Scaling laws for laser driven exploding pusher targets

Measurements of yield, ion temperature, areal density (ρR), shell convergence, and bang time have been obtained in shock-driven, D 2 and D 3 He gas-filled "exploding-pusher" inertial confinement fusion (ICF) implosions at the National Ignition Facility (NIF) to assess the impact of ion kinetic effects. These measurements probed the shock convergence phase of ICF implosions, a critical stage in hot-spot ignition experiments. The data complement previous studies of kinetic effects in shock-driven implosions. Ion temperature and fuel ρR inferred from fusion-product spectroscopy are used to estimate the ion-ion mean free path in the gas. A trend of decreasing yields relative to the predictions of 2D draco hydrodynamics simulations with increasing Knudsen number (the ratio of ion-ion mean free path to minimum shell radius) suggests that ion kinetic effects are increasingly impacting the hot fuel region, in general agreement with previous results. The long mean free path conditions giving rise to ion kinetic effects in the gas are often prevalent during the shock phase of both exploding pushers and ablatively-driven implosions, including ignition-relevant implosions.

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“…With ρR f 0 ∼0.13 mg/cm 2 for these three D 2 -filled implosions, convergence ratios of ∼5. [3][4][5][6].0 are inferred.…”

Section: ρR and Convergencementioning

confidence: 99%

Investigation of ion kinetic effects in direct-drive exploding-pusher implosions at the NIF

et al. 2014

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“…Shock-driven exploding-pusher implosions [2][3][4][5] are an ideal platform to isolate and probe ion kinetic and multiple-ion-fluid effects in ICF implosions, 6,7 as the bulk of fusion reactions (and diagnosis of implosion conditions) occurs when the plasma is at kinetica) Electronic mail: mros@lle.rochester.edu; Present institution: Laboratory for Laser Energetics, University of Rochester. like conditions.…”

Section: Introductionmentioning

confidence: 99%

Assessment of ion kinetic effects in shock-driven inertial confinement fusion implosions using fusion burn imaging

et al. 2015

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The significance and nature of ion kinetic effects in D 3 He-filled, shock-driven inertial confinement fusion implosions is assessed through measurements of fusion burn profiles. Over this series of experiments the ratio of ion-ion mean free path to minimum shell radius (the Knudsen number, N K ) was varied from 0.3 to 9 in order to probe hydrodynamic-like to strongly kinetic plasma conditions; as the Knudsen number increased, hydrodynamic models increasingly failed to match measured yields, while an empirically-tuned, first-step model of ion kinetic effects better captured the observed yield trends [Rosenberg et al. Phys. Rev. Lett. 112, 185001 (2014)]. Here, spatially-resolved measurements of the fusion burn are used to examine kinetic ion transport effects in greater detail, adding an additional dimension of understanding that goes beyond zero-dimensional integrated quantites to one-dimensional profiles. In agreement with the previous findings, a comparison of measured and simulated burn profiles shows that models including ion transport effects are able to better match the experimental results. In implosions characterized by large Knudsen numbers (N K ∼3), the fusion burn profiles predicted by hydrodynamics simulations that exclude ion mean free path effects are peaked far from the origin, in stark disagreement with the experimentally observed profiles, which are centrally-peaked. In contrast, a hydrodynamics simulation that includes a model of ion diffusion is able to qualitatively match the measured profile shapes. Therefore, ion diffusion or diffusion-like processes are identified as a plausible explanation of the observed trends, though further refinement of the models is needed for a more complete and quantitative understanding of ion kinetic effects.

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“…The 8-lm shells absorb virtually all of the incident laser energy and explode, directing approximately half the energy inward to compress the 5-atm D 2 gas load, a so-called exploding pusher. 8 both, a total laser drive of $17.5 kJ is delivered in a 1-ns square pulse. Distributed phase plates were used for an 850-lm focal spot, and maximum spectral dispersion for beam smoothing.…”

Section: The Omega Experimental Platformmentioning

confidence: 99%

Asymmetric directly driven capsule implosions: Modeling and experiments—A requirement for the National Ignition Facility

et al. 2012

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Direct-drive experiments at the University of Rochester's OMEGA laser [T. R. Boehly, R. L. McCrory, C. P. Verdon et al., Fusion Eng. Des. 44, 35 (1999)] have been performed to prototype eventual campaigns on the National Ignition Facility (NIF) [E. I. Moses and C. R. Wuest, Fusion Sci. Technol. 43, 420 (2003)] to investigate the mixing of target materials. Spherical-implosion targets with equatorial defects have been irradiated with polar direct drive, a requirement for direct-drive experiments at NIF. The physics question addressed by these results is whether simulations can match data on 0th-order hydrodynamics and implosion symmetry, the most basic implosion features, with and without the defect. The successful testing of hydrodynamic simulations leads to better designs for experiments and guides accurate planning for polar-direct-drive-ignition studies on the NIF platform.

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Scaling laws for laser driven exploding pusher targets

Cited by 22 publications

References 9 publications

Investigation of ion kinetic effects in direct-drive exploding-pusher implosions at the NIF

Investigation of ion kinetic effects in direct-drive exploding-pusher implosions at the NIF

Assessment of ion kinetic effects in shock-driven inertial confinement fusion implosions using fusion burn imaging

Asymmetric directly driven capsule implosions: Modeling and experiments—A requirement for the National Ignition Facility

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