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 TI3: Shocks and ICF |
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Chair: Rip Collins, Lawrence Livermore National Laboratory Room: Plaza F |
Thursday, November 14, 2013 9:30AM - 10:00AM |
TI3.00001: Observations of strong ion-ion correlations in dense plasmas Invited Speaker: Tammy Ma The strong ion-ion correlation peak characteristic of warm dense matter (WDM) plasmas has recently been observed for the first time using simultaneous angularly, temporally, and spectrally resolved x-ray scattering measurements in laser-driven shock-compressed aluminum. High-energy (17.9 keV) laser-produced x-ray line emission has been employed to probe aluminum compressed to a density of greater than 8 g/cc. These experiments show a well-pronounced peak in the static structure factor at a wave number of k $=$ 4 A$^{-1}$. The measurements of the magnitude and position of this correlation peak are precise enough to test different theoretical models for the ion structure and show that only models taking the complex interaction in WDM into account agree with the data. These studies have demonstrated a new highly accurate diagnostic technique to directly measure the state of compression and the ion-ion correlations. This new method is presently being applied in numerous experiments to characterize the physical properties of dense plasmas. In this talk, we will discuss the first demonstration of this novel technique, present applications to characterize shock conditions in solids and liquid, and innovative ideas for measuring new high-pressure material properties such as electrides. [Preview Abstract] |
Thursday, November 14, 2013 10:00AM - 10:30AM |
TI3.00002: Full Equation of State Measurements of Warm Dense Carbon Using a Novel Technique of Shock and Release Invited Speaker: Katerina Falk The equation of state of light elements at high densities and moderate temperatures falling in to the warm dense matter (WDM) regime is essential to understanding the structure of Jovian planets as well as inertial confinement fusion (ICF). In these systems quantum degeneracy and strong inter-particle forces are significant making the theoretical description of WDM extremely challenging. Here we present results from a combination of experimental techniques used to characterize thermodynamic properties of warm dense carbon at different conditions. The Omega laser was used to create WDM conditions at solid density and temperature $\sim 1-10$ eV, using the novel technique of laser driven shock and release. The graphite or diamond targets are first strongly shocked by a direct laser drive in planar geometry and then let undergo a large pressure release into the well-characterized low density pressure standard (SiO$_2$ aerogel foam) [1] creating conditions significantly different from the Hugoniot states typically studied on high power laser facilities. Direct measurement of electron temperature and density/ionization of warm dense carbon was obtained by spatially resolved x-ray Thomson scattering (XRTS). The Imaging X-ray Thomson Spectrometer [2], recently developed for Omega by LANL and the University of Michigan, provided the spatial resolution crucial to isolating the signal from the release wave avoiding contamination of the XRTS signal. VISAR and SOP were used to determine the shock velocity in the pressure standard which provided the pressure in the released carbon. X-ray radiography was employed to obtain an independent measurement of the mass density by transmission through the warm dense carbon. Various equation of state models are compared to the experimental results.\\[4pt] [1] M. D. Knudson, J. R. Asay, and C. Deeney, J. Appl. Phys. 97, 073514 (2005).\\[0pt] [2] E. J. Gamboa, D. S. Montogomery, I. M. Hall, and R. P. Drake, JINST 6, P04004 (2011); E. J. Gamboa et al., Rev. Sci. Instrum. 83, 10E108 (2012). [Preview Abstract] |
Thursday, November 14, 2013 10:30AM - 11:00AM |
TI3.00003: Isentropic compression experiments on LIL and their applications to planetary physics Invited Speaker: Michel Koenig The recent discovery of extra-solar planets, especially earth-like ones open a new field of application for high energy lasers. Indeed the extreme conditions (330-1500 GPa, 5000-10000K) expected in the core of those objects make lasers as the only tool to be able to generate such high pressures. However traditional dynamical techniques to compress matter involve shock waves that overheat the sample relative to conditions occurring in planetary cores. To overcome this issue, we developed, following work done at Livermore a quasi-isentropic laser driven compression technique based here on direct drive interaction. Here, we report on recent measurements performed on the LIL (Ligne d'Int\'{e}gration Laser) laser facility at CEA-CESTA in Bordeaux where we did used a dedicated ramp-tailored laser pulse (2-10 kJ, 20 ns). Two materials of interest for telluric planets (iron and quartz) were investigated. Visible diagnostics (VISAR and SOP) were used as main diagnostics giving both velocities and temperature of the sample. The analysis of our results leads to assess that we achieved conditions close to the iron melting curve in the whole range 200-1000 GPa on a single shot. Similar conditions were also achieved for quartz. This ability of using very high energy lasers opens a new route for planetary science especially when isentropic compression will be associated to x-ray sources inferring the microscopic structure of the sample. We will discuss the opportunities that will be possible in the next few years in this field. [Preview Abstract] |
