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First HED experiment at XFEL

Professor Justin Wark

Professor of Physics

Sub department

  • Atomic and Laser Physics

Research groups

  • Oxford Centre for High Energy Density Science (OxCHEDS)
Justin.Wark@physics.ox.ac.uk
Telephone: 01865 (2)72251
Clarendon Laboratory, room 029.9
  • About
  • Publications

The structure of liquid carbon elucidated by in situ X-ray diffraction.

Nature (2025)

Authors:

D Kraus, J Rips, M Schörner, MG Stevenson, J Vorberger, D Ranjan, J Lütgert, B Heuser, JH Eggert, H-P Liermann, II Oleynik, S Pandolfi, R Redmer, A Sollier, C Strohm, TJ Volz, B Albertazzi, SJ Ali, L Antonelli, C Bähtz, OB Ball, S Banerjee, AB Belonoshko, CA Bolme, V Bouffetier, R Briggs, K Buakor, T Butcher, V Cerantola, J Chantel, AL Coleman, J Collier, GW Collins, AJ Comley, TE Cowan, G Cristoforetti, H Cynn, A Descamps, A Di Cicco, S Di Dio Cafiso, F Dorchies, MJ Duff, A Dwivedi, C Edwards, D Errandonea, S Galitskiy, E Galtier, H Ginestet, L Gizzi, A Gleason, S Göde, JM Gonzalez, MG Gorman, M Harmand, NJ Hartley, PG Heighway, C Hernandez-Gomez, A Higginbotham, H Höppner, RJ Husband, TM Hutchinson, H Hwang, DA Keen, J Kim, P Koester, Z Konôpková, A Krygier, L Labate, A Laso Garcia, AE Lazicki, Y Lee, P Mason, M Masruri, B Massani, EE McBride, JD McHardy, D McGonegle, C McGuire, RS McWilliams, S Merkel, G Morard, B Nagler, M Nakatsutsumi, K Nguyen-Cong, A-M Norton, N Ozaki, C Otzen, DJ Peake, A Pelka, KA Pereira, JP Phillips, C Prescher, TR Preston, L Randolph, A Ravasio, D Santamaria-Perez, DJ Savage, M Schölmerich, J-P Schwinkendorf, S Singh, J Smith, RF Smith, J Spear, C Spindloe, T-A Suer, M Tang, M Toncian, T Toncian, SJ Tracy, A Trapananti, CE Vennari, T Vinci, M Tyldesley, SC Vogel, JPS Walsh, JS Wark, JT Willman, L Wollenweber, U Zastrau, E Brambrink, K Appel, MI McMahon

Abstract:

Carbon has a central role in biology and organic chemistry, and its solid allotropes provide the basis of much of our modern technology1. However, the liquid form of carbon remains nearly uncharted2, and the structure of liquid carbon and most of its physical properties are essentially unknown3. But liquid carbon is relevant for modelling planetary interiors4,5 and the atmospheres of white dwarfs6, as an intermediate state for the synthesis of advanced carbon materials7,8, inertial confinement fusion implosions9, hypervelocity impact events on carbon materials10 and our general understanding of structured fluids at extreme conditions11. Here we present a precise structure measurement of liquid carbon at pressures of around 1 million atmospheres obtained by in situ X-ray diffraction at an X-ray free-electron laser. Our results show a complex fluid with transient bonding and approximately four nearest neighbours on average, in agreement with quantum molecular dynamics simulations. The obtained data substantiate the understanding of the liquid state of one of the most abundant elements in the universe and can test models of the melting line. The demonstrated experimental abilities open the path to performing similar studies of the structure of liquids composed of light elements at extreme conditions.
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Isostructural phase transition of Fe2O3 under laser shock compression

Physical Review Letters American Physical Society 134:17 (2025) 176102

Authors:

Alexis Amouretti, Celine Crepisson, Sam Azadi, Francois Brisset, Delphine Cabaret, Thomas Campbell, David Chin, Gilbert Rip Collins, Linda Hansen, Guillaume Fiquet, Alessandro Forte, Thomas Gawne, Francois Guyot, Patrick Heighway, Eva Heripre, Eric Cunningham, Hae Ja Lee, David McGonegle, Bob Nagler, Juan Pintor, Danae Polsin, Gaelle Rousse, Yuanfeng Shi, Ethan Smith, Justin Wark, Sam Vinko, Marion Harmand

Abstract:

