Polarization analysis of CuXX-lines emitted from X-pinch

International audienceSoft x-ray emission from CuXX L-shell lines emitted by a dense X-pinch plasma have been investigated with high-resolution curved Bragg crystals at different angles of orientation. Single shot time integrated spectra show clear evidences of polarization for the Ne-like spectral lines 2s22p6 1S0 → 2s22p53s 1P1 (λ = 12.570 Å), 2s22p6 1S0 → 2s22p53s 3P1 (λ = 12.8277 Å). The variation of the intensity ratio of these two well-separated L-shell lines is discussed in view of its application for suprathermal electron characterization under real experimental conditions of pinch plasmas. We demonstrated that the simultaneous use of two different polarization spectrometers (means 4 Bragg crystals) permitted a high level of confidence for the analysis of the variation of the line ratios due to polarization

Vulnerability of optical detection systems to megajoule class laser radiative environment

The Laser MegaJoule (LMJ) facility will host inertial confinement fusion experiments in order to achieve ignition by imploding a Deuterium-Tritium filled microballoon [1]. In this context an X-ray imaging system is necessary to diagnose the core size and the shape of the target in the 10-100 keV band. Such a diagnostic will be composed of two parts: an X-ray optical system and a detection assembly. The survivability of each element of this diagnostic has to be ensured within the mixed pulse consisting of X-rays, gamma rays and 14 MeV neutrons created by fusion reactions. The design of this diagnostic will take into account optics and detectors vulnerability to neutron yield of at least 1016. In this work, we will present the main results of our vulnerability studies and of our hardening-by-system and hardening-by-design studies

Z-pinch research in France an overview over 4 décades (1976-2016)

International audienceThe Z-pinch (ZP) is a rather unique source of dense, hot, transient plasma which has attracted interest early, in the quest for fusion. France has participated to this effort in few national Institutions and has developed a renowned expertise in pulsed power science and technology. After recalling the physical background, we will give a chronological presentation of case studies. ZP machines were built in French labs, Atomic Energy Commission, Armament Agency and Ecole Polytechnique for larger ones, as well as in universities with compact devices. For each we will describe the performances and the main scientific achievements. The research has been mainly oriented to the generation of copious doses of x-rays. Based on theoretical considerations, drawbacks were expected from some instabilities growing during the compression. Thus, Z-pinch stabilization was a major issue and was addressed by various techniques: gas-puff profiling, staged ZP, Bz, plasma puff, plasma on wire, composite ZP. In general, the generators were based on capacitive storage but a strong effort was done of inductive storage. Moreover, the work in France has been strongly connected to other Z-pinch programs in the UK, in Russia and in the USA and a number of joint experiments were performed. Selected results of these cooperative works will be given too. Last but not least, we will conclude by new trends. The laboratory has contributed to introduce innovative approaches of the load, supported by complete numerical simulations. They are currently tested, even used routinely, on world-class generators : load current multiplier, flat array ZP, multiple-ZP hohlraum

Compréhension des mécanismes régissant le fonctionnement d'un tube hyperfréquence de type MILO (Magnetically Insulated Line Oscillator)

PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Absolute Spectral Radiation Measurements From 200-ns 200-kA X-Pinch in 10-eV-10-keV Range With 1-ns Resolution

International audienceA series of seven X-ray diodes and four Si p-i-n detectors with K- and L-filters was employed to measure the absolute time-resolved spectra of 200-ns 200-kA molybdenum and copper X-pinch plasmas. We observe a 10-mum-size 0.4-0.7-ns X-ray source at a total power yield level of 1.5 GW with about 35% in the range above 1 keV. The extreme ultraviolet part of the spectrum can be fitted by a Planckian function with a temperature of 65-75 eV. In the region above 800 eV, the spectrum can be fitted by an exponential distribution with an effective temperature of ~1 keV for Mo X-pinch and ~500 eV for Cu plasma. The X-ray source yields 200-550 mJ in this spectral range. The total XUV and X-ray yield varies in the range 10-30 J

