Showing 1–10 of 10 results for author: Appel, K

Structural evolution of iron oxides melts at Earth's outer-core pressures

Authors: Céline Crépisson, Mila Fitzgerald, Domenic Peake, Patrick Heighway, Thomas Stevens, Adrien Descamps, David McGonegle, Alexis Amouretti, Karim K. Alaa El-Din, Michal Andrzejewski, Sam Azadi, Erik Brambrink, Carolina Camarda, David A. Chin, Samuele Di Dio Cafiso, Ana Coutinho Dutra, Hauke Höppner, Kohdai Yamamoto, Zuzana Konôpkovà, Motoaki Nakatsutsumi, Norimasa Ozaki, Danae N. Polsin, Jan-Patrick Schwinkendorf, Georgiy Shoulga, Cornelius Strohm , et al. (10 additional authors not shown)

Abstract: Oxygen and other light elements comprise up to 5 wt% of the Earth's outer-core, and may significantly influence its physical properties and the operation of the geodynamo. Here we report in situ x-ray diffraction measurements of Fe, Fe + 4.5 FeO (atomic proportion), and Fe2O3 melts at 177-438 GPa, achieved using laser-driven shock compression at an x-ray free-electron laser. The melts exhibit Fe-O… ▽ More Oxygen and other light elements comprise up to 5 wt% of the Earth's outer-core, and may significantly influence its physical properties and the operation of the geodynamo. Here we report in situ x-ray diffraction measurements of Fe, Fe + 4.5 FeO (atomic proportion), and Fe2O3 melts at 177-438 GPa, achieved using laser-driven shock compression at an x-ray free-electron laser. The melts exhibit Fe-O coordination numbers between 4.0(0.4) and 4.5(0.4), indicating predominantly four-fold coordination environments. These coordination states are significantly smaller than those of Fe-bearing lower-mantle phases such as bridgmanite and ferropericlase. Shorter Fe-Fe interatomic distances in compressed iron oxide melts drive the denser packing relative to ambient melts, while the structural differences between Fe + 4.5 FeO and Fe2O3 melts under shock indicate that the oxidation state modulates oxygen solubility in liquid Fe. At around 177 GPa (380 km below the core-mantle boundary), Fe2O3 melts exhibit higher Fe-O coordination, suggesting that local variations in oxygen content could contribute to the stratification in the uppermost outer-core inferred from seismological and geomagnetic observations. △ Less

Submitted 25 November, 2025; originally announced November 2025.

Comments: 14 pages, 7 figures, under review

Experimental validation of electron correlation models in warm dense matter

Authors: Dmitrii S. Bespalov, Ulf Zastrau, Zhandos A. Moldabekov, Thomas Gawne, Tobias Dornheim, Moyassar Meshhal, Alexis Amouretti, Michal Andrzejewski, Karen Appel, Carsten Baehtz, Erik Brambrink, Khachiwan Buakor, Carolina Camarda, David Chin, Gilbert Collins, Celine Crepisson, Adrien Descamps, Jon Eggert, Luke Fletcher, Alessandro Forte, Gianluca Gregori, Marion Harmand, Oliver S. Humphries, Hauke Hoeppner, Jonas Kuhlke , et al. (37 additional authors not shown)

Abstract: We report X-ray Thomson scattering measurements of warm dense aluminium at densities 3.75-4.5 g/cm$^3$ and a temperature of approximately 0.6 eV, performed at the HED-HiBEF instrument of the European XFEL using the DiPOLE-100X drive laser. By probing plasmon dispersion across momentum transfers $k$ = 0.99-2.57 Angstrom$^{-1}$ with high statistical fidelity, we directly test competing theories of e… ▽ More We report X-ray Thomson scattering measurements of warm dense aluminium at densities 3.75-4.5 g/cm$^3$ and a temperature of approximately 0.6 eV, performed at the HED-HiBEF instrument of the European XFEL using the DiPOLE-100X drive laser. By probing plasmon dispersion across momentum transfers $k$ = 0.99-2.57 Angstrom$^{-1}$ with high statistical fidelity, we directly test competing theories of electron dynamics under extreme conditions. Time-dependent density functional theory (TDDFT) reproduces both the observed plasmon energies and spectral shapes across the full $k$ range, whereas the random phase approximation (RPA) and static local-field-correction (LFC) models systematically overestimate the plasmon frequency, even for aluminium (a canonical uniform electron gas metal). Considering electron localisation around ions and the loss of crystalline symmetry due to liquid-state disorder, our measurements provide direct evidence that simple uniform electron gas models fail in warm dense matter and establish TDDFT as a reliable approach for electronic correlations in this regime. △ Less

Submitted 12 September, 2025; originally announced September 2025.

