BEGIN:VCALENDAR VERSION:2.0 PRODID:-//linuxsoftware.nz//NONSGML Joyous v1.4//EN BEGIN:VEVENT SUMMARY:Atomic processes in XFEL-driven plasmas DTSTART:20250605T100000Z DTEND:20250605T120000Z DTSTAMP:20260427T025604Z UID:4891a2b4-de8c-4699-96ef-603d0a20281b SEQUENCE:2 CREATED:20250604T082841Z DESCRIPTION:Over the past two decades\, X-ray free-electron lasers (XFELs) have made significant progress\, achieving peak brightness X-ray regions that were previously only attainable in the infrared. This has opened new possibilities in high-energy density science\, enabling the creation of so lid-density plasmas with larger volumes and better uniformity. XFEL heatin g proceeds through photoionisation and thermalisation\, initially creating non-thermal electron distributions\, offering a new platform for generati ng plasmas with tailored properties.We investigate the effects of inelasti c thermalisation in iron under intense X-ray irradiation using the atomic model BigBarT\, which evolves the electron distribution self-consistently. Our study focuses on collisional M-shell ionisation\, identified as the m ost efficient relaxation mechanism for non-thermal electrons. This could i mpact high-energy electron transport and points to the relevance of includ ing atomic processes in kinetic models. Comparing calculated spectra with experimental data may also help refine collisional cross sections\, which are challenging to compute due to screening and continuum effects. We also report the observation of the shake-off process in solid-density XFEL-pro duced plasmas. Titanium foils were irradiated with XFEL pulses at 5.1 and 6 keV. Emission spectra show satellite features only at the higher energy\ , consistent with the threshold for simultaneous K- and L-shell ionisation . These signatures are absent at lower energies and cannot be explained by standard collisional or Auger ionisation mechanisms. LAST-MODIFIED:20250604T083501Z LOCATION:DF Seminar Room (2-8.3)\, 2nd floor of Physics Building URL:http://df.vps.tecnico.ulisboa.pt/pt/eventos/atomic-processes-in-xfel-d riven-plasmas/ X-ALT-DESC;FMTTYPE=text/html:

Over the past two d ecades\, X-ray free-electron lasers (XFELs) have made significant progress \, achieving peak brightness X-ray regions that were previously only attai nable in the infrared. This has opened new possibilities in high-energy de nsity science\, enabling the creation of solid-density plasmas with larger volumes and better uniformity. XFEL heating proceeds through photoionisat ion and thermalisation\, initially creating non-thermal electron distribut ions\, offering a new platform for generating plasmas with tailored proper ties.


We investigate the effects of inelastic thermalisation in iron under intense X-ray irradiation using the atomic model BigBarT\, which evolves the electron distribution self-consistently. Our study focus es on collisional M-shell ionisation\, identified as the most efficient re laxation mechanism for non-thermal electrons.

This could impact high-energy electron transport and points to the relevance of including at omic processes in kinetic models. Comparing calculated spectra with experi mental data may also help refine collisional cross sections\, which are ch allenging to compute due to screening and continuum effects.

We also report the observation of the shake-off process in solid-density XFEL -produced plasmas. Titanium foils were irradiated with XFEL pulses at 5.1 and 6 keV. Emission spectra show satellite features only at the higher ene rgy\, consistent with the threshold for simultaneous K- and L-shell ionisa tion. These signatures are absent at lower energies and cannot be explaine d by standard collisional or Auger ionisation mechanisms.

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