In a corona fusion target, laser beams directly ablate a layer of fusion fuel on the inner surface of a capsule. As the ablative flows converge, the plasma particles transition to collisional stagnation, heating the ions and generating fusion reactions. These targets show promise as a neutron source, with extrapolated yields at National Ignition Facility (NIF) scale of up to 1x1017. Additionally, these targets are robust to low-mode drive asymmetries, enabling the possibility of single-sided laser drive and making them an ideal backlighter source for neutron-radiography applications.
In this project, we looked at inverted-corona targets in particular, testing a number of variations as neutron sources for high-energy-density applications using the OMEGA laser. The 1.8-mm diameter plastic (CH) capsules featured either one or two laser-entrance holes (LEHs) and were either lined with deuterated plastic (CD) or filled with 1.5-atm deuterium gas. Contrary to predictions by the hydrodynamics code HYDRA, the experiments exhibited a strong correlation between total neutron yield and CD liner thickness, indicating substantial mix of CH wall material into the ablated CD coronal plasma. Performance of the thickest liner targets, with approximately 10 kJ of incident laser energy, was consistent with previously published data. Data at 18 kJ laser energy may also be subject to mix from wall material. The yield from the gas-filled capsules was less than that from 10-µm CD-lined targets at the same laser energy, which may be explained by wall material mixing into the fusion fuel. Finally, the experiments demonstrated similar performance between a 1-LEH and a 2-LEH target irradiated with comparable laser energies, a key finding for demonstrating the utility of the inverted-corona neutron source for radiography applications. The unexpected yield scaling with CD liner thickness provides a unique opportunity to study coronal plasmas and compare the data to state-of-the-art simulations.
Our research leveraged and advanced Lawrence Livermore National Laboratory's core competency in high-energy-density science. Our results enhance NIF capabilities, in particular as a neutron source and for neutron radiography to support Livermore mission areas. Our work on this project attracted interest from academic collaborators through the NIF Discovery Science program and the OMEGA Laboratory Plasma Physics program.
Meezan, N., et al. 2019. "Developing Corona Fusion Targets as Neutron Sources." Nuclear Explosives Design Physics Conference 2019, Los Alamos, NM, October 2019. LLNL-ABS-773441.
Riedel, W., et al. 2019. "Kinetic Effects and Neutron Generation in Converging Fully-Ionized Plasma Jets." 61st Annual Meeting of the APS Division of Plasma Physics, Fort Lauderdale, FL, October 2019. LLNL-ABS-771745.
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