Showing papers by "Siegfried Glenzer published in 2019"

Characterizing the ionization potential depression in dense carbon plasmas with high-precision spectrally resolved x-ray scattering

Abstract: Author(s): Kraus, D; Bachmann, B; Barbrel, B; Falcone, R W; Fletcher, L B; Frydrych, S; Gamboa, E J; Gauthier, M; Gericke, D O; Glenzer, S H; Gode, S; Granados, E; Hartley, N J; Helfrich, J; Lee, H J; Nagler, B; Ravasio, A; Schumaker, W; Vorberger, J; Doppner, T

Terahertz-based subfemtosecond metrology of relativistic electron beams

Abstract: We demonstrate single-shot temporal characterization of relativistic electron bunches using single-cycle terahertz (THz) field streaking. A transverse deflecting structure consisting of a metal slit enables efficient coupling of the THz field and electron bunch. The intrinsically stable carrier envelope phase and strong gradient of the THz pulses allow simultaneous, self-calibrated determination of the time-of-arrival with subfemtosecond precision and bunch duration with single-femtosecond precision, respectively, opening up new opportunities for ultrafast electron diffraction as well as accelerator technologies in general.

Evidence for Crystalline Structure in Dynamically-Compressed Polyethylene up to 200 GPa.

Abstract: We investigated the high-pressure behavior of polyethylene (CH2) by probing dynamically-compressed samples with X-ray diffraction. At pressures up to 200 GPa, comparable to those present inside icy giant planets (Uranus, Neptune), shock-compressed polyethylene retains a polymer crystal structure, from which we infer the presence of significant covalent bonding. The A2/m structure which we observe has previously been seen at significantly lower pressures, and the equation of state measured agrees with our findings. This result appears to contrast with recent data from shock-compressed polystyrene (CH) at higher temperatures, which demonstrated demixing and recrystallization into a diamond lattice, implying the breaking of the original chemical bonds. As such chemical processes have significant implications for the structure and energy transfer within ice giants, our results highlight the need for a deeper understanding of the chemistry of high pressure hydrocarbons, and the importance of better constraining planetary temperature profiles.

Measurements of the momentum-dependence of plasmonic excitations in matter around 1 Mbar using an X-ray free electron laser

Abstract: We present measurements of the plasmon shift in shock-compressed matter as a function of momentum transfer beyond the Fermi wavevector using an X-ray Free Electron Laser. We eliminate the elastically scattered signal retaining only the inelastic plasmon signal. Our plasmon dispersion agrees with both the random phase approximation (RPA) and static Local Field Corrections (sLFC) for an electron gas at both zero and finite temperature. Further, we find the inclusion of electron-ion collisions through the Born-Mermin Approximation (BMA) to have no effect. Whilst we cannot distinguish between RPA and sLFC within our error bars, our data suggest that dynamic effects should be included for LFC and provide a route forward for higher resolution future measurements.

Visualization of ultrafast melting initiated from radiation-driven defects in solids.

Abstract: Materials exposed to extreme radiation environments such as fusion reactors or deep spaces accumulate substantial defect populations that alter their properties and subsequently the melting behavior. The quantitative characterization requires visualization with femtosecond temporal resolution on the atomic-scale length through measurements of the pair correlation function. Here, we demonstrate experimentally that electron diffraction at relativistic energies opens a new approach for studies of melting kinetics. Our measurements in radiation-damaged tungsten show that the tungsten target subjected to 10 displacements per atom of damage undergoes a melting transition below the melting temperature. Two-temperature molecular dynamics simulations reveal the crucial role of defect clusters, particularly nanovoids, in driving the ultrafast melting process observed on the time scale of less than 10 ps. These results provide new atomic-level insights into the ultrafast melting processes of materials in extreme environments.

High-Pressure Melt Curve and Phase Diagram of Lithium.

