HEDS Publications

  1. A strong diffusive ion mode in dense ionized matter predicted by Langevin dynamics

    P. Mabey, S. Richardson, T.G. White, L.B. Fletcher, S.H. Glenzer, N.J. Hartley, J. Vorberger, D.O. Gericke and G. Gregori

    Nature Communications 8, 14125

    2017

    The state and evolution of planets, brown dwarfs and neutron star crusts is determined by the properties of dense and compressed matter. Due to the inherent difficulties in modelling strongly coupled plasmas, however, current predictions of transport coefficients differ by orders of magnitude. Collective modes are a prominent feature, whose spectra may serve as an important tool to validate theoretical predictions for dense matter. With recent advances in free electron laser technology, X-rays with small enough bandwidth have become available, allowing the investigation of the low-frequency ion modes in dense matter. Here, we present numerical predictions for these ion modes and demonstrate significant changes to their strength and dispersion if dissipative processes are included by Langevin dynamics. Notably, a strong diffusive mode around zero frequency arises, which is not present, or much weaker, in standard simulations. Our results have profound consequences in the interpretation of transport coefficients in dense plasmas.

  2. The design of the optical Thomson scattering diagnostic for the National Ignition Facility

    P. Datte, J. S. Ross, D. H. Froula, K. D. Daub, J. Galbraith, S. Glenzer, et al.

    Review of Scientific Instruments 87, 11E549

    2016

    The National Ignition Facility (NIF) is a 192 laser beam facility designed to support the Stockpile Stewardship, High Energy Density and Inertial Confinement Fusion (ICF) programs. We report on the design of an Optical Thomson Scattering (OTS) diagnostic that has the potential to transform the community’s understanding of NIF hohlraum physics by providing first principle, local, time-resolved measurements of under-dense plasma conditions. The system design allows operation with different probe laser wavelengths by manual selection of the appropriate beam splitter and gratings before the shot. A deep-UV probe beam (λ-210 nm) will be used to optimize the scattered signal for plasmadensities of 5 × 1020 electrons/cm3 while a 3ω probe will be used for experiments investigating lower density plasmas of 1 × 1019 electrons/cm3. We report the phase I design of a two phase design strategy. Phase I includes the OTS telescope, spectrometer, and streak camera; these will be used to assess the background levels at NIF. Phase II will include the design and installation of a probe laser.

  3. A single-shot spatial chirp method for measuring initial AC conductivity evolution of femtosecond laser pulse excited warm dense matter

    Z. Chen, P. Hering, S. B. Brown, C. Curry, Y. Y. Tsui, and S. H. Glenzer

    Review of Scientific Instruments 87, 11E548

    2016

    To study the rapid evolution of AC conductivity from ultrafast laser excited warm dense matter (WDM), aspatial chirp single-shot method is developed utilizing a crossing angle pump-probe configuration. The pump beam is shaped individually in two spatial dimensions so that it can provide both sufficient laser intensity to excite the material to warm dense matter state and a uniform time window of up to 1 ps with sub-100 fs FWHM temporal resolution. Temporal evolution of AC conductivity in laser excited warm densegold was also measured.

  4. Dual crystal x-ray spectrometer at 1.8 keV for high repetition-rate single-photon counting spectroscopy experiments

    E. J. Gamboa, B. Bachmann, D. Kraus, M.J. MacDonald, et al.

    Journal of Instrumentation 11

    2016

    With the recent development of high-repetition rate x-ray free electron lasers (FEL), it is now possible to perform x-ray scattering and emission spectroscopy measurements from thin foils or gasses heated to high-energy density conditions by integrating over many experimental shots. Since the expected signal may be weaker than the typical CCD readout noise over the region-of-interest, it is critical to the success of this approach to use a detector with high-energy resolution so that single x-ray photons may be isolated. Here we describe a dual channel x-ray spectrometer developed for the Atomic and Molecular Optics endstation at the Linac Coherent Light Source (LCLS) for x-ray spectroscopy near the K-edge of aluminum. The spectrometer is based on a pair of curved PET (002) crystals coupled to a single pnCCD detector which simultaneously measures x-ray scattering and emission in the forward and backward directions. The signals from single x-ray photons are accumulated permitting continuous single-shot acquisition at 120 Hz.

  5. High-intensity laser-accelerated ion beam produced from cryogenic micro-jet target

    M. Gauthier, J. B. Kim, B. Aurand, E. J. Gamboa, et al.

    Review of Scientific Instrumnets 87, 11D827

    2016

    We report on the successful operation of a newly developed cryogenic jet target at high intensity laser-irradiation. Using the frequency-doubled Titan short pulse laser system at Jupiter Laser Facility, Lawrence Livermore National Laboratory, we demonstrate the generation of a pure proton beam a with maximum energy of 2 MeV. Furthermore, we record a quasi-monoenergetic peak at 1.1 MeV in the proton spectrumemitted in the laser forward direction suggesting an alternative acceleration mechanism. Using a solid-density mixed hydrogen-deuterium target, we are also able to produce pure proton-deuteron ion beams.With its high purity, limited size, near-critical density, and high-repetition rate capability, this target is promising for future applications.

  6. Development of a cryogenic hydrogen microjet for high-intensity, high-repetition rate experiments

    J. B. Kim, S. Goede, S. H. Glenzer

    Review of Scientific Instruments

    2016

    SLAC-PUB-16543

    The advent of high-intensity, high-repetition-rate lasers has led to the need for replenishing targets of interest for high energy density sciences. We describe the design and characterization of a cryogenic microjet source, which can deliver a continuous stream of liquid hydrogen with a diameter of a few microns. The jet has been imaged at 1 m resolution by shadowgraphy with a short pulse laser. The pointing stability has been measured at well below a mrad, for a stable free-standing filament of solid-density hydrogen.

