Bulletin of the American Physical Society
56th Annual Meeting of the APS Division of Plasma Physics
Volume 59, Number 15
Monday–Friday, October 27–31, 2014; New Orleans, Louisiana
Session TO5: Warm Dense Matter |
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Chair: Gianluca Gregori, University of Oxford, UK Room: Galerie 2 |
Thursday, October 30, 2014 9:30AM - 9:42AM |
TO5.00001: Results from an Orion proton heating experiment for Warm Dense Matter studies Peter Allan, Steven James, Colin Brown, Lauren Hobbs, Matthew Hill, David Hoarty, Hui Chen, Andy Hazi The properties of warm dense matter covering densities and temperatures in the ranges 0.1-10x solid and 1-100eV, fall between ideal plasma and condensed matter theories. Studies have highlighted uncertainties in EoS predictions using methods based on the Thomas-Fermi and ion-cell models. In particular, such models predict large departures from ideal gas behaviour for low Z material at low densities and temperatures. In an extension of previous work, material has been isochorically heated using short-pulse laser-generated proton beams. Here, the method of Foord et al. was used toinfer isentropes oflow Z materials and provide data to validate model predictions. Earlier measurements were limited by the eV backlighterenergy to relatively low densities and pressures below 1.5Mbar, and were conducted in cylindrical geometry. More recent experiments performed at the Orion laser use a parabolic crystal imaging system in order to measure to higher pressures by probing planar expansion of aluminium foils at 1.8keV. The imaging system is described and results are presented showing a spatial resolution of 6um, which was then streaked to give temporal resolution of 10ps. Preliminary analysis of the foil expansion indicates a peak temperature of 30eV. The proton and ion spectra used to heat the sample were measured by a magnetic spectrometer and a Thomson parabola. These results are presented and the effect on the measured expansion discussed. Plans for future measurements are discussed in the light of results obtained so far. [Preview Abstract] |
Thursday, October 30, 2014 9:42AM - 9:54AM |
TO5.00002: Equation Of State Measurements of Warm Dense Copper Heated By Laser Accelerated Proton Beams Gilliss Dyer, Samuel Feldman, Donghoon Kuk, Craig Wagner, Erhard Gaul, Michael Donovan, Mikael Martinez, Teddy Borger, Michael Spinks, Sheng Jiang, Franki Aymond, Kramer Akli, Todd Ditmire We report equation of state (EOS) measurements of solid density transition metals heated to temperatures of 1 to 50 eV by laser accelerated pulsed proton beams. Matter at these densities and temperatures, referred to as warm dense matter (WDM), will exhibit long-range coupling, partial ionization and thermal energies comparable to the Fermi energy, making theoretical predictions of state properties very challenging. Mbar pressures likewise make such states difficult to study in the lab. In this work we use a terawatt or petawatt laser to accelerate MeV protons from a source foil, which then heat an adjacent sample foil. We probe the sample foil on a picosecond timescale using streaked optical pyrometery, time resolved interferometry, and XUV imaging. Previously we and various other groups have applied these techniques to the study of aluminum, one of the best-understood metals from the standpoint of high energy density equations of state. Here we present measurements of Cu, Cr, and Ag. Transition metals such as these are of particular interest because of modeling challenges posed by a partially filled $d-$orbital. [Preview Abstract] |
Thursday, October 30, 2014 9:54AM - 10:06AM |
TO5.00003: First Results from Shocked Foam XRTS on Z E.C. Harding, T. Ao, J.E. Bailey, S.B. Hansen, R.W. Lemke, D.B. Sinars, G.A. Rochau, M.P. Desjarlais, I.C. Smith, J. Reneker, D. Romero, J.F. Benage, I. Golovkin, G. Gregori For the first time, a space-resolved X-ray Thomson Scattering (XRTS) spectra from shocked foam was recorded on the Z machine. The large electrical current produced by Z was used to launch an Al flyer plate to 25 km/s. The impact of the flyer plate on a CH$_{2}$ foam target produced a shocked state with an estimated pressure of 0.75 Mbar, density of 0.47 g/cc, and temperature of 4.3 eV. Both unshocked and shocked portions of the foam target were probed with 6 keV x-rays produced by focusing the Z-Beamlet laser onto a nearby Mn foil. The data comprises of three, spatially distinct spectra that were simultaneously captured with a single spectrometer. These three spectra originated from the following target locations: the laser spot, the unshocked foam, and the shocked foam. The spatial resolution was made possible by the use of a spherically-bent crystal spectrometer. The analysis of this data using the new SPECT3D scattering tool will be presented, as well as future improvements to the experimental hardware. [Preview Abstract] |
