Oxford Centre for High Energy Density Science (OxCHEDS)

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Bounding elastic photon-photon scattering at √s ≈ 1 MeV using a laser-plasma platform

Physics Letters B Elsevier 861 (2025) 139247

Authors:

R Watt, B Kettle, E Gerstmayr, B King, A Alejo, S Astbury, C Baird, S Bohlen, M Campbell, C Colgan, D Dannheim, C Gregory, H Harsh, Peter Hatfield, J Hinojosa, D Hollatz, Y Katzir, J Morton, Cd Murphy, A Nurnberg, J Osterhoff, G Pérez-Callejo, K Põder, Pp Rajeev, C Roedel, F Roeder, Fc Salgado, Gm Samarin, G Sarri, A Seidel, C Spindloe, S Steinke, Mjv Streeter, Agr Thomas, C Underwood, W Wu, M Zepf, Steven Rose, Spd Mangles

Abstract:

We report on a direct search for elastic photon-photon scattering using x-ray and 𝛾 photons from a laser-plasma based experiment. A 𝛾 photon beam produced by a laser wak­field accelerator provided a broadband 𝛾 spectrum extending to above 𝐸𝛾 = 200 MeV. These were collided with a dense x-ray field produced by the emission from a laser heated germanium foil at 𝐸𝑥 ≈ 1.4 keV, corresponding to an invariant mass of √𝑠 = 1.22 ± 0.22 MeV. In these asymmetric collisions elastic scattering removes one x-ray and one high-energy 𝛾 photon and outputs two lower energy 𝛾 photons. No changes in the 𝛾 photon spectrum were observed as a result of the collisions allowing us to place a 95% upper bound on the cross section of 1.5 × 1015 μb. Although far from the QED prediction, this represents the lowest upper limit obtained so far for √𝑠 ≲ 1 MeV.
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Femtosecond temperature measurements of laser-shocked copper deduced from the intensity of the x-ray thermal diffuse scattering

(2025)

Authors:

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

Nature Astronomy Nature Research 9:3 (2025) 438-448

Authors:

Patrick Reichherzer, Archie Bott, Robert Ewart, Gianluca Gregori, Kempski Philipp, Kunze Matthew, Alexander Schekochihin

Abstract:

Cosmic rays (CRs) play a pivotal role in shaping the thermal and dynamical properties of astrophysical environments, such as galaxies and galaxy clusters. Recent observations suggest a stronger confinement of CRs in certain astrophysical systems than predicted by current CR-transport theories. Here, we show that the incorporation of microscale physics into CR-transport models can account for this enhanced CR confinement. We develop a theoretical description of the effect of magnetic microscale fluctuations originating from the mirror instability on macroscopic CR diffusion. We confirm our theory with large-dynamical-range simulations of CR transport in the intracluster medium (ICM) of galaxy clusters and kinetic simulations of CR transport in micromirror fields. We conclude that sub-teraelectronvolt CR confinement in the ICM is far more effective than previously anticipated on the basis of Galactic-transport extrapolations. The transformative impact of micromirrors on CR diffusion provides insights into how microphysics can reciprocally affect macroscopic dynamics and observable structures across a range of astrophysical scales.
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A molecular dynamics framework coupled with smoothed particle hydrodynamics for quantum plasma simulations

University of Oxford (2025)

Authors:

Thomas Campbell, Sam Vinko, Gianluca Gregori

Abstract:

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Dataset for Measurement of turbulent velocity and bounds for thermal diffusivity in laser shock compressed foams by X-ray photon correlation spectroscopy

University of Oxford (2025)

Authors:

Charles Heaton, Gianluca Gregori

Abstract:

Data for the plots in Measurement of turbulent velocity and bounds for thermal diffusivity in laser shock compressed foams by X-ray photon correlation spectroscopy
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