  7. High resolution x-ray Thomson scattering measurements from cryogenic hydrogen gets using the linac coherent light source

    L. B. Fletcher, U. Zastrau, E. Galtier, E. J. Gamboa, et al.

    Review of Scientific Instruments 87, 11E524

    2016

    We present the first spectrally resolved measurements of x-rays scattered from cryogenic hydrogen jets in the single photon counting limit. The 120 Hz capabilities of the LCLS, together with a novel hydrogen jet design [J. B. Kim et al., Rev. Sci. Instrum. (these proceedings)], allow for the ability to record a near background free spectrum. Such high-dynamic-range x-ray scattering measurements enable a platform to study ultra-fast, laser-driven, heating dynamics of hydrogen plasmas. This measurement has been achieved using two highly annealed pyrolytic graphite crystal spectrometers to spectrally resolve 5.5 keVx-rays elastically and inelastically scattered from cryogenic hydrogen and focused on Cornell-SLAC pixel array detectors [S. Herrmann et al., Nucl. Instrum. Methods Phys. Res., Sect. A 718, 550 (2013)].

  8. Measurement of high-dynamic range x-ray Thomson scattering spectra for the characterization of nano-plasmas at LCLS

    M. J. MacDonald, L. B. Fletcher, E. J. Gamboa, S. H. Glenzer, et al.

    Review of Scientific Instruments 87, 11E709

    2016

    Atomic clusters can serve as ideal model systems for exploring ultrafast (∼100 fs) laser-driven ionization dynamics of dense matter on the nanometer scale. Resonant absorption of optical laser pulses enables heating to temperatures on the order of 1 keV at near solid density conditions. To date, direct probing of transient states of such nano-plasmas was limited to coherent x-ray imaging. Here we present the firstmeasurement of spectrally resolved incoherent x-ray scattering from clusters, enabling measurements of transient temperature, densities, and ionization. Single shot x-ray Thomson scattering signals were recorded at 120 Hz using a crystal spectrometer in combination with a single-photon counting and energy-dispersive pnCCD. A precise pump laser collimation scheme enabled recording near background-free scattering spectra from Ar clusters with an unprecedented dynamic range of more than 3 orders of magnitude. Such measurements are important for understanding collective effects in laser-matter interactions on femtosecond time scales, opening new routes for the development of schemes for their ultrafast control.

  9. Single-shot mega-electronvolt ultrafast electron diffraction for structure dynamic studies of warm dense matter

    M. Z. Mo, X. Shen, Z. Chen, R. K. Li, M. Dunning, et al.

    Review of Scientific Instruments 87, 11D810

    2016

    We have developed a single-shot mega-electronvolt ultrafast-electron-diffraction system to measure the structural dynamics of warm dense matter. The electron probe in this system is featured by a kinetic energy of 3.2 MeV and a total charge of 20 fC, with the FWHM pulse duration and spot size at sample of 350 fs and 120 μm respectively. We demonstrate its unique capability by visualizing the atomic structural changes of warm dense gold formed from a laser-excited 35-nm freestanding single-crystal gold foil. The temporal evolution of the Bragg peak intensity and of the liquid signal during solid-liquid phase transitionare quantitatively determined. This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime.

  10. Simulated performance of the optical Thomson scattering diagnostics designed for the National Ignition Facility

    J. S. Ross, P. Datte, L. Divol, J. Galbraith, D. H. Froula, S. Glenzer, et al.

    Review of Scientific Instruments 87, 11E510

    2016

    An optical Thomson scattering diagnostic has been designed for the National Ignition Facility to characterize under-dense plasmas. We report on the design of the system and the expected performance for different target configurations. The diagnostic is designed to spatially and temporally resolve the Thomson scattered light from laser driven targets. The diagnostic will collect scattered light from a 50 × 50 × 200 m volume. The optical design allows operation with different probe laser wavelengths. A deep-UV probe beam (  = 210 nm) will be used to Thomson scatter from electron plasma densities of ∼5 × 1020 cm−3 while a 3 probe will be used for plasma densities of ∼1 × 1019 cm−3. The diagnostic package contains two spectrometers: the first to resolve Thomson scattering from ion acoustic wave fluctuations and the second to resolve scattering from electron plasma wave fluctuations. Expected signal levels relative to background will be presented for typical target configurations (hohlraums and a planar foil).

  11. Absolute dosimetric characterization of Gafchromic EBT3 and HDv2 films using commercial flat-bed scanner and evaluation of the scanner response function variability

    S. Chen, M. Gauthier, et al.

    Review of Scietific Instruments 87, 073301

    2016

    Radiochromic films (RCF) are commonly used in dosimetry for a wide range of radiation sources (electrons, protons, and photons) for medical, industrial, and scientific applications. They are multi-layered, which includes plastic substrate layers and sensitive layers that incorporate a radiation-sensitive dye. Quantitative dose can be retrieved by digitizing the film, provided that a prior calibration exists. Here, to calibrate the newly developed EBT3 and HDv2 RCFs from Gafchromic™, we used the Stanford Medical LINAC to deposit in the films various doses of 10 MeV photons, and by scanning the films using three independent EPSON Precision 2450 scanners, three independent EPSON V750 scanners, and two independent EPSON 11000XL scanners. The films were scanned in separate RGB channels, as well as in black and white, and film orientation was varied. We found that the green channel of the RGB scan and the grayscale channel are in fact quite consistent over the different models of the scanner, although this comes at the cost of a reduction in sensitivity (by a factor ∼2.5 compared to the red channel). To allow any user to extend the absolute calibration reported here to any other scanner, we furthermore provide acalibration curve of the EPSON 2450 scanner based on absolutely calibrated, commercially available, optical density filters.