Comments: 25 pages, 12 figures

Observation of Body-Centered Cubic Iron above 200 Gigapascals

Authors: Zuzana Konopkova, Eric Edmund, Orianna B Ball, Agnes Dewaele, Helene Ginestet, Rachel J Husband, Nicolas Jaisle, Cornelius Strohm, Madden S Anae, Daniele Antonangeli, Karen Appel, Marzena Baron, Silvia Boccato, Khachiwan Buakor, Julien Chantel, Hyunchae Cynn, Anand P Dwivedi, Lars Ehm, Konstantin Glazyrin, Heinz Graafsma, Egor Koemets, Torsten Laurus, Hauke Marquardt, Bernhard Massani, James D McHardy , et al. (12 additional authors not shown)

Abstract: The crystallographic structure of iron under extreme conditions is a key benchmark for cutting-edge experimental and numerical methods. Moreover, it plays a crucial role in understanding planetary cores, as it significantly influences the interpretation of observational data and, consequently, insights into their internal structure and dynamics. However, even the structure of pure solid iron under… ▽ More The crystallographic structure of iron under extreme conditions is a key benchmark for cutting-edge experimental and numerical methods. Moreover, it plays a crucial role in understanding planetary cores, as it significantly influences the interpretation of observational data and, consequently, insights into their internal structure and dynamics. However, even the structure of pure solid iron under the Earth's core conditions remains uncertain, with the commonly expected hexagonal close-packed structure energetically competitive with various cubic lattices. In this study, iron was compressed in a diamond anvil cell to above 200 GPa, and dynamically probed near the melting point using MHz frequency X-ray pulses from the European X-ray Free Electron Laser. The emergence of an additional diffraction line at high temperatures suggests the formation of an entropically stabilized bcc structure. Rapid heating and cooling cycles captured intermediate phases, offering new insights into iron's phase transformation paths. The appearance of the bcc phase near melting at extreme pressures challenges current understanding of the iron phase diagram under Earth's core conditions. △ Less

Submitted 21 May, 2025; originally announced May 2025.

High-Quality Ultra-Fast Total Scattering and Pair Distribution Function Data using an X-ray Free Electron Laser

Authors: Adam F. Sapnik, Philip A. Chater, Dean S. Keeble, John S. O. Evans, Federica Bertolotti, Antonietta Guagliardi, Lise J. Støckler, Elodie A. Harbourne, Anders B. Borup, Rebecca S. Silberg, Adrien Descamps, Clemens Prescher, Benjamin D. Klee, Axel Phelipeau, Imran Ullah, Kárel G. Medina, Tobias A. Bird, Viktoria Kaznelson, William Lynn, Andrew L. Goodwin, Bo B. Iversen, Celine Crepisson, Emil S. Bozin, Kirsten M. Ø. Jensen, Emma E. McBride , et al. (26 additional authors not shown)

Abstract: High-quality total scattering data, a key tool for understanding atomic-scale structure in disordered materials, require stable instrumentation and access to high momentum transfers. This is now routine at dedicated synchrotron instrumentation using high-energy X-ray beams, but it is very challenging to measure a total scattering dataset in less than a few microseconds. This limits their effective… ▽ More High-quality total scattering data, a key tool for understanding atomic-scale structure in disordered materials, require stable instrumentation and access to high momentum transfers. This is now routine at dedicated synchrotron instrumentation using high-energy X-ray beams, but it is very challenging to measure a total scattering dataset in less than a few microseconds. This limits their effectiveness for capturing structural changes that occur at the much faster timescales of atomic motion. Current X-ray free-electron lasers (XFELs) provide femtosecond-pulsed X-ray beams with maximum energies of approximately 24 keV, giving the potential to measure total scattering and the attendant pair distribution functions (PDFs) on femtosecond timescales. Here, we show that this potential has been realised using the HED scientific instrument at the European XFEL and present normalised total scattering data for 0.35 Å-1 < Q < 16.6 Å-1 and their PDFs from a broad spectrum of materials, including crystalline, nanocrystalline and amorphous solids, liquids, and clusters in solution. We analyse the data using a variety of methods, including Rietveld refinement, small-box PDF refinement, joint reciprocal-real space refinement, cluster refinement, and Debye scattering analysis. The resolution function of the setup is also characterised. We conclusively show that high-quality data can be obtained from a single approximately 30 fs XFEL pulse. Our efforts not only significantly increase the existing maximum reported Q-range for an S(Q) measured at an XFEL but also mean that XFELs are now a viable X-ray source for the broad community of people using reciprocal space total scattering and PDF methods in their research. △ Less

Submitted 13 June, 2025; v1 submitted 30 April, 2025; originally announced April 2025.

