M. M. Marinak

Point design targets, specifications, and requirements for the 2010 ignition campaign on the National Ignition Facility

Point design targets have been specified for the initial ignition campaign on the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 443, 2841 (2004)]. The targets contain D-T fusion fuel in an ablator of either CH with Ge doping, or Be with Cu. These shells are imploded in a U or Au hohlraum with a peak radiation temperature set between 270 and 300 eV. Considerations determining the point design include laser-plasma interactions, hydrodynamic instabilities, laser operations, and target fabrication. Simulations were used to evaluate choices, and to define requirements and specifications. Simulation techniques and their experimental validation are summarized. Simulations were used to estimate the sensitivity of target performance to uncertainties and variations in experimental conditions. A formalism is described that evaluates margin for ignition, summarized in a parameter the Ignition Threshold Factor (ITF). Uncertainty and shot-to-shot variability in ITF are evaluated, and...

Three-dimensional HYDRA simulations of National Ignition Facility targets*

The performance of a targets designed for the National Ignition Facility (NIF) are simulated in three dimensions using the HYDRA multiphysics radiation hydrodynamics code. [M. Marinak et al., Phys. Plasmas 5, 1125 (1998)] In simulations of a cylindrical NIF hohlraum that include an imploding capsule, all relevant hohlraum features and the detailed laser illumination pattern, the motion of the wall material inside the hohlraum shows a high degree of axisymmetry. Laser light is able to propagate through the entrance hole for the required duration of the pulse. Gross hohlraum energetics mirror the results from an axisymmetric simulation. A NIF capsule simulation resolved the full spectrum of the most dangerous modes that grow from surface roughness. Hydrodynamic instabilities evolve into the weakly nonlinear regime. There is no evidence of anomalous low mode growth driven by nonlinear mode coupling.

The development and advantages of beryllium capsules for the National Ignition Facility

Capsules with beryllium ablators have long been considered as alternatives to plastic for the National Ignition Facility laser ; now the superior performance of beryllium is becoming well substantiated. Beryllium capsules have the advantages of relative insensitivity to instability growth, low opacity, high tensile strength, and high thermal conductivity. 3-D calculation with the HYDRA code NTIS Document No. DE-96004569 (M. M. Marinak et.al. in UCRL-LR-105821-95-3) confirm 2-D LASNEX U. B. Zimmerman and W. L. Kruer, Comments Plasmas Phys. Controlled Thermonucl. Fusion, 2, 51(2975) results that particular beryllium capsule designs are several times less sensitive than the CH point design to instability growth from DT ice roughness. These capsule designs contain more ablator mass and leave some beryllium unablated at ignition. By adjusting the level of copper dopant, the unablated mass can increase or decrease, with a corresponding decrease or increase in sensitivity to perturbations. A plastic capsule with the same ablator mass as the beryllium and leaving the same unablated mass also shows this reduced perturbation sensitivity. Beryllium`s low opacity permits the creation of 250 eV capsule designs. Its high tensile strength allows it to contain DT fuel at room temperature. Its high thermal conductivity simplifies cryogenic fielding.

The experimental plan for cryogenic layered target implosions on the National Ignition Facility—The inertial confinement approach to fusion

Ignition requires precisely controlled, high convergence implosions to assemble a dense shell of deuterium-tritium (DT) fuel with ρR>∼1 g/cm2 surrounding a 10 keV hot spot with ρR ∼ 0.3 g/cm2. A working definition of ignition has been a yield of ∼1 MJ. At this yield the α-particle energy deposited in the fuel would have been ∼200 kJ, which is already ∼10 × more than the kinetic energy of a typical implosion. The National Ignition Campaign includes low yield implosions with dudded fuel layers to study and optimize the hydrodynamic assembly of the fuel in a diagnostics rich environment. The fuel is a mixture of tritium-hydrogen-deuterium (THD) with a density equivalent to DT. The fraction of D can be adjusted to control the neutron yield. Yields of ∼1014−15 14 MeV (primary) neutrons are adequate to diagnose the hot spot as well as the dense fuel properties via down scattering of the primary neutrons. X-ray imaging diagnostics can function in this low yield environment providing additional information about ...

Review of indirect-drive ignition design options for the National Ignition Facility

Several inertial confinement fusion (ICF) capsule designs have been proposed as possible candidates for achieving ignition by indirect drive on the National Ignition Facility (NIF) laser [Paisner et al., Laser Focus World 30, 75 (1994)]. This article reviews these designs, their predicted performance using one-, two-, and three-dimensional numerical simulations, and their fabricability. Recent design work at a peak x-ray drive temperature of 250 eV with either 900 or 1300 kJ total laser energy confirms earlier capsule performance estimates [Lindl, Phys. Plasmas 2, 3933 (1995)] that were based on hydrodynamic stability arguments. These simulations at 250 eV and others at the nominal 300 eV drive show that capsules having either copper doped beryllium (Be+Cu) or polyimide (C22H10N2O4) ablators have favorable implosion stability and material fabrication properties. Prototypes of capsules using these ablator materials are being constructed using several techniques: brazing together machined hemishells (Be+Cu)...

