Evidence of Free‐Bound Transitions in Warm Dense Matter and Their Impact on Equation‐of‐State Measurements
8 affiliations
- 1Lawrence Livermore National Laboratory (LLNL) Livermore California USA
- 2SLAC National Accelerator Laboratory Menlo Park California USA
- 3Sandia National Laboratories Albuquerque New Mexico USA
- 4Center for Advanced Systems Understanding (CASUS) Görlitz Germany
- 5Helmholtz‐Zentrum Dresden‐Rossendorf (HZDR) Dresden Germany
- 6Institut für Physik Universität Rostock Rostock Germany
- 7First Light Fusion Oxfordshire UK
- 8European XFEL Schenefeld Germany
Abstract
Warm dense matter (WDM) is now routinely created and probed in laboratories around the world, providing unprecedented insights into conditions achieved in stellar atmospheres, planetary interiors, and inertial confinement fusion experiments. However, the interpretation of these experiments is often filtered through models with systematic errors that are difficult to quantify. Due to the simultaneous presence of quantum degeneracy and thermal excitation, transitions in which free electrons are de‐excited into thermally unoccupied bound states transferring momentum and energy to a scattered x‐ray photon become viable. Here we show that such free‐bound transitions are a particular feature of WDM and vanish in the limits of cold and hot temperatures. The inclusion of these transitions into the analysis of recent X‐ray Thomson Scattering experiments on WDM at the National Ignition Facility and the Linac Coherent Light Source is required to obtain a physically consistent temperature from the Chihara decomposition. This interpretation is corroborated by agreement with a recently developed model‐free thermometry technique and presents an important step for precisely characterizing and understanding the complex WDM state of matter.
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BibTeX
@article{bohme2026evidence,
title = {{Evidence of Free‐Bound Transitions in Warm Dense Matter and Their Impact on Equation‐of‐State Measurements}},
author = {Maximilian Böhme and L. B. Fletcher and Andrew Baczewski and Hannah M. Bellenbaum and Zhandos A. Moldabekov and Jan Vorberger and D. A. Chapman and M. J. MacDonald and Sebastian Schwalbe and Thomas R. Preston and D. Kraus and Thomas Gawne and Frank R. Graziani and Sébastien Hamel and T. Döppner and Tobias Dornheim},
journal = {Contributions to Plasma Physics},
year = {2026},
month = jul,
doi = {10.1002/ctpp.70149},
url = {https://doi.org/10.1002/ctpp.70149},
note = {CC BY},
}
RIS
TY - JOUR
TI - Evidence of Free‐Bound Transitions in Warm Dense Matter and Their Impact on Equation‐of‐State Measurements
AU - Maximilian Böhme
AU - L. B. Fletcher
AU - Andrew Baczewski
AU - Hannah M. Bellenbaum
AU - Zhandos A. Moldabekov
AU - Jan Vorberger
AU - D. A. Chapman
AU - M. J. MacDonald
AU - Sebastian Schwalbe
AU - Thomas R. Preston
AU - D. Kraus
AU - Thomas Gawne
AU - Frank R. Graziani
AU - Sébastien Hamel
AU - T. Döppner
AU - Tobias Dornheim
PY - 2026
DA - 2026/07/07
JO - Contributions to Plasma Physics
DO - 10.1002/ctpp.70149
UR - https://doi.org/10.1002/ctpp.70149
AB - Warm dense matter (WDM) is now routinely created and probed in laboratories around the world, providing unprecedented insights into conditions achieved in stellar atmospheres, planetary interiors, and inertial confinement fusion experiments. However, the interpretation of these experiments is often filtered through models with systematic errors that are difficult to quantify. Due to the simultaneous presence of quantum degeneracy and thermal excitation, transitions in which free electrons are de‐excited into thermally unoccupied bound states transferring momentum and energy to a scattered x‐ray photon become viable. Here we show that such free‐bound transitions are a particular feature of WDM and vanish in the limits of cold and hot temperatures. The inclusion of these transitions into the analysis of recent X‐ray Thomson Scattering experiments on WDM at the National Ignition Facility and the Linac Coherent Light Source is required to obtain a physically consistent temperature from the Chihara decomposition. This interpretation is corroborated by agreement with a recently developed model‐free thermometry technique and presents an important step for precisely characterizing and understanding the complex WDM state of matter.
SN - 0863-1042
SN - 1521-3986
ER -