Strong geometry dependence of the X-ray Thomson Scattering Spectrum in single crystal silicon

Authors: Thomas Gawne, Zhandos A. Moldabekov, Oliver S. Humphries, Karen Appel, Carsten Baehtz, Victorien Bouffetier, Erik Brambrink, Attila Cangi, Celine Crépisson, Sebastian Göde, Zuzana Konôpková, Mikako Makita, Mikhail Mishchenko, Motoaki Nakatsutsumi, Lisa Randolph, Sebastian Schwalbe, Jan Vorberger, Ulf Zastrau, Tobias Dornheim, Thomas R. Preston

Abstract: We report on results from an experiment at the European XFEL where we measured the x-ray Thomson scattering (XRTS) spectrum of single crystal silicon with ultrahigh resolution. Compared to similar previous experiments, we consider a more complex scattering setup, in which the scattering vector changes orientation through the crystal lattice. In doing so, we are able to observe strong geometric dep… ▽ More We report on results from an experiment at the European XFEL where we measured the x-ray Thomson scattering (XRTS) spectrum of single crystal silicon with ultrahigh resolution. Compared to similar previous experiments, we consider a more complex scattering setup, in which the scattering vector changes orientation through the crystal lattice. In doing so, we are able to observe strong geometric dependencies in the inelastic scattering spectrum of silicon at low scattering angles. Furthermore, the high quality of the experimental data allows us to benchmark state-of-the-art TDDFT calculations, and demonstrate TDDFT's ability to accurately predict these geometric dependencies. Finally, we note that this experimental data was collected at a much faster rate than another recently reported dataset using the same setup, demonstrating that ultrahigh resolution XRTS data can be collected in more general experimental scenarios. △ Less

Submitted 31 January, 2025; originally announced January 2025.

Femtosecond temperature measurements of laser-shocked copper deduced from the intensity of the x-ray thermal diffuse scattering

Authors: J. S. Wark, D. J. Peake, T. Stevens, P. G. Heighway, Y. Ping, P. Sterne, B. Albertazzi, S. J. Ali, L. Antonelli, M. R. Armstrong, C. Baehtz, O. B. Ball, S. Banerjee, A. B. Belonoshko, C. A. Bolme, V. Bouffetier, R. Briggs, K. Buakor, T. Butcher, S. Di Dio Cafiso, V. Cerantola, J. Chantel, A. Di Cicco, A. L. Coleman, J. Collier , et al. (100 additional authors not shown)

Abstract: We present 50-fs, single-shot measurements of the x-ray thermal diffuse scattering (TDS) from copper foils that have been shocked via nanosecond laser-ablation up to pressures above 135~GPa. We hence deduce the x-ray Debye-Waller (DW) factor, providing a temperature measurement. The targets were laser-shocked with the DiPOLE 100-X laser at the High Energy Density (HED) endstation of the European X… ▽ More We present 50-fs, single-shot measurements of the x-ray thermal diffuse scattering (TDS) from copper foils that have been shocked via nanosecond laser-ablation up to pressures above 135~GPa. We hence deduce the x-ray Debye-Waller (DW) factor, providing a temperature measurement. The targets were laser-shocked with the DiPOLE 100-X laser at the High Energy Density (HED) endstation of the European X-ray Free-Electron Laser (EuXFEL). Single x-ray pulses, with a photon energy of 18 keV, were scattered from the samples and recorded on Varex detectors. Despite the targets being highly textured (as evinced by large variations in the elastic scattering), and with such texture changing upon compression, the absolute intensity of the azimuthally averaged inelastic TDS between the Bragg peaks is largely insensitive to these changes, and, allowing for both Compton scattering and the low-level scattering from a sacrificial ablator layer, provides a reliable measurement of $T/Θ_D^2$, where $Θ_D$ is the Debye temperature. We compare our results with the predictions of the SESAME 3336 and LEOS 290 equations of state for copper, and find good agreement within experimental errors. We thus demonstrate that single-shot temperature measurements of dynamically compressed materials can be made via thermal diffuse scattering of XFEL radation. △ Less

Submitted 6 January, 2025; originally announced January 2025.