Thursday, October 30, 2014 10:06AM - 10:18AM |
TO5.00004: X-ray Absorption Near-Edge Spectroscopy (XANES) of Warm Dense Silicon Dioxide Kyle Engelhorn, Byoung-ick Cho, Ben Barbrel, Vanina Recoules, Stephane Mazevet, Denise Krol, Roger Falcone, Phil Heimann The electronic structure of warm dense silicon dioxide has been investigated by X-ray Absorption Near-Edge Spectroscopy (XANES). An ultrafast optical laser pulse isochorically heats a thin sample. The measured XANES spectra are compared with simulations generated by molecular dynamics and density functional theory. Three new features are observed: a peak below the band gap, absorption within the band gap and a broadening of the absorption edge. From comparison with the calculations, the peak below the band gap provides a measurement of the electron temperature while the spectral features above the O K-edge constrain the ion temperature. Further, the absorption within the gap presents evidence for broken Si-O bonds. The XANES is interpreted as that of a non-equilibrium liquid. [Preview Abstract] |
Thursday, October 30, 2014 10:18AM - 10:30AM |
TO5.00005: Pump-probe studies of radiation induced defects and formation of warm dense matter with pulsed ion beams T. Schenkel, A. Persaud, H. Gua, P.A. Seidl, W.L. Waldron, E.P. Gilson, I.D. Kaganovich, R.C. Davidson, A. Friedman, J.J. Barnard, A.M. Minior We report results from the 2$^{\mathrm{nd}}$ generation Neutralized Drift Compression Experiment at Berkeley Lab. NDCX-II is a pulsed, linear induction accelerator designed to drive thin foils to warm dense matter (WDM) states with peak temperatures of $\sim$ 1 eV using intense, short pulses of 1.2 MeV lithium ions [1]. Tunability of the ion beam enables pump-probe studies of radiation effects in solids as a function of excitation density, from isolated collision cascades to the onset of phase-transitions and WDM. Ion channeling is an in situ diagnostic of damage evolution during ion pulses with a sensitivity of \textless 0.1{\%} displacements per atom [2]. We will report results from damage evolution studies in thin silicon crystals with Li$+$ and K$+$ beams. Detection of channeled ions tracks lattice disorder evolution with a resolution of $\sim$ 1 ns using fast current measurements. We will discuss pump-probe experiments with pulsed ion beams and the development of diagnostics for WDM and multi-scale (ms to fs) access to the materials physics of collision cascades e.g. in fusion reactor materials.\\[4pt] [1] W.L. Waldron, et al., NIM A733,226(2014);\\[0pt] [2] T. Schenkel, et.al., NIM B315, 350(2013) [Preview Abstract] |
Thursday, October 30, 2014 10:30AM - 10:42AM |
TO5.00006: Pseudo-atom molecular dynamics for warm dense plasma mixtures Charles Starrett, Jerome Daligault, Didier Saumon We have developed a new method for calculating the thermodynamics of warm dense mixtures. It combines an average atom-like approach to calculate the electronic structure of one ``pseudo-atom'' with classical molecular dynamics (MD) for the ionic structure. The result is a model in which both electronic and ionic structures of a plasma can be calculated rapidly and the resulting thermodynamics agree excellently with the much more expensive {\it ab initio} DFT-MD methods. We will present an outline of the new method and comparisons with DFT-MD for the ion-ion structure and the thermodynamics. [Preview Abstract] |
Thursday, October 30, 2014 10:42AM - 10:54AM |
TO5.00007: Understanding Generalized Coulomb Logarithms Paul Grabowski The Coulomb logarithm is ubiquitous in plasma physics. For ideal classical plasmas, physically motivated simple formulas suffice, but in warm dense matter, low temperature, or high-density plasmas, these simple prescriptions break down. Recent work [P. Grabowski et al., {\it Phys. Rev. Lett.} {\bf 111}, 215002 (2013)] used classical molecular dynamics to understand how strong correlation should be treated in the electron-ion collision operator of a uniform electron gas. In this talk, I will quantify quantum and inhomogeneous corrections to this operator and present simple Coulomb logarithm formulas that are fit to calculations using convergent kinetic theories. [Preview Abstract] |
Thursday, October 30, 2014 10:54AM - 11:06AM |
TO5.00008: Coupling Strength and Coupling Parameters in One-Component Plasmas Torben Ott, Michael Bonitz, Liam Stanton, Michael Murillo Strong correlations in plasmas are a subject of continuing interest in many experiments. How to quantify the degree of correlations in systems with varying charge state, temperature and screening length is, however, a question of some debate. In this contribution, we propose a one-to-one mapping between the structural properties of a one-component plasma and its coupling strength. This allows one to assess the degree of correlation without knowledge of the charge state or temperature. We furthermore define an effective coupling parameter for screened Coulomb systems which allows one to compare systems with different screening lengths to one another and Coulomb systems. [Preview Abstract] |
