Bulletin of the American Physical Society
55th Annual Meeting of the APS Division of Plasma Physics
Volume 58, Number 16
Monday–Friday, November 11–15, 2013; Denver, Colorado
Session UO6: HED Science |
Hide Abstracts |
Chair: Alex Arefiev, University of Texas Room: Governor's Square 11 |
Thursday, November 14, 2013 2:00PM - 2:12PM |
UO6.00001: ABSTRACT WITHDRAWN |
Thursday, November 14, 2013 2:12PM - 2:24PM |
UO6.00002: Measurement of Stellar Opacities with Short-Pulse Lasers Richard London, John Castor, James Dunn, Alexander Steel, Carlos Iglesias, Joseph Nilsen Radiative opacity is a key physical property determining the structure and evolution of stars. It is fundamental to check the theoretical opacities that are used in stellar models with direct experimental measurements. Due to a disagreement between model predictions and helio-seismic observations, there is current interest in opacity in the radiative zone of the Sun. Previous experimental techniques, based on long pulse lasers and Z-pinch machines cannot easily obtain the high temperatures and densities required to address this problem. A complementary technique using short-pulse lasers can access higher temperature and density regimes. We discuss radiation-hydrodynamic simulations of such experiments, considering a range of laser and target parameters. We present experimental designs that can achieve the conditions of the upper radiative zone of the Sun with sufficient spatial and temporal uniformity to enable accurate opacity measurements. [Preview Abstract] |
Thursday, November 14, 2013 2:24PM - 2:36PM |
UO6.00003: The first data from the Orion laser; measurements of the spectrum of hot, dense aluminum Matthew Hill, Peter Allan, Colin Brown, James Harris, David Hoarty, Lauren Hobbs, Steven James, John Morton, Ed Marley, Ronnie Shepherd, Jim Dunn, Jim Emig, Steve Fulkerson, Hui Chen, Peter Beiersdorfer The newly commissioned Orion laser system has been used to study dense plasmas created by combined short pulse laser heating and laser driven shock compression, using the ns and sub-ps laser beams available at the facility. The plasma density was systematically varied between 1 g/cc and 10 g/cc by using aluminum samples buried in plastic or diamond sheets. The aluminum was heated to electron temperatures between 500 eV and 700 eV allowing the plasma conditions to be diagnosed by K-shell emission spectroscopy. These were inferred from comparison with a variety of codes, including FLY and FLYCHK and from radiation-hydrodynamic simulations. Time-resolved X-ray emission was recorded using a spectrometer coupled to an X-ray streak camera, with additional time-integrated spectrometers recording onto image plate. The K-shell spectra show evidence of the lowering of the ionization potential, where the data are in reasonable agreement with FLY and FLYCHK when using the standard treatment proposed by Stewart and Pyatt. The data have also been compared to more sophisticated models and the results are presented. [Preview Abstract] |
Thursday, November 14, 2013 2:36PM - 2:48PM |
UO6.00004: Creating Uniform Temperature Solid Density Plasmas with Intense Femtosecond Lasers K. George, S. Jiang, S. Wilks, A. Link, D.W. Schumacher, R.R. Freeman, K.U. Akli The isochoric heating of reduced mass targets was investigated with the SCARLET laser using 10J, \textless~100 fs pulses. Laser intensity (focal spot size) as well as target dimensions (transverse and longitudinal) were varied in an effort to generate plasmas of uniform temperature and density. XUV imaging at 68 eV was employed to infer spatially resolved temperature maps while K-alpha spectroscopy was used to determine bulk target temperature. For 100 micron diameter, 3 micron thick Al/Cu/Al disk targets a bulk temperature in excess of 50 eV was achieved at solid density over a spatial temperature scale length of approximately 70 microns. A reduction of the target thickness and thus total mass was observed to increase target temperature. [Preview Abstract] |
Thursday, November 14, 2013 2:48PM - 3:00PM |
UO6.00005: Laser Generated Anisotropic Drives for Radiation Transport Validation N.E. Lanier, J.K. Kline, J.D. Hager Many astrophysical phenomena are studied in the laboratory by developing a scaled platform whose energy drive is produced via a laser or pulsed power facility. The push to reach more energetic regimes often results in radiation drives that diverge from well-behaved Lambertian Planckian sources. In these cases, typical diffusive radiation flow models can break down. A new platform, that deliberately generates a well-characterized non-Planckian, anisotropic source, has been developed for the OMEGA laser. The resulting data will help validate more complex computational transport schemes like Sn or implicit Monte-Carlo (IMC) models. The platform contains a SiO$_{2}$ foam mounted on a half-hohlraum. Anisotropy is achieved by inserting an obstruction of either a singular round aperture or annular ring between the foam and hohlraum. In addition, a thin beryllium layer delays the thermal component of the drive while the higher energy M-shell radiation propagates unhindered. The result is a highly non-Planckian, anisotropic, supersonic drive that eventually transitions to sub-sonic. Spectroscopic measurements constrain the source anisotropy, magnitude, and spectral content. Moreover, the Marshak position coupled with spectroscopic absorption measurements quantify the foam's internal energy. [Preview Abstract] |