Comments: 17 pages, 9 figures in main article; 10 pages, 5 figures in supplementary material

Formation of high-aspect-ratio nanocavity in LiF crystal using a femtosecond of x-ray FEL pulse

Authors: Sergey S. Makarov, Sergey A. Grigoryev, Vasily V. Zhakhovsky, Petr Chuprov, Tatiana A. Pikuz, Nail A. Inogamov, Victor V. Khokhlov, Yuri V. Petrov, Eugene Perov, Vadim Shepelev, Takehisa Shobu, Aki Tominaga, Ludovic Rapp, Andrei V. Rode, Saulius Juodkazis, Mikako Makita, Motoaki Nakatsutsumi, Thomas R. Preston, Karen Appel, Zuzana Konopkova, Valerio Cerantola, Erik Brambrink, Jan-Patrick Schwinkendorf, István Mohacsi, Vojtech Vozda , et al. (8 additional authors not shown)

Abstract: Sub-picosecond optical laser processing of metals is actively utilized for modification of a heated surface layer. But for deeper modification of different materials a laser in the hard x-ray range is required. Here, we demonstrate that a single 9-keV x-ray pulse from a free-electron laser can form a um-diameter cylindrical cavity with length of ~1 mm in LiF surrounded by shock-transformed materia… ▽ More Sub-picosecond optical laser processing of metals is actively utilized for modification of a heated surface layer. But for deeper modification of different materials a laser in the hard x-ray range is required. Here, we demonstrate that a single 9-keV x-ray pulse from a free-electron laser can form a um-diameter cylindrical cavity with length of ~1 mm in LiF surrounded by shock-transformed material. The plasma-generated shock wave with TPa-level pressure results in damage, melting and polymorphic transformations of any material, including transparent and non-transparent to conventional optical lasers. Moreover, cylindrical shocks can be utilized to obtain a considerable amount of exotic high-pressure polymorphs. Pressure wave propagation in LiF, radial material flow, formation of cracks and voids are analyzed via continuum and atomistic simulations revealing a sequence of processes leading to the final structure with the long cavity. Similar results can be produced with semiconductors and ceramics, which opens a new pathway for development of laser material processing with hard x-ray pulses. △ Less

Submitted 5 September, 2024; originally announced September 2024.

X-ray induced grain boundary formation and grain rotation in Bi2Se3

Authors: Kento Katagiri, Bernard Kozioziemski, Eric Folsom, Sebastian Göde, Yifan Wang, Karen Appel, Darshan Chalise, Philip K. Cook, Jon Eggert, Marylesa Howard, Sungwon Kim, Zuzana Konôpková, Mikako Makita, Motoaki Nakatsutsumi, Martin M. Nielsen, Alexander Pelka, Henning F. Poulsen, Thomas R. Preston, Tharun Reddy, Jan-Patrick Schwinkendorf, Frank Seiboth, Hugh Simons, Bihan Wang, Wenge Yang, Ulf Zastrau , et al. (2 additional authors not shown)

Abstract: Optimizing grain boundary characteristics in polycrystalline materials can improve their properties. Many processing methods have been developed for grain boundary manipulation, including the use of intense radiation in certain applications. In this work, we used X-ray free electron laser pulses to irradiate single-crystalline bismuth selenide (Bi2Se3) and observed grain boundary formation and sub… ▽ More Optimizing grain boundary characteristics in polycrystalline materials can improve their properties. Many processing methods have been developed for grain boundary manipulation, including the use of intense radiation in certain applications. In this work, we used X-ray free electron laser pulses to irradiate single-crystalline bismuth selenide (Bi2Se3) and observed grain boundary formation and subsequent grain rotation in response to the X-ray radiation. Our observations with simultaneous transmission X-ray microscopy and X-ray diffraction demonstrate how intense X- ray radiation can rapidly change size and texture of grains. △ Less

Submitted 26 October, 2024; v1 submitted 12 March, 2024; originally announced March 2024.

