Optimized beryllium target design for indirectly driven inertial confinement fusion experiments on the National Ignition Facility

Simakov, Andrei N.; Wilson, D. C.; Yi, Sunghwan; Kline, J. L.; Clark, Daniel; Milovich, J. L.; Salmonson, J. D.; Batha, S. H.

doi:10.1063/1.4864331

Cited by 64 publications

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“…Furthermore, they show the resulting mix of the Cu-doped Be into the hot spot has a negligible impact on the yield at a convergence ratio (initial outer radius/final hot-spot radius) of ∼10. These results bolster ongoing efforts [7,18] to develop a Be ignition platform at the NIF. Furthermore, this platform utilized some targets with a thin W tracer layer which provided a valuable test of mix calculations.…”

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confidence: 69%

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“…The basic ablation properties of Be [5,8], such as the high ablation velocity, can result in higher velocity and improved stability in simulated ignition designs when compared to CH or HDC designs [7,18]. It is possible that at higher convergence inhomogeneities, sputter material impurities, and dopant nonuniformity may seed unstable growth that could compromise performance.…”

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“…This means that, in principle, Be can achieve higher implosion velocities or operate at lower R=ΔR for a fixed driver energy. Simakov et al show that the potential benefits of Be target designs still exist even with Cu-doped Be shells currently being considered for ignition experiments [7]. Wilson et al [8] summarized many of the additional mechanical and hydrodynamic advantages of Be, such as high initial density, high tensile strength, and high thermal conductivity.…”

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confidence: 99%

“…The Be capsules were made by coating Be onto a spherical mandrel. The inner 7.5 μm of Be was doped with 4% Cu before removal of the mandrel by pyrolysis to be as relevant as possible to the current Be designs [7,18] and to provide radiographic contrast. After pyrolysis, the Cu dopant diffused into the undoped Be bringing the maximum Cu concentration to 2.5% with a decreasing linear radial gradient toward the outer radius of the capsule.…”

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Performance and Mix Measurements of Indirect Drive Cu-Doped Be Implosions

et al. 2015

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The ablator couples energy between the driver and fusion fuel in inertial confinement fusion (ICF). Because of its low opacity, high solid density, and material properties, beryllium has long been considered an ideal ablator for ICF ignition experiments at the National Ignition Facility. We report here the first indirect drive Be implosions driven with shaped laser pulses and diagnosed with fusion yield at the OMEGA laser. The results show good performance with an average DD neutron yield of ∼2 × 10 9 at a convergence ratio of R 0 =R ∼ 10 and little impact due to the growth of hydrodynamic instabilities and mix. In addition, the effect of adding an inner liner of W between the Be and DD is demonstrated. DOI: 10.1103/PhysRevLett.114.205002 PACS numbers: 52.57. Fg, 52.70.La In inertial confinement fusion (ICF) experiments, like those performed at the National Ignition Facility (NIF) [1] and the OMEGA laser facility [2], capsules of deuterium and tritium fuel are imploded to high densities and temperatures to initiate fusion burn. The indirect drive ICF concept uses a laser to irradiate a hohlraum, which produces a nearly uniform thermal x-ray drive. The x-ray drive then ablates the outer capsule material imploding the remaining cryogenically frozen DT shell-mass inward. The conditions necessary for ignition are related to a minimum requirement of the energy density delivered to the DT hot spot and the confinement time of that energy, or equivalently Pτ, the product of the hot-spot pressure (P), a measure of the hotspot energy density, and the energy confinement time (τ) [3]. Betti et al. [4] showed that P is related to the implosion velocity (v) by balancing the hot-spot internal energy to the shell kinetic energy via 2πPR 3 ∼ θ 1 2 Mv 2 , where R is the radius of the hot spot, θ is the fraction of the shell kinetic energy converted to hot-spot energy, and M is the mass of the shell. Note that assuming a thin shell results in M ∼ 4πR 2 × ρR; where ρR is the areal density of the imploded shell. From Newton's law, the hot-spot confinement time is related to the shell inertia like τ ∼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ffi M=4πPR p . Combining these expressions shows that Pτ ∝ v × ρR [4]. This means that a successful ignition experiment must achieve high v and high ρR. In the attempt to achieve these conditions, several ablator materials have been considered, i.e., plastic (CH), high density carbon (HDC), and beryllium. The choice of ablator material has important consequences for the implosion hydrodynamics. For example, the mass ablation rate ( _ m) can be quite different for different materials. Olson et al.[5] measured _ m (in mg=cm 2 =ns) experimentally and found it to be 0.75T 3 r for Be (with and without 1% Cu dopant), 0.50T 3 r for HDC, and 0.35T 3 r for CH (0.6% Ge dopant), where T r is the drive radiation temperature in units of hundreds of eV (or heV). Because the ablation velocity is V a ¼ _ m=ρ, where ρ is the ablator density, Be has the highest V a for the same in-flight ρ. Als...

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