Thursday, November 14, 2013 3:00PM - 3:12PM |
UO6.00006: Experimental Comparison of Tantalum Material Strength between Single Crystal [100] and [111] Samples at High Pressure and Strain Rates Christopher Plechaty, Hye-Sook Park, Rob Cavallo, Shon Prisbrey, Robert Rudd, Christopher Wehrenberg, Channing Huntington, Brian Maddox, Mark May, Bruce Remington Experiments were performed using the OMEGA laser to investigate Ta material strength at high pressure (1 Mbar), and high strain rates (10$^{6}$- 10$^{8}$ s$^{-1})$. To achieve these pressures and strain rates in experiment without melting the sample, a quasi-isentropic drive [1] was employed to drive the growth of pre-imposed sinusoidal perturbations embedded on the surface of the Ta sample, via the Rayleigh-Taylor (RT) instability. By measuring the ripple amplitude using face-on high energy ($\sim$ 22 KeV) radiography [2], the strength of the Ta sample was inferred from the amount of RT growth observed. Under these experimental conditions, the Ta material strength can be modeled by the Multiscale (MS) model [3], developed at LLNL. In this study, we performed a side-by-side comparison of the ripple growth on [100] and [111] orientated single-crystal Ta samples for the same shot and drive conditions. The objective was to determine if a difference in the growth predicted by the MS model could be observed at the high pressure and strain rates present in our experiments, and within the error bars of the experimental technique. [1] H.S. Park, et al., PRL \textbf{104}, 135504 (2010). [2] H.S. Park, et al., POP \textbf{15}, 072705 (2008). [3] N. R. Barton, et al., JAP \textbf{109} (7), 073501 (2011). [Preview Abstract] |
Thursday, November 14, 2013 3:12PM - 3:24PM |
UO6.00007: Cylindrically converging radiative shocks in noble gases driven by the MAGPIE pulsed-power device Guy Burdiak, S. Lebedev, Adam Harvey-Thompson, G. Swadling, F. Suzuki-Vidal, J. Skidmore, L. Suttle, M. Bennet, G. Hall, L. Pickworth, P. de Grouchy, S. Bland, N. Niasse, R. Rodriguez, J. Gil, G. Espinosa Experimental data from gas-filled cylindrical liner z-pinch experiments are presented. The current discharge from the MAGPIE pulsed-power device at Imperial College London (1.4MA,240ns) is applied to a thin walled (80$\mu$m) Al tube with a static gas-fill inside (initial gas density 10-5 g/cc). The system is used to drive cylindrically converging strong shock waves (U$_{s}$ $=$ 20km/s) into different gases. Axial diagnostics include interferometry, optical streak photography and time gated, spatially resolved optical spectroscopy. The experimental geometry is nominally uniform along the diagnostic line of sight and in addition the shock waves show a high degree of azimuthal symmetry. This allows determination of the radial dependence of axially averaged plasma parameters (n$_{e}$,T$_{e})$. The spectroscopy diagnostic is used to determine the temperature profile across the shock (in the precursor and post-shock regions) in different noble gases. Comparisons are made between experimental temperature and electron density profiles and the 1D radiation-MHD code HELIOS-CR. In addition, varying degrees of shock stability are seen in different noble gases. These observations will be briefly compared to cooling function calculations and analytical stability models. [Preview Abstract] |
Thursday, November 14, 2013 3:24PM - 3:36PM |
UO6.00008: Observations of plasma instability and precursor plasma in thin liners driven with a compact linear transformer driver Julio C. Valenzuela, Gilbert Collins, Derek Mariscal, Farhat Beg Results of surface instability formation in thin liners driven by a compact linear transformer driver, capable of producing 250kA in 150ns, are presented. Two different materials, Cu and Ni, were investigated in order to study the liner's resistivity effect on formation and evolution of the instabilities. Dimensions of the liners were kept constant (7mm length, 1mm radius and 3um thickness). Laser probing was implemented to diagnose instability formation and growth. Time-integrated extreme ultraviolet spectroscopy as well as filtered diodes were used to study plasma temperature and density. A constant expansion rate for the liners was observed, independent of liner material. Significant difference was found between the Cu and Ni instability growth; the most significant perturbations in copper grow rapidly and saturate reaching a limiting wavelength of the order of the liner radius, while the most significant wavelength in nickel slowly increases and saturates, also close to the liner radius. A comparison of end on and side on XUV emission indicates formation of precursor plasma. Both materials exhibited precursor plasma temperatures around 40eV and ion densities of 1e19cm$^{-3}$. [Preview Abstract] |
