Bulletin of the American Physical Society
50th Annual Meeting of the Division of Plasma Physics
Volume 53, Number 14
Monday–Friday, November 17–21, 2008; Dallas, Texas
Session KI2: Warm Dense Matter and Laser-Plasma Interactions |
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Chair: Siegfried Glenzer, Lawrence Livermore National Laboratory Room: Landmark B |
Tuesday, November 18, 2008 3:00PM - 3:30PM |
KI2.00001: A new approach to understanding Warm Dense Matter Invited Speaker: The physical state of matter at density $\sim $ 1 g/cm$^{3}$ and temperature $\sim $ 1 eV - called Warm Dense Matter (WDM) -- has been a misty island in the phase plane describing the structure of matter. Logical approaches (starting from hot solids, dense chemically-reacting fluids, low-temperature plasmas or release from shock-compressed solids) reach a barrier in the WDM range beyond which the theories do not converge and fail to describe the strongly interacting mix of atoms, molecules, ions and semi-free electrons. This talk will describe the most challenging scientific questions for WDM and will sketch a new approach, based on a high-density version of the Saha (chemical-equilibrium) method.\footnote{This work was done in collaboration with Dr. M. P. Desjarlais of the Sandia National Laboratories, Albuquerque, NM.} The advantage of the new method is that it incorporates a great deal of existing experimental data in a coherent thermodynamic structure. The method can be tested against quantum molecular dynamics, which has provided surprising ideas about the importance of dimers (weakly bound molecules) and the metal-insulator transition in WDM. On the experimental side, good results require rapid heating to produce the desired conditions, along with rapid diagnostics to acquire data, before the sample has time to disassemble. While electrical heating is relatively slow and laser heating is inherently non-uniform, new heating technologies such as intense pulsed ion-beam and x-ray deposition can be faster and more homogeneous. Recent progress on developing experiments using these methods will be presented. [Preview Abstract] |
Tuesday, November 18, 2008 3:30PM - 4:00PM |
KI2.00002: Probing the dynamic structure of warm dense matter Invited Speaker: Materials under extreme compression, as the one achieved by direct laser illumination, exhibit almost-equal thermal and Coulomb energies and structural properties that are in between those of ideal gases and solids. Their understanding is critical for the calculation of the equation-of-state of the interior of giant planets as well as for inertial confinement fusion research. In the recent years x-ray scattering has emerged as a powerful technique to accurately measure the microscopic properties (electron temperature and ionization state) of warm and dense matter states. At the same time it allows to extract the correlation and the dynamics of a semi-degenerate and strongly coupled systems. In this work, we will describe the details of the scattering models with a few examples drawn from experiments conducted in low-Z materials (Li, B and CH) using high power lasers. In addition to x-ray scattering, the shock properties have been monitored with a dual color VISAR, shock break-out, as well as with a XUV flat-field spectrometer, in order to provide independent cross validation of the diagnostic method. Further progress of the x-ray scattering techniques will be discussed, with particular attention on how to extend these methods to new 4th generation light sources to achieve both sub-picosecond and micron-scale resolution to investigate non-equilibrium and transient systems. [Preview Abstract] |
Tuesday, November 18, 2008 4:00PM - 4:30PM |
KI2.00003: Ultra-fast x-ray Thomson scattering measurements on dense shock-compressed plasmas Invited Speaker: Novel x-ray Thomson scattering measurements of heating and compression of shocked solid-density plasmas are presented. These experiments apply ultra-short pulse laser produced K-$\alpha $ x rays to characterize plasmas at pressures above 400 GPa that are produced with a second energetic nanosecond laser. Evolution of the elastic (Rayleigh) scattering component shows rapid heating to temperatures of 2.2 eV. The measured frequency shift of collective plasmon oscillations determined the material compression, which was found to be a factor of three at 7ns after a 400J, 6ns heater beam was turned on, reaching conditions in the laboratory that are important for studying dense plasmas and astrophysics phenomena.the full characterization of strong shocks in dense matter, x-ray sources that provide picosecond temporal resolution over a small scattering volume are required. These results provide the first experimental validation of modeling of compression and heating of shocked matter with a temporal resolution of approximately 10 ps. This technique is opportune for inertial confinement fusion experiments that will achieve plasmas at extreme densities, e.g., on the National Ignition Facility, which will require high temporal resolution for characterization of short-lived states of compression. [Preview Abstract] |
Tuesday, November 18, 2008 4:30PM - 5:00PM |
KI2.00004: Energy transport in laser-plasma interactions: a UK perspective Invited Speaker: A range of experimental and theoretical work has been performed recently to gain a greater insight into energy transport in laser plasma interactions. Experiments have been performed on the VULCAN Petawatt facility in the UK and the LULI2000 facility in France to look at energy transport as a function of a number of different parameters. The parameters studied range from the introduction of controlled pre-pulses, material properties / target geometry through to absorption as a function of density scale length. A wide range of diagnostics were used such as transverse shadowgraphy, rear-side optical emission imaging, X-ray imaging and spectroscopy, and streaked harmonic measurements. To support and stimulate this work, computational tools such as Vlasov-Fokker-Planck (LEDA,\footnote{A.P.L Robinson et al, Phys. Rev. Lett. 100 025002 2008} K2\footnote{K.L.Lancaster et al, submitted to Phys. Rev. Lett (K2 constructed by M. Sherlock)}) and radiation hydrodynamic codes. One highlight that will be discussed in detail is the observation of changes to the beam divergence pattern with the addition of a cone-guide. Preliminary results from very recent studies conducted at the VULCAN facility to study the characterization and energy transport in warm dense matter in the context of the HiPER\footnote{www.hiper-laser.org} project will be presented. [Preview Abstract] |
Tuesday, November 18, 2008 5:00PM - 5:30PM |
KI2.00005: Ab Initio Petaflop-scale Particle-in-Cell Simulation of Laser-Plasma Interaction Invited Speaker: Large three-dimensional (3D) particle-in-cell (PIC) simulations have been performed using the VPIC code on some of the world's largest supercomputers, including the Roadrunner supercomputer, the first machine capable of a petaflop/s. These simulations have revealed the complex physical mechanisms underlying laser-plasma interactions and show an emerging universal picture of nonlinear saturation of LPI in the kinetic regime. Moreover, with the advent of peta-scale computing, we are entering an era of ``at-scale'' modeling necessary to understand the essential nonlinearity of LPI in solitary laser speckles, the building-blocks of multi-speckle beams. Under NIF-relevant conditions, stimulated Raman scattering (SRS) vs. speckle intensity shows a sharp onset at a threshold intensity (below linear estimates) and saturation at higher intensity, as validated in Trident experiments. Wavefront bowing of electron plasma waves (EPW) from trapped electron nonlinear frequency shift and amplitude-dependent damping is observed in 3D. This is followed by trapped particle modulational instability, which evolves nonlinearly into self-focusing, rapid transverse EPW phase variation, increased loss of trapped electrons, and EPW damping. In 3D, EPW turbulence may also exhibit loss of coherence through azimuthal filamentation. This reduction of source coherence for backscattered light and increased damping limit how much backscatter can obtain in a speckle. In addition, 3D modeling of novel ultraintense laser-ion acceleration mechanisms will be shown. Collaborators: L. Yin, K. J. Bowers, B. Bergen, D. S. Montgomery, J. L. Kline, H. A. Rose, B. M. Hegelich, K. A. Flippo, J. C. Fern\'andez. [Preview Abstract] |
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