Three-dimensional simulations of Nova high growth factor capsule implosion experiments

Capsule implosion experiments carried out on the Nova laser [E. M. Campbell et al., Rev. Sci. Instrum. 57, 2101 (1986)] are simulated with the three‐dimensional HYDRA radiation hydrodynamics code [NTIS Document No. DE‐96004569 (M. M. Marinak et al. in UCRL‐LR‐105821‐95‐3)]. Simulations of ordered, near single mode perturbations indicate that structures which evolve into round spikes can penetrate farthest into the hot spot. Bubble‐shaped perturbations can burn through the capsule shell fastest, in which case they cause even more damage. A simulation of a capsule with a multimode perturbation of moderate amplitude shows spike amplitudes evolving in good agreement with a saturation model during the deceleration phase. The presence of sizable low mode asymmetry, caused either by drive asymmetry or perturbations in the capsule shell, can dramatically affect the manner in which spikes approach the center of the hot spot. Three‐dimensional coupling between the low mode shell perturbations intrinsic to Nova caps...

Capsule implosion optimization during the indirect-drive National Ignition Campaign

Capsule performance optimization campaigns will be conducted at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, 228 (2004)] to substantially increase the probability of ignition. The campaigns will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models using a variety of ignition capsule surrogates before proceeding to cryogenic-layered implosions and ignition experiments. The quantitative goals and technique options and down selections for the tuning campaigns are first explained. The computationally derived sensitivities to key laser and target parameters are compared to simple analytic models to gain further insight into the physics of the tuning techniques. The results of the validation of the tuning techniques at the OMEGA facility [J. M. Soures et al., Phys. Plasmas 3, 2108 (1996)] under scaled hohlraum and capsule conditions relevant to the ignition design are shown ...

Single‐mode and multimode Rayleigh–Taylor experiments on Nova

Rayleigh–Taylor (RT) experiments have been conducted with planar CH(Br) foils accelerated by x‐ray ablation from a shaped, low adiabat drive. The surface perturbations investigated consisted of single‐mode, two‐mode, and eight‐mode sinusoids. The perturbation evolution begins during the shock transit phase, when perturbations show gradual growth due to Richtmyer–Meshkov‐like dynamics. After shock breakout, the compressed foils accelerate and perturbation growth continues due to the Rayleigh–Taylor instability. Detailed comparisons with simulations indicate that in the linear Rayleigh–Taylor regime, the single‐mode perturbations grow exponentially in time. In the nonlinear regime, the growth slows and the perturbation shape changes from sinusoidal to ‘‘bubble and spike’’ with the appearance of higher Fourier harmonics. In the multimode perturbations, the individual modes grow independently in the linear regime, but become coupled in the nonlinear regime. In addition to the higher harmonics of the individua...

A high-resolution integrated model of the National Ignition Campaign cryogenic layered experiments

A detailed simulation-based model of the June 2011 National Ignition Campaign cryogenic DT experiments is presented. The model is based on integrated hohlraum-capsule simulations that utilize the best available models for the hohlraum wall, ablator, and DT equations of state and opacities. The calculated radiation drive was adjusted by changing the input laser power to match the experimentally measured shock speeds, shock merger times, peak implosion velocity, and bangtime. The crossbeam energy transfer model was tuned to match the measured time-dependent symmetry. Mid-mode mix was included by directly modeling the ablator and ice surface perturbations up to mode 60. Simulated experimental values were extracted from the simulation and compared against the experiment. Although by design the model is able to reproduce the 1D in-flight implosion parameters and low-mode asymmetries, it is not able to accurately predict the measured and inferred stagnation properties and levels of mix. In particular, the measu...

A comparison of three-dimensional multimode hydrodynamic instability growth on various National Ignition Facility capsule designs with HYDRA simulations

Three similar cryogenic ignition capsule designs for the National Ignition Facility [J. Lindl, Phys. Plasmas 2, 3933 (1995)] are analyzed to determine surface roughness specifications required to mitigate the growth of hydrodynamic instabilities. These capsule utilize brominated plastic, polyimid and copper-doped beryllium ablator materials respectively. Direct three-dimensional numerical simulations with the HYDRA radiation hydrodynamic code [M. M. Marinak et al., Phys. Plasmas 3, 2070 (1996)] examine the growth of multimode perturbations seeded by roughness on the outer ablator and inner ice surfaces. The simulations, which showed weakly nonlinear behavior for optimized surfaces, were carried through ignition and burn. A three-dimensional multimode perturbation achieves somewhat larger amplitudes in the nonlinear regime than a corresponding two-dimensional simulation of the same rms amplitude. The beryllium and polyimid capsules exhibit enhanced tolerance of roughness on both the ice and ablator surfaces.