  12. Tracking the density evolution in counter-propagating shock waves using imaging X-ray scattering

    U. Zastrau, E. J. Gamboa, et al.

    Applied Physics Letters 109, 031108

    2016

    SLAC-REPRINT-2016-027

    We present results from time-resolved X-ray imaging and inelastic scattering on collective excitations. These data are then employed to infer the mass density evolution within laser-driven shock waves. In our experiments, thin carbon foils are first strongly compressed and then driven into a dense state by counter-propagating shock waves. The different measurements agree that the graphite sample is about twofold compressed when the shock waves collide, and a sharp increase in forward scattering indicates disassembly of the sample 1 ns thereafter. We can benchmark hydrodynamics simulations of colliding shock waves by the X-ray scattering methods employed.

  13. Matter of extreme conditions experiments at the Linac Coherent Light Source

    S. H. Glenzer, L. B. Fletcher, E. Galtier, B. Nagler, et al.

    Journal of Physics B 49 092001

    2016

    SLAC-WP-128

    The matter in extreme conditions end station at the Linac Coherent Light Source (LCLS) is a new tool enabling accurate pump–probe measurements for studying the physical properties of matter in the high-energy density (HED) physics regime. This instrument combines the world's brightest x-ray source, the LCLS x-ray beam, with high-power lasers consisting of two nanosecond Nd:glass laser beams and one short-pulse Ti:sapphire laser. These lasers produce short-lived states of matter with high pressures, high temperatures or high densities with properties that are important for applications in nuclear fusion research, laboratory astrophysics and the development of intense radiation sources. In the first experiments, we have performed highly accurate x-ray diffraction and x-ray Thomson scattering measurements on shock-compressed matter resolving the transition from compressed solid matter to a co-existence regime and into the warm dense matter state. These complex charged-particle systems are dominated by strong correlations and quantum effects. They exist in planetary interiors and laboratory experiments, e.g., during high-power laser interactions with solids or the compression phase of inertial confinement fusion implosions. Applying record peak brightness x-rays resolves the ionic interactions at atomic (Ångstrom) scale lengths and measure the static structure factor, which is a key quantity for determining equation of state data and important transport coefficients. Simultaneously, spectrally resolved measurements of plasmon features provide dynamic structure factor information that yield temperature and density with unprecedented precision at micron-scale resolution in dynamic compression experiments. These studies have demonstrated our ability to measure fundamental thermodynamic properties that determine the state of matter in the HED physics regime.

  14. X-ray scattering measurements of dissociation-induced metallization of dynamically compressed deuterium

    P. Davis, T. Doppner, J. R. Rygg et al.

    Nature Communications 7, 11189

    2016

    SLAC-PUB-16446

    Hydrogen, the simplest element in the universe, has a surprisingly complex phase diagram. Because of applications to planetary science, inertial confinement fusion and fundamental physics, its high-pressure properties have been the subject of intense study over the past two decades. While sophisticated static experiments have probed hydrogen’s structure at ever higher pressures, studies examining the higher-temperature regime using dynamic compression have mostly been limited to optical measurement techniques. Here we present spectrally resolved x-ray scattering measurements from plasmons in dynamically compressed deuterium. Combined with Compton scattering, and velocity interferometry to determine shock pressure and mass density, this allows us to extract ionization state as a function of compression. The onset of ionization occurs close in pressure to where density functional theory-molecular dynamics (DFT-MD) simulations show molecular dissociation, suggesting hydrogen transitions from a molecular and insulating fluid to a conducting state without passing through an intermediate atomic phase.

  15. Calculation of Debye-Scherrer diffraction patterns from arbitratily stressed polycrustalline materials

    M. MacDonald et al.

    Journal of Applied Physics

    2016

    Calculations of Debye-Scherrer diffraction patterns from polycrystalline materials have typically been done in the limit of small deviatoric stresses. Although these methods are well suited for experiments conducted near hydrostatic conditions, more robust models are required to diagnose the large strainanisotropies present in dynamic compression experiments. A method to predict Debye-Scherrerdiffraction patterns for arbitrary strains has been presented in the Voigt (iso-strain) limit [Higginbotham, J. Appl. Phys. 115, 174906 (2014)]. Here, we present a method to calculate Debye-Scherrer diffractionpatterns from highly stressed polycrystalline samples in the Reuss (iso-stress) limit. This analysis useselastic constants to calculate lattice strains for all initial crystallite orientations, enabling elastic anisotropyand sample texture effects to be modeled directly. The effects of probing geometry, deviatoric stresses, and sample texture are demonstrated and compared to Voigt limit predictions. An example of shock-compressed polycrystalline diamond is presented to illustrate how this model can be applied and demonstrates the importance of including material strength when interpreting diffraction in dynamic compression experiments.

  16. High-Power Laser Pump-Probe Experiments at the Linac Coherent Light Source

    S. H. Glenzer, L. B. Fletcher, E. Gamboa, M. Gauthier, J. Kim, M. MacDonald, et. al.

    High-Brightness Sources and Light-Driven Interactions (OSA) EM6A.3

    2016

    SLAC-PUB-16445

    The Matter in Extreme Conditions end station at the Linac Coherent Light Source (LCLS) is a new tool enabling ultrafast pump-probe measurements of laser-matter interactions. This instrument combines the worlds brightest x-ray source, the LCLS x-ray beam, with high-power lasers consisting of two nanosecond Nd:glass laser beams and a 25 TW short-pulse Ti:sapphire laser. These lasers produce short-lived states of matter with high pressures, high temperatures or high densities whose properties are investigated with highly accurate x-ray measurements. Here, we report on new results using x-ray imaging, diffraction, and scattering that resolve the short-pulse laser beam propagation and heating of matter.