We present in situ x-ray diffraction and velocity measurements of Fe2⁢O3 under laser shock compression at pressures between 38–122 GPa. None of the high-pressure phases reported by static compression studies were observed. Instead, we observed an isostructural phase transition from 𝛼−Fe2⁢O3 to a new 𝛼′−Fe2⁢O3 phase at a pressure of 50–62 GPa. The 𝛼′−Fe2⁢O3 phase differs from 𝛼−Fe2⁢O3 by an 11% volume drop and a different unit cell compressibility. We further observed a two-wave structure in the velocity profile, which can be related to an intermediate regime where both 𝛼 and 𝛼′ phases coexist. Density functional theory calculations with a Hubbard parameter indicate that the observed unit cell volume drop can be associated with a spin transition following a magnetic collapse.
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Femtosecond temperature measurements of laser-shocked copper deduced from the intensity of the x-ray thermal diffuse scattering

Journal of Applied Physics American Institute of Physics 137:15 (2025) 155904

Authors:

Justin Wark, Domenic J Peake, Thomas Stevens, Patrick G Heighway

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 factor, providing a temperature measurement. The targets were laser-shocked with the DiPOLE 100-X laser at the High Energy Density endstation of the European X-ray Free-Electron Laser. 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 /Θ2 D, where ΘD 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 radiation.
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Bounds on Heavy Axions with an X-Ray Free Electron Laser

Physical Review Letters American Physical Society (APS) 134:5 (2025) 55001

Authors:

Jack WD Halliday, Giacomo Marocco, Konstantin A Beyer, Charles Heaton, Motoaki Nakatsutsumi, Thomas R Preston, Charles D Arrowsmith, Carsten Baehtz, Sebastian Goede, Oliver Humphries, Alejandro Laso Garcia, Richard Plackett, Pontus Svensson, Georgios Vacalis, Justin Wark, Daniel Wood, Ulf Zastrau, Robert Bingham, Ian Shipsey, Subir Sarkar, Gianluca Gregori

Abstract:

<jats:p>We present new exclusion bounds obtained at the European X-Ray Free Electron Laser facility (EuXFEL) on axionlike particles in the mass range <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mrow><a:msup><a:mrow><a:mn>10</a:mn></a:mrow><a:mrow><a:mo>−</a:mo><a:mn>3</a:mn></a:mrow></a:msup><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mrow><a:mi>eV</a:mi></a:mrow><a:mo>≲</a:mo><a:msub><a:mrow><a:mi>m</a:mi></a:mrow><a:mrow><a:mi>a</a:mi></a:mrow></a:msub><a:mo>≲</a:mo><a:msup><a:mrow><a:mn>10</a:mn></a:mrow><a:mrow><a:mn>4</a:mn></a:mrow></a:msup><a:mtext> </a:mtext><a:mtext> </a:mtext><a:mi>eV</a:mi></a:mrow></a:math>. Our experiment exploits the Primakoff effect via which photons can, in the presence of a strong external electric field, decay into axions, which then convert back into photons after passing through an opaque wall. While similar searches have been performed previously at a third-generation synchrotron [Yamaji , ], our work demonstrates improved sensitivity, exploiting the higher brightness of x-rays at EuXFEL.</jats:p> <jats:sec> <jats:title/> <jats:supplementary-material> <jats:permissions> <jats:copyright-statement>Published by the American Physical Society</jats:copyright-statement> <jats:copyright-year>2025</jats:copyright-year> </jats:permissions> </jats:supplementary-material> </jats:sec>
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Shock-driven amorphization and melting in Fe2⁢O3

Physical Review B American Physical Society 111:2 (2025) 024209

Authors:

Celine Crépisson, Alexis Amouretti, Marion Harmand, Chrystele Sanloup, Patrick Heighway, Sam Azadi, David McGonegle, Thomas Campbell, Juan Pintor, David A Chin, Ethan Smith, Linda Hansen, Alessandro Forte, Thomas Gawne, Hae Ja Lee, Bob Nagler, Yuanfeng Shi, Guillaume Fiquet, Francois Guyot, Makita Mikako, Alessandra Bennuzi-Mounaix, Tommaso Vinci, Kohei Miyanishi, Norimasa Ozaki, Tatiana Pikuz, Hirotaka Nakamura, Keiichi Sueda, Toshinori Yabuushi, Makina Yabashi, Justin S Wark, Danae N Polsin, Sam M Vinko

Abstract:

We present measurements on Fe2O3 amorphization and melt under laser-driven shock compression up to 209(10) GPa via time-resolved in situ x-ray diffraction. At 122(3) GPa, a diffuse signal is observed indicating the presence of a noncrystalline phase. Structure factors have been extracted up to 182(6) GPa showing the presence of two well-defined peaks. A rapid change in the intensity ratio of the two peaks is identified between 145(12) and 151(12) GPa, indicative of a phase change. The noncrystalline diffuse scattering is consistent with shock amorphization of Fe2O3 between 122(3) and 145(12) GPa, followed by an amorphous-to-liquid transition above 151(12) GPa. Upon release, a noncrystalline phase is observed alongside crystalline α-Fe2O3. The extracted structure factor and pair distribution function of this release phase resemble those reported for Fe2O3 melt at ambient pressure.
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