Abstract: We investigate the phase diagram of lithium at temperatures of 200 to 400 K, to pressures over 100 GPa using x-ray diffraction in diamond anvil cells, covering the region in which the melting curve is disputed. To overcome degradation of the diamond anvils by dense lithium we utilize a rapid compression scheme taking advantage of the high flux available at modern synchrotrons. Our results show the $hR1$ and $cI16$ phases to be stable to higher temperature than previously reported. The melting minima of lithium is found to be close to room temperature between 40 and 60 GPa, below which the solid is crystalline. Analysis of the stability fields of the $cI16$ and $oC88$ phases suggest the existence of a triple point between these and an undetermined solid phase at 60 GPa between 220 and 255 K.

All-optical structuring of laser-driven proton beam profiles

Abstract: Extreme field gradients intrinsic to relativistic laser-interactions with thin solid targets enable compact MeV proton accelerators with unique bunch characteristics. Yet, direct control of the proton beam profile is usually not possible. Here we present a readily applicable all-optical approach to imprint detailed spatial information from the driving laser pulse onto the proton bunch. In a series of experiments, counter-intuitively, the spatial profile of the energetic proton bunch was found to exhibit identical structures as the fraction of the laser pulse passing around a target of limited size. Such information transfer between the laser pulse and the naturally delayed proton bunch is attributed to the formation of quasi-static electric fields in the beam path by ionization of residual gas. Essentially acting as a programmable memory, these fields provide access to a higher level of proton beam manipulation.Shaping particle beams generated from laser-plasma accelerators is challenging. Here the authors demonstrate an all-optical method to structure the accelerated proton beam by modulating and imprinting the spatial laser profile onto the proton beam.

Improved large-energy-range magnetic electron-positron spectrometer for experiments with the Texas Petawatt Laser

Abstract: We present the design, construction, and first use of a magnetic electron-positron spectrometer at the Texas Petawatt Laser facility. The Global Spectrometer for Positron and Electron Characterization (GSPEC) is capable of detecting electrons and positrons over a large energy range from 3–150 MeV and has been designed to diagnose the electrons and positrons accelerated by high-intensity laser interactions with over-critical targets.

Comment on “Isochoric, isobaric, and ultrafast conductivities of aluminum, lithium, and carbon in the warm dense matter regime”

Abstract: Dharma-wardana et al. [M. W. C. Dharma-wardana et al., Phys. Rev. E 96, 053206 (2017)2470-004510.1103/PhysRevE.96.053206] recently calculated dynamic electrical conductivities for warm dense matter as well as for nonequilibrium two-temperature states termed "ultrafast matter" (UFM) [M. W. C. Dharma-wardana, Phys. Rev. E 93, 063205 (2016)2470-004510.1103/PhysRevE.93.063205]. In this Comment we present two evident reasons why these UFM calculations are neither suited to calculate dynamic conductivities nor x-ray Thomson scattering spectra in isochorically heated warm dense aluminum. First, the ion-ion structure factor, a major input into the conductivity and scattering spectra calculations, deviates strongly from that of isochorically heated aluminum. Second, the dynamic conductivity does not show a non-Drude behavior which is an essential prerequisite for a correct description of the absorption behavior in aluminum. Additionally, we clarify misinterpretations by Dharma-wardana et al. concerning the conductivity measurements of Gathers [G. R. Gathers, Int. J. Thermophys. 4, 209 (1983)IJTHDY0195-928X10.1007/BF00502353].