  17. Nanosecond formation of diamond and lonsdaleite by shock compression of graphite

    D. Kraus, A. Ravasio, M. Gauthier et al.

    Nature Communications 7, 10970

    2016

    SLAC-REPRINT-009

    The shock-induced transition from graphite to diamond has been of great scientific and technological interest since the discovery of microscopic diamonds in remnants of explosively driven graphite. Furthermore, shock synthesis of diamond and lonsdaleite, a speculative hexagonal carbon polymorph with unique hardness, is expected to happen during violent meteor impacts. Here, we show unprecedentedin situ X-ray diffraction measurements of diamond formation on nanosecond timescales by shock compression of pyrolytic as well as polycrystalline graphite to pressures from 19 GPa up to 228 GPa. While we observe the transition to diamond starting at 50 GPa for both pyrolytic and polycrystalline graphite, we also record the direct formation of lonsdaleite above 170 GPa for pyrolytic samples only. Our experiment provides new insights into the processes of the shock-induced transition from graphite to diamond and uniquely resolves the dynamics that explain the main natural occurrence of the lonsdaleite crystal structure being close to meteor impact sites.

  18. Enhanced ion acceleration in transition from opaque to transparent plasmas

    R. Mishra

    Journal of Physics

    2016

    SLAC-PUB-16489

    Using particle-in-cell (PIC) simulations, we investigate ion acceleration in the interaction of high intensity lasers with plasmas which transition from opaque to transparent during the interaction process. We show that the highest ion energies are achieved when the laser traverses the target around the peak intensity and re-heats the electron population responsible for the plasma expansion, enhancing the corresponding sheath electric field. This process can lead to an increase of upto 2x in ion energy when compared with the standard Target Normal Sheath Acceleration (TNSA) in opaque targets under the same laser conditions. A theoretical model is developed to predict the optimal target areal density as a function of laser intensity and pulse duration. A systematic parametric scan for a wide range of target density and thickness is performed in 1D and 2D and shown consistent with the theory. These results open the way for a better optimization of the ion energy in future laser-solid experiments.

  19. Nonthermal electron energization from magnetic reconnection in laser-driven plasmas

    S. Totorica, T. Abel, F. Fiuza

    Physical Review Letters

    2016

    SLAC-PUB-16465

    The possibility of studying non-thermal electron energization in laser-driven plasma experiments of magnetic reconnection is studied using two- and three-dimensional particle-in-cell simulations. It is demonstrated that non-thermal electrons with energies more than an order of magnitude larger than the initial thermal energy can be produced in plasma conditions currently accessible in the laboratory. Electrons are accelerated by the reconnection electric field, being injected at varied distances from the X-points, and in some cases trapped in plasmoids, before escaping the finite-sized system. Trapped electrons can be further energized by the electric field arising from the motion of the plasmoid. This acceleration gives rise to a non-thermal electron component that resembles a power-law spectrum, containing up to ~ 8% of the initial energy of the interacting electrons and ~ 24 % of the initial magnetic energy. Estimates of the maximum electron energy and of the plasma conditions required to observe suprathermal electron acceleration are provided, paving the way for a new platform for the experimental study of particle acceleration induced by reconnection.

  20. Resonance between heat-carrying electrons and Langmuir waves in inertial confinement fusion plasmas

    W. Rozmus, S. H. Glenzer, et al.

    Physics of Plasmas 23, 012707

    2016

    SLAC-REPRINT-010

    In ignition scale hot plasmas,temperature gradients and thermal transport modify electron distributions in a velocity range resonant with Langmuir waves typical of those produced by stimulated Raman scattering. We examine the resultant changes to the Landau damping experienced by these Langmuir waves and the levels of thermal plasma fluctuations. The form factor and Thomson scattering cross-section in such plasmas display unique characteristics of the background conditions. A theoretical model and high-order Vlasov-Fokker-Planck simulations are used in our analysis. An experiment to measure changes in thermal plasma fluctuation levels due to a thermal gradient is proposed.

  21. Ultrafast electron kinetics in short pulse laser-driven dense hydrogen

    U. Zastrau, P. Sperling, S. Glenzer, et al.

    Journal of Physics B

    2015

    SLAC-PUB-16138

    Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities of 1015 - 1016 W cm−2. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about 25 and 40 eV for simulated delay times up to +70 fs after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 8–18 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and 30 eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. We resolved the time-scale for laser-heating of hydrogen, and PIC results for laser–matter interaction were successfully tested against the experiment data.

  22. Free-electron x-ray laser measurements of collisional-damped plasmons in isochorically heated warm dense matter

    P. Sperling, E. J. Gamboa, H. J. Lee, et al.

    Phys. Rev. Letters 115, 115001

    2015

    SLAC-REPRINT-2016-002

    We present the first highly resolved measurements of the plasmon spectrum in an ultrafast heated solid. Multi-keV x-ray photons from the Linac Coherent Light Source have been focused to one micrometer diameter focal spots producing solid density aluminum plasmas with a known electron density of ne=1.8 × 1023 cm-3. Detailed balance is observed through the intensity ratio of up- and down-shifted plasmons in x-ray forward scattering spectra measuring the electron temperature. The plasmon damping is treated by electron-ion collision models beyond the Born approximation to determine the electrical conductivity of warm dense aluminum.

  23. Ab inition calculation of the ion feature in x-ray Thomson scattering

    K.-U. Plagemann, H. Rueter, T. Bornath, et al.

    Phys. Rev. E 92, 013103

    2015

    The spectrum of x-ray Thomson scattering is proportional to the dynamic structure factor. An important contribution is the ion feature which describes elastic scattering of x rays off electrons. We apply an ab initio method for the calculation of the form factor of bound electrons, the slope of the screening cloud of free electrons, and the ion-ion structure factor in warm dense beryllium. With the presented method we can calculate the ion feature from first principles. These results will facilitate a better understanding of x-ray scattering in warm dense matter and an accurate measurement of ion temperatures which would allow determining nonequilibrium conditions, e.g., along shock propagation.

