Characterization of thermal transport and the evolution of directly driven spherical ICF targets using Thomson scattering

In this talk we demonstrate how optical Thomson scattering (OTS) may be used to make measurements of thermal transport [1] in ICF relevant HED plasmas. OTS theory and plasma simulations are applied to the interpretation of experimental measurements of laser-produced plasma from spherical gold and beryllium targets on the OMEGA laser facility [2], in concert with supporting radiation hydrodynamic and kinetic simulations of electron thermal transport and plasma evolution. The experimental data are captured at a range of different radial locations, allowing measurements of spatial gradients relevant to transport processes. To accurately model the experimental conditions the model for the dynamical form factor of electron density fluctuations that is used in the fitting of Thomson scattering spectra is enhanced to include the effects of ion-ion collisions and non-Maxwellian distribution functions. 

The OTS transport measurements and their interpretation are shown to be consistent with the nonlocal transport model used in the radiation hydrodynamic simulations as well as with kinetic simulations for most of the laser pulse duration. In particular, the reversal of heat transport during cooling is observed to be consistent with simulations, however some discrepancies are noted during the initial heating of the Au targets. 

[1] C. Bruulsema, W.A. Farmer, M. Sherlock et al. Phys. Plasmas, submitted (2021).

[2] W.A. Farmer, M.D. Rosen G.F. Swadling, et al. Phys. Plasmas, 28, 032707 (2021).