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We have derived a 3-dimensional synthetic model for NIF implosion conditions, by predicting and optimizing fits to a broad set of x-ray and nuclear diagnostics obtained on each shot. By matching x-ray images, burn width, neutron time-of-flight ion temperature, yield, and fuel r, we obtain nearly unique constraints on conditions in the hotspot and fuel in a model that is entirely consistent with the observables. This model allows us to determine hotspot density, pressure, areal density (r), total energy, and other ignition-relevant parameters not available from any single diagnostic. This article describes the model and its application to National Ignition Facility (NIF) tritium-hydrogen-deuterium (THD) and DT implosion data, and provides an explanation for the large yield and r degradation compared to numerical code predictions. To optimize the target and laser parameters for ignition (1, 2), it is important to understand the implosion conditions achieved in a given experiment, independent of the design predictions. To this end, we developed and applied a model to estimate the performance of an implosion and assess temperature, density, and composition distributions within the assembled core, solely from the experimental data taken during the shot. Using radiative, equation of state, nuclear fusion relations for relevant materials, and an approximation of pressure equilibrium within the hotspot (3), we derive a 3-dimensional representation of the capsule density and temperature profiles at stagnation, by predicting and optimizing fits to a broad set of x-ray and nuclear diagnostics. This model allows us to determine hotspot density, pressure, areal density (r), total energy, and other ignition-relevant parameters not available from any single diagnostic. This approach has been validated by comparing results with radiation-hydrodynamic simulations and has produced semi-quantitative (10-20%) agreement. We begin by constructing a 3D model for the temperature and density conditions of the imploded core at neutron bang time, defined as the time of peak neutron and 10-20keV x-ray production in the capsule (4). We further assume that this imploded core, including both hotspot and fuel, is at a uniform pressure Phs. So for a given density profile (r, , ), we derive an associated temperature profile using the hydrogenic equation-of-state, which includes effects of Fermi degeneracy in the dense shell (5). This description produces a relatively complete characterization of the implosion temperature and density distributions, and from this we can calculate the complete properties of the x-ray emission and nuclear fusion processes to predict the ensemble of diagnostic signatures from the implosion. Given an assumed pressure and density profile, we calculate the waist and polar x-ray emission images, using a free-free emissivity derived from the VISTA opacity model, and a Detailed This is an Open Access article distributed under the terms of the Creative Commons Attribution License 2.0, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Ignition implosions on the National Ignition Facility (NIF) [Lindl et al., Phys. Plasmas 11 , 339 (2004)] are driven with a very carefully tailored sequence of four shock waves that must be timed to very high precision in order to keep the fuel on a low adiabat. The first series of precision tuning experiments on NIF have been performed. These experiments use optical diagnostics to directly measure the strength and timing of all four shocks inside the hohlraum-driven, cryogenic deuterium-filled capsule interior. The results of these experiments are presented demonstrating a significant decrease in the fuel adiabat over previously un-tuned implosions. The impact of the improved adiabat on fuel compression is confirmed in related deuterium-tritium (DT) layered capsule implosions by measurement of fuel areal density (ρR), which show the highest fuel compression (ρR ∼ 1.0 g/cm2 ) measured to date.

Shock-ignition experiments with peak laser intensities of ∼8 × 1015 W/cm2 were performed. D2 -filled plastic shells were compressed on a low adiabat by 40 of the 60 OMEGA beams. The remaining 20 beams were delayed and tightly focused onto the imploding shell to generate a strong shock. Up to 35% backscattering of laser energy was measured at the highest intensity. Hard x-ray measurements reveal a relatively low hot-electron temperature of ∼40 keV, independent of intensity and spike onset time.

We have studied the energy dependence of the reaction mechanism of the T(t,2n)4 He reaction at stellar energies and of its charge symmetric analog reaction 3 He(3 He,2p)4 He at energies up 10 MeV. We find that the reaction mechanism changes dramatically over this energy range in part due to the interference of the two identical fermions in the three-body final state.

High-convergence polar-drive experiments are being conducted on OMEGA [T. R. Boehly et al., Opt. Commum. 133, 495 (1997)] using triple-picket laser pulses. The goal of OMEGA experiments is to validate modeling of oblique laser deposition, heat conduction in the presence of nonradial thermal gradients in the corona, and implosion energetics in the presence of laser–plasma interactions such as crossed-beam energy transfer. Simulated shock velocities near the equator, where the beams are obliquely incident, are within 5% of experimentally inferred values in warm plastic shells, well within the required accuracy for ignition. High, near-one-dimensional areal density is obtained in warm-plastic-shell implosions. Simulated backlit images of the compressing core are in good agreement with measured images. Outstanding questions that will be addressed in the future relate to the role of cross-beam transfer in polar drive irradiation and increasing the energy coupled into the target by decreasing beam obliquity.

The overall goal of the indirect-drive inertial confinement fusion (1) tuning campaigns (2 )i s to maximize the probability of ignition by experimentally correcting for likely residual uncertainties in the implosion and hohlraum physics (3) used in our radiation-hydrodynamic computational models, and by checking for and resolving unexpected shot-to-shot variability in performance (4). This has been started successfully using a variety of surrogate capsules that set key laser, hohlraum and capsule parameters to maximize ignition capsule implosion velocity, while minimizing fuel adiabat, core shape asymmetry and ablator-fuel mix.

The measurement of the absolute neutron yield produced in inertial confinement fusion target experiments conducted on the National Ignition Facility (NIF) is essential in benchmarking progress towards the goal of achieving ignition on this facility. This paper describes three independent diagnostic techniques that have been developed to make accurate and precise DT neutron yield measurements on the NIF.