  24. Single-shot measurements of plasmons in compressed diamond with an x-ray laser

    E. J. Gamboa, L. B. Fletcher, M. J. MacDonald, et al.

    Physics of Plasmas 22, 056319

    2015

    SLAC-REPRINT-007

    Strong plasmon resonances characteristics of electron density fluctuations have recently been observed in dynamically compressed diamond for the first time at the Linac Coherent Light Source. These experiments observe the forward scattering spectra from 8 keV x-ray pulses at record peak brightness to probe laser-compressed diamond foils at the Matter in Extreme Conditions instrument. We demonstrate single-shot measurements of the x-ray scatteringspectrum, which are sensitive to the temperatures and densities of the compressed samples. The inferred values from the inelastic scattering are compared to simulations, finding good agreement with the temperature and demonstrating the need to include solid state effects in the modeling of the plasmon oscillation.

  25. Measurement of charged-particle stopping in warm dense plasma

    A. B. Zylstra, J. A. Frenje, P. E. Grabowski et al.

    Phys. Rev. Letters 114, 215002

    2015

    We measured the stopping of energetic protons in an isochorically heated solid-density Be plasma with an electron temperature of ∼32  eV, corresponding to moderately coupled [(e^{2}/a)/(k_{B}T_{e}+E_{F})∼0.3] and moderately degenerate [k_{B}T_{e}/E_{F}∼2] "warm-dense matter" (WDM) conditions. We present the first high-accuracy measurements of charged-particle energy loss through dense plasma, which shows an increased loss relative to cold matter, consistent with a reduced mean ionization potential. The data agree with stopping models based on an ad hoc treatment of free and bound electrons, as well as the average-atom local-density approximation; this work is the first test of these theories in WDM plasma.

  26. X-ray Thomson scattering diagnostics of impact ionization in laser-driven carbon foils

    P. Sperling, U. Zastrau, S. Toleikis et al

    Journal Physics B 48, 125701

    2015

    We have studied the light–matter interaction of ultra-short, intense optical laser fields with thin carbon foils via particle-in-cell simulations. Especially, the influence of additional impact ionization on the density and temperature of the generated plasma and on the corresponding Thomson scattering spectra was investigated. We predict a pump–probe experiment at the free electron laser FLASH in order to verify the importance of this effect in the laser–matter interaction on ultra-short time scales and to check our predictions quantitatively.

  27. Observation of finite-wavelength screening in high-energy-density matter

    D. A. Chapman, J. Vorberger, L. B. Fletcher, R. A. Baggott, L. Divol, T. Doeppner, R. W. Falcone, S. H. Glenzer, G. Gregori, T. M. Guymer, A. L. Kritcher, O. L. Landen, T. Ma, A. E. Pak and D. O. Gericke

    Nature Communications 6 6839

    2015

    SLAC-REPRINT-006

    A key component for the description of charged particle systems is the screening of the Coulomb interaction between charge carriers. First investigated in the 1920s by Debye and Hückel for electrolytes, charge screening is important for determining the structural and transport properties of matter as diverse as astrophysical and laboratory plasmas, nuclear matter such as quark-gluon plasmas, electrons in solids, planetary cores and charged macromolecules. For systems with negligible dynamics, screening is still mostly described using a Debye–Hückel-type approach. Here, we report the novel observation of a significant departure from the Debye–Hückel-type model in high-energy-density matter by probing laser-driven, shock-compressed plastic with high-energy X-rays. We use spectrally resolved X-ray scattering in a geometry that enables direct investigation of the screening cloud, and demonstrate that the observed elastic scattering amplitude is only well described within a more general approach.

  28. Ultrabright X-ray laser scattering for dynamic warm dense matter physics

    L. B. Fletcher, H. J. Lee, T. Döppner, et al.

    Nature Photonics 9 Issue 4, 274-279

    2015

    In megabar shock waves, materials compress and undergo a phase transition to a dense charged-particle system that is dominated by strong correlations and quantum effects. This complex state, known as warm dense matter, exists in planetary interiors and many laboratory experiments (for example, during high-power laser interactions with solids or the compression phase of inertial confinement fusion implosions). Here, we apply record peak brightness X-rays at the Linac Coherent Light Source to resolve ionic interactions at atomic (ångström) scale lengths and to determine their physical properties. Our in situ measurements characterize the compressed lattice and resolve the transition to warm dense matter, demonstrating that short-range repulsion between ions must be accounted for to obtain accurate structure factor and equation of state data. In addition, the unique properties of the X-ray laser provide plasmon spectra that yield the temperature and density with unprecedented precision at micrometre-scale resolution in dynamic compression experiments.

  29. Resolving ultrafast heating of dense cryogenic Hydrogen

    U. Zastrau, P. Sperling, M. Harmand et al.

    Phys. Rev. Letters 112, 105002

    2014

    We report on the dynamics of ultrafast heating in cryogenic hydrogen initiated by a 300  fs, 92 eV free electron laser x-ray burst. The rise of the x-ray scattering amplitude from a second x-ray pulse probes the transition from dense cryogenic molecular hydrogen to a nearly uncorrelated plasmalike structure, indicating an electron-ion equilibration time of 0.9  ps. The rise time agrees with radiation hydrodynamics simulations based on a conductivity model for partially ionized plasma that is validated by two-temperature density-functional theory.

