being able to produce and diagnose radiative shocks under controlled laboratory conditions is a key aspect to understand their role in astrophysical processes such as accretion in stellar formation. The ongoing study of radiative shocks using high-power lasers has significantly advanced our understanding on the physics of these complex flows. In particular, experiments at the Prague Asterix Laser System (PALS) have demonstrated the formation of radiative shocks in Xenon with a characteristic velocity of 50-60 km/s. Latest results on the generation on radiative shocks at PALS demonstrate the feasibility of fielding novel probing techniques such as time-resolved imaging using an X-ray laser at 21.2 nm, allowing to probe simultaneously the high-density shock-front together with the lower-density radiative precursor in front of the shock. These results will be compared with 2-D radiative-hydrodynamic simulations using the code ARWEN. Future experimental campaigns will focus on spectroscopic measurements of the different shock regions together with new experimental configurations such as the interaction of counter-streaming radiative shocks. These prospects will be presented and discussed from both experimental and simulation point of view. This work is supported by french ANR STARSHOCK (grant 08-BLAN-0263-07), Programme National de Physique Stellaire" (PNPS) of CNRS/INSU, France, Observatoire de Paris and labex Plas@Par ( ANR-11-IDEX-0004-02 )

International audience; Parmi les chocs forts présents en astrophysique, comme les chocs d’accrétion lors de la formation des étoiles jeunes, les chocs radiatifs sont caractérisés par un pic de température localisé et une forte émission de rayonnement capable de structurer le choc. Par exemple, l’ionisation par ce rayonnement chauffe la matière en amont et modifie la propagation du choc (phénomène précurseur). L’astrophysique de laboratoire étudie ces chocs depuis une décennie en générant des chocs quasi plans par impact laser à haut flux. Récemment les auteurs ont ainsi pu mesurer des vitesses de 50 km/s dans le xénon dense. Il est apparu utile de créer des chocs forts par un moyen plus commode à mettre en œuvre au laboratoire, permettant d’étudier une large gamme de chocs, de multiplier les expériences et de développer des diagnostics avec des contraintes d’encombrement réduites. Or, des chocs d’accrétion en gaz peu denses ont été documentés dans les années 70 dans les canons à plasma coaxiaux. Dans ces dispositifs, la pression magnétique générée par un courant fort (100 kA et plus) accélère une lame de plasma, ce qui constitue le lanceur du dispositif dit plasma focus. La puissance instantanée d’un tel générateur ultra compact dépasse alors couramment les 500MWe. Après avoir obtenu d’empêcher l’étape de focalisation du plasma, il a été possible de montrer qu’un choc quasi plan est créé et se déplace à une vitesse élevée dans un tube dont les dimensions sont d’un ordre de grandeur supérieures à celles d’un tube pour choc induit par laser. On présentera le mécanisme de formation et d’accélération du plasma puis un modèle paramétrique régissant la vitesse terminale. Des exemples de mesures de la vitesse (de 5 à 20 km/s) et du profil du choc seront également présentés. Ce travail est soutenu par le DIM ACAV 2012 et par l’OBSPM.

International audience; Radiative shocks are high Mach number shocks with a strong coupling between radiation and hydrodynamics. These shocks occour in astrophysical system and in high-energy density laboratory experiments. High-energy lasers can be used to simulate astrophysical phenomena in the Laboratory. PALS Laser facility provides irradiance of 10¹4 W/cm², lasting less than 1 ns, and allows to produce radiative shocks in high atomic gas medium at low pressure. The radiative energy is converted into mechanical energy, generating the shock in the gas. The system is optimized for reaching conditions where the shock is radiative, i.e. it presents a radiative precursor. The experimental results of two new diagnostics: first a XUV instantaneous imaging at 21.2 mm, and second, a time and space resolved plasma self-emission using fast diodes will be highlighted. communication orale Atelier S08 Actes à paraître 2013 sur le site de la SF2A

