Studying the drive deficit and NLTE plasma conditions with gold sphere experiments at the NIF

Experiments at the National Ignition Facility (NIF) have shown that incomplete modeling of non-LTE plasmas leads to overestimated X-ray emission from the gold M-band and underestimated elec-tron temperatures of the non-LTE hohlraum plasma¹. To match experimental data, simulations may include self-generated magnetic fields and multipliers on energy-specific opacity, the underlying physics of which is not yet fully understood. To further investigate this, NIF experiments used polar direct drive pointing to uniformly drive a 2.2 mm diameter Au sphere with ~1e15 W/cm² of laser energy, generating a range of coronal plasma conditions and x-ray emission similar to those found within the hohlraum. The sphere platform creates an approximately 1-D problem, where several diagnostics observe similar X-ray drive and coronal plasma emission, and self-generated magnetic fields are not important. Total flux and M-band emission were measured with Dante² and spatially resolved Au L-shell emission spectra were measured to infer the electron temperature distribution. These results will be presented and compared against rad-hydro models varying key atomic kinetics parameters.

[1] H. Chen, D. T. Woods, et al. Phys. Rev. E. 110, L013201 (2024)

[2] E. L. Dewald, et al., et al. Rev. Sci. Instrum. 75, 3759 (2004)