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 NM10: Mini-Conference: Frontier HED Science Enabled by Advanced Light Sources II |
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Chair: Thomas Cowan, Institute of Radiation Physics, Germany Room: Governor's Square 17 |
Wednesday, November 13, 2013 9:30AM - 9:42AM |
NM10.00001: Nonequilibrium electron dynamics in matter irradiated by short and intense x-ray pulses Stefan Hau-Riege X-ray free-electron lasers (XFELs) provide intense fs x-ray pulses that allow isochoric heating of solid-density matter. The large x-ray penetration depth enables uniform excitation of qualitatively thicker samples than, for example, heating by optical lasers. The primary x-ray absorption process is inner-shell photoionization, leading to the release of high-energy photoelectrons. The core-excited ions relax through fluorescence and Auger decay. The photo- and Auger-electrons equilibrate with the low-energy electrons through a cascade of inelastic scattering events. It is expected that the pulse length of XFELs may be so short that the electron system is highly nonthermal during and right after the pulse, and that a large fraction of the absorbed x-ray energy resides with the fast photo- and Auger-electrons. This leads to nonequilibrium ionization states and calls standard equilibrium models to describe the effects of the plasma environment on the atomic states into question, which, in turn, has important implications for designing and analyzing plasma experiments at XFELs. In this presentation we will review the mechanisms and time scales for the distribution of energy among the electrons as a function of pulse energy, pulse length, and sample geometry. [Preview Abstract] |
Wednesday, November 13, 2013 9:42AM - 9:54AM |
NM10.00002: Ionization Potential Depression in Strongly Coupled Plasmas Justin Wark, Orlando Ciricosta, Sam Vinko, Basil Crowley The focusing of the output of 4$^{\rm th}$ generation femtosecond X-ray sources to ultra-high intensities has enabled the creation of hot (close to 200-eV) aluminum plasmas at exactly solid density. [1] Tuning of the X-ray FEL energy that produces the plasma, and observation of the subsequent K-$\alpha$ fluorescence from the highly charged ions allows direct measurements of the K-edges, and hence ionization potential depression (IPD). [2] The results of these experiments show far higher depressions than those predicted by the frequently-used Stewart-Pyatt model, but appear to be in contradiction with laser-plasma experimental data at similar densities, but with hotter, less strongly-coupled plasmas. [3] We present here new calculations of the IPD, both {\it ab initio} and analytic, and discuss the relevance of the coupling parameter to the IPD. We further explore what constitutes our understanding of the physics of IPD, and how it should be modelled.\\[4pt] [1] S. Vinko {\it et al.}, Nature {\bf 482}, 59 (2012).\\[0pt] [2] O. Ciricosta {\it et al.}, Phys. Rev. Lett. {\bf 109}, 065002 (2012).\\[0pt] [3] D. Hoarty {\it et al.}, Phys. Rev. Lett. {\bf 110}, 265003 (2013). [Preview Abstract] |
Wednesday, November 13, 2013 9:54AM - 10:06AM |
NM10.00003: Frontier experimental research at LCLS/MEC Hae Ja Lee Since the advent of a new technique using the Linac Coherent Light Source (LCLS), an x-ray free electron laser source, MEC instrument offers new experimental-platforms combining LCLS with high power optical lasers for high energy density science. 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$2 micron at MEC. The research areas that MEC instrument will address include equation of state under extreme conditions, behavior of materials under high-pressure, and phenomena of shock compressed matter. In this talk, we present the details of the MEC instrument and highlight several experiments. [Preview Abstract] |
Wednesday, November 13, 2013 10:06AM - 10:18AM |
NM10.00004: Frontier WDM experimental research on advanced light sources Patrick Renaudin, Patrick Audebert Investigations of matter properties in extreme conditions have attracted numerous experimental and theoretical studies motivated by the wide range of application where these conditions are found. An accurate description of the regime of interest here, i.e., warm dense matter (WDM), is of importance for the study of planetary objects, inertial confinement fusion or basic properties of heated solids. In the temperature and density ranges of several eV and near solid density, matter is difficult to describe theoretically as WDM is strongly coupled, partially disordered and degenerate. This provides the motivation to experimentally create and accurately diagnose matter in this regime. Generating a uniform high energy density sample in laboratory requires: (i) transfer of energy to the matter in a time short compared to its hydrodynamic expansion duration; (ii) optimized heating efficiency to reach high temperatures (several eVs); and, (iii) creating a temperature and density gradient-free heated material for extracting accurate information on its properties. Due to short duration (100 fs), high brightness (few 10$^{12}$ photons/pulse) and large penetration depth (up to tens of $\mu $m) hard x-ray free-electron laser opens unique opportunity to obtain a deeper insight into the formation and nature of WDM. [Preview Abstract] |
