Design considerations for indirectly driven double shell capsules

Abstract

Double shell capsules are predicted to ignite and burn at relatively low temperature (∼3 keV) via volume ignition and are a potential low-convergence path to substantial α-heating and possibly ignition at the National Ignition Facility. Double shells consist of a dense, high-Z pusher, which first shock heats and then performs work due to changes in pressure and volume (PdV work) on deuterium-tritium gas, bringing the entire fuel volume to high pressure thermonuclear conditions near implosion stagnation. The high-Z pusher is accelerated via a shock and subsequent compression of an intervening foam cushion by an ablatively driven low-Z outer shell. A broad capsule design parameter space exists due to the inherent flexibility of potential materials for the outer and inner shells and foam cushion. This is narrowed down by design physics choices and the ability to fabricate and assemble the separate pieces forming a double shell capsule. We describe the key physics for good double shell performance, the trade-offs in various design choices, and the challenges for capsule fabrication. Both 1D and 2D calculations from radiation-hydrodynamic simulations are presented.

Interspecies radiative transition in warm and superdense plasma mixtures

“…Possible experiments on inter-atomic Kα emissions. Experimental verification of these first-principles predictions of interatomic Kα emissions can possibly be conducted at the Omega Laser Facility utilizing the platform of double-shell implosions 14,15,42,43 . In a double-shell target, the inner metal shell can be made of mid-Z Fe-Cu or Fe-Zn alloys with a core of D2-gas fill.…”

“…When a low-Z outer shell (beryllium or polystyrene) is driven symmetrically by the 60-beam OMEGA laser to spherically impact on the inner shell, it can cause the inner Fe-Zn (or Fe-Cu) shell to implode. A small convergence ratio of C R = R initial /R final ∼8-10 of the metal shell could give rise to a mass density of ρ = 500 to 2000 g cm −3 for the inner Fe-Zn (or Fe-Cu) shell at its stagnation 42,43 . To create the 1s holes of Fe and Zn/Cu ions, one option is to use the high-intensity OMEGA EP beam to generate MeV electrons that can remove some of the 1s electrons of Fe and Zn/Cu ions through collisions.…”

Convergent Richtmyer–Meshkov instability of light gas layer with perturbed outer surface

“…It was found that the interface coupling effect, the distorted transmitted shock and the geometric constraint greatly affect the development of instability. However, the problem of a light gas layer accelerated by a converging shock has not yet been well investigated -which is more relevant to the so-called double-shell implosion (Montgomery et al 2018). This motivates the current study.…”

First experiments on Revolver shell collisions at the OMEGA laser

“…This ignition scheme, which has dominated inertial confinement fusion (ICF) for decades, has yet to produce ignition in the laboratory, primarily due to the effects of asymmetry and mix 3,4 . Ignition schemes that abandon the propagating burn wave concept and instead aim to ignite the fuel volume simultaneously have recently gained interest, with Revolver 5 and Double Shell targets 6,7 being the prime examples.…”

“…In fact, higher implosion velocity is not necessarily a benefit. Although faster implosions could reduce the convergence required to reach ignition, the fuel would be less compressed and susceptible to premature disassembly 5,6 . For the Revolver design, a pusher implosion velocity of u I = 19 cm/µs results in a required pusher convergence ratio of 9.4.…”