Commutation rapide déclenchée par filamentation laser femtoseconde

International audienceLa revue scientifique de l'Ecole polytechnique (parution annuelle) ISSN : 1775-0385 Le phénomène de filamentation laser dans lair a été décrit dans un précédent numéro (Flash X n° 12) par A. Houard et A. Mysyrowicz, chercheurs du LOA (Laboratoire dOptique appliquée). Rappelons ici quil apparaît spontanément le long dun faisceau laser de durée femtoseconde (fs) quand sa puissance dépasse un seuil critique de quelques GW. un équilibre dynamique entre la diffraction naturelle du faisceau, leffet Kerr, et la défocalisation par lair ionisé, maintient lintensité dans le coeur du faisceau sur une distance qui peut dépasser un mètre, entraînant la formation dun canal de plasma dans le sillage de limpulsion. Le point de démarrage, la longueur des canaux de plasma et leur distribution transverse sont contrôlables en jouant sur les paramètres de limpulsion laser initiale (énergie, durée, diamètre du faisceau)

Generation of high pulsed magnetic field using a low inductance surface switch

International audienceIn experimental physics, a number of domains need the intense magnetization of a rather large volume, namely in condensed matter science. In laser-matter interaction and plasma science, the magnetic field may extend the interaction time of the charged particles. But the B-field values of interest, as predicted by analytical study or by numerical simulation, commonly overtake the 50-60T range, a limit for a reasonable capital investment. Moreover, the existing materials cannot withstand fields of 100T or more and some experiments are conducted in a semi-destructive mode, i.e. the coils explode radially, preserving the cell and the diagnostics. The single turn coil (STC) is an option for reaching such fields in a non-destructive pulsed mode. In order to study the generation of high energy particles for neutron production, we have have estimated that convenient operating conditions are a peak value of 50T in few cm3. Translated in current intensity, this objective is close to IMA with a rising time of 1 μs. To get such a very high current, we have built a low impedance transmission line connected to a massive brass STC with a 10 to 16mm bore. Two types of capacitor banks were used, based on 4.2-μF 50-kV low-inductance Haefely caps, charged under 30kV. The key component in the flat transmission line is a surface switch which has been described previously and can have an insertion inductance as low as few nH. In this switch, a number of channels are triggered along a melamina surface by an underlying conducting comb. Under the present conditions, when the channel number is 15 or more, a significant reduction of the inductance is observed (typ. 13 to 16nH for the whole circuit) and the peak current can reach 850kA, corresponding to 26 to 30T on axis. The field mapping, recorded with a mm axial resolution, is coherent with STC calculation. The paper will describe in detail the experimental setup, the associated probes, the calibration procedure and the results. We will conclude by presenting an alternative switch, currently under construction, able to increase the peak current, the reproducibility of B and the device lifetime. oral communicatio

Laboratory experiments of Radiative Shocks, in the context of stellar accretion

International audienceRadiative 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 SF2

Generation of High Pulsed magnetic field using low inductance switches

International audienceOn présente plusieurs dispositifs de production de courants intenses (jusqu'à 900 kA sous 30 kV) pour magnétiser des volumes d'interaction laser-matière de quelques cm3 pendant environ 1 µs. L'accent est mis sur la réalisation de deux types d'éclateur à très faible inductance et sur la connexion à une chambre à vide

Experimental study of X-pinch in a submicrosecond regime

International audienceX-pinch plasmas are known as point-like X-ray sources with the potential application for backlighting diagnostics. X-pinches are commonly driven by large pulsed power generators delivering high-voltage pulses with short rise-times, typically under 100 ns. When operating with slower capacitor banks, X-pinches become less reliable because of the arising X-ray pulse jitter and because of the appearance of two or more X-ray bursts coming from multiple hot spots. In this paper, a very compact inductance-capacitance (LC) generator with the current rise-time of 200 ns was used to drive molybdenum and tungsten wire X-pinches. A single peak, small shot-to-shot jitter emission of X-rays was obtained. Time-integrated penumbral imaging recorded the X-ray source dimension of less than 15 μm in the spectral region above 2.4 keV. The total yield of more than 80 mJ was registered with the radiation pulse duration as short as 1.5 ns. The appearance of single- or multiple-source core structures is discussed in correlation with used wire material and X-pinch torsion angle. The results confirm the possibility of using an X-pinch driven by a fast compact capacitor bank for backlighting applications