Marble Experiments on the National Ignition Facility: One- and Two-Shock Implosions for Studying the Effect of Heterogeneous Mix on Thermonuclear Burn *

The performance of inertial confinement fusion implosions can be affected by mix through many different mechanisms, including the dilution of the fusion fuel by ablator material. The magnitude of the effect is dependent not only on the amount of mix, but also on the morphology, that is, the heterogeneity of the mix. Los Alamos National Laboratory has developed a model [1] that describes the effect of heterogeneous mix on thermonuclear burn. The Marble [2] campaign on NIF was developed to test this model. MARBLE utilizes capsules filled with deuterated plastic foam and a gas mixture that includes tritium. The foam is structured with voids, termed “macropores,” to control the degree of heterogeneity of the mix of foam and gas at burn time, and greater heterogeneity is expected to result in decreased DT neutron yield. The ratio of DT to DD neutron yield can be compared with simulations using the burn model. Initial experiments [3] utilizing an HT gas mixture failed to demonstrate the expected decrease in yield ratio with increased macropore diameter [3]. Detailed simulations [4] of similar OMEGA experiments have shown that ion temperature differences between gas and foam can persist until burn time, resulting in temperature correlations with species concentration, an effect not included in the burn model. Recent experiments with an argon/tritium gas mixture have shown a reduction in the ion temperature variation and have demonstrated a yield ratio that is consistent with simulations.

[1] N A Denissen et al, LA-UR-14-28935 (2014); J R Ristorcelli, Phys Fluids 29, 020705 (2017).

[2] T J Murphy et al, J Phys:Conf Series 717, 012072 (2016).

[3] T J Murphy et al, HEDP 38, 100929 (2021).

[4] B A Haines et al, Nat. Comm. 11, 544 (2020).