  30. Probing matter at Gbar pressures at the NIF

    A. L. Kritcher, T. Doeppner, D. Swift et al.

    High Energy Density Physics 10, 27

    2014

    We describe a platform to measure the material properties, specifically the equation of state and electron temperature, at pressures of 100 Mbar to a Gbar at the National Ignition Facility (NIF). In these experiments we launch spherically convergent shock waves into solid CH, CD, or diamond samples using a hohlraum radiation drive, in an indirect drive laser geometry. X-ray radiography is applied to measure the shock speed and infer the mass density profile, enabling determination of the material pressure and Hugoniot equation of state. X-ray scattering is applied to measure the electron temperature through probing of the electron velocity distribution via Doppler broadening.

  31. Angular dependence of betatron x-ray spectra from a laser-wakefield accelerator

    F. Albert, B. B. Pollock, J. L. Shaw et al.

    Phys. Rev. Letters 111, 235004

    2013

    We present the first measurements of the angular dependence of the betatron x-ray spectrum produced by electrons inside the cavity of a laser-wakefield accelerator. Electrons accelerated up to 300 MeV energies produce a beam of broadband, forward-directed betatron x-ray radiation extending up to 80 keV. The angular resolved spectrum from an image plate-based spectrometer with differential filtering provides data in a single laser shot. The simultaneous spectral and spatial x-ray analysis allows for a three-dimensional reconstruction of electron trajectories with micrometer resolution, and we find that the angular dependence of the x-ray spectrum is showing strong evidence of anisotropic electron trajectories.

  32. Early-time symmetry tuning in the presence of cross-beam energy transfer in ICF experiments on the National Ignition Facility

    E. L. Dewald, J. L. Milovich, P. Michel et al.

    Phys. Rev. Letters 111, 235001

    2013

    On the National Ignition Facility, the hohlraum-driven implosion symmetry is tuned using cross-beam energy transfer (CBET) during peak power, which is controlled by applying a wavelength separation between cones of laser beams. In this Letter, we present early-time measurements of the instantaneous soft x-ray drive at the capsule using reemission spheres, which show that this wavelength separation also leads to significant CBET during the first shock, even though the laser intensities are 30× smaller than during the peak. We demonstrate that the resulting early drive P2/P0 asymmetry can be minimized and tuned to <1% accuracy (well within the ±7.5% requirement for ignition) by varying the relative input powers between different cones of beams. These experiments also provide time-resolved measurements of CBET during the first 2 ns of the laser drive, which are in good agreement with radiation-hydrodynamics calculations including a linear CBET model.

  33. Performance of high-convergence, layered DT implosions with extended-duration pulses at the National Ignition Facility

    V. A. Smalyuk, L. J. Atherton, L. R. Benedetti et al.

    Phys. Rev. Letters 111, 215001

    2013

    Radiation-driven, low-adiabat, cryogenic DT layered plastic capsule implosions were carried out on the National Ignition Facility (NIF) to study the sensitivity of performance to peak power and drive duration. An implosion with extended drive and at reduced peak power of 350 TW achieved the highest compression with fuel areal density of 1.3±0.1  g/cm2, representing a significant step from previously measured 1.0  g/cm2 toward a goal of 1.5  g/cm2. Future experiments will focus on understanding and mitigating hydrodynamic instabilities and mix, and improving symmetry required to reach the threshold for thermonuclear ignition on NIF.

  34. Plasmon measurements with a seeded x-ray laser

    L. B. Fletcher, E. Galtier, P. Heimann et al.

    Journal of Instrumentation 8, C11014

    2013

    SLAC-PUB-15839

    Plasmon measurements hold great promise for providing highly accurate data on the physical properties of plasmas in the high-energy density physics regime. To this end we demonstrate in recent experiments at the Linac Coherent Light Source the first spectrally-resolved measurements of plasmons using a seeded 8-keV x-ray laser beam. Forward x-ray Thomson scattering spectra from isochorically heated solid aluminum show a well-resolved plasmon feature that is down-shifted in energy by 19 eV from the incident 8 keV elastic scattering feature. In this spectral range, the simultaneously measured backscatter spectrum shows no spectral features indicating observation of collective plasmon oscillations on a scattering length comparable to the screening length. This technique is a prerequisite for Thomson scattering measurements in compressed matter where the plasmon shift is a sensitive function of the free electron density and where the plasmon intensity provides information on temperature.

  35. A review of laser-plasma interaction physics of indirect-drive fusion

    R. K. Kirkwood, J. D. Moody, J. Kline et al.

    Plasmas Phys. Controlled Fusion 55, 103001

    2013

    The National Ignition Facility (NIF) has been designed, constructed and has recently begun operation to investigate the ignition of nuclear fusion with a laser with up to 1.8 MJ of energy per pulse. The concept for fusion ignition on the NIF, as first proposed in 1990, was based on an indirectly driven spherical capsule of fuel in a high-Z hohlraum cavity filled with low-Z gas (Lindl et al 2004 Phys. Plasmas 11 339). The incident laser energy is converted to x-rays with keV energy on the hohlraums interior wall. The x-rays then impinge on the surface of the capsule, imploding it and producing the fuel conditions needed for ignition. It was recognized at the inception that this approach would potentially be susceptible to scattering of the incident light by the plasma created in the gas and the ablated material in the hohlraum interior. Prior to initial NIF operations, expectations for laser–plasma interaction (LPI) in ignition-scale experiments were based on experimentally benchmarked simulations and models of the plasma effects that had been carried out as part of the original proposal for NIF and expanded during the 13-year design and construction period. The studies developed the understanding of the stimulated Brillouin scatter, stimulated Raman scatter and filamentation that can be driven by the intense beams. These processes produce scatter primarily in both the forward and backward direction, and by both individual beams and collective interaction of multiple beams. Processes such as hot electron production and plasma formation and transport were also studied. The understanding of the processes so developed was the basis for the design and planning of the recent experiments in the ignition campaign at NIF, and not only indicated that the plasma instabilities could be controlled to maximize coupling, but predicted that, for the first time, they would be beneficial in controlling drive symmetry. The understanding is also now a critical component in the worldwide effort to produce a fusion energy source with a laser (Lindl et al 2011Nucl. Fusion 51 094024, Collins et al 2012 Phys. Plasmas 19 056308) and has recently received its most critical test yet with the inception of the NIF experiments with ignition-scale indirect-drive targets (Landen et al 2010 Phys. Plasmas 17 056301, Edwards et al 2011 Phys. Plasmas 18 051003, Glenzer et al 2011 Phys. Rev. Lett. 106 085004, Haan et al 2011 Phys. Plasmas 18 051001, Landen et al2011 Phys. Plasmas 18 051001, Lindl et al 2011 Nucl. Fusion 51 094024). In this paper, the data obtained in the first complete series of coupling experiments in ignition-scale hohlraums is reviewed and compared with the preceding work on the physics of LPIs with the goal of recognizing aspects of our understanding that are confirmed by these experiments and recognizing and motivating areas that need further modeling. Understanding these hohlraum coupling experiments is critical as they are only the first step in a campaign to study indirectly driven implosions under the conditions of ignition by inertial confinement at NIF, and in the near future they are likely to further influence ignition plans and experimental designs.