Comments: 37 pages, 11 figures including 6 supplemental figures

Ultra-fast yttrium hydride chemistry at high pressures via non-equilibrium states induced by x-ray free electron laser

Authors: Emily Siska, G. Alexander Smith, Sergio Villa-Cortes, Lewis J. Conway, Rachel J. Husband, Joshua Van Cleave, Sylvain Petitgirard, Valerio Cerantola, Karen Appel, Carsten Baehtz, Victorien Bouffetier, Anand Dwiwedi, Sebastian Göde, Taisia Gorkhover, Zuzana Konopkova, Mohammad Hosseini, Stephan Kuschel, Torsten Laurus, Motoaki Nakatsutsumi, Cornelius Strohm, Jolanta Sztuk-Dambietz, Ulf Zastrau, Dean Smith, Keith V. Lawler, Chris J. Pickard , et al. (2 additional authors not shown)

Abstract: Controlling the formation and stoichiometric content of desired phases of materials has become a central interest for the study of a variety of fields, notably high temperature superconductivity under extreme pressures. The further possibility of accessing metastable states by initiating reactions by x-ray triggered mechanisms over ultra-short timescales is enabled with the development of x-ray fr… ▽ More Controlling the formation and stoichiometric content of desired phases of materials has become a central interest for the study of a variety of fields, notably high temperature superconductivity under extreme pressures. The further possibility of accessing metastable states by initiating reactions by x-ray triggered mechanisms over ultra-short timescales is enabled with the development of x-ray free electron lasers (XFEL). Utilizing the exceptionally high brilliance x-ray pulses from the EuXFEL, we report the synthesis of a previously unobserved yttrium hydride under high pressure, along with non-stoichiometric changes in hydrogen content as probed at a repetition rate of 4.5\,MHz using time-resolved x-ray diffraction. Exploiting non-equilibrium pathways we synthesize and characterize a hydride with yttrium cations in an \textit{A}15 structure type at 125\,GPa, predicted using crystal structure searches, with a hydrogen content between 4.0--5.75 hydrogens per cation, that is enthalpically metastable on the convex hull. We demonstrate a tailored approach to changing hydrogen content using changes in x-ray fluence that is not accessible using conventional synthesis methods, and reveals a new paradigm in metastable chemical physics. △ Less

Submitted 20 July, 2023; originally announced July 2023.

Thermomechanical response of thickly tamped targets and diamond anvil cells under pulsed hard x-ray irradiation

Authors: J. Meza-Galvez, N. Gomez-Perez, A. Marshall, A. L. Coleman, K. Appel, H. P. Liermann, M. I. McMahon, Z. Konopkova, R. S. McWilliams

Abstract: In the laboratory study of extreme conditions of temperature and density, the exposure of matter to high intensity radiation sources has been of central importance. Here we interrogate the performance of multi-layered targets in experiments involving high intensity, hard x-ray irradiation, motivated by the advent of extremely high brightness hard x-ray sources, such as free electron lasers and 4th… ▽ More In the laboratory study of extreme conditions of temperature and density, the exposure of matter to high intensity radiation sources has been of central importance. Here we interrogate the performance of multi-layered targets in experiments involving high intensity, hard x-ray irradiation, motivated by the advent of extremely high brightness hard x-ray sources, such as free electron lasers and 4th-generation synchrotron facilities. Intense hard x-ray beams can deliver significant energy in targets having thick x-ray transparent layers (tampers) around samples of interest, for the study of novel states of matter and materials' dynamics. Heated-state lifetimes in such targets can approach the microsecond level, regardless of radiation pulse duration, enabling the exploration of conditions of local thermal and thermodynamic equilibrium at extreme temperature in solid density matter. The thermal and mechanical response of such thick layered targets following x-ray heating, including hydrodynamic relaxation and heat flow on picosecond to millisecond timescales, is modelled using radiation hydrocode simulation, finite element analysis, and thermodynamic calculations. Assessing the potential for target survival over one or more exposures, and resistance to damage arising from heating and resulting mechanical stresses, this study doubles as an investigation into the performance of diamond-anvil high pressure cells under high x-ray fluences. Long used in conjunction with synchrotron x-ray radiation and high power optical lasers, the strong confinement afforded by such cells suggests novel applications at emerging high intensity x-ray facilities and new routes to studying thermodynamic equilibrium states of warm, very dense matter. △ Less

Submitted 4 December, 2019; v1 submitted 28 June, 2018; originally announced June 2018.