Thursday, October 30, 2014 11:06AM - 11:18AM |
TO5.00009: Ab initio thermodynamic quantities of the strongly degenerate electron gas from Configuration Path Integral Monte-Carlo simulations Michael Bonitz, Tim Schoof, Simon Groth Thermodynamic properties of the homogeneous electron gas (HEG) at finite temperatures are of high importance for many systems, including dense quantum plasmas, warm dense matter or plasmas in the interior of compact stars. Recently, Restricted Path Integral Monte-Carlo data for low to moderate densities ($r_s={\bar r}/a_B \ge 1$) have been presented [1], while the high-density regime was not accessible due to the Fermion sign problem. Here we apply the recently developed Configuration PIMC (CPIMC) method [2,3] to the HEG at high densities ($r_s \alt 0.5$) and low to moderate temperatures ($\Theta=k_BT/E_F\leq1$). We demonstrate that CPIMC allows for efficient ab-initio quilibrium calculations of thermodynamic properties of highly degenerate, moderately coupled electrons. It is based on the representation of the N-particle density operator in a basis of antisymmetrized N-particle states [2]) and does not suffer from the Fermion sign problem in the non-interacting limit.\\[4pt] [1] E. W. Brown et al. Phys. Rev. Lett. {\bf 110}, 146405 (2013).\\[0pt] [2] T. Schoof, M. Bonitz, A. Filinov, D. Hochstuhl, and J. Dufty, Contrib. Plasma Phys. {\bf 51}, 687 (2011).\\[0pt] [3] T. Schoof, S. Groth and M. Bonitz, Chapter in: {\it Complex Plasmas}, Springer, 2014 [Preview Abstract] |
Thursday, October 30, 2014 11:18AM - 11:30AM |
TO5.00010: Current status of the HED instrument design at the European XFEL for studying plasma physics M. Nakatsutsumi, K. Appel, I. Thorpe, G. Priebe, A. Pelka, T. Cowan, Th. Tschentscher The High Energy Density Physics (HED) instrument at the European XFEL will provide an unique platform for experiments combining hard x-ray FEL radiation (3 - 24 keV range) and the capability to generate matter under extreme conditions of pressure, temperature or electric field using high energy optical lasers (100 TW Ti-Sapphire and 100 J/ns diode-pumped laser) or pulsed magnets (30 T). Scientific applications will be studies of matter occurring inside exoplanets, of new extreme-pressure phases and solid-density plasmas, and of structural phase transitions of complex solids in high magnetic fields. Following the delivery of the technical design documents, the HED instrument is presently completed with the goal of first x-ray beam in spring 2017. User operation shall start at the end of 2017. The talk includes a presentation of the current HED instrument design as following from specific experiment requirements, which will be discussed. [Preview Abstract] |
Thursday, October 30, 2014 11:30AM - 11:42AM |
TO5.00011: The LCLS Matter under Extreme Conditions Instrument Philip Heimann, Hae Ja Lee, Bob Nagler, Eric Galtier, Eduardo Granados, Brice Arnold, Zhou Xing The LCLS MEC instrument is comprised of x-ray optics and diagnostics, a large target chamber and nanosecond and femtosecond laser systems. The x-ray focusing is accomplished by Be lenses. An upgrade of the femtosecond laser system is underway first to an energy of 1 J and then to 7 J. Diagnostics include forward and backward scattering x-ray spectrometers, a VISAR interferometer and area detectors for x-ray diffraction. A multiplexing method, to provide beamtime at two instruments, has been developed by translating a mirror. Examples of scattering, diffraction and imaging experiments at MEC will be presented. [Preview Abstract] |
Thursday, October 30, 2014 11:42AM - 11:54AM |
TO5.00012: X-ray scattering measurements of magnesium at the transition from the condensed matter to the warm dense matter regime Luke Fletcher, Art Pak, Tammy Ma, Tilo Doppner, Benjamin Bachmann, Sebastien LePape, Ulf Zastrau, Bob Nagler, Haeja Lee, Eric Galetier, Maxence Gauthier, Eliseo Gamboa, Michael MacDonald, Mingsheng Wei, Zhijiang Chen, Mianzhen Mo, Benjamin Barbrel, Dominik Kraus, Roger Falcone, Jerry Hastings, Siegfried Glenzer Direct measurements of the strength in the ionic structure factor at various scattering angles is important for accurate first-principle calculations of material properties in the high pressure and temperature phase. In this study, spectrally resolved XRTS measurements in combination with proof-of-principle, single shot 2D angularly resolved x-ray scattering measurements of changes in the solid-state structure and the ion-ion correlation peak for both single and double (counter-propagating) shocks have been observed in Mg foils. The 527 nm, 2 GW laser system available at the MEC station of the LCLS facility has been used to compress magnesium foils using laser-driven shocks. In our study, 25 \textunderscore m and 50 \textunderscore m thick Mg targets were compressed 2x and 3x the solid density respectively using 3 ns pulses with a total laser energy of 6 J per beam. A drive intensity of 4x10$^{14}$ W/cm$^{2\, }$on each irradiated surface was used to generate high pressure shock waves into the sample while 8 keV x-rays from the LCLS were used to probe the compressed targets for both single and double shocked geometries. [Preview Abstract] |
