Abstract
In inertial confinement fusion, deuterium–tritium (DT) fuel is brought to densities and temperatures where fusion ignition occurs. However, mixing of the ablator material into the fuel may prevent ignition by diluting and cooling the fuel. MARBLE experiments at the National Ignition Facility provide new insight into how mixing affects thermonuclear burn. These experiments use laser-driven capsules containing deuterated plastic foam and tritium gas. Embedded within the foam are voids of known sizes and locations, which control the degree of heterogeneity of the fuel. Initially, the reactants are separated, with tritium concentrated in the voids and deuterium in the foam. During the implosion, mixing occurs between the foam and gas materials, leading to DT fusion reactions in the mixed region. Here, it is shown that by measuring the ratios of DT and deuterium–deuterium neutron yields for different macropore sizes and gas compositions, the effects of mix heterogeneity on thermonuclear burn may be quantified, supporting an improved understanding of these effects.
Highlights
Inertial confinement fusion (ICF) ignition involves compressing thermonuclear fuels to densities and temperatures where fusion heating exceeds losses from radiation, thermal conduction, and hydrodynamic work.[1,2] Though recent experiments on the National Ignition Facility (NIF) indicate that we may be on the cusp of ignition,[3] achieving this has proven difficult, in part because of the presence of contaminant material in the fuel
The DT reactivity increases with temperature more quickly than does the DD reactivity, with the result that the burn-averaged ion temperature is weighted by shock yield more for the DT neutrons than for the DD neutrons, leading to a large observed temperature discrepancy
Data are shown for NIF shots N180729-001 and N181028-002, which are representative of the observed behavior of HT and ArT gas fills, respectively
Summary
Inertial confinement fusion (ICF) ignition involves compressing thermonuclear fuels to densities and temperatures where fusion heating exceeds losses from radiation, thermal conduction, and hydrodynamic work.[1,2] Though recent experiments on the National Ignition Facility (NIF) indicate that we may be on the cusp of ignition,[3] achieving this has proven difficult, in part because of the presence of contaminant material in the fuel (mix). Previous separated reactants experiments[14,15] studied mix in layered capsules containing deuterium with a tritium gas fill. These experiments suffer from a degree of ambiguity, as the mixing occurs far from the hot spot and difficult to diagnose hydrodynamic features such as fill tube jetting and perturbations from surface defects may complicate interpretations of the mixing dynamics.[16]. In MARBLE experiments, in contrast, the bulk of the thermonuclear burn occurs in plasma generated from macroporous foam in the central volume of the capsule far from the capsule walls, avoiding many of these complications.
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