  36. Onset of hydrodynamic mix in high-velocity, highly compressed inertial confinement fusion implosions

    T. Ma, P. K. Patel, N. Izumi et al.

    Phys. Rev. Letters 111, 085004

    2013

    Deuterium-tritium inertial confinement fusion implosion experiments on the National Ignition Facility have demonstrated yields ranging from 0.8 to 7×1014, and record fuel areal densities of 0.7 to 1.3  g/cm2. These implosions use hohlraums irradiated with shaped laser pulses of 1.5–1.9 MJ energy. The laser peak power and duration at peak power were varied, as were the capsule ablator dopant concentrations and shell thicknesses. We quantify the level of hydrodynamic instability mix of the ablator into the hot spot from the measured elevated absolute x-ray emission of the hot spot. We observe that DT neutron yield and ion temperature decrease abruptly as the hot spot mix mass increases above several hundred ng. The comparison with radiation-hydrodynamic modeling indicates that low mode asymmetries and increased ablator surface perturbations may be responsible for the current performance.

  37. Structure measurements of compressed liquid boron at megabar pressures

    S. Le Pape, A. A. Correa, C. Fortmann et al.

    New Journal of Physics 15, 085011

    2013

    We report on the first measurements of the structure of compressed liquid boron, as it crosses the melt line in dynamic shock-compression experiments at a pressure of 100 GPa. Temporally, spectrally and angularly resolving x-ray scattering provides an independent and accurate measurement of the compression factor 1.5 and the electron density of 4 × 1023 cm−3 at moderate temperatures of 0.2–1 eV. At these conditions, the elastic scattering measurements provide the structure factor and indicate the liquid compressed phase with a coordination number of 8.3 in good agreement with predictions from first-principles molecular dynamic simulations.

  38. Progress towards ignition on the National Ignition Facility

    M. J. Edwards, P. K. Patel, J. D. Lindl et al.

    Phys. Plasmas 20, 070501

    2013

    The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory includes a precision laser system now capable of delivering 1.8 MJ at 500 TW of 0.35-μm light to a target. NIF has been operational since March 2009. A variety of experiments have been completed in support of NIF's mission areas: national security, fundamental science, and inertial fusion energy. NIF capabilities and infrastructure are in place to support its missions with nearly 60 X-ray, optical, and nuclear diagnostic systems. A primary goal of the National Ignition Campaign (NIC) on the NIF was to implode a low-Z capsule filled with ∼0.2 mg of deuterium-tritium (DT) fuel via laser indirect-drive inertial confinement fusion and demonstratefusion ignition and propagating thermonuclear burn with a net energy gain of ∼5–10 (fusion yield/input laser energy). This requires assembling the DT fuel into a dense shell of ∼1000 g/cm3 with an areal density (ρR) of ∼1.5 g/cm2, surrounding a lower density hot spot with a temperature of ∼10 keV and a ρR ∼0.3 g/cm2, or approximately an α-particle range. Achieving these conditions demand precise control of laser and target parameters to allow a low adiabat, high convergence implosion with low ablator fuel mix. We have demonstrated implosion and compressed fuel conditions at ∼80–90% for most point design values independently, but not at the same time. The nuclear yield is a factor of ∼3–10× below the simulated values and a similar factor below the alpha dominated regime. This paper will discuss the experimental trends, the possible causes of the degraded performance (the off-set from the simulations), and the plan to understand and resolve the underlying physics issues.

  39. X-ray Thomson scattering measurements of temperature and density from multi-shocked CH capsules

    L. B. Fletcher, A. Kritcher, A. Pak et al.

    Phys. Plasmas 20, 056316

    2013

    Proof-of-principle measurements of the electron densities, temperatures, and ionization states of spherically compressed multi-shocked CH (polystyrene) capsules have been achieved using spectrally resolved x-ray Thomson scattering. A total energy of 13.5 kJ incident on target is used to compress a 70 μm thick CH shell above solid-mass density using three coalescing shocks. Separately, a laser-produced zinc He-α x-ray source at 9 keV delayed 200 ps-800 ps after maximum compression is used to probe theplasma in the non-collective scattering regime. The data show that x-ray Thomson scattering enables a complete description of the time-dependent hydrodynamic evolution of shock-compressed CH capsules, with a maximum measured density of ρ > 6 g cm−3. In addition, the results demonstrate that accuratemeasurements of x-ray scattering from bound-free transitions in the CH plasma demonstrate strong evidence that continuum lowering is the primary ionization mechanism of carbon L-shell electrons.