Thursday, November 14, 2013 11:00AM - 11:30AM |
TI3.00004: Compression dynamics and lattice kinetics in laser driven shocks of BCC metals using dynamic Laue diffraction Invited Speaker: Christopher Wehrenberg Laue diffraction experiments were used to directly observe the strain relaxation process in Ta shock compressed along the [001] direction. The unit cell aspect ratio was measured from Laue patterns at times ranging 0.1 to 1.6 ns relative to the shock wave entering the Ta sample. For 50 GPa shocks, the aspect ratio increases asymptotically to a value of 0.95 over the course of $\sim$ 1 ns. The 1 ns time scale is on the order of predictions of the relaxation time scale made using the Livermore multiscale strength model [Rudd, R SCCM 2011]. In contrast, ultra-fast (less than 10 ps) relaxation times are expected above the homogeneous nucleation threshold. Consistent with this behavior, Ta subjected to shocks at 90 GPa relaxes faster than the resolution of the diffraction experiments (approximately 150 ps). As the relaxation time will be dependent on the dislocation density, one can infer a dislocation density behind the 50 GPa shock front. Dislocation densities estimated in this manner agree with in an order of magnitude both with predictions by the multiscale model and with residual dislocation densities observed in post-mortem samples. [Preview Abstract] |
Thursday, November 14, 2013 11:30AM - 12:00PM |
TI3.00005: Exploring the matter of extremes at the Linac Coherent Light source Invited Speaker: Hae Ja Lee A new technique using the Linac Coherent Light Source (LCLS), an x-ray free electron laser source, was developed at Matter in Extreme Conditions (MEC) endstation to study wide range of extreme conditions in phase space. The LCLS has $\ge $3 mJ per 60 fs pulse enabling an intensity x-ray beam between 4 keV -9.5 keV to be focused onto a small spot $\sim$ 2 micron at MEC. Short pulse optical laser system with 40fs, 150mJ, 10Hz at 800nm and long pulse optical laser system with variable pulse duration of 2-200ns, \textless 50 J, 1 shot/7 min at 527nm serve to create high energy density state or shock compression state. MEC instrument is equipped with a suite of target diagnostics like as emission spectrometers, scattering spectrometers, area detectors for x-ray diffraction, VISAR, and FDI. We present capabilities of the MEC instrument and give an overview of several experiments which are performed at MEC. [Preview Abstract] |
Thursday, November 14, 2013 12:00PM - 12:30PM |
TI3.00006: Laboratory Experiments on the Generation of Perpendicular, Magnetized Collisionless Shocks by a Laser-Ablated Piston Invited Speaker: Derek Schaeffer Collisionless shocks occur ubiquitously in space plasmas and have been extensively studied $\textit{in situ}$ by spacecraft, though they are inherently limited in their flexibility. We present laboratory experiments utilizing a highly flexible laser geometry at UCLA to study the generation of magnetized, perpendicular collisionless shocks by a super-Alfv\'{e}nic laser-ablated piston. Experiments were carried out on the LArge Plasma Device (LAPD), which can create a highly reproducible $20$ m long by \O$1$ m H or He magnetized ($\leq2$ kG) ambient plasma. The $100$ J Raptor laser was used to ablate perpendicular to the background magnetic field a carbon target embedded in the LAPD plasma. Emission spectroscopy revealed a significant spread between laser debris charge states, consistent with 2D hybrid simulations that show fast-moving, highly ionized debris slipping through the ambient plasma, while slower, lower charge states drive a diamagnetic cavity. The cavity grew to several ion gyroradii and lasted around one gyroperiod, large and long enough to act like a piston by allowing laminar fields at the cavity edge to transfer energy from the debris to the background plasma. This is confirmed by spectroscopy, which shows a reduction in debris velocities relative to a non-magnetic case, and Thomson scattering, which shows an increase in electron densities and temperatures in the ambient plasma. An increase in the intensity of the ambient plasma seen by gated imaging also indicates an energetic population of electrons coincident with the cavity edge, while Stark-broadened ambient lines may indicate strong local electric fields. Magnetic flux probes reveal that the cavity launches whistler waves parallel to the background field, as well as a super-Alfv\'{e}nic magnetosonic wave along the blowoff axis that has a magnetic field compression comparable to the Alfvenic Mach number, consistent with simulations that suggest a weak collisionless shock was formed. [Preview Abstract] |
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