Thursday, November 14, 2013 3:36PM - 3:48PM |
UO6.00009: Preliminary characterization of a laser-generated plasma sheet Paul Keiter, Matt Trantham, Guy Malamud, Sallee Klein, Jeff Fein, Josh Davis, Robb Gillespe, R. Paul Drake A reverse shock is a shock formed when a freely expanding plasma encounters an obstacle. Reverse shocks can be generated by a blast wave propagating through a medium. They can also be found in binary star systems where the flowing gas from a companion star interacts with the accretion disk of the primary star. Previous experiments [Krauland et al 2013] created a reverse radiative shock, in which, flowing plasma, representing the flowing plasma from the secondary star, interacted with a stationary object, which represented the accretion disk. Future experiments will replace the stationary object with a flowing plasma to represent the accretion disk and create a reverse radiative shock from the interaction of two flowing plasmas. Recent experiments created a flowing sheet of plasma. We will present the experimental results, including measurements of the spatial extent, density and velocity of the flowing plasma sheet. We will also discuss the implications for future experiments. [Preview Abstract] |
Thursday, November 14, 2013 3:48PM - 4:00PM |
UO6.00010: Filamentation instability in relativistic pair plasmas M. D'Angelo, L. Fedeli, A. Sgattoni, A. Macchi, F. Pegoraro The filamentation instability in relativistic $e^+$-$e^-$ pair plasmas is relevant to several astrophysical contexts, such as GRBs, AGNs and pulsar wind nebulae. 1D3P and 2D3P relativistic PIC simulations were carried out to study the filamentation instability in the extreme conditions typical of these astrophysical scenarios. Counter-propagating charge neutral beams with $\gamma$ factor in the range $1, 1000$ were simulated in a symmetric configuration. Long-runs were performed in order to explore the nonlinear saturation phase far beyond the well understood linear growth phase. In both 1D and 2D simulations, during the final stage of the linear phase, a small fraction of the particles was accelerated up to twice their initial momentum. These particles are not confined by the filamentary structures of the magnetic field. The particle energy spectrum shows a broad distribution with a bump on the high energy tail. Radiation Reaction effects due to Radiative losses were included in the simulations. Significant energy losses were observed for $\gamma > 100$ and pair plasma density $> 10^{20}$ cm$^{-3}$. While the magnetic field structures were only mildly affected by these losses, particles in the high energy tail of the distribution were significantly decelerated. [Preview Abstract] |
Thursday, November 14, 2013 4:00PM - 4:12PM |
UO6.00011: Using XFELs for Probing of Complex Interaction Dynamics of Ultra-Intense Lasers with Solid Matter T.E. Cowan, T. Kluge, C. Gutt, L.G. Huang, J. Metzkes, U. Schramm, M. Bussmann Hard x-ray FELs provide revolutionary new techniques for investigating HED matter. Particularly exciting is to probe the interaction of ultra-intense lasers with solid-density plasma, in order to improve our understanding and ability to predictively model the very complex interaction dynamics. Important processes include the electron acceleration at the target surface, return current generation by rapid ionization, relativistic electron transport, resistive magnetic fields in filaments and at interfaces, and the bulk plasma response; which are important for applications such as ion acceleration, attosecond harmonics, and isochoric heating,. XFELs extend optical techniques into the x-ray regime -- Faraday rotation, phase contrast imaging, interferometry. Coherent diffraction allows to directly measure the electron-electron correlations inside the solid plasma with few nm-resolution on the fs time scale [1]. Absorptive coherent diffraction tuned to bound-bound transitions of a particular ion charge state is proposed as a probe of the termporal and spatial evolution of the laser-driven ionization dynamics. \\[4pt] [1] T. Kluge et al, arXiv:1306.0420 [Preview Abstract] |
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