Thursday, October 30, 2014 11:54AM - 12:06PM |
TO5.00013: Free-electron x-ray laser measurements of collisional-damped plasmons in isochorically heated warm dense matter Philipp Sperling, Hae-Ja Lee, Eliseo Gamboa, Heidi Reinholz, Gerd Roepke, Ulf Zastrau, Luke Fletcher, Siegfried Glenzer Collisional-damped plasmons were obtained in highly-spectrally resolved measurements of isochorically heated solid aluminum providing for the first time the determination of electron-electron and strong electron-ion collisions. $8$~keV x-rays from the Linac Coherent Light Source have been focused to micrometer diameter focal spots heating solid aluminum foils to temperatures up to $7$~eV. The forward scattering spectra show plasmons that directly determine the density and temperature from the plasmon frequency shift and from the detailed balance relation indicating a warm dense matter state with large ion coupling parameters of up to $40$. These experiments show a non-quadratic plasmon dispersion relation shifted to lower plasmon energy shifts at wave numbers of $0.5$~{\AA} $ < k < 2$~{\AA} not predictable by dispersion relations like the Gross-Bohm relation and the Born-Mermin approximation. Therefore, the measured collisional-damped plasmons indicate collisions beyond the Born approximation and have been described successfully by taking into to account electron-electron collisions as well as strong electron-ion collisions. In this talk, we will discuss the first measurement of strong collisions affecting strong collisions in the electron-ion collision model and conductivity. [Preview Abstract] |
Thursday, October 30, 2014 12:06PM - 12:18PM |
TO5.00014: Investigation of the melting of shock compressed Iron with XANES technique at LCLS A. Ravasio, M. Harmand, A. Denoeud, A. Benuzzi-Mounaix, M. Koenig, T. Vinci, S. Mazevet, R. Musella, F. Guyot, G. Morard, F. Dorchies, C. Fourment, J. Gaudin, Y. Feng, D. Zhu, H.J. Lee, B. Nagler, E.C. Galtier, N. Ozaki, K. Miyanishi, S. Toleikis, J. Bouchet, V. Recoules, M. Nakatsutsumi, U. Zastrau X-ray Absorption Near Edge Spectroscopy is a powerful technique of both the electronic structure and the atomic short-range order in various media, from molecules to condensed matter. In a recent experiment performed at LCLS-MEC, we have applied this technique to study the melting of Iron under shock compression. An accurate knowledge of its properties at high pressures and temperatures is indeed crucial for geophysics and planetary science. In particular, detailed information on melting curves and solid phases are required to anchor the Earth's thermal profile and assess the solid or liquid nature of exoplanets' cores. Here we will present the obtained results and discuss how XANES data unambiguously evidenced the melting of iron on the high pressure Hugoniot. [Preview Abstract] |
Thursday, October 30, 2014 12:18PM - 12:30PM |
TO5.00015: Electron dynamics in WDM with x-ray pump/x-ray probe at LCLS Benjamin Barbrel, Roger Falcone, Phil Heimann, Siegfried Glenzer, Alessandra Ravasio, Eric Galtier, Kyle Engelhorn, Hyun-Kyung Chung, Giulio Monaco, Alison Saunders, Luke Fletcher, Jerome Hastings, Ulf Zastrau, Mac MacDonald, Will Schumaker, Maxence Gautier, Hae Ja Lee, Bob Nagler, Eliseo Gamboa Recent machine developments at LCLS have led to the capability for the FEL to deliver two x-ray pulses separated both in time and photon energy. This enables x-ray pump/x-ray probe experiments to be performed to study the ultrafast dynamics of electrons in warm dense matter (WDM) plasmas. Such experiments open a window over the first tens of femtoseconds of the time evolution of non-equilibrium electronic distribution in dense plasmas. We recently conducted an LCLS-MEC experiment in which thin metallic foils where irradiated with two x-ray pulses. The first x-ray pulse isochorically heats up the material, and the second one probes the electronics properties of the sample in the first 100fs of its evolution via x-ray Thomson scattering. In this presentation I will discuss the first results of this experiments as well as the potential of x-ray pump/x-ray probe experiments for WDM science. [Preview Abstract] |
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