Wednesday, November 13, 2013 10:18AM - 10:30AM |
NM10.00005: X-ray scattering measurements of the structure of strongly coupled plasmas at x-ray free electron lasers Paul Neumayer, Tilo D\"oppner, Luke Fletcher, Eric Galtier, Dirk Gericke, Siegfried Glenzer, Gianluca Gregori, Nicholas Hartley, Dimitri Khaghani, Hae Ja Lee, Tammy Ma, Bob Nagler, Art Pak, Ronald Redmer, Ulf Zastrau Laser-plasma x-ray sources have been an indispensable probe to diagnose and characterize plasmas in the warm-dense matter regime. The latest generation of bright x-ray free-electron lasers now enables such diagnostic techniques to be implemented at FEL facilities. Even more, FEL parameters, such as collimation, pulse duration, focusability, bandwidth, or repetition rate, are far superior compared to laser-driven sources, enabling measurements of unprecedented resolution and accuracy. As an example, we present measurements of the static structure factor in high energy density matter. Angle-resolved x-ray scattering was performed at the Matter at Extreme Conditions (MEC) instrument at the Linac Coherent Light Source (LCLS). Strongly coupled warm-dense aluminium was produced by laser shock compression. Covering a wide range of scattering angles with unprecedented angular resolution the correlation peak of the ion-ion structure factor could be well resolved. The exceptional collimation of the LCLS beam enabled measurements at small scattering angles, thus approaching the long wavelength limit. [Preview Abstract] |
Wednesday, November 13, 2013 10:30AM - 10:42AM |
NM10.00006: Ion Transport in Solid and Warm Dense Targets F.N. Beg, B. Qiao, C. McGuffey, J. Kim, M.-S. Wei, R.B. Stephens High intensity proton/ion beam transport and energy deposition in solids and Warm Dense Matter (WDM) is not well understood even though it is important to several applications including heavy ion fusion and laser-produced ion beam driven fast ignition fusion. Ion stopping power models have been developed for the relevant regimes but thus far lack experimental validation. One of the challenges to understand ion beam transport and energy deposition in solid density cold matter and WDM is self-consistently accounting for the matter's response to the intense beam (heating, ionization, strong return currents and self-generated electric and magnetic fields) and in turn the beam's response to the matter (temperature gradients, current-driven fields). In this presentation, ion stopping-power module implemented in the hybrid particle-in-cell code LSP and its applications in modeling intense proton beam transport and heating in solids and WDM targets will be discussed. In addition, relevance of this work to the Matter in Extreme Condition end station with the unique capability of the combined high flux hard x-ray pulse and the high intensity short pulse optical laser at the Linac Coherent Light Source (LCLS) will be presented. [Preview Abstract] |
Wednesday, November 13, 2013 10:42AM - 10:54AM |
NM10.00007: The Electronic Structure of Warm Dense Silicon Dioxide Philip Heimann, Kyle Engelhorn, Byoung-ick Cho, Vanina Recoules, Stephane Mazevet, Denise Krol, Roger Falcone Silicon dioxide is an important material for optics as well as for the earth's crust and mantle. We present an x-ray absorption spectroscopic study of warm dense silicon dioxide performed at the Advanced Light Source. A femtosecond optical pulse is used to isochorically heat the silicon dioxide sample. A custom x-ray streak camera is employed to detect the oxygen K edge x-ray absorption spectrum with 2 ps time resolution. The heated silicon dioxide spectra are compared with calculations based on molecular dynamics and density functional theory, which determine the electronic density of states and transition matrix elements at elevated temperatures. Three new features are observed in the high temperature absorption spectra: a peak below the band gap, absorption within the gap and a broadening of the absorption edge. All three of these features are present in the calculated spectra as well. The magnitude of the absorption peak below the band gap is sensitive to the electronic temperature. The broadening of the absorption edge is only observed in the simulations with high ionic temperature. [Preview Abstract] |
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