Thermal transport in warm dense matter revealed by refraction-enhanced x-ray radiography with a deep-neural-network analysis*

Transport properties of high energy density matter affect the evolution of many systems, ranging from the Earth's core to the inertial confinement fusion (ICF) capsules. Large uncertainties of these properties are present in the warm dense matter (WDM) regime where both plasma and condensed matter models become invalid. I will present the measurement of thermal conductivity of CH and Be in WDM using x-ray differential heating and time-resolved refraction-enhanced radiography. A novel technique with a deep neural network has been developed to retrieve the detailed density profiles. Multiple observables, including wave propagation and refractive features, enable simultaneous constraints on density, temperature, and thermal conductivity.

The data indicate that the thermal conductivity of CH at about 8 eV and solid density agrees with widely used models such as Purgatorio [1, 2], Spitzer [3], Lee-More-Desjarlais [4, 5], and quantum molecular dynamics [6], but requires a correction term for electron-electron collisions. For Be in the 4-5 eV range, the measured data consistently exceed predictions from most models when including this term. The results necessitate the improvement of transport models in the WDM regime and could impact the understanding of the implosion performance for ICF.

I would like to acknowledge the co-authors, O. L. Landen, H. D. Whitley, S. Hamel, R. London, D. S. Clark, P. Sterne, S. B. Hansen, S. X. Hu, G. W. Collins and Y. Ping. This work has been published in [7].

[1] B. Wilson et al., J. Quant. Spectrosc. Radiat. Transf. 99, 658 (2006)

[2] P. A. Sterne et al., HEDP 3, 278 (2007)

[3] L. Jr. Spitzer, R. Harm, Phys. Rev. 89, 977 (1953)

[4] Y. T. Lee, R. M. More, Phys. Fluids 27, 1273 (1984)

[5] M. P. Desjarlais, Contrib. Plasma Phys. 41, 267 (2001)

[6] S. X. Hu et al., Phys. Plasmas 23, 042704 (2016)

[7] S. Jiang et al., Comm. Phys. 6, 98 (2023)