International audience; communication orale actes à paraître sur http://2013.sf2a.eu/

International audience; Shock waves play a significant role in several astrophysical phenomena. Among them, Radiative shocks are strong shocks, in which the shock front is heated to very high temperature and thus emit an important radiation flux. The interesting feature of the radiative shocks is that their structure is strongly influenced by the coupling between hydrodynamics and radiation. They occur in astrophysical system in the different stages of the stellar evolution, for instance during the accretion processes in the stellar infancy, and are studied in high-energy density laboratory experiments using kJ class lasers. Such laser facilities enable to drive shocks in which the radiative flux may prevail hydrodynamic mechanism of energy transfer. Typical irradiances of 10**14 W.cm-2, allows to produce radiative shocks in high atomic gas medium at low pressure, where the important radiation generated by the shocked plasma leads to the formation of an ionizing wave, also call radiative precursor, in the cold upstream xenon. I will present new experimental results realized on the PALS laser installation aiming at improving the present knowledge of these complex flows. The greatest attention is paid to the application of to new diagnostics, namely, the instantaneous imaging of the whole shock structure using an auxiliary laser at 21.2 nm and a time-and-space resolved plasma self-emission using fast diodes. This work is supported by french ANR STARSHOCK (grant 08-BLAN-0263-07) and by Laserlab-Europe II programme.

International audience; The aim of the project (ANR STARSHOCK) is to understand the dynamics and the radiative properties of accretion columns, linking the circumstellar disk to the surface photosphere of Young Stellar Objects. The hydrodynamics is computed first, using a high resolution hydrodynamic 1D ALE code (AS-TROLABE) coupled to radiative transfer and line cooling, along with a model for the acoustic heating of the chromospheric plasma. Spectra are then post-processed with a 1D radiative transfer code (SYNSPEC), using DFE solver and an extended atomic database covering a wavelength range from X rays to visible.

International audience; High-energy lasers are used to simulate astrophysical phenomena in the laboratory. The PALS laser facility, with a typical irradiance of 10 14 W.cm −2 , allows in particular to produce radiative shocks in high atomic number gases. The system is optimized for reaching conditions where the shock is radiative, i.e. it presents a "radiative precursor". This kind of shock is expected to occur during various astrophysical accretion processes. We present preliminary experimental results with emphasis on two diagnostics, namely the study of the laser impact on the target and an instantaneous imaging using an X-ray laser.

International audience; poster P.We₇9

We present the simulations of two relevant hydrodynamical problems related to astrophysical phenomena performed by three different codes. The numerical results from these codes will be compared in order to test both the numerical method implemented inside them and the influence of the physical phenomena simulated by the codes. Under some conditions laser produced plasmas could be scaled to the typical conditions prevailing in astrophysical plasmas. Therefore, such similarity allows to use existing laser facilities and numerical codes suitable to a laser plasma regime, for studying astrophysical proccesses. The codes are the radiation fluid dynamic 2D ARWEN code and the 3D HERACLES, and, without radiation energy transport, a Smoothed-Particle Hydrodynamics (SPH) code. These codes use diferent numerical techniques and have overlapping range of application, from laser produced plasmas to astrophysical plasmas. We also present the first laser experiments obtaining cumulative jets with a velocity higher than 100 km/s.

International audience; Theoretical Stark profiles of Balmer and Lyman series of H-like ions of carbon, nitrogen, and oxygen are presented for a range of plasma conditions where these ions are dominant within their species. A convenient parametric formula is derived to fit the theoretical profiles, depending only on electronic density and the principal quantum number of the upper level of the transition. This analytic expression makes it easy to introduce these new profiles in many astrophysical applications. The effect of including these profiles in the calculation of radiative acceleration (g rad) following the method developed in an earlier paper is presented. The contributions of bound-bound (b-b) transitions of H-like ions to g rad is found to be smaller than previously computed, giving more importance to boundfree (b-f) and free-free (f-f) contributions.