Showing papers by "Roger Alan Vesey published in 2011"

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

Abstract: 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...

Measurements of magneto-Rayleigh–Taylor instability growth during the implosion of initially solid metal liners a)

Abstract: A recent publication [D. B. Sinars et al., Phys. Rev. Lett. 105, 185001 (2010)] describes the first controlled experiments measuring the growth of the magneto-Rayleigh–Taylor instability in fast (∼100 ns) Z-pinch plasmas formed from initially solid aluminum tubes (liners). Sinusoidal perturbations on the surface of these liners with wavelengths of 25–400 μm were used to seed single-mode instabilities. The evolution of the outer liner surface was captured using multiframe 6.151 keV radiography. The initial paper shows that there is good agreement between the data and 2-D radiation magneto-hydrodynamic simulations down to 50 μm wavelengths. This paper extends the previous one by providing more detailed radiography images, detailed target characterization data, a more accurate comparison to analytic models for the amplitude growth, the first data from a beryllium liner, and comparisons between the data and 3D simulations.

Progress towards ignition on the National Ignition Facility

Abstract: The National Ignition Facility at Lawrence Livermore National Laboratory was formally dedicated in May 2009. The hohlraum energetics campaign with all 192 beams began shortly thereafter and ran until early December 2009. These experiments explored hohlraum-operating regimes in preparation for experiments with layered cryogenic targets. The hohlraum energetic series culminated with an experiment that irradiated an ignition scale hohlraum with 1 MJ. The results demonstrated the ability to produce a 285 eV radiation environment in an ignition scale hohlraum while meeting ignition requirements for symmetry, backscatter and hot electron production. Complementary scaling experiments indicate that with ~1.3 MJ, the capsule drive temperature will reach 300 eV, the point design temperature for the first ignition campaign. Preparation for cryo-layered implosions included installation of a variety of nuclear diagnostics, cryogenic layering target positioner, advanced optics and facility modifications needed for tritium operations and for routine operation at laser energy greater than 1.3 MJ. The first cyro-layered experiment was carried out on 29 September 2010. The main purpose of this shot was to demonstrate the ability to integrate all of the laser, target and diagnostic capability needed for a successful cryo-layered experiment. This paper discusses the ignition point design as well as findings and conclusions from the hohlraum energetics campaign carried out in 2009. It also provides a brief summary of the initial cryo-layered implosion.

Monochromatic 6.151-keV Radiographs of a Highly Unstable Inertial Confinement Fusion Capsule Implosion

Abstract: Monochromatic 6.151-keV radiographs of a highly unstable inertial confinement fusion capsule are shown. The capsule was driven by a 70-eV peak radiation temperature and exhibits numerous small-scale features down to the resolution of the backlighting diagnostic (about 15 μm ). The capsule experiment was done using the double-ended Z -pinch-driven hohlraum on the Sandia Z facility.

Initiation of Quasi Spherical Direct Drive capsules for inertial fusion

Abstract: Summary form only given. Magnetically driven, Quasi Spherical Direct Drive (QSDD) fusion capsules potentially offer much higher efficiency implosions for inertial fusion energy than x-ray driven implosions with the comparable pulsed power generator. However, these solid liners must initiate uniformly to produce a quality implosion. Previous experiments by Stinnett, et al, showed that 20 to 200 nm thick aluminum liners on thick insulating substrates require a local action integral of ~6×108 (A/cm2)2-s or ~8×1016 A/cm2 rising in 7 ns to initiate uniformly. The underlying physical processes are complicated by the presence of ~3 monolayers of adsorbed gas and 7.5 nm of AlO2O3. Since QSDD liners are typically 100 micron thick beryllium, we have used a rad-hydro MHD code to analyze the initiation of both thin aluminum liners, to understand the underlying physics, and thick beryllium liners, to predict the drive requirements for uniform initiation of QSDD implosions. Both simulations had 3 monolayers of adsorbed hydrogen on the metal. The simulations provided the local electric field, density, and temperature profile of the metal and gas. The results were analyzed with J. C. Martin's multi-channel switching relationships. We infer that the metal must reach approximately 1 eV temperature before the gas, which is heated by thermal conduction, can expand to provide an alternative path for current channel formation through the gas. The results also suggest that an ignition-class QSDD capsule will need ~40 ns implosion times with a 40 MA drive pulse. A 2 micron polyimide coating may significantly improve the initiation of solid liners, as it has improved the initiation of wire arrays in work by D. B. Sinars, et. al., and by G. S. Sarkisov, et. al.