  40. Radiative shocks produced from spherical cryogenic implosions at the National Ignition Facility

    A. Pak, L. Divol, G. Gregori et al.

    Phys. Plasmas 20, 056315

    2013

    Spherically expanding radiative shock waves have been observed from inertially confined implosion experiments at the National Ignition Facility. In these experiments, a spherical fusion target, initially 2 mm in diameter, is compressed via the pressure induced from the ablation of the outer target surface. At the peak compression of the capsule, x-ray and nuclear diagnostics indicate the formation of a central core, with a radius and ion temperature of ∼20 μm and ∼ 2 keV, respectively. This central core is surrounded by a cooler compressed shell of deuterium-tritium fuel that has an outer radius of ∼40 μm and a density of >500 g/cm3. Using inputs from multiple diagnostics, the peak pressure of the compressed core has been inferred to be of order 100 Gbar for the implosions discussed here. The shock front, initially located at the interface between the high pressure compressed fuel shell and surrounding in-falling low pressure ablator plasma, begins to propagate outwards after peak compression has been reached. Approximately 200 ps after peak compression, a ring of x-ray emission created by the limb-brightening of a spherical shell of shock-heated matter is observed to appear at a radius of ∼100 μm. Hydrodynamic simulations, which model the experiment and include radiation transport, indicate that the sudden appearance of this emission occurs as the post-shock material temperature increases and upstream density decreases, over a scale length of ∼10 μm, as the shock propagates into the lower density (∼1 g/cc), hot (∼250 eV) plasmathat exists at the ablation front. The expansion of the shock-heated matter is temporally and spatially resolved and indicates a shock expansion velocity of ∼300 km/s in the laboratory frame. The magnitude and temporal evolution of the luminosity produced from the shock-heated matter was measured at photon energies between 5.9 and 12.4 keV. The observed radial shock expansion, as well as the magnitude and temporal evolution of the luminosity from the shock-heated matter, is consistent with 1-D radiationhydrodynamic simulations. Analytic estimates indicate that the radiation energy flux from the shock-heated matter is of the same order as the in-flowing material energy flux, and suggests that this radiation energy flux modifies the shock front structure. Simulations support these estimates and show the formation of a radiative shock, with a precursor that raises the temperature ahead of the shock front, a sharp -scale thick spike in temperature at the shock front, followed by a post-shock cooling layer.

  41. Visualizing electromagnetic fields in laser-produced counter-streaming plasma experiments for collision less shock laboratory astrophysics

    N. Kugland, J. S. Ross, P.-Y. Chang et al.

    Phys. Plasmas 20, 056313

    2013

    Collisionless shocks are often observed in fast-moving astrophysical plasmas, formed by non-classical viscosity that is believed to originate from collective electromagnetic fields driven by kinetic plasmainstabilities. However, the development of small-scale plasma processes into large-scale structures, such as a collisionless shock, is not well understood. It is also unknown to what extent collisionless shocks contain macroscopic fields with a long coherence length. For these reasons, it is valuable to explore collisionless shock formation, including the growth and self-organization of fields, in laboratory plasmas.The experimental results presented here show at a glance with proton imaging how macroscopic fields can emerge from a system of supersonic counter-streaming plasmas produced at the OMEGA EP laser. Interpretation of these results, plans for additional measurements, and the difficulty of achieving truly collisionless conditions are discussed. Future experiments at the National Ignition Facility are expected to create fully formed collisionless shocks in plasmas with no pre-imposed magnetic field.

  42. Simulation of X-ray scattering diagnostics in multi-dimensional plasma

    I. Golovkin, J. J. MacFarlane, P. Woodruff et al.

    High Energy Density Physics 9, 510

    2013

    X-ray scattering is a powerful diagnostic technique that has been used in a variety of experimental settings to determine the temperature, density, and ionization state of warm dense matter. In order to maximize the intensity of the scattered signal, the x-ray source is often placed in close proximity to the target plasma. Therefore, the interpretation of the experimental data can become complicated by the fact that the detector records photons scattered at different angles from points within the plasma volume. In addition, the target plasma that is scattering the x-rays can have significant temperature and density gradients. To address these issues, we have developed the capability to simulate x-ray scattering for realistic experimental configurations where the effects of plasma non-uniformities and a range of x-ray scattering angles are included. We will discuss the implementation details and show results relevant to previous and ongoing experimental investigations.

  43. Comparison between x-ray scattering and velocity-interferometry measurements from shocked liquid deuterium

    K. Falk, S. P. Regan, J. Vorberger et al.

    Phys. Rev. E 87, 043112

    2013

    The equation of state of light elements is essential to understand the structure of Jovian planets and inertial confinement fusion research. The Omega laser was used to drive a planar shock wave in the cryogenically cooled deuterium, creating warm dense matter conditions. X-ray scattering was used to determine the spectrum near the boundary of the collective and noncollective scattering regimes using a narrow band x-ray source in backscattering geometry. Our scattering spectra are thus sensitive to the individual electron motion as well as the collective plasma behavior and provide a measurement of the electron density, temperature, and ionization state. Our data are consistent with velocity-interferometry measurements previously taken on the same shocked deuterium conditions and presented by K. Falk et al. [High Energy Density Phys. 8, 76 (2012)]. This work presents a comparison of the two diagnostic systems and offers a detailed discussion of challenges encountered.

  44. X-ray scattering measurements of strong ion-ion Correlations in shock-compressed Aluminum

    T. Ma, T. Doeppner, R. W. Falcone, L. Fletcher, S. H. Glenzer, et. al.

    Phys. Rev. Letters 110, 065001

    2013

    The strong ion-ion correlation peak characteristic of warm dense matter (WDM) is observed for the first time using simultaneous angularly, temporally, and spectrally resolved x-ray scattering measurements in laser-driven shock-compressed aluminum.

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