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A new class of inertial fusion capsules is presented that combines multishell targets with laser direct drive at low intensity (2.8 × 10 14 W=cm 2 ) to achieve robust ignition. The targets consist of three concentric, heavy, metal shells, enclosing a volume of tens of μg of liquid deuterium-tritium fuel. Ignition is designed to occur well "upstream" from stagnation, with minimal pusher deceleration to mitigate interface Rayleigh-Taylor growth. Laser intensities below thresholds for laser plasma instability and cross beam energy transfer facilitate high hydrodynamic efficiency (∼10%). DOI: 10.1103/PhysRevLett.116.255003 A large convergence ratio and high implosion velocity have been the hallmarks of inertial fusion from its inception [1,2]. Target design has evolved over the past forty-plus years to culminate in the National Ignition Facility (NIF) ignition targets fired during the Ignition Campaign of 2009-2012. These targets sought to ignite a central hot spot formed by a small fraction of fuel that could be heated to ignition temperatures. Burn was then projected to propagate to the main fuel and produce high gain. A specific example (Fig. 107 of Ref.[2]) composed entirely of light materials is driven by 1.35 MJ of laser light. It required an implosion velocity u I ¼ 41 cm=μs and convergence ratio (initial capsule radius, R i divided by final radius R f ) of C ¼ 36 from a plastic and deuterium-tritium (DT) ice shell with an in-flight aspect ratio of 40. The predicted yield of 15 MJ from 180 μg of DT fuel corresponds to a burn fraction of 25%. Nearly perfect spherical symmetry was essential. The experimental results achieved to date on the NIF have underperformed predictions [3,4].A fundamentally different path to ignition is described in this Letter. A new class of targets capable of producing multi-megajoule yields from DT fuel masses of tens of μg, absorbed drive energies less than 2 MJ, and burn fractions exceeding 50% is defined. High gain is abandoned as a goal. Instead, we seek a mechanically robust implosion and large margin for ignition. The Revolver targets described here consist of three nested, spherical metal shells with buffer gas between the shells and a central volume filled with cryogenic liquid DT fuel. The baseline target is depicted in Fig. 1, which also shows the implosion diagram from a HYDRA [5] 1D simulation. Energy is absorbed by an ablator shell from a short laser pulse that leaves 70% of the ablator mass as payload to implode the target. The implosion is entirely mechanical, dominated by the metal shells. The metal multishell system is intended to be more robust hydrodynamically than a single plastic-DT ice shell. Ignition well upstream of stagnation is a key feature of the Revolver targets. This is controlled with a design parameter that allows for adjustment of the ignition margin.All the physics pieces we will assemble have long been known and studied. Metal pushers were first discussed in the literature by Kirkpatrick and co-workers [6,7], who showed the benefits of radiation t...

Previous work has shown that the one-dimensional (1D) inviscid compressible flow (Euler) equations admit a wide variety of scale-invariant solutions (including the famous Noh, Sedov, and Guderley shock solutions) when the included equation of state (EOS) closure model assumes a certain scale-invariant form. However, this scale-invariant EOS class does not include even simple models used for shock compression of crystalline solids, including many broadly applicable representations of Mie-Grüneisen EOS. Intuitively, this incompatibility naturally arises from the presence of multiple dimensional scales in the Mie-Grüneisen EOS, which are otherwise absent from scale-invariant models that feature only dimensionless parameters (such as the adiabatic index in the ideal gas EOS). The current work extends previous efforts intended to rectify this inconsistency, by using a scale-invariant EOS model to approximate a Mie-Grüneisen EOS form. To this end, the adiabatic bulk modulus for the Mie-Grüneisen EOS is constructed, and its key features are used to motivate the selection of a scale-invariant approximation form. The remaining surrogate model parameters are selected through enforcement of the Rankine-Hugoniot jump conditions for an infinitely strong shock in a Mie-Grüneisen material. Finally, the approximate EOS is used in conjunction with the 1D inviscid Euler equations to calculate a semi-analytical, Guderley-like imploding shock solution in a metal sphere, and to determine if and when the solution may be valid for the underlying Mie-Grüneisen EOS.