Laser-plasma interactions enabled by emerging technologies

Abstract: Author(s): Palastro, JP; Albert, F; Albright, B; Jr, TM Antonsen; Arefiev, A; Bates, J; Berger, R; Bromage, J; Campbell, M; Chapman, T; Chowdhury, E; Colaitis, A; Dorrer, C; Esarey, E; Fiuza, F; Fisch, N; Follett, R; Froula, D; Glenzer, S; Gordon, D; Haberberger, D; Hegelich, BM; Jones, T; Kaganovich, D; Krushelnick, K; Michel, P; Milchberg, H; Moloney, J; Mori, W; Myatt, J; Nilson, P; Obenschain, S; Peebles, J; Penano, J; Richardson, M; Rinderknecht, H; Rocca, J; Schmitt, A; Schroeder, C; Shaw, J; Silva, L; Strozzi, D; Suckewer, S; Thomas, A; Tsung, F; Turnbull, D; Umstadter, D; Vieira, J; Weaver, J; Wei, M; Wilks, S; Willingale, L; Yin, L; Zuegel, J | Abstract: An overview from the past and an outlook for the future of fundamental laser-plasma interactions research enabled by emerging laser systems.

Probing near-solid density plasmas using soft x-ray scattering

Abstract: X-ray scattering using highly brilliant x-ray free-electron laser (FEL) radiation provides new access to probe free-electron density, temperature and ionization in near-solid density plasmas. First experiments at the soft x-ray FEL FLASH at DESY, Hamburg, show the capabilities of this technique. The ultrashort FEL pulses in particular can probe equilibration phenomena occurring after excitation of the plasma using ultrashort optical laser pumping. We have investigated liquid hydrogen and find that the interaction of very intense soft x-ray FEL radiation alone heats the sample volume. As the plasma establishes, photons from the same pulse undergo scattering, thus probing the transient, warm dense matter state. We find a free-electron density of (2.6 ± 0.2) × 1020 cm−3 and an electron temperature of 14 ± 3.5 eV. In pump–probe experiments, using intense optical laser pulses to generate more extreme states of matter, this interaction of the probe pulse has to be considered in the interpretation of scattering data. In this paper, we present details of the experimental setup at FLASH and the diagnostic methods used to quantitatively analyse the data.

Equations of state for ruthenium and rhodium

Abstract: Ru and Rh are interesting cases for comparing equations of state (EOS), because most general purpose EOS are semi-empirical, relying heavily on shock data, and none has been reported for Ru. EOS were calculated for both elements using all-electron atom-in-jellium theory, and cold compression curves were calculated for the common crystal types using the multi-ion pseudopotential approach. Previous EOS constructed for these elements used Thomas-Fermi (TF) theory for the electronic behavior at high temperatures, which neglects electronic shell structure; the atom-in-jellium EOS exhibited pronounced features from the excitation of successive electron shells. Otherwise, the EOS matched surprisingly well, especially considering the lack of experimental data for Ru. The TF-based EOS for Ru may however be inaccurate in the multi-terapascal range needed for some high energy density experiments. The multi-ion calculations predicted that the hexagonal close-packed phase of Ru remains stable to at least 2.5 TPa and possibly 10 TPa, and that its c/a should gradually increase to the ideal value. A method was devised to estimate the variation in Debye temperature from the cold curve, and thus estimate the ion-thermal EOS without requiring relatively expensive dynamical force calculations, in a form convenient for adjusting EOS or phase boundaries. The Debye temperature estimated in this way was similar to the result from atom-in-jellium calculations. We also predict the high-pressure melt loci of both elements.

Generation of ultrathin free-flowing liquid sheets

Abstract: The physics and chemistry of liquid solutions play a central role in science, and our understanding of life on Earth. Unfortunately, key tools for interrogating aqueous systems, such as infrared and soft X-ray spectroscopy, cannot readily be applied because of strong absorption in water. Here we use gas dynamic forces to generate free-flowing, sub-micron, liquid sheets which are 2 orders of magnitude thinner than anything previously reported. Optical, infrared and X-ray spectroscopies are used to characterize the sheets, which are found to be tunable in thickness from over 1 micron down to less than 20 nanometers, which corresponds to fewer than 100 water molecules thick. At this thickness, aqueous sheets can readily transmit photons across the spectrum, leading to potentially transformative applications in infrared, X-ray, electron spectroscopies and beyond. The ultrathin sheets are stable for days in vacuum, and we demonstrate their use at free-electron laser and synchrotron light sources.