Using neutrons and x rays to measure plasma conditions in a solid sphere of deuterated polyethylene compressed to densities of 35 g/cc at temperatures of 2 keV and pressures of 40 Gbar

• Published in: Physics of plasmas 2021-12, Vol.28 (12)
• Main Authors: Nilsen, J., Bachmann, B., Zimmerman, G. B., Hatarik, R., Döppner, T., Swift, D. C., Hawreliak, J., Collins, G. W., Falcone, R. W., Glenzer, S. H., Kraus, D., Landen, O. L., Castor, J. I., Whitley, H. D., Kritcher, A. L.
• Format: Article
• Language: English
• Subjects: 70 PLASMA PHYSICS AND FUSION TECHNOLOGY; deuterium; hydrodynamics simulations; neutron emission; nuclear fusion; radiography; shock waves; x-ray diagnostics
• ISSN: 1070-664X; 1089-7674

This paper describes an experiment that shock compresses the center of a solid deuterated polyethylene sphere, CD2, to densities of 35 g/cc and temperatures of 2 keV with corresponding pressure of 40 Gbar. The design employs a strong spherically converging shock launched through a solid ball of material using a Hohlraum radiation drive. As the shock coalesces at the center it produces a hot spot that we characterize by measuring the x-ray self-emission and 2.45 MeV neutrons emitted. Two-dimensional images and time-resolved measurements of the x rays emitted determine the size and time duration of the hot spot, leading to an estimated 2k eV electron temperature. The neutron time of flight spectrometer measures an average ion temperature of 1.06 ± 0.15 keV and neutron yield of 7.0 (±0.5) × 109 DD neutrons. Our new distribution function tool enables us to create a forward model of the experimental data based on 1D radiation-hydrodynamic simulations, leading to a better understanding of the plasma conditions that produce the measured neutrons and x rays. Furthermore, our simulations indicate that the x rays are produced in a short-lived hot-dense core over tens of picoseconds, whereas the neutron emission continues for about 200 ps, as the hot core starts to expand, thereby leading to a lower mean temperature of the plasma during neutron production. This finding is in agreement with the experimental data, and we therefore conclude that the forward-modeling is a useful tool for inferring the conditions of the hot spot in a laser-driven implosion during burn.