Improving ICF implosion performance with alternative capsule supports

Abstract

The thin membrane that holds the capsule in-place in the hohlraum is recognized as one of the most significant contributors to reduced performance in indirect drive inertial confinement fusion (ICF) experiments on the National Ignition Facility. This membrane, known as the “tent,” seeds a perturbation that is amplified by Rayleigh-Taylor and can rupture the capsule. A less damaging capsule support mechanism is under development. Possible alternatives include the micron-scale rods spanning the hohlraum width and supporting either the capsule or stiffening the fill-tube, a larger fill-tube to both fill and support the capsule, or a low-density foam layer that protects the capsule from the tent impact. Experiments are testing these support features to measure their imprint on the capsule. These experiments are revealing unexpected aspects about perturbation development in indirect drive ICF, such as the importance of shadows coming from bright spots in the hohlraum. Two dimensional and 3D models are used to explain these features and assess the impact on implosion performance. Experiments and modeling suggest that the fill-tube supported by a perpendicular rod can mount the capsule without any additional perturbation beyond that of the fill tube.

A novel superconducting magnetic levitation method to support the laser fusion capsule by using permanent magnets

“…Capsule support is another important link in ICF experiments, which influences the symmetry around the capsule directly. Traditionally, people use thin wires, tents, low density foams or their hybrid systems [6] to support the deuterium-tritium fuel capsule. However, in all the traditional methods, the supporting materials require direct contact with the capsule.…”

“…However, in all the traditional methods, the supporting materials require direct contact with the capsule. Experimental results of National Ignition Facility (NIF) show that large perturbation exists where the tent departs from the capsule [6]. Researchers are trying to make the wires thinner and the foam density lower, sacrificing their mechanical strength, but perturbation to the spherical symmetry is still inevitable, no matter how small it could be.…”

Impact of asymmetries on fuel performance in inertial confinement fusion

“…Chimera is initialized after the end of the laser pulse using output from 1D HYADES [28] simulations, and run through convergence and disassembly. Previous work has shown that low-mode asymmetries can be expected to arise due to engineering features such as the stalk mount, fill tube and/or support tent used to hold and fill an ICF target [29][30][31][32][33], due to unintended laser drive asymmetries [9,[34][35], or due to unintentional capsule misalignment (offset) [36]. Capsule offsets are small for these room temperature implosions [37,38].…”

Capsule modeling of high foot implosion experiments on the National Ignition Facility

“…Alternate capsule support strategies, such as replacing the tent with a stalk or shrinking the contact area of the tent with the capsule, are being tested [65]. Simultaneously, alternative hohlraum designs with larger case-to-capsule ratios [66], or other more Figure 13.…”