Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session S1: X-ray Free Electron Lasers and Materials I |
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Chair: Hae Ja Lee, SLAC National Accelerator Laboratory, Ulf Zastau, Friedrich-Schiller-Universitaet Room: Grand E |
Thursday, June 18, 2015 9:15AM - 9:45AM |
S1.00001: The Matter in Extreme Conditions (MEC) instrument at LCLS Invited Speaker: Bob Nagler The last five years have seen the commissioning of and first user experiments on both the Free Electron Laser in Hamburg (FLASH) and the Linac Coherent Light Source (LCLS) in Stanford, and more are slated to come online in the next couple of years . The high photon frequency (i.e. larger than the plasma frequency of solid density), short pulse length (i.e. 10s to 100s of femtoseconds) and large photon number per pulse (i.e. 1012 photons per pulse) make it an ideal source to create and study states of matter at high energy density, a long-standing scientific challenge. Indeed, while matter in extreme conditions, which for the purpose of this talk we define as states under pressure up to hundreds of GPa and with temperatures ranging between 1eV and 1000eV, has been studied through dynamic shock compression and there has been significant progress made over many decades. However, large uncertainties still exist in the atomic structure and crystallographic structure, existence of high pressure phases, scattering factors, and equation of state of matter in extreme conditions. The Matter in Extreme Condition (MEC) instrument at LCLS is designed to overcome the unique experimental challenges that the study of matter in extreme conditions bring. It combines a suite of diagnostics and high power and energy optical lasers, which are standard fare in this research field, with the unmatched LCLS X-ray beam, to create an instrument that will be at the forefront of, and have a major impact on MEC science, in particular in the field of high pressure, warm dense matter, high energy density, and ultra-high intensity laser-matter interaction studies. The LCLS beam allows for unique investigation in all these extreme states using diagnostic methods such as X-ray Thomson Scattering, X-ray emission spectroscopy, X-ray diffraction, X-ray absorption spectroscopy, X-ray phase-contrast imaging, and pumping specific absorption lines to study (dense) plasma kinetics. Augmented with optical diagnostics, such as Velocity Interferometry for Any Reflector (VISAR) and Fourier Domain Interferometry (FDI), the instrument provides information of surface velocity, shock conditions and pressure that is reached. MEC instrument equips two relatively high power and high energy optical laser systems to produce extreme conditions. The long pulse beam at 527 nm from the frequency-doubled Nd-YAG MEC laser system is operated in a power-limited mode ($\sim$1.5 GW) within a flat-top or temporally-shaped 2-200ns pulse to produce high pressure through shock compression. A standard Ti:Sapphire laser system delivers 1J with a repetition rate of 5 Hz. In this presentation, we will show on overview of the MEC instrument and its capabilities, and show some selected results from past experiments. [Preview Abstract] |
Thursday, June 18, 2015 9:45AM - 10:00AM |
S1.00002: Ion Acoustic Modes in Warm Dense Matter Nicholas Hartley, Guilio Monaco, Thomas White, Gianluca Gregori, Peter Graham, Luke Fletcher, Karen Appel, Thomas Tschentscher, Hae Ja Lee, Bob Nagler, Eric Galtier, Eduardo Granados, Philip Heimann, Ulf Zastrau, Tilo Doeppner, Dirk Gericke, Sebastien LePape, Tammy Ma, Art Pak, Andreas Schropp, Siegfried Glenzer, Jerry Hastings We present results that, for the first time, show scattering from ion acoustic modes in warm dense matter, representing an unprecedented level of energy resolution in the study of dense plasmas. The experiment was carried out at the LCLS facility in California on an aluminum sample at 7 g/cc and 5 eV. Using an X-ray probe at 8 keV, shifted peaks at $\pm$150 meV were observed. Although the energy shifts from interactions with the acoustic waves agree with predicted values from DFT-MD models, a central (elastic) peak was also observed, which did not appear in modelled spectra and may be due to the finite timescale of the simulation. Data fitting with a hydrodynamic form has proved able to match the observed spectrum, and provide measurements of some thermodynamic properties of the system, which mostly agree with predicted values. Suggest for further experiments to determine the cause of the disparity are also given. [Preview Abstract] |
Thursday, June 18, 2015 10:00AM - 10:15AM |
S1.00003: X-ray diffraction experiments on the Materials in Extreme Conditions (MEC) LCLS x-ray FEL beamline Raymond Smith, Dayne Fratanduono, June Wicks, Tom Duffy, Hae Ja Lee, Eduardo Granados, Philip Heimann, Arianna Gleason, Cynthia Bolme, Damian Swift, Federica Coppari, Jon Eggert, Rip Collins The experiments described here were conducted on the MEC beamline hutch at the SLAC Linac Coherent Light Source. A 10 ns 527 nm laser pulse was used to shock compress 60-100 $\mu$m thick NaCl and Graphite samples. LCLS x-rays (40 fs, 8 keV), scattered off the shocked sample, were recorded on several pixel array detectors positioned downstream. The diffracted x-ray pattern allows us to determine changes in crystal structure at Mbar pressures and over nanosecond timescales. In this talk we detail the experimental setup, the current capabilities of the MEC laser and the considerations for optimizing the target design. We will describe the wave interactions within the shock-compressed target and the use of a 1D hydrocode to describe the pressure, temperature and density conditions within the target assembly as a function of time and Lagrangian position. We present observations of the B1-B2 phase transition in NaCl and subsequent back transformation during release to ambient pressure, and compare these findings to gas gun and static data. We also present results from a preliminary study of the shock-induced graphite to diamond transformation. [Preview Abstract] |
Thursday, June 18, 2015 10:15AM - 10:30AM |
S1.00004: Dynamics of structural transitions in SiO2 and implications for mineralogy of impact craters Arianna Gleason, Cindy Bolme, James Hawreliak, Hae Ja Lee, Bob Nagler, Eric Galtier, Wendy Mao Phase transitions in SiO2 at high pressure/temperature are of paramount importance to geophysics. We present experiments performed at the Matter in Extreme Conditions end-station at the LCLS, SLAC showing time-resolved X-ray diffraction (XRD) data of shock compressed quartz and fused silica transforming to stishovite on compression. These data are contrary to some studies concluding that a dense amorphous phase, rather than crystalline stishovite, forms along the SiO2 Hugoniot. XRD snap-shots of this reconstructive phase transition show single-crystal quartz undergoes an intermediate amorphization stage prior to crystallizing into stishovite - revealing the transformation pathway. On shock release, we observe the transformation of stishovite to an amorphous phase as evidenced by in situ XRD at long delay times and ex situ in recovered material. Interestingly, shock recovery experiments, or impact-metamorphosed natural samples, find only trace amounts of stishovite with a relative majority of densified (diaplectic) glass. Therefore our new data showing stishovite forming on compression up to applied pressures of 40 GPa and constraining the formation of glass to the release path are important clues to unraveling the impact history of Earth and the solar system. [Preview Abstract] |
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